Yet another 350 tbi problem

[GeorgiaK10]

Do Autozones test OBD I? The ones I've been to only fool with OBD II. The tach was a good diagnostic tool for that. Hmm... The mechanic would be an easy scapegoat, but there are only a couple things that I can think of that would have went wrong there. The ECM that went in there could have been bad even though your diagnostic circuit works as it should, which I wouldn't put it past either a junkyard or reman unit. ECMs share connectors, too, so it is possible, however unlikely, that the wrong ECM is in there. If it's a reman unit, it won't have the ID sticker on it, but if it's used, it should be a 1227747 ECM. I know the 1227165 ECM shares the connector set, and those come out of 86-89 F Bodies. Again, I don't think this is likely. Those are TPI cars that use a MAF system. I don't even think yours would run in that situation, but I haven't tested this so I have no clue what exactly it would do. It's fishy that it starts acting up after the ECM swap, though. It'd make sense that it's related to that, but it's also possible that they have nothing to do with it. Pin F on the ALDL is for TCC diagnostics. I know you can probe it to test the brake switch (12V resting, 0V with brake depressed), and I've read of people on here making manual switches that simply bridge Pin A (ground) and Pin F together, but the info is pretty vague. Maybe Jerry knows, and I'd like a more concrete explanation on the matter myself. @chengny

There is no sticker on the ecm..

 

[GeorgiaK10]

See anything fishy?

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[1987 GMC Jimmy]

Everything in that picture looks good to me, but it may not be something a visual inspection could solve. I gotcha on the ECM. It was a long shot, but I felt like it was at least worth looking at.

 

[4WDKC]

When the new ECM was installed was a key on self test/calibration done for the ecm to learn the ranges/position of new sensors? Did you check to see if the ecm had a chip in it? I have heard sometimes you have to reuse the chip from your old ecm (might be better also as it is the OEM chip for the truck). A quick test to see if it is a sensor is disconnect the TPS and start the truck. It will put it in limp home mode operating of predetermined values instead of sensor input.

 

[GeorgiaK10]

When the new ECM was installed was a key on self test/calibration done for the ecm to learn the ranges/position of new sensors? Did you check to see if the ecm had a chip in it? I have heard sometimes you have to reuse the chip from your old ecm (might be better also as it is the OEM chip for the truck). A quick test to see if it is a sensor is disconnect the TPS and start the truck. It will put it in limp home mode operating of predetermined values instead of sensor input.

I didnt install the new ecm. My old mechanic did. And ever sense then it has slowly got worse. I do not know much about what he did. How should i diagnose it?

 

[4WDKC]

I didnt install the new ecm. My old mechanic did. And ever sense then it has slowly got worse. I do not know much about what he did. How should i diagnose it?

https://www.thirdgen.org/forums/tech-general-engine/101946-iac-resetting-procedure.html

 

[chengny]

[QUOTE="GeorgiaK10, post: 368363, member: 12779"I recently had my ecu replaced bc some water got on it while i was driving. This started after my ecu went bad and the idle has progressivly got worse.[/QUOTE]


Do you know where your fuel pressure regulator is located. If not, you should look into that and make sure it isn't leaking through the diaphragm or not properly regulating the fuel pressure. Then again, if were an FPR issue, it probably wouldn't fix itself 30 seconds after initial start. So...disregard.

 

[1987 GMC Jimmy]

That's a good idea on checking the PROM chip. Of course, reman ECMs don't come with a new PROM so your old one had to be reused. It should also give a PROM code if it was installed wrong.