Bad ECM?
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
Likes: 0
From: Oswego Illinois
Bad ECM?
1993 Stock lt1
When engine temp reach 180-190* the engine starts to run like crap.
Had started a previous thread about that.
I checked the codes and it showed a code 43(knock sensor circuit error) but it did not show a code 12 which worried me. I then cleared the codes and changed both knock sensors. The problem did not go away but now there are no engine codes and a code 12 is present.
So is the ECM not showing a code 12 then showing a code 12 a sign of a faulty but not completely dead ECM. Is there any way to test the ECM?
When engine temp reach 180-190* the engine starts to run like crap.
Had started a previous thread about that.
I checked the codes and it showed a code 43(knock sensor circuit error) but it did not show a code 12 which worried me. I then cleared the codes and changed both knock sensors. The problem did not go away but now there are no engine codes and a code 12 is present.
So is the ECM not showing a code 12 then showing a code 12 a sign of a faulty but not completely dead ECM. Is there any way to test the ECM?
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
A better detailed description of the symptom will help a great deal. You could have any number of things other than a bad ECM. It does not sound like you have any codes and it appears normal. Check link.
http://www.corvettephotographs.com/c4vettes/codes.htm
If it runs bad when hot, that is a symptom of a bad opti. But doing the basic checks as fuel pressure, arking wires and others are routine tests before replacing a ICM or opti.
http://www.corvettephotographs.com/c4vettes/codes.htm
If it runs bad when hot, that is a symptom of a bad opti. But doing the basic checks as fuel pressure, arking wires and others are routine tests before replacing a ICM or opti.
Le Mans Master
Joined: Mar 2001
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From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
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St. Jude Donor '12
Check the ICM, they are prone to heat sink issues and do not usually throw a code.
Pro
Joined: Oct 2009
Posts: 679
Likes: 0
From: vero beach florida
1st off, you only get a C12 when in diagnostic step 1 and the is nothing wrong w/CCM.
in step 4(ECM), you will get --- if there are no codes.
Check for vacuum leaks, a lot of times when a vacuum line is going bad, it will lose it's seal so to speak when the engine is hot.
in step 4(ECM), you will get --- if there are no codes.
Check for vacuum leaks, a lot of times when a vacuum line is going bad, it will lose it's seal so to speak when the engine is hot.
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
A better detailed description of the symptom will help a great deal. You could have any number of things other than a bad ECM. It does not sound like you have any codes and it appears normal. Check link.
http://www.corvettephotographs.com/c4vettes/codes.htm
If it runs bad when hot, that is a symptom of a bad opti. But doing the basic checks as fuel pressure, arking wires and others are routine tests before replacing a ICM or opti.
http://www.corvettephotographs.com/c4vettes/codes.htm
If it runs bad when hot, that is a symptom of a bad opti. But doing the basic checks as fuel pressure, arking wires and others are routine tests before replacing a ICM or opti.
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Melting Slicks
Joined: Feb 2010
Posts: 2,077
Likes: 72
From: Reno Nv
1st off, you only get a C12 when in diagnostic step 1 and the is nothing wrong w/CCM.
in step 4(ECM), you will get --- if there are no codes.
Check for vacuum leaks, a lot of times when a vacuum line is going bad, it will lose it's seal so to speak when the engine is hot.
in step 4(ECM), you will get --- if there are no codes.
Check for vacuum leaks, a lot of times when a vacuum line is going bad, it will lose it's seal so to speak when the engine is hot.
Then you can go into each module to look for them.
So, if there's a code in module 4 (ECM) you'll see it when you turn on the key and again when you run the buttons to get to modume 4.
Melting Slicks
Joined: Feb 2010
Posts: 2,077
Likes: 72
From: Reno Nv
BTW, the last thing I think it would be is the ECM.
You're going to have to do a proper diagnosis as mentioned above.
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
Likes: 0
From: Oswego Illinois
Yeah im starting to think it might not be the ecm, but maybe a icm/coil or opti issue.
Im going to get the icm and coil tested asap and if they check out ok i think ill have to replace the opti original opti and 70xxx but if either icm or coil fail hopefully I wont have to replace the opti
Im going to get the icm and coil tested asap and if they check out ok i think ill have to replace the opti original opti and 70xxx but if either icm or coil fail hopefully I wont have to replace the opti
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
Also, probably a shot in the dark but clean your MAF sensor as well, if it's not reading correctly when it goes Closed Loop the car can do some weird things until the computer is able to somewhat adjust for it, which I guess is another question for you, after a period of it running like crap, does it get any better or just continues to run like crap?
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
Le Mans Master
Joined: Mar 2001
Posts: 7,999
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From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
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St. Jude Donor '12
Regular - ran like crap and had no power. Crappy gas mileage
Mid-grade - ran better and better power. OK gas mileage
Premium (93 in my area) - ran best and best power. Best gas mileage
I go ahead and pay the extra $0.30 a gallon, extra $2 - $3 a tank won't kill me.
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
Likes: 0
From: Oswego Illinois
ok so the icm and coil checked fine.
Im thinking about taking the ECM out of my 92 putting putting the prom from my dads 93 in it and seeing if it actually the ECM causing the problem.
The oxygen sensors, knock sensor, and coolant temp sensor have all been recently replaced. So im thinking it has to be the ECM or opti but I think a bad opti would throw a code and there are no codes.
Im thinking about taking the ECM out of my 92 putting putting the prom from my dads 93 in it and seeing if it actually the ECM causing the problem.
The oxygen sensors, knock sensor, and coolant temp sensor have all been recently replaced. So im thinking it has to be the ECM or opti but I think a bad opti would throw a code and there are no codes.
Last edited by vetteguy216; Apr 8, 2010 at 12:52 AM.
Racer
Joined: May 2009
Posts: 421
Likes: 2
From: van buren ar
ecms can be hard to find or time consuming to have repaired.i thought i had a bad ecm and it turned out to be something else.im pretty sure you could swap your dads ecm into your 92 and see if that works or you could put your ecm in his car and see if the problem moves to his car.
Burning Brakes
Joined: Oct 2009
Posts: 773
Likes: 2
From: Minneapolis MN
Remember that sensors can test fine at certain temps(colder) & fail at higher temps.Ohm injectors while engine is cold then right after problem starts.Also just because the ICM tested ok does not that its working properly after being "heat soaked".Hook up scan tool & check readings when engine is cold & when problem starts.Also check fuel pressure & check for leaking fuel pressure regulator
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
If it is running good cold (before 120F) and not good above that, it sounds like it is running OK in "open loop" but failing when it goes into "closed loop."
If that is the case, I suspect a sensor problem -- like O2 sensor or exhaust manifold leak.
Tom Piper
If that is the case, I suspect a sensor problem -- like O2 sensor or exhaust manifold leak.
Tom Piper
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
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From: Oswego Illinois
I tested his ecm in my 92 which was running perfect. Put my eprom in the ecm from the 93 then put it in my 92 and my car ran perfectly fine with his ecm in my car but. After I put everything back in their original spots "my ecm back in my 92 with the 92 eprom in it". I go to start my car and it is running rich/rough "could definitely smell gas" turn it off go out to dinner try to start my 92 when I get home and it cranks for a couple of seconds and then you hear a metal sounding clunk/bang and it stops cranking. It does it every time I try to start now, but being worried about the Clunk/bank ive only tried about 4 times
So now we have two vettes with problems and the only
Last edited by vetteguy216; Apr 10, 2010 at 01:22 PM.