Bad ECU?
12-17-08, 05:13 PM
#1
Bad ECU?
Ive been having problems with my seven running rough. When I checked the ECU for codes by connecting TEN and GND, the check engine light just stays aluminated. My friend tells me that he thinks this indicates a bad ECU, so we switched out the stock ECU for another however, the light still stays lit. Has anyone incountered this problem before, or might be able to point me in the right direction.
Ryan
Ryan
12-17-08, 08:52 PM
#2
Recovering Miataholic
That can happen if the TEN-GND jumper is not well connected, in which case the CEL will stay on until the engine is started. What are you using for a jumper?
12-17-08, 09:25 PM
#3
It's not likely that it's a bad ecu.
Running the stock ecu on my FD, the light would stay on, even though the car would run fine, pass Cali smog, etc. I later discovered the CEL was due to a melted connector under the hood.
The light's on for a reason; it's the ecu telling you there's something wrong.
Is there a vacuum leak or a connector unplugged? There's a lot of both under the hood.
Some investigating is probably in order.
Josh
Running the stock ecu on my FD, the light would stay on, even though the car would run fine, pass Cali smog, etc. I later discovered the CEL was due to a melted connector under the hood.
The light's on for a reason; it's the ecu telling you there's something wrong.
Is there a vacuum leak or a connector unplugged? There's a lot of both under the hood.
Some investigating is probably in order.
Josh
12-17-08, 11:13 PM
#4
I use a paper clip to connect to TEN and GND. Also I have eliminated all of rats nest except for turbo control stuff, and have looked at all the obvious things vac leak, TPS, ext.... So far the problem for it running rough seems to be related to ingnition issues that I have yet to pin point. I doughted that it could be a bad ECU because I have swaped several in to see. The car just runs rough at lower RPMs such as, 3000 and below.
Thanks for the imput so far. Has anyone else incountered this engine light phenomenon?
Ryan
Thanks for the imput so far. Has anyone else incountered this engine light phenomenon?
Ryan
12-18-08, 11:00 AM
#7
Recovering Miataholic
You can usually tell if you have a good jumper connection by hearing the idle speed change slightly when the jumper is in vs. when it is out. (This will NOT work if you have adjusted the idle speed exactly, though.) I used to have problems using a paper clip, so I switched to a solid copper jumper wire.
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12-18-08, 12:37 PM
#8
I will try a solid copper wire. I have used copper wires to check it too with same result. The rats nest and air pump have been removed for some time now. I cut the wires and used butt connectors with 330-Ohm 1/2 watt 5% tolerance Resistors, then taped them to the harness. Maybe one got streched and came out of one of the butt connectors. Would this cause a code, I dont remember which solenoids will throw a code if a resistance connection is lost.
Ryan
Ryan
12-18-08, 10:51 PM
#10
No the check engine light just stays on when I check for codes. The only reason I even noticed it was because the car was running rough, that is untill today when I fixed that problem. All the fuses under the hood are ok, I will check the ones in the car tomarrow.
Ryan
Ryan
01-01-09, 06:58 PM
#13
Im still working on the problem. I replaced some ingnition stuff and the car got better. However, when I start her up she runs ok then goes down hill soon after warm up. Then just continues to deteriorate the more I drive it. Almost like it goes into limp mode, although it will hardly idle. I bought a replacment harness from Cam at Petit Racing when I replaced the motor this summer. He told me that it had been tested and that it was in great condition.
01-20-09, 12:52 AM
#14
The Fix
She’s fixed. The problem was the little prong on the crank that the crank shaft position sensor reads. Somehow the gap was out of specification. To fix it all I had to do was tap it back into spec. Now the car runs so smooth. The only thing that is still the same is the check engine light problem. In case you’re wondering about the symptoms the car had before the fix they were:
Rough idle.
Black suet at idle.
Rich air fuel mixtures as in 9.00-10.00 at idle and at cruse.
The motor would bog after throttle was applied before it would rev.
When motor did rev it was as if it weighed a ton, instead of effortlessly.
If you tried to hold the rev at a cretin RPM the motor would hesitate and in general just run like crap.
The biggest clue is that the motor would run ok when cold and then deteriorate as it warmed up. At its worst it would barley run just like when in limp mode. I believe that this was because the crank shaft position sensors would warm up as the motor warmed up, causing the resistance to change. Under normal conditions this is fine. However, with the prong bent it caused the motor to go downhill.
Rough idle.
Black suet at idle.
Rich air fuel mixtures as in 9.00-10.00 at idle and at cruse.
The motor would bog after throttle was applied before it would rev.
When motor did rev it was as if it weighed a ton, instead of effortlessly.
If you tried to hold the rev at a cretin RPM the motor would hesitate and in general just run like crap.
The biggest clue is that the motor would run ok when cold and then deteriorate as it warmed up. At its worst it would barley run just like when in limp mode. I believe that this was because the crank shaft position sensors would warm up as the motor warmed up, causing the resistance to change. Under normal conditions this is fine. However, with the prong bent it caused the motor to go downhill.
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