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