Fun Electrical Problem: Dead ECM?

[Crazy K]

maybe you got a bad ECM...?

[ManicMechanic]

maybe you got a bad ECM...?

 

That's my conclusion as well.

[ns87]

maybe you got a bad ECM...?

 

That's my conclusion as well.

 

I was thinking that, but it bothers me that 2 in a row have the exact same problem. Plus I'm stuck at school where there is no junkyards. Anyone have one they're willing to sell?

[cperna15]

well i do not have one but i can get one for you vor VERY CHEAP at harrys u pull it, just give me a list make/models that i can get a ecm from

[RobertISaar]

1227727

 

1990-92 2.5 L4 TBI “R†LR8 (“W†body)

1987-89 2.8 V6 PFI “W†LB6 (“W†body)

1989-93 3.1 V6 PFI “T†LH0 (“W†body)

1989-90 3.1 V6 PFI turbo “V†LG5

1990-91 5.7 V8 TPI “8†L98 (“Y†body)

1990-92 5.7 V8 TPI "8" L98 ("F" body)

 

thats a rather short list... put it this way, they're in a lot of shit

 

i believe it was also refered to as 16197128 and 16198260

[ManicMechanic]

CORVETTE 90-91 Elec Cont Module (ECM); base

 

CUTLASS 88-89 Elec Cont Module (ECM); 6-173 (2.8L)

 

CUTLASS 89-92 Elec Cont Module (ECM); 6-191 (3.1L)

 

CUTLASS 93 Elec Cont Module (ECM); 6-191 (3.1L), VIN (8th digit) "T", TH125

 

GRAND PRIX 88-89 Elec Cont Module (ECM)

 

GRAND PRIX 90-92 Elec Cont Module (ECM); 6-191 (3.1L)

 

GRAND PRIX 93 Elec Cont Module (ECM); 6-191 (3.1L), TH125

 

LUMINA CAR 90 Elec Cont Module (ECM)

 

LUMINA CAR 91-92 Elec Cont Module (ECM); 4-151 (2.5L)

 

LUMINA CAR 91-92 Elec Cont Module (ECM); 6-191 (3.1L), gasoline

 

LUMINA CAR 93 Elec Cont Module (ECM); 6-191 (3.1L), gasoline, TH125

 

REGAL 88-89 Elec Cont Module (ECM)

 

REGAL 90-92 Elec Cont Module (ECM); 6-191 (3.1L)

 

To add to Robert's list. And you are correct on the part numbers.

 

If I had an extra (I used to, but threw them out) I'd send them to you.

[cperna15]

is that the comp that is under the hood in the pass side by the headlights

[ns87]

well i do not have one but i can get one for you vor VERY CHEAP at harrys u pull it, just give me a list make/models that i can get a ecm from

 

I'll let you know very soon. I just want to exhaust all my other options before I replace this AGAIN.

[ns87]

is that the comp that is under the hood in the pass side by the headlights

 

yes

[cperna15]

well pm me and let me know, also i can bring it to you if you would like cause u live in ny and im in jersey so were pretty close

[spiderw31]

When you mentioned the the wires "had resistance", what were you getting for a reading? If it was anything substantially higher than 0, you may have found the problem.

[ns87]

When you mentioned the the wires "had resistance", what were you getting for a reading? If it was anything substantially higher than 0, you may have found the problem.

 

Hmmm, they were all getting between 1-3ohms. I figured it was nowhere near infinity, so I was ok there.

 

well pm me and let me know, also i can bring it to you if you would like cause u live in ny and im in jersey so were pretty close

 

Haha not that close. I'm an hour north of binghamton. PM sent

[spiderw31]

Assuming a properly calibrated meter (i.e. one that reads 0 when the leads are touched together), I'd be worried if any power or ground leads had a resistance greater than 1 Ohm. With the relatively low voltages that cars run at any more resistance than that can cause a noticeable voltage drop. Also, resistance on the ground lines can cause a ground loop, where some voltage sneaks through another circuit to ground. if that is whats happening, you will DEFINITELY get some weird issues!

[ns87]

Well tomorrow I'll go look at it again. I can tell you there wasn't a single wire that read near 1. This is a really cheapo meter, so maybe that's my problem too.

 

I'll keep ya'll posted

[RobertISaar]

hold the probes together and see what reading that gives you. if its zero, then it knows what zero resistance looks like, so if it shows more than that, its probably right.

[ns87]

Ok, went and took a look. When I touch the leads together, I get just under 2 ohms. Now that is my baseline.

 

Then I checked my grounds again:

 

I went and touched 1 end of the probe to the appropriate ECM plug pin, and the other to the negative terminal of the battery. Is that the correct procedure?

 

I found two grounds with a resistance of almost negative infinity. Looking at my handy shop manual, they both happen to connect to the Coolant level sensor, MAT sensor (which one is that again and where?), the TPS, MAP, and coolant temperature sensor. Explaining why I've had such random and diverse problems.

 

Here's the question of the day: Where on earth do I go from here? That's a lot of wire

[RobertISaar]

well you were right about the multimeter: it not showing zero could be an issue.

MAT sensor is the little piece sticking in the top of your airbox.

 

it does sound like you've found your issue though. having MAT/TPS/MAP and coolant temp not working will definitely cause some issues.

 

and negative almost infinity is saying there is just barely enough copper in the wire for it to not be completely seperated. so take a look around for any wires that look like they got folded, crushed or otherwise damaged.

 

have you ever cleaned the grounds on the motor? i believe there are two main ones and they are for the sensors listed above. i'll get a diagram.

[RobertISaar]

should be easy to find. i've seen some nasty stuff build up on/around them and cause issues

 

brake cleaner will cut through oil pretty easily

[ns87]

Thank you so much for the picture. I tested those grounds in the same way, and they checked out ok. But just because they connect well to the battery, doesn't mean they connect well to the sensors right?

 

If those don't pan out, can I do this? :

 

According to my manual, once those two grounds leave the ECM, their next stop is the TPS and MAT. So

could I probe between the ground on the MAT to the ground on the TPS? Should that show up around 0 (or in my case 2)?

 

 

[RobertISaar]

right, and any significant resistance found between those 2 points would indicate a problem area. not necessarily your only one, but it would be one.

[spiderw31]

Yep, you can measure for continuity between any two points that are supposed to be connected according the the diagram. Any points that indicate they are connected on the diagram yet have a resistance substantially higher than 0 are problematic, exactly as Robert said.

[ns87]

I cleaned those grounds today robertisaar. No dice

 

Today Jay (19Cutlass94) came by to give me a hand. We decided to ground the two bad wires ourselves, rather than search through the entire loom. They now OHM at 0 (fixed my meter to read 0 as 0 lol).

 

Unfortunately, I still have the same no start condition. I checked the resistance between all the other connectors on the circuit, and they were all at 0. The fuel pump relay clicks and we manually primed my fuel pump to make sure that wasn't the problem.

 

Since this crappy ground did a lot weird fast flickers, our latest theory is THAT is what has killed my computer twice in a row. We took apart my original one, and a big red capacitor? was melted and chipped. The newer JY one seemed fine, but still did not work. He is going to get me an ECM from the store he works at, and we'll try that. Luckily if it doesn't work, he can return and I will be none the poorer.

 

Thanks again for stopping by!

 

 

[RobertISaar]

big red capacitor? was melted and chipped.

 

wow, i've never actually seen that... i guess a intermittent ground could cause a cap to overcycle or something. i don't know if they have duty cycles or recomended amounts of time before charge/discharge but i guess massive amounts of current then nothing then repeating that a lot could cause shit to go FUBAR

[spiderw31]

Depending on how a circuit is designed, a bad ground can cause voltage to travel though unexpected, unintentional paths. Put that voltage onto the right (or wrong) circuit, and you wind up with voltage a capacitor can't handle, and pop! I've not seen it happen specifically in the electronics in a car, but I've seen it several times in computers / electronics, so I know it happens. In fact, I've done it myself accidentally. I wound up wiring an electrolytic (the bid can type, probably the same as you observed) backwards. It worked for a short while, then *POP* followed by smoke.

 

Hopefully those were the only two bad lines, and a new ECM does the trick!

[ns87]

Well, I just sucked it up and bought a Reman ECM. Popped in my memcal, and guess what? Still dead as a door nail. No SES or Low Coolant light when I turn the car to "ON". And of course it doesn't start

 

In a few days, I'll be returning the computer. But seriously considering putting the car up for sale.