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

If I nail it down I will share.

I'm probably having a "thick" moment, but it is my understanding (and the experience of many a poster on this and other forums) that if a CKP is malfunctioning, the PCM does not receive a "valid" signal from the CKP, the PCM just cuts spark and fuel and the engine stops. There is no in between that would account for stalling at cold launch and key/off on restarting. The CKP is either in failure mode or it's not. The stalling to me sounds like more of a A/F mix issue, which could be perturbed by many a condition.

Being an SL1, could this be an intake manifold gasket tiny tiny leak that self seals (so to speak) when everything expands as the engine warms up? I know the misfire code is random misfire but you never know.

Aside:
I drove my 97 around on a completely dead cyl (injector unplugged) for 9 months, knowing I was going to do a swap in. I had to keep the code reader plugged in 100% of the time because it would either throw a random misfire or a cyl 4 misfire code or both (usually). The key was which one it threw first.

If it through cyl4 first, I could drive around reasonably normally. If it threw a random misfire first, it would cripple the accel (presumably removing all of the timing advance) and basically requiring me to periodically pull to the shoulder, erase, and drive on, hoping for the cyl 4 to pop first. Yes, there were times I had to disconnect the battery so inevitably I would have to keep playing this game. You would think that throwing a random misfire at any point would lead to crippling performance but that was not my personal experience.
End of Aside

I throw this out there in contradiction to my own suggestion that this may be due to a sticky injector, leading to the rich smell and misfiring. The intake manifold possibility would not however account for the rich odor. The only time my s cars smell rich are in open loop, when they are in fact running rich, and in the rare event I manage to do the equivalent of flooding it, and have to plaster the gas pedal to the floor to clear it. It will then sputter sputter but eventually turn over, but it smells obnoxiously like fuel---which ---considering how much I just dumped, kinda makes sense.

The car had a dead miss at idle, so I replaced the intake manifold gasket last summer. I ended up discovering that a narrow gapped spark plug on no. 1 was the cause of the miss. The intake manifold gasket came out in pieces.

I'm a diesel guy in my knowledge, so in the big truck world, when the crank pos. Sensor goes bad, the ECM defaults to the Camshaft position sensor to get you home. Is is that way with Cummins engines any way. Never been a Cat guy, and never had electrical problems on a 60 series Detroit. I assumed that small gas cars would be the same, but then again, heavy Diesel engines don't have timing chains.

in an s car, when the PCM does not receive a valid signal from the CKP such that it can determine where the crank is in it's rotation, it has always been my understanding that the PCM says "oh crap, now I don't know where the pistons are; I better not let anything fire" so it kills the fuel to the injectors and kills the spark (prob by disabling the ICM).

End of story.

This is why it's so annoying when they flake out as they die, because it usually tracks with heat, so you'll drive 10 mi to the grocery store, buy only dairy products, and come out to an S car that cranks and cranks and cranks. But won't start. But if you let everything cool off for 20 min, the CKP may begin functioning again so the car will fire right up, you'll drive home with your warm dairy products, not really knowing what the issue was unless you had the tools to check spark (the socket and extensions are kinda key), because you're not gonna crawl under the car in a parking lot and be able to reach the CKP connector to see if the R is in spec.

Ah, reminds me of coils on old 2 cylinder Deeres. Run fine cold, but get them up to operating temp and they start missing and backfiring.

any news to share?

No, the alternator finally gave it up, so I am replacing that this weekend. The car has ran fine for the last 2 weeks. Still averaging 39.6 mpg at 75 mph. Also going to do the hid retrofit this weekend as well. Future right up pending.

Replacing the alternator has solved the battery light issue. It did the misfiring once last week. I was off the throttle because a car was turning off the road in front of me. When I got back on the gas, it started missing. Pushed the clutch in, killed the ignition, and restarted and it was running fine. So, maybe injector, or injector wiring harness, or injector driver in the ECM. Who knows. With it happening so sparsly, I may never track it down.

Try throwing in some Techron fuel system treatment w your next fillup.
You have seen an improvement since your last fuel injector cleaner addition.

No, of course I can't prove the two are related.
but we CAN try to isolate the issue to one portion of the vehicle......

I credit the mpg gain to the warmer weather. It was getting down in the low 50s here at night. Colder weather always nets worse economy, but not too hot to have to run the AC on the way home.

Engine went into a missing fit twice on the way to work this morning. Seems to happen under higher throttle application. This morning it did it after I set cruise, and as I was going up a pretty steep hill both times.

throttle position sensor flaking out and sending crap data telling the ECM to cut back on the fuel and timing advance? And who knows what after that? Without that part of the feedback loop you're gonna have a mess.

If you have a real-time data monitoring tool, config to follow the TPS signal and just keep driving.

Or it could be a bad coil that only acts up when it feels like it......

Ok, as I sit here waiting on the parts to put my John Deere 3020's transmission back together, I have gone back to tracking down the problem with the car stalling. So, it has gotten considerably worse last week. I bought some high dollar injector cleaner, and it seems to have fixed it. I replaced the tps with an AC Delco part, and no change. I'm thinking inspectors. So, there appears to be 2 types. Skinny long ones and fat short ones. Rock auto claims both will fit my 2001 SOHC. Any benefit to each?

buy the stock style and reduce the variables by one.....

The listings for some of the injectors have a note, "SL1 to 600" and "SL1 from 600".

Looks like hey used the stubbies up to 600 (not sure if that is part of the VIN or what), then switched to the long thin ones mid year.

So you need to solve the 600 mystery to figure out which one is the right one for your vehicle -- or just pull one from your car.

Ok, my car has the skinny injectors. Just didn't know if they were interchangeable, or if one was more reliable than the other.

Ladies and gentlemen, we have a cause of all my problems with the engine stalling.

Before I reveal the cause, let me stress how much of a diesel guy I am. Out of 4 vehicles, and 3 tractors, this is the only gas powered vehicle I have, other than the bike. Now, I have changed countless spark plugs in my life, so you would think I could accomplish a simple task as such.

So, when I pulled the plugs to change them out with the NGK units I got from Rock Auto (in an original Saturn box!) I noticed that they had signs of blowback. I noticed after I had installed the new plugs to what I thought was snug enough. Well, got the torque wrench out and torqued them to 20 ft-lbs. They turned another 3/4 turn.

Turns out my problems were self inflicted. I was so worried about stripping the threads in the head, that I didn't seal the plugs. Mistake on my part, but I normally deal with cast iron heads that are nice and thick.

Changed the plugs two days ago, and it has not died yet. If it does, I'll report back. On the other hand, the engine runs smoother with the new injectors. Seems to have a bit more power too.

Face palm!!!!!