87 305 tbi crank/ no start issue

[Seamus Langley]

I have had this truck for two years and three weeks ago the truck cut out while driving. over the course of the past few weeks I have replaced the driver side fuel pump, tested both via the pigtail coming from the relay (would like to have known that before I bought a new pump) unplugged the harnesses and check for corrosion. after unplugging and reconnecting the harnesses the truck began to start, and ran for a short amount of time. after turning the truck off and on a few times, the fuel gauge went to past full and is stuck there, no matter which tank I select. I can hear each pump turn on when I turn the ignition to the on position, I have spark, no fuel coming from tbi. I amabot to pull m hair out, I do not have a lot of money to take this to a mechanic and would like to solve this issue myself. I suspect the selector valve ma be the next culprit but they are not cheap. any thoughts or suggestions would be greatly appreciated.

 

[Old77]

Moved out of the introduction subforum and into a more appropriate section

 

[Charlie]

 

[chengny]

I have had this truck for two years and three weeks ago the truck cut out while driving. over the course of the past few weeks I have replaced the driver side fuel pump, tested both via the pigtail coming from the relay (would like to have known that before I bought a new pump) unplugged the harnesses and check for corrosion. after unplugging and reconnecting the harnesses the truck began to start, and ran for a short amount of time. after turning the truck off and on a few times, the fuel gauge went to past full and is stuck there, no matter which tank I select. I can hear each pump turn on when I turn the ignition to the on position, I have spark, no fuel coming from tbi. I amabot to pull m hair out, I do not have a lot of money to take this to a mechanic and would like to solve this issue myself. I suspect the selector valve ma be the next culprit but they are not cheap. any thoughts or suggestions would be greatly appreciated.

The following would suggest that the common lead (from the gauge to the Pollak valve) has an open

after turning the truck off and on a few times, the fuel gauge went to past full and is stuck there, no matter which tank I select.


Read the attached documents and do the diagnostic procedure - from the 1987 Service Manual - and see what you can find out. Disregard the wiring diagram on the 3rd image and use the one at the very bottom:

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Also, you might want to read this thread:

https://www.gmsquarebody.com/threads/1987-fuel-selector-valve-help.11117/#post-244052

 

[Seamus Langley]

Thank you! I will follow these steps and see what I come up with.

 

[Seamus Langley]

here is a follow up on where I am at:
I used a wire from the positive post to the injectors, both spray. replaced the tank selector switch. when this problem initially began the truck had spark, showed code 12 (in test mode) with a reader and would run after siting a couple of days. after disconnecting and reconnecting all connections in regards to the issues the truck sat overnight. it started the next day like it had no problems at all, I let it run for 10 minutes. turned off the engine and tried again with success. repeated this process abt 4 more times and then the truck began to run extremely rough. my first thought was maybe bad gas from the old tank. this was not the case as that fuel pump would not click on via the switch.... I decided to check if the truck had spark a few days ago... now it has no spark. now the truck also shows no code whatsoever when the reader is connected, nor does the service engine light turn on at all when the key is first turned forward like it used to. my final conclusion is that the ECM has given up the ghost. I have no idea what else may be the source and given my research all signs point to the ECM being the culprit. if anyone has an last minute checks that I should perform before swapping that out or confirmations that the ECM is indeed the culprit I give m thanks in advance.

 

[Jppr26]

Check your ESC module in the distributor, also I recently has a similar issue with my truck, and the magnet on the pickup coil was bad, the esc module was about $60. I replaced my whole distributor$120 and that fixed it for me. I dont have a cap mounted coil on my distributor

 

[chengny]

here is a follow up on where I am at:
now the truck also shows no code whatsoever when the reader is connected, nor does the service engine light turn on at all when the key is first turned forward like it used to. my final conclusion is that the ECM has given up the ghost. I have no idea what else may be the source and given my research all signs point to the ECM being the culprit. if anyone has an last minute checks that I should perform before swapping that out or confirmations that the ECM is indeed the culprit I give m thanks in advance.

Yeah, no SES light - with the ignition switch in RUN - is bad medicine. But before you condemn the ECM (and buy a new one), do a couple of checks. Be sure there is power available to the ECM on circuit 440 (pins C16/B1 - these are common) and circuit 439 (A6 - key in RUN). See the wiring diagram below for how the power is supplied on these circuits - ECM fuses and fusible links.

Also confirm good system grounds on 2 pins A12 (450) and D1 (551).

Pin locations are shown at the bottom - power supply traced in red and grounds traced in green.

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As I'm sure you know, without an SES light...that engine just isn't going to start.

 

[Seamus Langley]

I will be following the above procedures immediately. thank you very much for the information!

 

[Seamus Langley]

update: performed the provided instructions and everything points to bad ecm as per the troubleshooting tree. I am not sure if these degenerate in time or if there is another underling cause but I cannot find anything that would've caused this to short or fail.

 

[1987 GMC Jimmy]

update: performed the provided instructions and everything points to bad ecm as per the troubleshooting tree. I am not sure if these degenerate in time or if there is another underling cause but I cannot find anything that would've caused this to short or fail.

Sometimes they do, but if it got wet, a static source discharged into it, like someone wearing a fuzzy jacket touching it for any reason, or you soldered wires on the ECM harness, that can cause it too. They can also fail partially, but it sounds like yours is dead as Dillinger.