Beelzeburb, The Story More Than a Decade in the Making

[Beelzeburb]

Originally Posted by jbclassix

what are your plans for your t-case shifter?

Excellent question. I plan on recreating the linkage my Dad fabricated / adapted for the Blazer. It'll basically just reuse stock parts from a newer truck. I have two separate t-case shifters, but the one I planned on using broke. Sorta disappointed the yard I went to last week didn't have any 4x4s around with the shifter and linkage the Suburban needs.

To wrap up the fuel filler flap install:

The piece I sectioned from the van's fuel filler tube:


New height of fill and vent tubes:


All the old filler pieces and accompanying parts removed to make room for the new stuff:


A couple of small pieces of sheetmetal trimmed, bent then welded in to seal out the elements:

The welds back here didn't need to be very pretty because they're covered by the interior side panel anyway. I'll smear some seam sealer on the joints though, can't be too safe in preventing rust. I'll also cut a half-moon piece of plywood to fill in the hole in the floor where the old fill tube used to run and seal everything up tight.

Two feet of 1 3/4” fuel filler hose @ $20 a foot and five feet of 5/8” vent line (the fill neck on the tank was relocated, but not the vent outlet so it makes a big loop).


So happy everything lined up and fit on the first try:


A quick coat of etching primer and voilà!


That was one of the last obstacles to overcome before I could drive the Suburban. Still plenty of little stuff to take care of (like dropping off the front driveshaft today to have it re-tubed), but most of the 'major' hurdles are out of the way.

[mosesburb]

Looks good man!! With a nice straight hose like that, it should have nice fueling manners at the pump. Nothing more frustrating than having a thirsty vehicle that can only be filled one "click" at a time.

[FRENCHBLUE72]

Looks good..

[Beelzeburb]

Oh, I'm sure the neighbors love me by now.

YouTube - Beelzeburb, She Lives!

[Beelzeburb]

Well, so far I've uncovered about a half dozen ways in which I can throw wooden shoes into my own machinery. Sabotage, get it?

Since completing the fuel filler neck (and cutting a hole in the column for a NSS which I didn't take any pictures of), I'd dumped about 2 gallons into the tank. After fiddling with the wiring a bit, the fuel pump now engages with the turning of the key like it should. Fuel gauge still doesn't register correctly but all the others work fine. The first time the pump powered up, there formed a rather sizable puddle of gasoline underneath. Turns out I just hadn't tightened the fitting on the “out” end of the fuel filter. Simple fix. With it wrenched down, the rest of the fuel system held pressure just fine. Not that the pump generates more than approx. 15 psi anyway.

Next fluid on the list to be checked was coolant. It was low about two gallons because I hadn't yet refilled the system after taking a shower from it a couple years ago (post #38). With the radiator topped up, I noticed a rivulet of green liquid trailing down the front of the block. Again, something else I'd only left finger tight for reasons unknown. The front most coolant temperature sensor (of three on this engine) only needed a smidgen of thread sealant and a little torquing to put an end to that leak. The other fluids looked good; oil and ATF were at acceptable levels and no other connections had dripped yet, so I was ready to start the engine and break it in. It didn't want to play my little game though.

So far I'd been able to run the engine one short burst at a time using starting fluid. Then even that stopped. Unphased, I began following the troubleshooting flowcharts in the Fuel & Emissions Supplement. After rigging up a temporary Service Engine Soon light, I knew that the ECM was getting power and could command a ground. The next items to check were the fuel injectors and their associated wiring. After balancing a test light precariously perched where I could see it while cranking the engine, it didn't flash. Flowchart A-4 told me the next step was to probe a purple/white wire on the distributor with a second test light to see if the first test light would flash momentarily. I thought something was fishy when none of the wires leading to the distributor were purple with a white stripe. After probing each of the connectors without the desired result, it was back to simply tracing the wiring and looking for faults or shorts. So I followed the purple/white wire from pin B5 on the ECM all the way down the harness, across the cabin, through the firewall, into the engine bay and finally to the IAC solenoid. I was quite sincerely desirous to know which GM engineer decided to make the IAC solenoid and distributor wiring connectors exactly the same dimensions. Cheerfully though, I swapped the two, glad to have found the culprit.

With a little more cranking of the starter, fuel began to squirt from the injectors which was a great victory. Now I had to figure out why the motor wasn't getting spark anymore. Surmising that having the wiring reversed might have fried the HEI module in the dizzy, I swapped it out with another. There happened to be an entire spare distributor on hand to liberate one from (not sure why I've got one, it was just there in my parts pile). That did the trick though, and the engine roared to life, running on gasoline for the first time. By now it was getting a little late in the evening and I didn't want to disturb my neighbors any more. Today though, well, I broke in the camshaft by running it at 2300-3300 rpm for nearly 20 minutes. I hadn't been paying attention to all of the gauges for a couple minutes and the coolant got a little above 200 degrees and began spewing out of the overflow (I'd ordered an overflow bottle from the Chevy dealership in town earlier today) onto the engine. The motor started stumbling, so I shut it off. No harm done to anything mechanical. Looks like it's time to finally hook up the auxiliary cooling fan though. Now the Suburban is close to being ready for a drive to the muffler shop to have a dual exhaust system bent up. On a side note, my sister stopped by today while I was in the middle of breaking it in. She later told me that she'd been a bit confused when exiting her car and had begun looking around for a low flying aircraft only to find me varying the throttle in my Suburban instead.

One second to last aside. That freshly re-tubed front driveshaft is the perfect length. No more splines sticking halfway out or fears of it coming apart when raising the front end with a floor jack (or coming out of a steep driveway).



Oh, and my transmission temperature code went away when I unplugged and replugged the connector. It's nice when fixes are simple like that. As it sits, there are no problem codes in the engine or transmission controllers, and the only wires that aren't hooked up are for dash warning lights. Those lights will include high beam indicator, brake warning, SES light, alternator/charge warning, cruise control engaged light and possibly a 4x4 indicator. Electrically, I'm basically done.

[VA72C10]

looking and sounding good!

[FRENCHBLUE72]

Nice job good to see it running and hear that you got your problems figured out ..

[Beelzeburb]

Originally Posted by mosesburb

Looks good man!! With a nice straight hose like that, it should have nice fueling manners at the pump. Nothing more frustrating than having a thirsty vehicle that can only be filled one "click" at a time.

Thanks man. I'd have been happy just to have the unleaded restrictors in place, but with a nearly straight shot it seems to fill just fine so far from 5 gallon cans. I drove my Z nearly 1000 miles a couple of weekends ago and it was very tricky getting the pump nozzle and tube (about a 3" ID straight down) lined up in such a way as to prevent fuel splatter while trying to fill it to the top. There is one small pinhole in the Suburban's newly modified fill tube that leaks a bit when filling, so It'll come back off for a quick zap and pressure test.

Originally Posted by VA72C10

looking and sounding good!

Thanks, it's getting there little by little. It was popping a bit in the video, but I think that's gone away now.

Originally Posted by FRENCHBLUE72

Nice job good to see it running and hear that you got your problems figured out ..

Well, most of the problems are sorted so far. Yesterday I finally set the timing properly. The engine had been 'idling' at 1600 rpm. It was sitting at 30° because I’d only eyeballed the rotor orientation before. All that needed to be done turn the dizzy until it came closer to the 4° called for by the service manual and the idle speed is much more inline with what the book calls for. The current list of problems are: figuring out why it doesn't like to fire up without a starting fluid boost, or fire at all when warm and figuring out why it won't go into gear. I can move the shifter around all I want, but it doesn't engage any gear. Meanwhile, the transmission controller shows that it's in 1st no matter what (even with the engine running). Hmmm, time to peruse the service manuals again. And no, the transfer case is not in neutral. I checked.

[jbclassix]

I'm only saying this because I thought you'd laugh, not because I think this is your problem. A guy I used to work for changed out his torque converter, and once he was completely buttoned up found 6 short fine thread bolts... TC to flexplate bolts. IF you used a factory harness, disconnect the single brown wire with a black stripe when setting the timing(should be close to your bulkhead connector)... That one kicked my but for a while

[Beelzeburb]

Hey, believe it or not, one of my next ideas was to pull the t/c cover and watch to see if it's spinning. It's been too many years since I put it together to even begin to remember if every hole had a bolt in it.

-edit-
Well, waddaya know? Huh, look at all them purdy holes with no bolts in 'em.

[jbclassix]

Sorry...

[Beelzeburb]

Originally Posted by jbclassix

Sorry...

Sorry for being such an awesome guy and helping me remember to check the flexplate to torque converter connection? That's a funny thing to be sorry for.

Well, it's a little late now, but tomorrow the Suburban might move under it's own power for the first time since the summer of 2002.

[jbclassix]

Na, just sorry you got it all back together first!

[Beelzeburb]

5 miles. That's how far I drove it yesterday, straight from the house to the muffler shop.

I had found the appropriate flexplate bolts with the help of a friend and torqued the three of them down to 33 lb-ft. I think the flexplate is the original T400 piece and even though it has six holes, three of them just don't quite align. Yesterday morning (after two trips to the auto parts store for more fluid) it sucked down approx. 10 quarts of ATF before the dipstick registered the correct level. The CompuSHIFT controller's readout was now displaying the correct gears while shifting, and I added the Suburban to my insurance policy so it was ready to go.

There were so many simultaneous sensory inputs to interpret and adapt to. The first thing I noticed was that the acceleration wasn't like it should be. I knew why too, the gas pedal needs more of a bend because even mashed to the floor I could only get half throttle. Not that I really wanted more throttle than that though because 3-4K RPM was way too loud. I felt bad for everyone in a half mile radius and was on a constant lookout for police. I only saw one police Durango in the 5 mile journey and it was coming the other way as I approached a red light, so I let the Suburban idle as he passed. Whew.

Some things worked wonderfully though. The brakes were excellent and immediate, very happy with that. The transmission shifted flawlessly. Bwwwwwaaaaaaaaaa, second, bwwwwwaaaaaa, third, BWWWWWWWAAAAAAAA!, fourth, and then I could feel lockup too. Power steering did it's thing and made it very easy to turn. It was a bit of a handful on the highway though because I've got about 1/4 turn of play total in the wheel from one side to the other. Just like it was in High School. The Autometer speedometer hasn't been calibrated yet, so I used the CompuSHIFT display's speed reading (based on the axle ratio and my best guess on tire size) to know how fast I was going. I had someone following me for safety and they said it was about 5mph off at highway speed.

I arrived at the muffler shop before 5:00 on Friday, but they were gone already. I gave the Suburban a quick once over before locking it up for the weekend, and there were no leaks or fluid drips anywhere. On Monday morning I'll leave the keys with them and discuss the exhaust routing. Once it's back home (and much quieter) I can resume troubleshooting. I've got a few theories I want to investigate. Still need to get to the bottom of the 'lack of fuel while cranking' problem. I think it might be the previously kinked flexible fuel hoses that attach to the TBI or perhaps the short piece of flexible hose on the in-tank fuel pump is rotted.

[Beelzeburb]

The saga of the lost fuel pressure continues.

The exhaust shop had finished with my Suburban by about 1 p.m. on Monday (05-02) at which time I picked it up. The drive home was much quieter but still sluggish and full of backfiring. The computer had logged a “lean fuel condition” code when I checked it later. All signs seemed to be pointing to a fuel delivery problem.

First let's check out some of that shiny new exhaust system.



2.5” all the way back with twin Dynaflow non-chambered 3” in/out mufflers (must have been out of the 2.5” style that day) and chrome tips that exit just behind the rear tires. I could have saved some cash had I gone with the shop owner's suggestion and done a single 3” system but I requested the more traditional look. Once home I could finally hear that there was an exhaust leak which lead to a torquing of the headers. I also pulled the fuel fill hose back off to weld shut the one pinhole in it. Now the fill cap has a 'whoosh' when it is unscrewed because the system can hold pressure properly.

On Wednesday morning (05-04) the parts arrived to replace those kinked fuel lines which I hoped would alleviate some of the driveability symptoms I'd experienced. 20' of -6 braided stainless over synthetic nitrile with hose ends and adapters for the metric o-ring fittings the TBI uses.



Aaaaand a couple close-ups of the old fuel feed line:



This was the first time I'd assembled my own hose with re-usable ends. Fairly simple and straightforward if done properly.



After tightening the lines and a throwing on a new WIX fuel filter I also removed the gas pedal and bent it an inch or two. Post modification the TPS now read 0.88V closed and nearly 5V with the pedal to the floor. We'd found full throttle. Then, after recalibrating the transmission controller to accept the new TPS reading it was time for a test drive. The same symptoms were still present. Back to the manuals and research. The Fuel & Emissions supplement has some great troubleshooting charts. All signs seemed to point to low fuel pressure. The only gauge I had that registered fuel pressure in the needed p.s.i. range was an old vacuum gauge with a very small orifice. Before buying a new ornament for my gauge drawer I decided to drop the tank to inspect the fuel pump and it's attached hose instead. I should probably mention that just last year I replaced a bad in tank fuel hose on my DD, so I'd been down that road before.

The tank and pump on the Suburban had come from a ‘87 - ‘91 Blazer w/ EFI. The other pump / sending unit assembly sitting in my parts cache came from the '88 C3500 (I scrapped the tank some time ago). Speculating that perhaps the Blazer pump wasn't cutting the mustard any more, I swapped it out for the truck unit and slapped the tank back in place. When the pump didn't engage I had to remove the tank once more to diagnose a loose wiring connection. Now that everything was back in place, the engine started from cold without needing an extra boost of starter fluid, but it still backfired and wouldn't run right on the first test drive. Pooh. Soon thereafter I ordered a fuel pressure gauge and tee fitting. Section A-4 of the Fuel & Emissions supplement has a flowchart with fuel pressure diagnosis instructions which I followed precisely (pages 3-34 to 3-35 for those of you playing the home game). 9 p.s.i. is the minimum pressure the engine needs to run right.
8.5 p.s.i. was the reading on the gauge with the key turned to the 'on' position (pump runs for 2 seconds and then turns off which causes fuel pressure to return to 0 p.s.i.)
11.5 p.s.i. was the reading with the return line blocked and the pump wired to run constantly

Neither of those reading were really abnormal according to the manual. Fuel pressure should have been able to climb straight up between 13 and 18 p.s.i. with the feed line deadheaded (max pressure the pump should be able to output). With the return line deadheaded instead (fuel is able to flow through the pressure regulator) the pressure should not exceed 13 p.s.i. and if it did, then the regulator needed to be replaced. Mine was 11.5 p.s.i. which wasn't above the max. Still confused I started the engine which gave me the most worrisome reading of all, 6.5 p.s.i. at idle. It seemed to me that if the engine wasn't getting enough fuel, then it must have been a problem with the fuel pump not flowing enough. Well, that or a faulty fuel pressure regulator not letting enough pressure build up. Crap, which was it?

Turns out it probably wasn't the fuel pump. I took a gamble and ordered a nice, new Walbro 190 l/hr unit, dropped the tank once more (third time's the charm?) and installed it. That only raised fuel pressure by .5 p.s.i. at idle. Pooh again. Still, it ran much better on the test drive around the neighborhood. Now it was time to investigate the fuel pressure regulator. Instead of messing with trying to rebuild the stock unit I ordered a JET Performance adjustable FPR. I'd read that once one increases the airflow in these engines that the fuel pressure usually needed to be raised a smidgen in order to keep the A/F ratio from leaning out too much under WOT conditions when the computer operates in open loop mode.

With time to kill between bolting on parts that didn't entirely solve existing problems and ordering new parts in the hopes that they would, I tried my hand at a few other small projects. Cut a couple new holes in the dash for those side A/C vents.



Picked up the coolant recovery tank and cap I'd ordered from the Chevrolet dealership in town. I'd told the parts guy that I wanted these pieces for a 2WD '93 Astro van.



Sure, I could have traipsed around a few wrecking yards looking for junked Astro vans, but this way I got brand new parts, not 20 year old plastic with an unknown history. This also offered a much cleaner and more hidden install compared with trying to reuse the bulky '88 C3500 tank I still had in my possession.



I tried forming the needed bends in the hose using an approach I'd read about on another forum. The instructions said to run a wire through the hose then form it to the needed curves and angles. After that it was supposed to spend some time in the oven at around 400°. That didn't go over so well because the hose started emitting a faint smoke with a foul odor once the oven got up to temp. I took it outside immediately and doused the whole thing in cold water from the garden hose. It was a calm day so the house took a while to de-stinkify. The hose did still retain most of it's shape after I removed the wire though.

I also got around to tackling the transfer case shifter. It was a toss up between repairing a broken GM NP241 shifter or adapting a Dodge transfer case shifter I had on hand.



I liked the shallow packaging of the GM shifter so I decided to disassemble it and weld the broken bits back together.



The transmission hump had to be modified slightly. I offset the shifter to the passenger side in order to clear the transmission itself.



After a little trimming and a few minor adjustments it could engage all the gear positions.



It seems that the shift pattern on the stick, from front to rear is 2HI – 4HI – N – 4LO.

I killed some more time by cutting a leftover scrap of pine shelving to fill the hole where the old gas fill tube passed in the rear.



Then, yesterday, the adjustable FPR arrived.
Old (L) vs. New (R).


It's a very straightforward install, but the instructions were still quite spartan. They didn't bother to mention anything about which way to turn the Allen screw to raise or lower the pressure. I simply guesstimated and set it right in the middle of the adjustment range. After replacing the old gaskets with the ones supplied in the kit and tightening all of the little Torx screws I fired the engine up. Fuel pressure was immediately holding steady at 11.5 p.s.i. That actually caused the engine to run too rich during open loop startup mode and I had a few drips coming out the tailpipes. Once it warmed up and the computer took control of air/fuel mixture duties I took it out for a test drive. It immediately felt and sounded different. Puttering around the neighborhood below 25 mph didn't cause it to bog or backfire anymore. Getting out on the highway it seemed to do much better. But, at certain spots in the gas pedal's throw, it still bucked and popped, just not as much as it had before. I came back to the garage and grabbed my scanner. With it hooked up I tried a WOT run getting on the highway. The O2 sensor registered between 900 and 950 mV, so I know that it wasn't running lean (below 800 mV).

When I got back home and shut the engine off, I tried starting it again to see if the hot start problem was still present. A dilemma arose when the engine didn't crank. I'd guessed at the problem the other day and finally confirmed it, the alternator wasn't charging with the engine running. I'd been driving around on battery voltage only this whole time and it was now down to about 11.1 V with the engine running. That simply wouldn't do. My initial conjecture was that the alternator was a goner. I'd even gone as far as eyeballing a 140 amp Powermaster to replace it. After that I'd kept reading and researching alternator function and came across this line on page 6D3-2 of the FSM, “Either the “L” or “I” terminal (or both) is used to turn the regulator on and allow field current to flow when the switch is closed. The “L” terminal must be connected through an indicator lamp or suitable resistor.”



I'd only had the brown wire from the alternator dangling about, not connected to anything. Pulling out the wiring schematics involving the charge warning light I was able to identify the components involved. In it's stock configuration, the brown wire simply connected straight to the instrument cluster circuit board where all the appropriate connections were made, including one with a resistor.



That's the board, and in the upper left hand corner is the resistor that I pulled off of it to wire inline. The temporary wiring I crimped together in 5 minutes (two wires, a bulb and the resistor) solved the problem and the alternator started charging. Having a fully functioning charging system didn't fix the backfiring (of course), so there's still some investigation to be done.

[jbclassix]

I love watching your build progress! Mostly because you are going the same direction I plan to go. I didn't read back through to see how you set the timing, but did you set your timing at 0deg with the brown/black wire disconnected? On both my 95 Yukon and 91 Suburban the timing has to be DEAD NUTS on or it runs like CRUD! I also had issues with an aftermarket distributor I bought for the Yukon. It would Detonate under load no matter what!

[mosesburb]

Your fuel pressure is too low. Turning the screw clockwise will increase the pressure. The range is 9-13, but anything less than 13 is just giving away power. I have several TBI systems in service and none of them are run less than 13--most are 15psi. Any more than 15 without burning a prom for it and it will run too rich (make good power doing it though). Now, I am not saying this will fix your problem, but it should be addressed before remoing any more of your hair trying to solve your drivability issue. Oh, and the drips from your exhaust are condensate, not fuel. So crank up the pressure to at least 13psi and see what happens. If it doesn't fix it, give it some more and see what happens. These injection systems were notoriously lean from the factory, so some more fuel pressure will help that situation as well.

[Beelzeburb]

Thanks for the suggestions guys. I'm spending the day whittling down my choices of possible problem causers.

Yesterday I relocated the fuel pressure gauge up to the engine bay (it had been down by the exhaust) so that heat soak would be less of a concern. The little liquid filled gauge had been getting too hot and reading lower and lower the longer the engine was running. I'm also going to poke a hole in the gauge's fill plug as a pressure relief. After removing the fuel pressure regulator again and turning the Allen screw a little bit more, the fuel pressure came up to 14 p.s.i. at idle. Perhaps I should have elaborated on the exhaust condensation the other day, it was dripping with black sooty deposits riding on the water. It was leaving stains on the driveway, just like when I've accidentally adjusted carbs to run too rich on other vehicles I've owned. I can't tell what it's doing now because it has been raining here for the past three days. Oh, I also unhooked the fuel hard lines and blew compressed air through them just in case there was some sort of blockage. No changes in performance yet.

I'm also definitely going to re-check the timing. I'll be sure to remove the appropriate wire this time. I was curious as to which brand of aftermarket distributor you tried jbclassix. I've heard good things about the GMPP one, but haven't heard anything about other brands.

The other likely problem causers I'm eyeballing right now are the EGR system and all of the ignition system (especially the coil). I had the dizzy cap off the other day, but both it and the rotor are fine. No cracks, no evidence of crossfiring. The firing order is correct and the plugs are sparking bright white. The spark plugs (stock AC Delco style) are gapped correctly and none look overly sooty so far. Both of the ECM grounds are solid, straight to the engine at the thermostat housing. The engine block itself is grounded straight to the battery (battery also grounds to body). The frame is grounded to the block and also the body. With the alternator now working, it holds steady at 14V with the engine running.

It's an EST system, not an ESC system, so there's no knock sensor to befuddle things. Coolant sensors read accurately and it holds a steady 195° when warmed up. The MAP sensor gets it's signal straight from the TBI, it's not teed. The heated O2 sensor is doing it's job properly. There are no air leaks at the base of the TBI, I've already checked that. There are currently no codes in the engine computer. Just making sure I've got all of the basics out of the way first before delving deeper.

[mosesburb]

Do you know what year truck the injection system came off of??

[Beelzeburb]

1988 C3500
Model #C30903, regular cab, 8' fleetside bed
L19 engine option code, 7.4L V8 engine w/ EFI
YF5 California emissions (same as Federal emissions equipment, just extra testing)
MX1 automatic transmission (TH400)
Most likely GT4 (3.73) or GT5 (4.10) rear axle gears
KC4 engine oil cooler and V02 H.D. cooling package
Probably had Z82 trailering package too (hitch, wiring, transmission oil cooler)

[jbclassix]

Originally Posted by Beelzeburb

I'm also definitely going to re-check the timing. I'll be sure to remove the appropriate wire this time. I was curious as to which brand of aftermarket distributor you tried jbclassix. I've heard good things about the GMPP one, but haven't heard anything about other brands.

It's an EST system, not an ESC system, so there's no knock sensor to befuddle things. Coolant sensors read accurately and it holds a steady 195° when warmed up. The MAP sensor gets it's signal straight from the TBI, it's not teed. The heated O2 sensor is doing it's job properly. There are no air leaks at the base of the TBI, I've already checked that. There are currently no codes in the engine computer. Just making sure I've got all of the basics out of the way first before delving deeper.

Originally Posted by Beelzeburb

1988 C3500
Model #C30903, regular cab, 8' fleetside bed
L19 engine option code, 7.4L V8 engine w/ EFI
YF5 California emissions (same as Federal emissions equipment, just extra testing)
MX1 automatic transmission (TH400)
Most likely GT5 rear axle gears, 4.10:1
KC4 engine oil cooler and V02 H.D. cooling package
Probably had Z82 trailering package too (hitch, wiring, transmission oil cooler)

The dizzy I used was a cheepo off cheepBay. It looked just like the summit one. I dream of having the GMPP one! I am gonna get the cheepo dizzy rebuilt cuz it has a billet base.

Your TBI system came off a 88 and you are running a 4L80E, what ECM are you using? I Know my 91 V2500 burb has the same sensors as my 95 (minus the ESC) as my 95, but they are WAY different from my Bro's 89. Does that make a difference?

[Beelzeburb]

The ECM is a 1227747, the sticker says it was remanufactured. I had just checked it the day before you brought it up. That ECM number corresponds correctly to the year and truck this engine came from. The ECM and the transmission have no connection to each other now. There were two wires from the ECM that did hook up to the TH400. One controlled torque converter lockup and the other went to a downshift control solenoid. I cut both of those because the 4L80E is completely controlled by the COMPUSHIFT unit (which works just fine, no problems there).

I've been working, testing and adjusting, but no change yet. I bought a Battery Tender Plus, so now the battery is fully charged and the starter spins the motor over quickly. I've checked for air leaks all around the intake manifold and found none. I followed the testing procedures for the EGR system in the service manual. The whole system checks out and functions as intended. I popped the valve covers off and adjusted the rockers according to factory specification (zero lash, then 3/4 of a turn). All of the valvetrain looks great, nothing broken, bent or misaligned. I unbolted the headers and applied a thin coat of high-heat silicone on both sides of the gaskets (a step called for in the instructions, but I didn't do it the first time around). That stopped the minor exhaust leaks I had had. I've always been careful to use sensor safe silicone on this engine. I replaced the spark plug wires with some that had more user friendly 90° boots. I even checked the resistance on the coil which didn't seem to give off the right readings, so it got replaced too, but to no avail.

It still needs starter fluid to fire up. It still stumbles and backfires out on the road. It still doesn't set any codes. It's still simply not running right. The symptoms seem to get worse when the engine is warmed up completely (well, to a point). I haven't completely run out of plausible components to check yet, but the 'normal' stuff doesn't seem to have been the cause so far.

[FRENCHBLUE72]

Have you checked out this thread?

[Beelzeburb]

Sorry, I can't see your link FRENCHBLUE72.

I did perform a compression test this morning. Nothing extraordinary there, all cylinders are good and within a close range of each other. This problem I'm having has got to be something electrical or fuel related.

[FRENCHBLUE72]

http://67-72chevytrucks.com/vboard/s...55#post4693255


MMMMMM Might help if I actually posted the link... Sorry about that..