Think this sounds like a bad ECM?

[y5mgisi]

So i went out and started going down this voltage checklist and all my numbers are way far off. Like not even in the ball park. I know im checking it right becasue all the ones that are supposed to be 12 volt are at 11.7ish. Think thats a bad ecm then? Heres a copy of the check list that i sort of just drew the numbers into the boxes of what my readings were. I didnt do all of them becasue everything was so damn far off!

 

[dyeager535]

Can't see the diagram here at work, sorry, so I may ask questions that could answer.

What are you measuring that's typically a 12V output on the ECM? I know there are a ton of pins, but I can only think of a couple that are 12V, and they are all feeds from the fuse panel, etc.

The TPI ECM's (same vintage, but slightly different of course) have offsets based on voltage, so GM somewhat expected voltage variations, or at least anticipated things like low batteries, or dead alternators.

If you aren't getting the same voltage out that you are in, I'd start looking at grounds and what not. But fairly uncommon for voltage to be exactly 12V anywhere in the vehicle, since there are many connections and fairly long distance wire runs.

 

[resurrected_jimmy]

Dorian, what his diagram shows are a few connection that have 12V "key on" or 14V eng run, those readings are coming out correct..... I think he is using those for a base to see if he's doing the test right..... To give an example of what's way off his MAP should be at 4.9 V and his actual reading is 0.7

 

[y5mgisi]

Yes what he said. Thanks I was outside playin with the truck. I also verified that all the grounds coming into the computer are good.

 

[dyeager535]

OK, well, I'd probably start with the MAP then, if the voltage seems to be off. Some sensors have a "reference" line from the ECM to the sensor, say 5V. Are even the reference line voltages wrong? (since the ECM controls those)

 

[y5mgisi]

The refrences were ok at about 4.85 but EVERYTHING was all off eamples;

egr control; Corect, 12v mine, .67
seriel data C 2v-5v Me, .3v

however

reverences C,5v Me, 4.8ish
and bat constant power C, 12v Me11.72ish

 

[Blue85]

What kind of meter are you using? Any idea what the input impedance is?

I see numbers in the "Key On" and "Engine On" columns, so the engine must run. If those signals were off by that much, I don't see how it would run.

What problem are you having with the vehicle?

 

[y5mgisi]

just a $20 digital multi meter. But it reads everything else just fine. I dont get it. Im having an issue with it running rough at idle along with a srging at idle issue. As long as its not idleing its fine.