1990 K2500 350 5.7 TBI Stalls in reverse or drive

[lessersivad]

Fix the exhaust 1st, THEN see how it runs/acts/behaves after that. I'm saying you may be VERY surprised what that'll do.

Either way it needs fixed. Do that first then go from there.

No sense in loading up the 'parts cannon' and start firing away.

 

[magimerlin]

I had the same delema about the stock manifolds.. Both mine where cracked.. I just bought some jegs/flowtech shorty headers(direct fit). I did sandblast the factory just coating off and gave it a good coating of header paint and heated it/cooked it per the instructions in an oven. Years later and no chipping or peeling or burned off areas of paint. It was well forth it in the long run, to me anyways.

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[skylark]

Take about 4 to 5 foot-long chunk of vacuum line and stick it in your ear. Take the other end and go around the manifolds with the engine running. The exhaust leak will be obvious. The sensor below is your knock sensor. The one on the passenger head isn't stock. The factory has one in the intake by the thermostat housing for the computer and one in the driver's side head for the gauge. Is there an electric fan on your truck? That is a common location to put a coolant switch for a fan.

 

[Joe B]

Man, you guys are on this stuff like no other! Thanks for all your help.

I have found a couple of different things not plugged in, misc wires without plugs and so forth. I have tried looking through the GM shop manual, but to no avail. At least now, I can look at the wiring diagram and figure out what and where these should be plugged into and find a wire and buy new connectors for them.

As for the knock sensor, I would think the truck would run like crap without it connected. From the looks of it, it has not been connected for a long time, probably before I bought the truck.

 

[Joe B]

The one on the passenger head isn't stock. The factory has one in the intake by the thermostat housing for the computer and one in the driver's side head for the gauge. Is there an electric fan on your truck? That is a common location to put a coolant switch for a fan.

I do not have an electric fan. I will work on getting all this stuff taken care of and get back to everyone.

Thanks for your help.

 

[Joe B]

You made no mention of checking/setting the base idle speed. It needs to be done any time you replace the TBI unit and/or the IAC.

The ECM controls the IAC. There is no way to measure this once it is installed. The correct setting procedure for setting the BASE IDLE is to ground the ALDL terminals A&B which are the top two terminals on the right side, turn the key to the run position and wait about 30 seconds. Then verify that the IAC pintel is seated by looking the idle passage of the TBI body. once you have verified that the pintel is seated unplug the IAC and set the base idle to the proper speed.(650 RPM'S in drive? I have to look up the spec). once that is done remove the grounding clip and reconnect the IAC. Cycle the key on for 10 seconds and of for 10 seconds and then start the truck.


I can dig up my 1990 light duty truck Fuel and Emissions manual if you need more specifics

Thanks for the info. I found this video helping explain how to do it.

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I found this pic, thought it might be helpful to the next guy reading searching though the treads.

https://www.obd-codes.com/faq/read-gm-2-digit-obd-codes-free.php

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[Tomcat58]

So I have been creeping around the forum for a while looking to see what I can do to fix my stall problem. I can keep the truck going it I hold the brake down and give it gas, but I need to get this fixed.

So here is what I did based on what I have read here on the forums.

Set the timing with the advance wire disconnected
Replaced gas filter
Tested gas pressure, its 12 PSI
Replaced the IAC and set it to the correct depth, 1 1/8"
Replaced EGR
Tested TPS - good
Test MAP - good
Replaced vacuum hoses, connectors and added a clamp to the brake booster end
Replaced the TDI, gas was coming out of the injectors, one has a small leak

One thing to note about the timing, when I set it, watching it with the timing light, I get it set, and then i bounces, then goes back to being set.

When it stalls, it winds down. Here's a video of it, so you can hear it if you want:

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Thanks in advance for your help.

Joe

This whole deal sounds like my problem on my 1991 C2500 5.7 and after testing sensors and all the other things posted here I was stumped. I then remembered what a old timer told me years ago on finding and fixing engines problems. I can hear his words clearly !!! Have you done a compression test ???? My problem started as a rough idle and slowly got worse. It got worse because the head gasket between 3 and 5 cylinders slowly failed. By the time I pulled the head it sounded like your video here. There was about a half inch of head gasket gone between the two cylinders.

 

[Schurkey]

I have a Snap-On MT2500 scanner and while I can see what other sensors and things are doing, I can't see anything but o2 sensor voltage. So I can see that it's working correctly but I can't graph it.

You should be able to see O2 crosscounts. You should be able to program one of the LEDs to indicate rich/lean.

You'd have to have an MTG2500 to do graphing.

I think short term fuel trims on these are "Integrator" values and long term fuel trim data is "Block Learn".

Yup.

131 is the target value IIRC. Anything above that means the computer is adding fuel, anything under that means it's trying to subtract it.

128 not 131.

 

[mountie]

Joe B... what year ??

 

[magimerlin]

Joe B... what year ??

Unless he edited his title it states it's a 1990...

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