Random engine stalling, IGN Volts dropping suddenly

[Tooky]

OK I got my truck back together and on the road and I've been working a lot on the tune but there's one problem that I can't make go away. Random stalling at idle!!

I've got the idle tuned better now and it's pretty decent so I take it into town for the first time this year, Tuesday evening. Get in heavy traffic at a stoplight and it decides to stall. :roll:

I noticed in the datalogs, EVERY time it does this behavior, the IGN volts drop -1.5v (from 13.0-13.2v down to 11.7-11.4v) just a few frames/seconds before the stall. Here's a DataMaster of the "scene of the crime". You can see I slow down for the stop sign and sit at 0 MPH, idling for 15 seconds:

Sometimes it will drop to 400-500 RPM and manage to recover but it's obviously "really close" to stalling. I would say it does this once every..........20 minutes or so?

What could be causing this? This problem is new as far as I can tell. What could suddenly be causing such a load on the electrical system, and why does it make the engine stall? Looking at the AFR line and RPM, you can see it's idling fairly smooth and consistent for 15 seconds while I'm at the stoplight, and suddenly it stalls out of nowhere.

 

[WyoSyclone]

Re: Random engine stalling, IGN Volts dropping suddenly

If the battery is old, plates can momentarily short out causing a voltage drop.... could be a bare wire somewhere along circuit path, or could be a bad connection causing voltage to drop out going to the ECM.

 

[Ty0279]

Re: Random engine stalling, IGN Volts dropping suddenly

Check this thread out if you haven't already: http://www.syty.net/forums/showthread.php?t=49380

Also, double check all the ECM connections to make sure none is loose.

 

[El_Jeffe]

Re: Random engine stalling, IGN Volts dropping suddenly

Check this thread out if you haven't already: http://www.syty.net/forums/showthread.php?t=49380

Also, double check all the ECM connections to make sure none is loose.

Definitely check the connections at the ECM. The pin connectors on the plugs sometimes become bent/enlarged and no longer make good contact with the pins on the ECM causing some of these electrical problems. Does the truck start right back up after it stalls or does it crank a while before firing up again?

 

[Tooky]

Re: Random engine stalling, IGN Volts dropping suddenly

It always restarts instantly. You can actually see the immediate re-start on the far right side of my DataMaster chart posted above. (The red line drops to 0 and quickly comes back up a few seconds later).

I still have my ECM dropped so I'll double check it and read that thread you linked. However I'm not sure it's the ECM since it doesn't cut out at WOT even when I'm flooring it hard enough to spin the tires from 30mph and the ECM is moving around a bit on the floormat from the G forces.. (I buffer it with some towels so that none of the wires get taut even under WOT.)

 

[cloneman315]

Re: Random engine stalling, IGN Volts dropping suddenly

electric fans?

 

[Tooky]

Re: Random engine stalling, IGN Volts dropping suddenly

Stock fan. A/C off. That's the weird thing. It's a LOT like when electric fans turn on.

 

[cloneman315]

Re: Random engine stalling, IGN Volts dropping suddenly

hmmm?fuel pump maybe going bad?or ic pump maybe

 

[Daryl H]

Re: Random engine stalling, IGN Volts dropping suddenly

I also had random drops in alternator voltage for no reason.
Went as far as installing two batteries and a new alternator.

What fixed my problem, and I attribute this to ONLY stock Sy's, is the excitation voltage for the alternator.
At low RPMs the excitation voltage drops and then you lose alternator output.
I put the smallest pulley on my truck possible and it fixed my problems.
Stock Ty's I believe have a higher idle RPM so this is not an issue for them.

 

[dgoodhue]

Re: Random engine stalling, IGN Volts dropping suddenly

I don't know if you have TunerPro, but have you tried emulating and looking at VE tables (with the bubble on) to see where you are?

 

[Tooky]

Re: Random engine stalling, IGN Volts dropping suddenly

OK I read all ~6 pages of Gary "gjp"'s thread on a similar problem. His problem sounds like it had to do with his grounding and alternator, etc. He had low voltage (low 12s) and thats the big difference between his and mine. Mine has 100% normal voltage 99% of the time. 14.1v at idle, 13.0 at WOT, 13.8 cruising around. It's JUST during this relatively rare "phenomenon" that it drops, and that's what makes it so suspicious to me. (BTW Gary also had a lean, 19:1 fueling problem causing it to run rough, that's not the case here at all.)

I really don't think it's a fueling issue because in the log, the AFR doesnt change and the Inj BPW also doesn't really change. The tell-tale sign is the sudden drop of Volts with a drop in RPM shortly afterwards.

The battery is a ~3 yr old AC Delco 70T. This heads/cam setup idles about 100-150 RPM higher than my old stock setup which never had this problem (Same stock-style alternator too).

I also don't think it's likely to be the ECM because DataMaster never dropped the connection, even when I restarted the engine! (A lot of times cranking draws enough current to drop DM but not in this case).

Maybe I will try a spare alternator just to rule that out.

 

[WyoSyclone]

Re: Random engine stalling, IGN Volts dropping suddenly

I'd still say a battery problem... If the battery was good, the voltage wouldn't drop below 12.1 or 12 during this very short duration event - the battery would have enough ampacity to run for the truck for a split second without a drop in voltage. I still vote for one cell in the battery momentarily shorting out.

Do you have another battery you can temporarily put in to test the theory??

 

[kentuc]

Re: Random engine stalling, IGN Volts dropping suddenly

I had the same thing. Changed batteries,alternators.rewired the battery, grounds. Raised the idle speed a bit and that cured it. I still think it`s electrical, but I am tired of chasing it,for now.