ECM fried?
Thread Starter
Instructor
Joined: May 2005
Posts: 162
Likes: 0
From: Lady Lake FL
ECM fried?
I bought a 93 six-speed coupe about three weeks ago. I've since replaced the opti, wires, plugs, coil, map, tps, cts, o2 sensors and the injectors. After all this it still runs rich and I think it may be ecm related. For starters, the digital coolant temp gauge wants to read about 108 degrees, no matter how hot the engine is, so I figured it may possibly be the sending unit. When the engine is cold it runs fine, however, when it warms up it runs extremely rich and bogs so bad when you rev it that it will stall, but, if you start the car and rev the motor up to about 4000 a few times, the temp will almost instantly jump to 220 and the car leans right out and runs like it should until you turn the key off. Then the only way to start it is with your foot to the floor to clear it out and then gauge stays at 108 until you rev it up a few times again. Something else that leads me to believe that its the ecm, is that with the key off, there is still a 5 volt signal to the cts, iat, and the ccp valve I don't know if this is normal but I checked my TPI motored car and a 96 s10 and neither one showed voltage with the key off. I hope someone can make some sense out of this before I go insane! 
Thanks in advance.
KC
Thanks in advance.
KC
Burning Brakes
Joined: Apr 2000
Posts: 980
Likes: 2
From: Chandler AZ
How does the wiring at the ECM look
Are there any signs of a tattered wiring harness? I am just wondering if there is a connector or wiring issue there.
There should be error codes generated if the ECM flakes out. It isn't always the case though.
Best of luck
There should be error codes generated if the ECM flakes out. It isn't always the case though.
Best of luck
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Try installing new coolant temperature sensors, there should be two. A faulty coolant sensor can keep the car stuck in open loop, thus the rich condition. It sounds like your coolant temp sensor is failing, based on the fact it reads 108 too long.
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
However, I see by your post that you already replaced the CTS. You may be right in suspecting the ECM seeing all the parts you have relpaced. Before you jump, triple check all the major grounds : battery, ECM, etc.
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
Try checking your FPR.Pull the vacuum after you turn the key on if gas comes out that is your problem. Sounds like a gas problem to me if it finally clears when hot.Yes fix the temp sensors they can keep it open loop.Youe description could be a little more detailed from start to hot what occurs?
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Thread Starter
Instructor
Joined: May 2005
Posts: 162
Likes: 0
From: Lady Lake FL
I think I have found my problem...I was swapping the battery out and noticed alot of corrosion on the bottom wiring harness that goes inside the car next to the battery. You can't hardly see it with the battery in the car. I then started and had my father lightly tap on the harness connector with a screwdriver and everything inside the car schized out. Maybe this could also explain my courtesy lights acting strange...so we pulled it apart and the corrosion had "grown" in a sense and I guess could have caused an intermittent short. One of the wires had actually came loose. I will keep you all posted. Thanks for the suggestions.
Also to answer one of the questions, the car will run fine until the coolant temp gets up past 110ish and then it just runs richer and richer as if the ecm isn't leaning it out accordingly. Its acts like it just stays in one cell of the "open loop vs. coolant temp table."
KC
Also to answer one of the questions, the car will run fine until the coolant temp gets up past 110ish and then it just runs richer and richer as if the ecm isn't leaning it out accordingly. Its acts like it just stays in one cell of the "open loop vs. coolant temp table."
KC
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by Alvin
Sounds to me like the wiring to the sensor is bad. It happens all the time.
Especially in older cars, I have seen sensors actually start leaking and force anti-freeze into the wiring from pressure in the cooling system.
Thread Starter
Instructor
Joined: May 2005
Posts: 162
Likes: 0
From: Lady Lake FL
Well, I fixed my corrosion problems and still it's a no go. I have checked the wiring from the ecm to the cts and I have little to no resistance so I imagine it (the wiring) is ok. I took the ecm out and took the case off to see if possibly there was something visibly toasted or wrong. Nothing appeared to be burnt, which doesn't surprise me, but the printed circuit on the opposite side from the chip was "wrinkled" all over like it had been hot or moisture has gotten into it. There was also sand in the case as well. Anyways, after seeing this I put it back together, tried to start it and it won't run at all now. All I get as far as sensor readings on the digital dash is "LO" or a flashing "SYS". I think now that there is a very good chance its my ecm. Someone in the past has "hot-wired" the fans to come on when the key is on, so I wonder if possibly they sent 12 volts back through the 5 volt signal wire and burnt something up. 
Any other thoughts or suggestions are greatly appreciated.
KC
I have checked the wiring from the ecm to the cts and I have little to no resistance so I imagine it (the wiring) is ok. I took the ecm out and took the case off to see if possibly there was something visibly toasted or wrong. Nothing appeared to be burnt, which doesn't surprise me, but the printed circuit on the opposite side from the chip was "wrinkled" all over like it had been hot or moisture has gotten into it. There was also sand in the case as well. Anyways, after seeing this I put it back together, tried to start it and it won't run at all now. All I get as far as sensor readings on the digital dash is "LO" or a flashing "SYS". I think now that there is a very good chance its my ecm. Someone in the past has "hot-wired" the fans to come on when the key is on, so I wonder if possibly they sent 12 volts back through the 5 volt signal wire and burnt something up. Any other thoughts or suggestions are greatly appreciated.
KC
