ECM going bad?
 

For the past few weeks I have been having some problems out of my car. The thing is, they are intermittent. It will randomly start missing, it is not an injector, because when it does it, I can smell gas. It only does it when the engine is cold. When it happens, I can shut off the ignition switch and wait a few seconds, and then start it back up and it runs fine.

Second thing, sometimes it stalls when I go to take off from a light, but it only happens again, when the engine is cold.

Lastly, again when the engine is cold, my battery light will come on, and the alternator won't charge. It goes on for about 5 min, and then the light goes off, and the alternator starts charging again.

My question, is the alternator exciter field coming from the ECM or the battery? I'm thinking ECM on the misfiring, because hard parts wouldn't fix themselves from a key cycle. At least I wouldn't think they would.

Thanks in advance,
Rob

Which car? the 94 or 2001 SL1? MPFI did not come in until 95 for the SL1's.

ALT

What's the alt output V with batt light on and after batt light goes out? MIGHT be an issue with the voltage regulator inside the alt, so monitoring the output V from cold start to batt light off should shed some light on whether the alt output V matches the batt light indication.

"Misfire"

If it is the 94, you will not get a misfire code compliments of OBD I 's lack of them. If it is the 01, you should absolutely get a SES and code, and see the SES flashing when the problem occurs.

If you're not getting a code on the 01, I'm going to question whether it is an actually a miss or something else that is causing the combustion in that cyl to be different than the others.

For example, you may have an injector sticking open occasionally; more likely when cold. That could explain both the smell of gas and the goofy lack of performance, since you're messing up the A/F ratio in one cyl. It is probably firing but with a screwy mix in the cyl. But it fires, so not detected as a miss and no code.


Key off / wait / key on

Turning the key off, waiting a few seconds, then turning it back on WHEN THE ENGINE IS COLD will / should trigger another round of priming of the fuel system. This rush of higher pressure in the system may be enough to get things to behave. Due for fuel filter change?

Recommend checking key on/engine off AND key on/ engine on fuel pressure at the test port of the rail and comparing to specs. Might be pump issue or pressure regulator issue.

Try a bottle of Techron fuel system treatment. I can't believe what I was missing!

Oh --- important----if you turn off the key while the engine is still cold but the batt light has gone out, does the batt light reappear?

Wow, I haven't guessed at so many things at once in a long time.

Derf,

Apologies for the confusion. This is my 2001 SL1. When the misfire happens, the SES light will flash, and a check of the codes gives random cylinder misfire, not one specific cylinder.
Fuel filter was changed 3 months ago. My only reason to think ecm is that it "fixes" itself after the key cycle.

The alternator question was to find out if the ECM commands the voltage to the exciter of the alternator to regulate the voltage. Since you said VR in the alternator, that tells me that it is self regulated. When the battery light is on, I have only battery potential at the alternator terminal.

The thing is, it will do this once a week, and then run fine for the next 7 to 10 days.

2/3 of the info (sigh)

(Just kidding --- even us regulars leave stuff out. No harm no foul.)

All the additional info being said:

1) POSSIBLE that Idle air control valve may need cleaning. may be hanging up when cold. Also check connector and wiring
Turning off the car and restarting resets the IAC (I THINK) so things start to behave again

Voltage regulation is done by the PCM (ECM). That does not mean that the PCM is bad, it may be detecting something that tells it to cut the load to the engine as much as possible.

This is sounding like the crankshaft position sensor starting to go south.

I have a CEL on right now. First time it has come on since this started happening. The bad news is my 15 dollar OBD II adapter went tits up. I'm not ruling out an alternator either. Had a power steering pump leaking at the seal for about a week until I could replace it. Guess where all the oil went. Right into the alternator. When I replaced the PS pump, I cleaned the alt. With brake clean, dried and reinstalled. Hopefully, the crank sensor will be the code that is in there. I will keep y'all updated.

CEL was evaporative emissions system, small leak. Stored not active, sometime down the road might need to get a new gas cap. That narrowed down nothing, except that I found out my OBD adapter still works.

Get some CRC electrical contact cleaner and spray the alternator with that. I THINK the brake cleaner may leave behind a slight film, but am not sure. Hell, if you can get the alternator out, pull it, crack the case open and check the brushes and armature. A little sanding with some emery cloth can do wonders for one of them.

True, if I pull the alternator again, I'll just replace it. Car just turned 100k miles. I'm leaning more to Keith's diagnosis. It hasn't done it again this week. Last night I did replace the plugs and wires, and dumped in some injector cleaner. We will see.

Keep us in the loop. Inquiring minds want to know! LOL