1988 V10 Suburban TBI running rough

[MudDiGGer25]

MOD/ADMIN: If I put this in the wrong Forum please move it. Thanks!



Ok, everybody im a noob on here, i have been lurking for a while, and i have read probably 400 webpages/forum pages trying to figure out my specific problem but since my vehicle/engine/trans combo is unique/unknown its hard to find a solution, I will try to list everything I can remember that I have tested or already done along with my suspicions that i have not investigated yet due to knee and back injuries, ( i just got out of knee surgery about 10 days ago and the dr allowed me walking and light work) I am a mechanic by day, I also have a mobile shop/Service truck I run from this vehicle as my own business. For background on me, I have attended 4 semesters of Automotive Mechanics in a Community College but no hands on, and i didnt stay long enough to get the Automotive Electronics part. I have been working on various vehicles since I was around 11, but by no means do i know it all or even close, i am always looking to learn more. And I apologize in advance for grammar, or anything i might say to offend someone, I have Asbergers, and ADHD.


Ok first things first; based on the title I have it is the body of a 1988 suburban with a 6.2L N/A originally, no Idea on miles on body. Ok heres where it gets interesting. this was originally purchased by a FD as a rescue rig, they even welded thier own 2" reciever to the front frame (handles a 18K lbs winch) they blew the 6.2L one way or another, now at this point I have 2 stories about the engine that is now in it, on one hand the FD Chief went to a Cali Auction and grabbed up a 5.7L TBI, L05 from a 9C1 police hwy interceptor, OR the other story I have is that the engine was simple pulled from a 1988 suburban from the local impound/auction. In either case I have been told the engine was rebuilt, (no i do not know if it was modified or simple a stock rebuild. I am currently digging deeper into that) they reset the ODO when the replacement engine went in, it currently says a little over 38K nothing is still there from the 6.2L they ran a harness and new relays (im assuming from the donor vehicle) they removed the A/C setup completely i.e condensor in front and in the blower box and sealed it, canister, pump and everything is GONE, i do have a beeline on a 1989 suburban that the engine was robbed from but they left the entire A/C system, compressor and all still sealed with freon. thinking of grabbing that and putting the A/C back in. anyway back to the description, I have also been told by several individuals that the TH350 (yes i am absolutely sure i have checked the pan, and adjusted the shift linkage, bc it used to have the 700R4) was also rebuilt and beefed up including a shift kit, which that i can believe because I have pulled over 6K for 400 miles with 3.42 gearing, and nice firm shifts, even when not towing nice firm secure shifts anywhere between 2K RPM and 5K RPM. Also I do not know why I have a Dual belt setup, i.e. I have a V-Belt to run my PS pump, water pump/fan, but the other side has a (4?) groove V-belt pulley system to run the A/C and ALT, i believe it also runs around the water pump/fan. have not found a stock engine in the parts store computer with the correct alt or compressor, meaning stock with Serp pulley. Also when I first got the suburban I was told it was bucking and spitting above 1/4 throttle because the fuel filter was clogged, would barely stay running at all.
So to recap, 1988 V10 suburban with 6.2L driveline, 5.7L TBI L05, TH350, NP208, Manual Locking hubs, 3.42 AR. 29X9.50R15 MT Radials
So here are the 3 main things I am trying to figure out

A) when I am applying "Light" throttle, i.e in 2nd or 3rd gear in town 25-35mph on a flat grade it, almost seems like the timing is retarding because it seems to bog and cant get out of its own way, does not do it when coasting, and stops it/returns to normal if i go to about 20%-25% throttle.
B) It has been doing this since i got it, If i leave it in 1st gear and apply no less than ~20% throttle, but no more than ~40% throttle, right at 25MPH/2500RPM (yes with my tires and gearing in 1st gear my MPHx100=RPM) it takes off without any change in throttle position, i mean it puts you back in the seat a bit, then returns to "normal" at 35mph/3500RPM will also do this in 2nd gear if i am off road/drifting/horseplaying. I can make it do it as many times as i want, always the same speed everytime, and if i put too much into the throttle it will not do it.
C) I am trying to get my kickdown cable (yes kickdown cable not kickdown rod, or TV cable, several people have tried to correct me) to obtain the correct tension at WOT, and idle, they way i have it now, it is taught at WOT but has slack at idle, I cant seem to get the best of both, im not sure if my arm radius is wrong and i need an adapter maybe?
I HAVE done the following all within the last 3 months for sure:
TPS: tested ok, but replaced it with a known working one, and tested that one before install
Igntion Coil= tested good, tried a brand new one, no change in behavior so i returned it.
MAF sensor= tested, but replaced with a known good one
ICM was seting a code recently and the bogging at light throttle was unbearable almost couldnt reach 20mph, I went to the yard and got 2 genuine GM ICM's the one I took out was a 369, so i replaced it with the 369 i found and kept the (048??) as a spare, I already know about the table differences contained within these two chips. This returned the engine to a manageable state, this was 11 days ago.
Plugs, Wires, Cap, Rotor were all changed together
Alt was failing when I bought the Burb. went to Carquest got REMAN, 78A 10SI since it was covered under a lifetime warranty. this was roughly a month ago.
Fuel Filter- changed the 2nd day I owned it because I could not get into the throttle more than 15% or it would start kicking/bucking/spitting/cuttng out it was really horrible. however this had no effect on anything.
Fuel Pump- As the light throttle problem got worse and i also started to notice I was slowing down when racing even though I should have ample power since the air up here has been 0 to -20F the last week, I hooked up a snap on FP guage, digital, FP was 11.5 when it primed, down to i think 8.5 when power braking in 4WD, and flooring it in 1st, and it sounded horrible too. I had a TBI pump around that was given to me months ago, I used to bypass my mech pump on my 77 ford when it failed 300 miles from home, it ran a 450HP engine with plenty to spare, I have not actually gotten a PSI reading yet due to my surgery but I can attest the Performance has GREATLY improved, and starting is slightly easier, however still takes 1-5 seconds to fire up. this was done the day before my surgery.
PVC Valve- I tested it and it failed my "shake test" so replaced it, this also slight improved idle and overall response.
Vacuum leaks- none that can be found with a unlit propane torch OR BrakeKleen
EGR, is functional however it starts to run ****ty at part throttle with it hooked up, so i bypassed it, and no the ECM has not set a code for it, even with multiple hwy runs 100 +miles each way. not sure why.
0W20 Mobil 1 Oil Change/Mobil1 w/ 1qt Lucas Syn Oil Stabilizer ( yes i can attest to it working, slightly lower oil temps, and a slight decrease in 0-60 times) extended filter. maybe 2200mi on so far
Air filter has been replaced with a 3" ( i think) open filter, set on top of the TBI in a "chrome" housing lol
AntiFreeze strength was increased to 70/30 for the constand subzero temps up here.
ECT tests good, and shows the proper temp F and has a very steady and gradual inscrease while engine is warming up ( my day shop has a very nice expensive snap on scanner that allows connection to anything with a computer port)
Injector pulse test- I have videos showing the pulse testers installed in place of the injector, pulses are as expected, however, as you can see if you want to in the videos, it barely runs on 1 injector, however when i swap sides it starts once, then refused to start up and idle, had to reconnect both injectors and crank crank and floor it, then it started up.
I have run lucas and Howes fuel injector system cleaner many many tankfuls, and B12 Chemtool spray to clean the throttle blades.
IAC valve, tested fine but replaced it with a know good one, no effect that i could notice
Timing, when I thought the timing was off, I grabbed snap on timing gun, finally found the ECT disconnect, and set the base timing, It was wayyyy advanced based on the stock balancer marking, but i experienced no PING however most fill ups I get 91 with NO ethanol. Reset the base timing to about 2 DEG BTDC, then hooked it back up and restarted it, I say "about" because the timing mark bounces around between 0-2 D BTDC even with it hooked back up the timing wiggles, but i checked the DIST, its exteremly clean might be reman too, but no slop in the shaft. Now that i think about it I might have set the timing wrong -doh- I think i hooked the timing light to the wire coming out of the coil and not the #1 -.- dammit ill have to check on monday after work'
I have cleaned EVERY ground, from frame to block, block to firewall, bat to block, bat to front panel, front panel to headlights, and a few aftermarket grounds I found also
Have not done the following:
I think i grabbed a extra Spark Control Module (next to the MAF) but unknown how to test it
Test the current FP
Test the Injectors themselves (when i had the timing light shining down the TBI, I could not see the fuel spray pattern whatsoever)
Check the FPR spring/assembly since I do not know how to dissasemble it yet


Intended upgrades that may pertain to these problems/solutions
LS1 High Pressure FP upgrade
FPR 15PSI spring upgrade
Certified Rebuilt 9C1 police flow matched injectors W/warranty and good reviews
CS130/CS144 Alt upgrade because the 78A model cannot maintain the aftermarket stereo/amp/additional running lights, 2 driving lights, and 4 OR lights + the rear fan.
Might get a better aftermarket Igntion coil since this burb will be playing around at Trucks Gone Wild in June & maybe september, and I enter most of the local mud bogs.

Pertaining to performance and fuel economy, before the fuel pump change i was getting 4-6mpg in town and you could forget about even trying the hwy. before the pump started acting up I started with 11-13 in town and 15-19hwy, gradually decreasing to 8hwy regardless of going 55 or 85 (yes i tested it on 3 separate trips on the same 200 mile drive however during all 3 runs I was using 87/10% corn) There is a very noticeable difference in running the 87/10% corn vs 87/ no corn vs 91/no corn, I even see an average 2mpg increase in hwy towing or not. And with 91/no corn I have very noticeable better throttle response and much easier to climb big hills when towing our camper. For example I have to downshift to 2nd when towing the camper up steep grades @55mph when using 87/10% however when i fill with 91/no corn I can stay in 3rd all the way up same hill same ambient temps and same load.


I can upload Pics if needed in the AM when its sunny out

[MudDiGGer25]

So my thread title is incorrect bc i was distracted while typing it, It should read engine quirks not lights

[MudDiGGer25]

bump, any help out there? ive been dealing with this for several months and keep banging my head into the wall. going to get above 32F this week and would like to see if i can make progress.

[68Timber]

First off, welcome to 67-72! Hopefully we can help you get that running better, I'm not much of a TBI mechanic but others here speak it fluently. Honestly, you've got three pretty significant hurdles to overcome, it being originally a diesel, unknown TBI motor swapped in, and having bought it running rough, unless you "knew" the truck before you bought it there's no way of knowing if the truck was ever converted to TBI properly. That's not to say it can't be sorted out, it'll just take some digging. First off, cancel those upgrades for now. There's no reason it can't run with stock components as long as they're in good working order and properly matched. Second, and you already figured this one out, set your timing the right way as soon as you can. I am suspect of the fuel pressure, but only because you say it drops when power brake it. Honestly I know they need 12 to 14 psi to run right but I don't know if the pressure drop in that scenario is normal or not. Last, the EGR needs to be figured out first. But you need to know what you've got first. Have you checked the numbers on the engine, TBI, or ECM to verify what you have? I'd want to know if you're working on a truck motor or 9C1, although admittedly they may be close enough that it wouldn't matter. I did find this: http://www.73-87chevytrucks.com/tech...TBISystems.pdf Hope this will help you get started, and that someone that knows these better will chime in.

[MudDiGGer25]

Originally Posted by BRUISER

First off, welcome to 67-72! Hopefully we can help you get that running better, I'm not much of a TBI mechanic but others here speak it fluently. Honestly, you've got three pretty significant hurdles to overcome, it being originally a diesel, unknown TBI motor swapped in, and having bought it running rough, unless you "knew" the truck before you bought it there's no way of knowing if the truck was ever converted to TBI properly. That's not to say it can't be sorted out, it'll just take some digging. First off, cancel those upgrades for now. There's no reason it can't run with stock components as long as they're in good working order and properly matched. Second, and you already figured this one out, set your timing the right way as soon as you can. I am suspect of the fuel pressure, but only because you say it drops when power brake it. Honestly I know they need 12 to 14 psi to run right but I don't know if the pressure drop in that scenario is normal or not. Last, the EGR needs to be figured out first. But you need to know what you've got first. Have you checked the numbers on the engine, TBI, or ECM to verify what you have? I'd want to know if you're working on a truck motor or 9C1, although admittedly they may be close enough that it wouldn't matter. I did find this: http://www.73-87chevytrucks.com/tech...TBISystems.pdf Hope this will help you get started, and that someone that knows these better will chime in.

Ok just wanted to let you know I have that pdf already lol I have done what it says as best as i have been able with injuries/surgery. It "USED" to drop to 8.5-95PSI when PB'ing, however it responds incredibly better now that I have swapped a different (albiet used) pump into the tank. I will be checking the number cast behind the ALT, in about 10 days when i upgrade it, thats not something that is optional because I have to charge or jump my truck atleast once a day if i use the radio/sub at all while driving, and when the temps are 10F above to -25F the bat doesnt have much in the first place and it drains pretty fast just to get it fired up, currently to combat this issue i have a 15V 1A power adapter i plug in when i get home, once the battery reaches full the excess energy is then turned to heat, although not very much but it keeps the bat a couple degrees warmer than ambient (my grandpa taught me that trick 15 years ago and he did it for over 40 years with no ill effects)

for the other upgrades they are not really necessary if I can get proper perfomance from what I have, however when mudding/racing I am in the 4000-5000 range in 4LO so thats why i was considering a better ignition coil (yes my 5.7 can turn over to 5500 before the internal resistance limits it) and no governer or delimiter present I can hold 5500rpm in 4lo or 4hi in any gear i choose.

its also getting an axle swap to 3.73, with stiffer springs if i can grab a set at the yard this week. and a 4" lift to boot that.

I am only in a hurry to find my headaches since I will be asking this rig to flat tow a 8K lb class C RV approx 250 miles, I have towed 13K with a 4bbl 6.6L and TH400 so 8K shouldnt be asking too much, and ill be keeping it under 45-60mph period.

AS far as "correctly" goes the PCM gives ALL readouts properly and the only code i was getting intermittently was a 43 (ICM somethingorother) IIRC but it never hard set it. I will check it tomorrow when i time it again to see if it sets.

PS, I personally have had 2 and know of atleast 3 TBI 5.7l 89-95 in trucks and vans that the EGR was bypassed or eliminated tens or thundreds of thousands of miles ago with no noticeable effects on performance or mpg.

Atleast they got rid of the crappy 700r4 lol ive burned up too many to count towing or mudding lol, even in D, but I push everything i own to its limits, only because i can usually fit it when it breaks lol

thanks for the input and hopefully this will bump enough to get some experience on my woes

[MudDiGGer25]

Originally Posted by BRUISER

Have you checked the numbers on the engine, TBI, or ECM to verify what you have?

I am not sure yet where the ECM has been put, I havent really looked for it either but would i be looking for printed numbers or "burned in" numbers?

Where should I look on the TBI for #'s? admittedly it may not be original to the block.

After doing some reading up on the 43 code IIRC, has something to do with the spark control unit by the MAP sensor (not sure if i accidentally called it a MAF earlier, i was tired) or the knock sensor by the ??oil filter??? is there a way I can unhook one of these without making the computer too mad to test drive? Logically I would think that unplugging the knock sensor on a obd1 would set a code but it would not be able to affect the timing due to the open circuit? anyone that knows better please chime in, but i do love process of elimination XD

[68Timber]

EGR - 10-4, I wondered when I typed that if I was confusing TBI w/Vortec. I guess I was. About the numbers, I meant to check for part numbers or any other way to identify what you have. Just to make sure it's all compatible. You'd think all of it came from one donor vehicle, but since you're getting conflicting stories I'd want to verify.

[MudDiGGer25]

Originally Posted by BRUISER

EGR - 10-4, I wondered when I typed that if I was confusing TBI w/Vortec. I guess I was. About the numbers, I meant to check for part numbers or any other way to identify what you have. Just to make sure it's all compatible. You'd think all of it came from one donor vehicle, but since you're getting conflicting stories I'd want to verify.

well I would like to assume it didnt make it 39K since the rebuild if it wasnt all compatible lol, but then again god only knows who did what in the meantime, but I mean considering the last 7-10 years of its life was reportedly only used for hunting once a year and 3-4 times a year to pull a camper, id say the overall drivetrain condition is pretty good, ive seen under the hood/frame look much worse on chevy's this age.

just sitting here waiting for some more troubleshooting tips i can go after tomorrow hopefully

definitely double checking the timing and codes

[cdub2010]

The combo v belt and ribbed belt is whats on my stock 87 k5 jimmy. not mine but heres an image. http://67-72chevytrucks.com/vboard/s...d.php?t=509407

You have high hopes if you want this engine to run at 5500 in any gear, the one in my truck had trouble turning 35's. These are no high reving powerhouses just a work truck engine.

Cant help much about the tbi problems but recheck your grounds and make sure your timing is set correctly. im sure youve read this site but it helped me so. http://tbichips.com/?page_id=351

good luck with your engine. I have been struggling with a tbi swap into an older truck. Im going to throw it all out and get a fitech setup if mine doesnt run good this spring.

[MudDiGGer25]

Originally Posted by cdub2010

The combo v belt and ribbed belt is whats on my stock 87 k5 jimmy. not mine but heres an image. http://67-72chevytrucks.com/vboard/s...d.php?t=509407

You have high hopes if you want this engine to run at 5500 in any gear, the one in my truck had trouble turning 35's. These are no high reving powerhouses just a work truck engine.

Cant help much about the tbi problems but recheck your grounds and make sure your timing is set correctly. im sure youve read this site but it helped me so. http://tbichips.com/?page_id=351

good luck with your engine. I have been struggling with a tbi swap into an older truck. Im going to throw it all out and get a fitech setup if mine doesnt run good this spring.

Grounds were checked and "refreshed" i.e. all shiny again about 9 days ago

almost looks the same, but they took my A/C away and i have a single groove PS pulley and no bracket above it.


As far as high hopes go, its not a hope, I can bring it up to 5500RPM at about 55MPH in 1st in 2HI or 4HI, As soon as I can grab a new tach I can post video/pic. Or just do the math, 55mph = 3.42 axles *2.52 1st gear TH350 =5500 RPM granted it does lose some tq somewhere after 45mph but still makes it to 5500 rpms everytime.

I had no problems clearing the mud drag pit (250-300ft) in a few seconds in 2-3ft deep mud. (yes my bumper was in the mud pushing it lol)

Im going either 33's or 35"s a buddy of mine has 33's on his (95?) TBI ext cab 4wd and he has power to spare but i think he still has the 4spd in it.



this is the main calculator i use

[MudDiGGer25]

https://www.youtube.com/watch?v=LgBRy81rujE

https://www.youtube.com/watch?v=sK62a75IZ0Q

Those 2 are videos of the data readouts 0-6000rpm and power braking (yes i know one is labeled wrong)

The next 2 are the timing with the ETC connector disconnected and with it connected, I could not hold the camera and the light and operate the throttle all at the same time but i did watch it advance a bit while the camera was off. this is just the camera built into my phone and i think there might have been some grease on the lense that I couldn't get off. Let me know what you think.

PS I left the timing right where it sat bc i believe that to be 0 BTDC or very close.

https://www.youtube.com/watch?v=OVSCI39k2BU

https://www.youtube.com/watch?v=nxZuWsY6sbI

[MudDiGGer25]

https://www.youtube.com/watch?v=Ep397imVhWA

Video of injector spray pattern and Vac reading at idle after short drive <2 miles

i know the guage is dirty but its sitting between 20-25 and my gauge reads around 2 because its not zero-d anymore, but its the only gauge I have access to ATM

[Front Range]

You might try swapping out the distributor if you haven't done it already. I chased a random stutter for a couple years that turned out to be a weak pickup in the distributor. Only when it began backfiring and cutting out in second gear did I get it figured out. Don't know if that's your problem or not but you never know. It was in a 77 longbed with 5.7 TBI and TH350.

[MudDiGGer25]

Originally Posted by Front Range

You might try swapping out the distributor if you haven't done it already. I chased a random stutter for a couple years that turned out to be a weak pickup in the distributor. Only when it began backfiring and cutting out in second gear did I get it figured out. Don't know if that's your problem or not but you never know. It was in a 77 longbed with 5.7 TBI and TH350.

I would but i dont have access to one, I was thinking maybe the pickup or stator they are both rusty but when tested with some thin ferrous metal all points had good magnetism, but if there was something wrong in the dist, would that not also affect the injector pulsing? and the timing? both of which are rock solid every which way i can test them, I do have a couple videos of the noid lights connected while running

Its not quite a stutter or backfire, i am fairly certain it is something pertaining to the timing advance/retard controls because it isnt random, I can get it to repeat anytime i desire by repeating the conditions, and its like the timing advances to "optimal" from around 3000-3900rpm under mid throttle only, not light throttle or WOT, but during mid throttle acceleration on flat or up a steep hill, when it reaches 3000rpm, the TPS,MAP, and 02 readings stay the same, and the pedal is not moved even in the slightest, however there is still noticeably more tq output in that rpm range, like you can hear and feel it, like it honestly feels like a small turbo kicks in during mid throttle at those rpms, but nothing when its WOT, or coasting uphill, Logically a weak pickup wouldn't be affected by throttle position (unless im wrong here), and i would think if it was weak that it would cause more mayhem the higher the RPM's got, but i can cruise in 1st @ 6000RPM for 6 or more blocks and no miss, no lack of power, no hesitation, but i could be wrong thats why i am asking for options to troubleshoot


on a side note when i changed the ICM, and cap/rotor/wires, the dist was extremely clean, as if it had been rebuilt with the engine at the same time, no crud or anything in there

[MudDiGGer25]

Ok for anyone who wants to know or think this might be useful, My starter went out on me yesterday and I swapped it with a NAPA 1.4kW unit, turns over nicely now,and i think its not as draining on the battery, I also disconnected the knock sensor and, I couldnt tell you for sure if its running any better performance wise however I have tried to get the "turbo" imitation to repeat at 2500RPM and now it wont do it, I have done nothing else so far besides starter, bat disconnected for about 30 minutes, and unhook the knock sensor, I have to pickup the mrs from work around midnight so i will slide under and reconnect it and see if the fake "turbo" happens again. The scanner showed it was running lean according to 02 data, so im almost thinking that my replacement fuel pump might be weak also, I will obtain PSI numbers later next week, however for the time being, Would a lean condition lend itself to more knock counts? and therefore affect the timing? next I guess i have to find out if i do have a lean condition and if so why, I will be increasing pressure to the injectors to about 15-18PSI so I should be able to richen the mix in a month or so, could having the EGR disconnected cause this also? since it only happens at part throttle, not idle or WOT, and if i do need to reconnect it, What would be causing it to run like crap as the EGR opens?

I may begin another thread once I have the axles/springs dismounted tomorrow morning, but I found this K20 in the yard and its the only 3/4 i found with both still in it, now from what I have found it should have either a SF or FF14 in the rear since it is a 1982 with the 6.2L, 4.10 AR and a 10 bolt front with 8 lug shafts.

Does anyone see why or why not this will work? I have not measured the springs end to end yet since i didnt have a tape with me, but otherwise should the shocks/axles/ yokes line up? There is a older 1/2 burb i got the RPO codes for in case the 3/4 doesnt work out, but the 3/4 stuff would be better for towing and playing.

[MudDiGGer25]

Update to original Topic:

I disconnected the knock sensor the same day my starter failed, it has been disconnected since then.

I feel underpowered, like it seems to drag itself along from 3500-6000rpm, but idle to 3500 seems pretty normal.

I can NOT get it to repeat the "turbo" effect from 2500-3500rpm, I have been trying for several days but to no avail.

I think my CEL is burnt out because it does not light up when KOEO, and it hasnt lit up since the knock sensor was unhooked. I have not connected a scanner yet to see if I do infact have a code.

I can currently cruise without it feeling like it wants to fall on itself 25-40mph.

also IMO i think the idle is high, but no vac leaks, ive even tried plugging all the ports with rubber plugs to eliminate possibilities. it sits around 900-1100 at idle, and even when up to 180F im still in the 900's.

I have seen a noticable in town MPG increase (1-3MPG) cannot give exact # because I havent refilled yet, but the tank is lasting longer, and I am not being any nicer to the throttle, I even went mudding a few days ago, and raced a jeep yesterday.

I am going to reconnect it later tonight and drive a couple days and see if the symptoms return.

I am wondering since the starter is right there, could the starter have been causing a false knock reading as it rattled around? it was pretty shot.

Also I am beginnning to suspect my used pump is getting tired, as I am almost always reading a lean condition, and I know a lean condition can lead to higher knock counts as well, I will get some free time towards the end of the week and test the FP again and see what i get. I am only wondering because it almost acts like its lean, and when i romp on it, it sounds like its sucking way too much air in comparison to the fuel coming in.

However what should be my next suspect if my knock counts remain high but my FP is actually ok? No VAC leaks, only minimal exhaust leaks, (less than 1/8th here and there) base timing is correct.

I have to tow a 25ft RV in a little over a week, so i need to be running as close to 100% as possible.

[MudDiGGer25]

Ok so did some more work and i installed a used 4wire narrowband heated o2 sensor from a 98 pontiac, that was working at time of pull (about 2 months ago)

I got my info from this forum since he also was using a 87 donor harness: http://67-72chevytrucks.com/vboard/s...d.php?t=352321

Ok here are all the pin outs and the color of the wires. My computer is the standard #1227747

A1- grn/wht- this wire is used to power the fuel pump-relay.
A2- no wire
A3- no wire
A4- gry- to egr-relay. This is a ground for the ECM to control the EGR relay.
A5- brn/wht- service soon light. This is a ground to turn on the light.
A6- pink/blk- switched 12v from the ignition relay.
A7- no wire
A8- ornange aldl serial data wire pin-e
A9- wht/blk-aldl pin B When jumpered to ground will set the computer to diagnostic mode.
A10- brn- VSS speed sensor signal to the computer, (This wire I will wire this to on side of a after market VSS sensor and the other wire on the sensor goes to ground).
A11- blk- MAP sensor ground.
A12- blk/wht- System ground. This wire is tied to other grounds in the harness and goes to engine ground.

B1- orn- 12v batt power ( I looked and traced down this wire on my 87 cab harness and this is fuesed I think it was a 15). I will probably use a inline fuse.
B2- tan/wht- Fuel pump signal from the relay. This one ties into several places, the fuel pump, the relay, and the ecm. When the relay is on it sends 12 volts to trun on the fuel pump.
B3- blk/red- Distributor plug
B4- no wire
B5- purple/wht- Distributor plug
B6- no wire
B7- blk- ESC signal This is the knock sensor signal to the computer.
B8- dk grn- AC signal. This tells the ECM that the AC is turned on. I am going to tie this into the ac clutch wire.
B9- no wire
B10-orange/blk- park neutral switch wire. some people say this is optional but I do not think it is because it gives a signal to the computer to give the engine a slight bump in rpm.(if you don't need it why did they put it there?)
B11- no wire
B12- no wire

C1- no wire
C2- brn- wire is not needed
C3-grn/blk- Idle air control
C4-grn/wht- Idle air control
C5-blue/wht- Idle air control
C6-blue/blk- Idle air control C3-C6 all go to the Idle air control valve plug on the TBI it's self.
C7- no wire
C8- no wire
C9- purple/wht-Starter crank signal wire. Goes to the small terminal of the starter.
C10- yel- Temp sender
C11- lt grn- Map sensor
C12- no wire
C13- dk blu- throtle position sensor
C14- gry- signal to map and TPS. ( you will see it tied together in the harness)
C15- on wire
C16- orange- This wire is tied with B1 so it is a 12volt wire

D1- brn/wht- system ground goes to the engine.
D2- blk- tied to the wires for the engine ground.
D3- no wire
D4- wht- distrbutor plug
D5- tan/blk- distrbutor bypass. This is the wire that you disconnect to set your timing.
D6- Tan- O2 sensor ground to engine.
D7- purple- plugs in to the o2 sensor
D8- D13 no wire
D14- grn- Injector plug plugs into the top of injector
D15- no wire
D16- blue- Injector plug plugs into the other injector


Assuming this is correct, and from my other searches the purple wire (D7) I cut and spliced into in the picture to run directly to the o2 sensor should have been correct, since the other threads said to follow it out of the loom on the passenger side coming from the PCM and it was the only purple wire besides the purple/white stripe. however I could not get a voltage reading at all on my analog meter set at 2VDC or 2V AC. I tried using the pigtail i found previously but it has 12V on two of the wires and i think a crappy ground on the 3rd. And from what I have been reading the pcm should be sending .5ish V down the wire not 12V. and the o2 sensor flashes back and forth constantly from .1V - .9V.

I do not have access to a live scanner until monday so I cannot get more detailed readings BUT when the o2 is connected to that wire, after a little bit warming up, when i try to rev to say 4000 it starts to want to die, then picks up again, then hesitates, then revs up. when i disconnect it from that wire it returns to the way it has been for months. I am wondering if i connected to the wrong wire, or if this is how it "learns" fuel trims once in closed loop.

I disconnected it just in case i was connected to the wrong wire.

I think my CEL bulb is burnt out since it did not flash when i jumped the terminals, nor does it turn on anymore when KOEO, but I cannot have the truck down long enough to change the bulb until tomorrow around noon.

I do not have the heater element wired just yet, since the bung is in the manifold before the exhaust attaches, so I was wrong about the location previously.

From what i understand a GM 3 or 4 wire narrowband is simply a 1 wire with a heater or a 1 wire with a heater and separate ground to avoid unwanted readings. And with the heater unplugged it will simply wait till the exhaust heats enough.

The pics also show what was previously in the o2 bung, and the wire i am using to carry the o2 signal, it is a 3wire household extension cord and should have no internal resistance but could be shortened a bit if needed.


I got no readings from the o2 or closed loop when connected to the 12V purple wire on the pigtail, while connected to the live scanner before the shop closed.

I am not getting a o2 code anymore after i reset the pcm.



I mainly need to know if i am on the right wire, and if i am, is the sporadic revving a sign that my used sensor is "getting lazy" and not switching fast enough?

https://www.facebook.com/photo.php?f...5&l=7d997039ae

[MudDiGGer25]

Here is a video of the data readouts this afternoon. I did let it warm up to the point where the needle just raised off the line on the gauge.

https://www.youtube.com/watch?v=IZn_...r#action=share

I still have some knock counts when i rev it quick but only then.

MY o2 seems to be operating properly even without the heater element hooked up yet. I was in closed loop already when I connected the scanner.

I have noticed more kick on the 1-2 shift at WOT anywhere from 3000-6000 (if i control it manually

I will let it learn for a few days since most drives are less than 1-2 miles. I should be taking a 300 mile round trip to get this 454 this coming weekend and I can report back if the hwy mpg has improved. however with the front sitting a solid 4 inches higher than the rear currently I really doubt it.

[MudDiGGer25]

Ok so got the replacement dizzy installed and re-installed my 369 module and my cap/rotor that were replaced roughly 4000ish miles ago.

Used the timing light at the shop to set timing, it is now at 1 BTDC, my "guesstimate" where it was running decent was about 8BDTC

Fuel pressure has not been tested although i am pretty sure its not my culprit.


I got the same hesitation as before just as bad as before, i tried disconnecting one sensor at a time then driving to see if it would improve, the only noticable difference was with the TPS unplugged it got so much worse i only made it 2 blocks and had to plug it back in. and by disconnecting the o2 it is not stumbling or bogging

I still have a miss though but that has been there a while and i think ive found the culprit for that : When i was trying to turn the dist to time it i got nailed quite a few times and for a while now i have heard a ticking sound when its idling, then a few nights ago i noticed visible arcs from some of the wires to the exhaust or block. these wires were new old stock, meaning brand new sealed but i had them around for over a year before installing them.

I am going to probably replace them all and/or rob the wireset from the RV in the meantime


My results are now that I can accelerate and cruise with the o2 unhooked only

I can watch the miss very noticeably on the timing mark, like it jumps 4-10 degrees retarded when it happens.

I was able to climb up one of the steepest hills (4%) in town during rush hour I went WOT and was able to reach 5000RPM before i really didnt have much more power probably due to lack of timing and i could feel it missing more from about 3300-5000.

Throttle response is excellent currently

I know timing is probably too far back since I used to be able to climb that hill and reach 6000RPM everyday.

[MudDiGGer25]

In case anyone was curious or if it helps the next guy or gal sometime in the future.

I installed the "rumble" glass packs and the miss was EXTREMELY noticable and actually was getting worse.

The weather got super cold the last couple days so i was putting off looking at it, however this is what i discovered and did to fix what i found

I checked the timing, i actually had it about 4-6BTDC and it was running pretty decent, however 2 days ago i adjusted the dist to 0 BTDC (by ear and using a vacuum gauge) no im not lying, i checked it with a timing light today and it was dead on 0 but at 0 BTDC i get that surge very noticeable at roughly 2000RPM again, so im thinking whatever they did during the rebuild that it likes a little more advance so i re-timed it using the method i use for my 77 450hp 302, max out the vacuum reading, then back it off just about an inhg, which put me about 3ish BTDC.


I got home and i knew the #1 had a miss, so i grabbed a new wire off the 400 and pulled off the #1 wire on the 350 and it literally was melted in half, no idea how since the split was up near the intake. i replaced it and now that miss is gone.


I notice a pitter patter in the exhaust but ONLY drivers side and i cant get past 5000ish RPM anymore. oil level is good and good oil in it. but I did the paper/dollar trick and it pulls it in and out with every revolution of the engine, and its steady. the otherside does NOT do this, and sounds perfectly normal.


From what i have read this is usually a sticking or bent exhaust valve or excessive overlap, im pretty sure the cam is not that aggresive. My next step will be to pull the valve cover off when it is running and make sure everything is tight and lifting evenly.


If that all checks out then my next check would be a compression test since some say the "flutter" could also be a headgasket


I think i may already need new plugs because of the pickup failing and the running lean for over 4000 miles, I will check them on the next warmish day.


Is there anything obvious im missing?


I reconnected the o2 to see if the broken wire was actually throwing off the o2 because of the misfire. My wife gets off work at 1130 and I will find out if it wants to run right.

[68Timber]

Interesting. What do you think the odds are the sticking valve is on the cylinder that wasn't firing?

[MudDiGGer25]

Originally Posted by 68Timber

Interesting. What do you think the odds are the sticking valve is on the cylinder that wasn't firing?

Not sure actually, I pulled all 4 plugs drivers side, and they all looked exactly the same, a little carbon buildup and looked lea. i have a special fine wire wheel for my drill i used to get them all freshened up. I am getting better response and whooped a dodge 3/4 ton easily at 4000rpm with no miss

I notice the vacuum guage flutters just ever so slightly but never by more than 1-2in hg at most usually less, if i bring it up to 2000-3000 it runs super smooth and sometimes it flutters slightly other times the vac holds steady. I have not had time to pull the valve cover just yet, but will do that tomorrow. no ticking like a loose rocker arm. I have to drive 100+ miles each way for dr appointments tuesday so i cant dig into it too deep. I might put some marvel mystery oil into the engine oil, ive seen it work wonders, and maybe lucas fuel injector cleaner for the hwy trip in the fuel see if that clears anything up without pulling the heads.


Its always done the pitterpatter since i bought it, i just thought it was an exhaust leak until now i have changed both mufflers and listened with the muffler off as well on both sides, and pass side is just perfect.



Another probably unrelated issue, with the o2 hooked up it still is messing up in closed loop. i.e. lots of power at WOT, and accelerating with more than 50% throttle, but if im just trying to cruise, any speed, 20-65 and just barely pressing the pedal the engine acts like its ether losing all fuel or spark, but no backfire so i think the fuel is being cut off. then if i dont do anything and just keep the pedal in the exact same spot it will suddenly surge back to life then repeat this until i let go of the gas or punch it.

This does not happen in open loop when the o2 is disconnected. this has now happened with 3 known good o2 sensors so i know the sensor is not at fault, and the live readout verified this.


No vac leaks, and i still cannot get past 5000RPM


Could it be trying to activate the EGR at part throttle and without it connected could cause this?

[SuburbanStevie]

Hello, what do you know about the condition of the distributor? In particular the journal bearings that support it. I had a similar issue, and took a long time to finally find that the bearings were so worn-down that the distributor shaft was rattling all over. Causing the plugs to fire as much as 10 degrees off.

Good luck

[MudDiGGer25]

Originally Posted by SuburbanStevie

Hello, what do you know about the condition of the distributor? In particular the journal bearings that support it. I had a similar issue, and took a long time to finally find that the bearings were so worn-down that the distributor shaft was rattling all over. Causing the plugs to fire as much as 10 degrees off.

Good luck

I just swapped the distributor a couple days ago and the one i put in was in immaculate shape, no slop or play and movement was very smooth. But i think i might have figured out the issue


My exhaust is not "perfectly airtight" at the flange because 1 bolt is snapped off, and i have either a loose rocker arm or a sticking valve because the exhuast pulls in a piece of paper on every revolution and im thinking that because the exhaust is not flowing smoothly in a single direction it is causing the o2 to read falsely and then the ECM over compensates to the point of almost stalling