1987 gmc with code 42

[jesdude7789]

okay i dont know what happened but basically i replaced my spark plugs, spark wires, and cap and rotor on my truck last week and within the same day of driving it around it started to die on me when coming to a stop at a stop light or at lower speeds in general. then it gave me a code 42 for the EST.
well i checked all my wires and everything was hooked up fine and the timing was set correctly.

I have a spare ignition module so i went to oreillys and tested it first to make sure it was still good and he cycled it 3 or 4 times so it would get hot and it still passed. okay then i swapped it out with the one on my truck and went and tested that one as well and it tested ok also, so both modules were good. the truck still had the same issue, dying on me randomly and setting the code.
i had to drive to beaumont the other day and i had no choice but to drive it and hope it doesnt die. during the drive it died once, then i got it restarted and kept driving it, several miles later it tried to die again so i throttled it and that kept it running but with the check engine light ON the whole rest of the way to beaumont.
while in beaumont i pulled the whole distributor out and replaced it with another one under warranty which is great but on the way back from beaumont it still did the same exact thing.

so... i have a completely new ignition system except for the ignition coil, the wiring that goes between all the components, and the ECM itself.

I'm thinking the wiring pigtails and such are just too old and i should splice all new ones in.

any thoughts?

[Big Port Jimmy 6]

Is it sputtering out like fuel, or cutting off like using the switch? I had a TBI truck that had marginal fuel pressure and it was unpredictable. Jay

[jesdude7789]

Originally Posted by Big Port Jimmy 6

Is it sputtering out like fuel, or cutting off like using the switch? I had a TBI truck that had marginal fuel pressure and it was unpredictable. Jay

its more like cutting off like a switch for a split second. the first couple times is was like one flip off and on of a switch. and then other times it did it like 3 or 4 flips of a switch in a row which is when i would play with the throttle to keep it going. then it would resume running for several miles. sometimes the SES like would blink and go away and others it would stay on for a while in dummy mode until it did it again and then it would be back in regular mode after it resumed running "smoothly" lol. like the module was failing but like i said, i had them all tested and now it even has an all new distributor with yet another new module that came with it.

could the ecm be failing? and if that was the case wouldnt it have a code for itself being bad?

i still havent checked the coil either though. its 4 years old. an accel unit.

oh and i did check the fuel pressure two weeks ago and adjusted it to 15 psi. i cant watch it though because i dont have a gauge set up for that. i need to get one. know of a decent kit?

[Big Port Jimmy 6]

Try to find a GM service manual, there should be a trouble tree for the est. The est module is square and has a flat plug, I do not remember how many wires in it, grab one from the pick and pull and swap it. They didn't really go bad that often. Jay

[jesdude7789]

Originally Posted by Big Port Jimmy 6

Try to find a GM service manual, there should be a trouble tree for the est. The est module is square and has a flat plug, I do not remember how many wires in it, grab one from the pick and pull and swap it. They didn't really go bad that often. Jay

I have both the chiltons and haynes manuals. I will check those. Where could I get an original gm tech service manual?
Thanks!
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[c10sport]

ebay will be your best bet.

[twoodson]

Make sure that the connectors are not coming loose on the coil. Mine did something similar and I called my mechanic while on the side of the road and he told me to check the connecters that connects to the top of the coil, one of the what i call snaps had broken so it would work its way up just enough to kill the truck, i mashed it back down and it restarted and I mde it home and went to the bone yard to get a good and replaced the broken one.