tbi issues, on my 88 gmt400

[Swims350]

I keep having the same issues with my 88 tbi and I'm wondering what would happen if it were driven with the timing connector unplugged?

I don't have much time to trouble shoot, don't have much time to get online and check questions from old threads and such either.

everything is new, brand new distributor, it's maybe 2-3 years old now, had the same issues since new.

Motor I rebuilt, stock replacement cam, couldn't run the old dist. to try it and see if it done the same thing as it rusted and the pickup coil fell apart, thus why I changed to the new one.

The truck I removed the egr valve, blocked the intake, removed the AIR system, run headers and still have an o2.

The issues, first put together, set it to zero with it unhooked, no power, run ok but no power no speed, wouldn't run over 40 mph. to the floor.

advanced the timing, ran great. tons of power.

the bad... when changing from drive to reverse or vice versa, truck would die. It also once warm will NOT refire unless it sits for 10 minutes or maybe 5. Then it will refire. Always done this, always would not refire even with the old dist. and before the engine rebuild. My uncle owned it before me and drove it so he knew how it did and told me.

I changed the sending unit, rebuilt the throttle body and cleaned it all, changed to a new tps sensor. I also check fuel pressure before and it was right at 12-13 I forget exactly which, my uncle had the FP changed before I got the truck.

new fuel filter 2 or 3 times and no change, ran fuel system cleaner, seafoam and everything, nothing.

truck does have a th350 now and not a 700r4.

and after the tbi rebuild no change done to the dist. from before when I dvanced it and it ran great, everytime you got on the pedal it would backfire or cough like.

advancing it helped eliminate that issue, but increased it's die when changing gears, now it's really bad, but when I unhooked the timing connector it won't die changing gears. It only does it once warmed up with the connector plugged in, when cold it doesn't die. Now with the connector unhooked it won't die, but it still will not warm refire. It has to sit a minute or two then it will refire.

I checked fuel pressure running, and it was steady, but once shut down dropped to zero, mine does not hold fuel pressure once turned off.

the dist. is from autozone, had a new ICM and pickup coil, and I bought a new rotor and cap for it, new coil.

so any ideas throw em out, and if not then let me know driving wise with it unhooked would it hurt anything?

 

[Jims86]

I keep having the same issues with my 88 tbi and I'm wondering what would happen if it were driven with the timing connector unplugged?

I don't have much time to trouble shoot, don't have much time to get online and check questions from old threads and such either.

everything is new, brand new distributor, it's maybe 2-3 years old now, had the same issues since new.

Motor I rebuilt, stock replacement cam, couldn't run the old dist. to try it and see if it done the same thing as it rusted and the pickup coil fell apart, thus why I changed to the new one.

The truck I removed the egr valve, blocked the intake, removed the AIR system, run headers and still have an o2.

The issues, first put together, set it to zero with it unhooked, no power, run ok but no power no speed, wouldn't run over 40 mph. to the floor.

advanced the timing, ran great. tons of power.

the bad... when changing from drive to reverse or vice versa, truck would die. It also once warm will NOT refire unless it sits for 10 minutes or maybe 5. Then it will refire. Always done this, always would not refire even with the old dist. and before the engine rebuild. My uncle owned it before me and drove it so he knew how it did and told me.

I changed the sending unit, rebuilt the throttle body and cleaned it all, changed to a new tps sensor. I also check fuel pressure before and it was right at 12-13 I forget exactly which, my uncle had the FP changed before I got the truck.

new fuel filter 2 or 3 times and no change, ran fuel system cleaner, seafoam and everything, nothing.

truck does have a th350 now and not a 700r4.

and after the tbi rebuild no change done to the dist. from before when I dvanced it and it ran great, everytime you got on the pedal it would backfire or cough like.

advancing it helped eliminate that issue, but increased it's die when changing gears, now it's really bad, but when I unhooked the timing connector it won't die changing gears. It only does it once warmed up with the connector plugged in, when cold it doesn't die. Now with the connector unhooked it won't die, but it still will not warm refire. It has to sit a minute or two then it will refire.

I checked fuel pressure running, and it was steady, but once shut down dropped to zero, mine does not hold fuel pressure once turned off.

the dist. is from autozone, had a new ICM and pickup coil, and I bought a new rotor and cap for it, new coil.

so any ideas throw em out, and if not then let me know driving wise with it unhooked would it hurt anything?

Wont hurt, will just be 4 degrees lower in timing, and it will not advance or retard. will trigger a light. When its warm, and doesnt want to start, hook a timing light to the coil wire to see if there is a delay in spark. May be one of those elusive power/ ground issues.
TBI does not hold pressure, like TPI.

 

[Swims350]

thanks for the info jim, I went down the road like a mile or less and it ran fine unhooked. idle is kinda high but ran good, no issues changing gears but refire of course couldn't much tell wasn't long enough trip to get her warmed up good.

 

[MrMarty51]

Do You have a good ground wire from engine to frame to cab ????

 

[RetroC10Sport]

Mine doesn't hold fuel pressure once shut off either.

 

[austinado16]

Since this is your rebuild, are you sure you have the cam timed to the crank correctly and not a tooth off? Are you sure you have all the plug wires on in the correct order and locations? Have you ever replaced the IAC (Idle Air Control valve) on the right rear side of the TBI? Any chance you could get a computer out of a similar year truck, either from the local wrecking yards, or ebay, and see if that doesn't make a difference?

Have you thought about hooking up a remote start button and leaving it under the hood, so that when it does it's hot-soak-no-start scenario, you could pop the hood, remove the air cleaner lid, and with the key "on" crank it over while standing there watching the injectors to see if they spray? And have an extra spark plug that you could put in a plug wire, in order to check for spark. If you knew what you were losing, you could focus your attention on what causes that. For example, maybe your headers are getting the fuel lines so hot that the pump can't pump fuel against the vapor lock that's being created. So maybe the fuel lines need some stainless heat shields put in place? Just thinking outloud, but you get the idea.

Think in terms of, "It didn't leave the factory this way, so what's different?".....either in what's failed, or what's been done by you or previous mechanics to change it from it's factory configuration, that is now causing all these issues. As a rule, returning a modified vehicle to it's factory configuration will usually cure most driveability issues. Using non-factory parts (as I've learned the hard way) can lead you down the path of, "It can't be that because I recently replaced it and it's basically new." Well, there's no getting around the failure rate of **** made in China.

 

[Jims86]

Fuel moves too quick in these for vapor lock.

 

[MrMarty51]

Also, ground wire from fuel tank to frame ???

I forgot, the fuel pump is grounded through the connector. be sure that the connectors for the fuel pump are clean and that the ground wire is making a good connection, and again, be sure that the frame has a good ground to the battery neg. post, either via the body or whatever grounding source there is.
A bad ground, or low voltage, caused from corroded connections, will cause excessive heat in the pumps motor.

 

[Jims86]

Hey Chris, not doubting your mechanical abilities, you definately have your **** together there, but dying when shifting kinda screams vac leak.
No accel over 40 sounds like a plugged exhaust, but I know you are catless.
And the timing issue...nuttier than Squirrel ****(Thanks for that saying, Imann)
The only randome thing that comes to mind, is to hook a vac accumulator to the MAP sensor, and see if it holds vac...I know thats a long shot, and a code for high voltage should come up in the ECM, but I am not so sure about trusting the OBD1 system after hearing soo much weird ****...for example, you unhook your EGr, and AIR, and get no codes, but then I see a bunch of trucks where someone has done the same, and their check engine lights burn like a ************. Maybe even check the VSs wire to make sure something didnt chhew through them.

I am searching for an artical that I saw about injector drivers taking a **** to the point to where the truck still runs, but causes driveability issues. There was a fix that the GM techs were doing by opening the ECMs, and soldering in capacitors on the driver circuits to correct the issue.
Now, dont haul of and get another ECM just yet...this is just me brainstorming out loud right now.

 

[Jims86]

**** me running...here it is!

ECM TBI Injector Driver Failures (long)

Posted by Tony H on June 30, 01 at 07:18:43:

In Reply to: Re: TBI injectors posted by Bryan on June 29, 01 at 23:47:31:

In addition to a faulty or dirty injectors, symptoms like both yours can sometimes be caused by one or both drivers in the computer starting to fail. Some time back I found the following on the Internet:

"GM TBI Pattern Failures

This document is an excerpt of a Help document within the software program Wavefile AutoPro. WF AutoPro is available from Mac Tools. The text that follows was written by Pete Sullivan of Progressive Diagnostics Inc. This information is copyrighted.

Many 1986 and newer GM cars, trucks, and vans and 3.1L Isuzu Rodeos with Dual TBI systems are afflicted by a disease that, in the advanced stages of failure, can cause hesitation on throttle tip in, rough idle, intermittent stall at idle, poor fuel mileage, and state emissions test failures. This unique disease has eluded the best of technicians. This disease is faulty injector drivers. Specifically, the "Hold" portion of the injector driver is oscillating when it should be holding steady (see notation on waveform example). This oscillation causes the magnetic field to fluctuate, which in turn causes the injector pintle to vibrate. The vibrating pintle reduces the amount of fuel delivered by the injector. The longer the injector on-time, the more inaccurate the fuel delivery is. The waveform examples were taken on a snap acceleration.

Replacing the PCM with factory rebuilt units usually doesn't help because, not only do some factory PCM rebuilders not check for partially damaged drivers in the rebuilding process, but often times they inadvertently damage the good ones in the rebuilding process. This inadvertent "spread of the electronic virus" occurs at the end of the rebuilding process when the PCM is put in a 600 degree oven and the drivers are operated at high speed. This is part of the final quality control stress check before the unit is sent out for resale. The problem is, technicians have been known to get PCM's from the factory rebuilding center with worse injector drivers than the PCM they sent in. These driver problems can occur as early as 15,000 miles.

There are, as previously mentioned, several stages of this failure. Since the Dual TBI systems each operate with their own independent injector driver, they both fail independently as well. Driveability problems really don't become noticeable to the operator of the vehicle until both drivers are "infected" with the virus. In the first stage of failure, driveability problems usually cannot be detected by the operator of the vehicle. In stage one failure, only one injector driver is "blown up". By "blown up" we mean that the oscillations range from about 30 volts to zero volts between the peaks. Partially blown up drivers will have lower oscillation amplitude and much more inconsistent oscillations. In the second stage of failure, driveability problems are sometimes noticed by the operator of the vehicle. In stage two failure one injector driver is fully blown up and one is partially blown up. In the third and final stage of failure, when both drivers look like the "bad" example on acceleration, then driveability problems are often times noticed by the operator.
A SOLUTION:

There is an inexpensive solution that has been known to fix the problem permanently. Unfortunately, this solution carries with its technical effectiveness, a political burden. First, the political burden. Installing the capacitors could, technically, be labeled as "tampering" with the emissions control system.
You are hereby warned. The flip side of the argument however, says that performing the fix is a valid electronic repair because it returns the circuit to its original EPA certified operating standard. Who is right? School's out on the final determination, but this is only a fix reported as received from the field. If you perform the fix, you are advised that you may have to assume the consequences of your actions. So much for the perfect world.

The technical fix: This solution consists of soldering in a 0.1 microfarad capacitor with a minimum 200 volt rating (Radio Shack part #272-1053, cost less than $1.00) across the injector harness connector terminals inside the plastic injector harness connector. The injector terminals first have to be slid out of their plastic connector. Then, each leg of the capacitor is slid underneath the Weather Pack seal, wrapped around the crimped metal part of the terminal and soldered in place. One capacitor is used for each injector. Polarity is not important. The metal injector terminals are then inserted back into the plastic connector and snapped back into place. Success of the repair can verified by rechecking the waveform under acceleration on the DSO. There should be no oscillations between the peaks. This is a one time permanent fix and has been known to be much more effective and much less expensive than replacing the PCM with a rebuilt unit that may not be any better and could be worse. In cases where a stage three failure was fixed, there should be an improvement in throttle response, acceleration, and idle quality that even the average layman vehicle operator can feel.

THE TURN-KEY SOLUTION:

Many aftermarket PCM rebuilding facilities replace the injector drivers on these units as part of their normal rebuilding procedure. Check with your jobber or aftermarket rebuilder for verification."

Long after I downloaded this, I had a just such a failure in my '87. In my case it was fairly easy to diagnose. I'm running an Edlebrock MPFI system with 8 injectors which fire one bank of 4 cylinders at a time. Pulling the plugs revealed one bank's plugs were heavily sooted while the other side was fine. Remembering the article, I swapped my spare computer in and the problem went away immediately. (The $35 I paid for it on eBay suddenly seemed like a good investment!)

Since the O2 sensor only 'reads' the left bank I suspected that one driver was in fact failing just as the article suggested and the O2 sensor was compensating one bank at the expense of the other. In talking with the Edelbrock technical folks later, they say they do hear about such failures from time to time.

I've not seen this failure mode mentioned elsewhere and had not given it much credit until it happened to me.

FWIW

Tony

Follow Ups:
Re: ECM TBI Injector Driver Failures (long) Matt R 12:42:12 6/30/01 (2)
Try this easy check to see if it might be the problem jcw 08:53:42 7/02/01 (0)
Re: ECM TBI Injector Driver Failures (long) Tony H 20:18:38 6/30/01 (0)
Re: ECM TBI Injector Driver Failures Traveler 09:47:12 6/30/01 (3)
Re: ECM TBI Injector Driver Failures Tony H 10:28:59 6/30/01 (2)
In your case... Traveler 13:01:29 6/30/01 (1)
Agreed. Tony H 20:26:49 6/30/01 (0)

Post a Followup

 

[RetroC10Sport]

Hmmmmmmmmmm...

 

[Jims86]

Hmmmmmmmmmm...

Thats what I said when I discovered that about a month ago, followed soon by an "awww ****" when my kid shut the computer off befor I could save it.

 

[89Suburban]

Subscribed

 

[Swims350]

well haven't read that entire article since I don't have internet and only use it at others ppl's houses but anyways...

as for cam and crank, nope not off. all were new, new timing gears chain cam, lined up the dots perfectly beofore buttoning it all up.

as for vac. leaks never heard or found one, all the lines are new rubber ones.

map sensor does indeed hold vac as it should. I have tested it several times.

vac. holds steady when running.

I do have a remote starter switch but just not installed nor have I ever tried it to watch for spark and fuel.

The warm refire I don't worry about usually, mostly because anywhere we go I'm in the for 10 minutes or so and it fires right up.

The dieing though screwed me over since it would die trying to change gears to park or back up into a place and what not, and leave you in the road waiting to refire it.

Oh another point, on the vapor lock, I had considered it strongly, reason, everytime and I mean EVERYTIME you get it to where it will not refire when warm, when it finally starts, it smells like it ran out of gas, like an old lawn mower, or something along those lines, like lawn mower gas or just like it ran dry and then refired.

The lines are still in the factory spot and it did this with manifolds on it too.

I also had considered starter heat soak.

The most testing I done was power loss on refire to the dist. block and such, it would fade my test light down but not off.

Now for grounds, yes brand new 2 ga. to the frame, from the battery, a 2ga. from the frame to the block, PLUS the factory braided strap. a braided strap and probably 12-14 ga. wire from the head to the firewall, and a new 12-14 ga. wire from sending unit to frame. All were ground completely clean before hooking up to be free of paint and rust.

not sure when I'll get back on but I'll try and reply and read that article more.

 

[Jims86]

well haven't read that entire article since I don't have internet and only use it at others ppl's houses but anyways...

as for cam and crank, nope not off. all were new, new timing gears chain cam, lined up the dots perfectly beofore buttoning it all up.

as for vac. leaks never heard or found one, all the lines are new rubber ones.

map sensor does indeed hold vac as it should. I have tested it several times.

vac. holds steady when running.

I do have a remote starter switch but just not installed nor have I ever tried it to watch for spark and fuel.

The warm refire I don't worry about usually, mostly because anywhere we go I'm in the for 10 minutes or so and it fires right up.

The dieing though screwed me over since it would die trying to change gears to park or back up into a place and what not, and leave you in the road waiting to refire it.

Oh another point, on the vapor lock, I had considered it strongly, reason, everytime and I mean EVERYTIME you get it to where it will not refire when warm, when it finally starts, it smells like it ran out of gas, like an old lawn mower, or something along those lines, like lawn mower gas or just like it ran dry and then refired.

The lines are still in the factory spot and it did this with manifolds on it too.

I also had considered starter heat soak.

The most testing I done was power loss on refire to the dist. block and such, it would fade my test light down but not off.

Now for grounds, yes brand new 2 ga. to the frame, from the battery, a 2ga. from the frame to the block, PLUS the factory braided strap. a braided strap and probably 12-14 ga. wire from the head to the firewall, and a new 12-14 ga. wire from sending unit to frame. All were ground completely clean before hooking up to be free of paint and rust.

not sure when I'll get back on but I'll try and reply and read that article more.

One thing to try, is to power the fuel pump manually, with a switch, or twist wires together..just temporary, bypassing ecm control and the oil pressure switch. Then use that for a day and see what happens....i dunno if it would take care of the gear change stall, but it might, especially if the pressure switch is going bad, and opening the circuit when the rpms drop from gear to gear....just reachin now, dont think I'm nutz or anything.