Perplexing Stall After Coasting

[joed]

For a while now, my truck has been experiencing an intermittent stall after downshifting into 3rd (5-spd manual) and then trying to accelerate. It has only done it after coasting with no throttle.

I usually do this downshift right before making a right turn. I go to accelerate, and nothing. I have to press the accel. pedal a few times and then when the truck starts running again, it gives out a big puff of white smoke and then runs fine. What's amazing is the consistency of the circumstances before it happens: it always happens going home from work at the same location after coasting down a long hill. The truck has been running a few minutes, the ECT is still warming up-at about 170 or so. I still seem to have ignition power - radio & lights work while this occurs. And it's not necessarily while turning- it has happend while going straight before the turn. This doesn't occur every day, but does seem to happen more often when it's colder out.

I've also been getting an occaisional code P1216 (Fuel Sol. response short, see my other posts), but not necessarily after this happens. In the process of trying to chase this down I've replaced the FSD with a remote unit (has happened with both), replaced the fuel filter, verified good fuel lift pump operation, and checked/cleaned grounds.

Any other thoughts. Thanks. Joe.

[JohnC]

This is total conjecture.

I expect that under certain conditions of coasting the PCM stops fuel delivery alltogether.

White smoke is unburnt fuel.

Only way I can see to get unburnt fuel is to inject fuel into a cold cylinder.

The PCM should NOT shut the fuel off if the ect is below some carefully engineered temperature value to prevent cold cylinders.

See where I'm headed? (me niether...)

Maybe the ECT sensor the PCM uses is off, maybe you've hit a glitch in the programming, or maybe it's something completely different. I had a similar thing happen twice down the same long hill right near my house a couple of years back. I have an automatic, so it stalled completely. Hasn't happened since...

[joed]

Hmm, could be something to the bad ECT sensor as it seems my timing if overly advanced when the engine's cold. Per my car-code scanner software it's as much as 17 degrees (not sure if that is accurate or not.) I'll have to check the resistance values of the sensor to see if it's flakey.

Another thought I had was a bad APP, but I would think the would create problems more often when trying to accelerate.

Thanks. Joe.

[donr]

Did you ever find a solution to your problem? My '98 K2500 has been doing the same, dying on light or coasting throttle for several weeks now. I've tried the new remote mount fsd from Heath - actually 2 of them, had 3 dealers look at it- no codes, no solutions. When it dies, it usually doesn't restart for 5-6 tries, sometimes not at all till next day. IP is only 6 months old, new filter, Lift pump press. 5# at idle, 2# full throttle. Trying new OPS and LP today. Scary to drive with this uncertainity.

[joed]

No, I've haven't found a definite answer, although it hasn't happened in a couple months. This leads me to believe it's temperature related, as the truck is started at higher temps and gets to operating temp much quicker than before.

When your truck stalls, does your dash/radio lights go off as well? If so, could be your ignition switch. Others have had that happen.

When my truck would "skip", the dash/radio lights always stayed on, and the truck never completely died, as in the more classic FSD failure relm.

Joe.

[donr]

My truck dies on a warm, not hot engine, always at near idle speed, and never restarts quickly. I know it's not the fsd, cuz when it began happening, I had Heath send me a new one, even tho the one on it was only 2 weeks old. Dash lights stay on, security light goes off after a couple seconds, like it's supposed to. But I noticed the glow plug light doesn't come on, which maybe it shouldn't with the engine warm. If I try restart several times, it will start if the glow plug light comes on, it seems. It seems unbelievable that GM won't do anything about this huge problem.

[donr]

Well, it quit on me again today. A warm. 70deg. at just above idle in traffic. Got it started after about 5min.had just put a new lift pump and OPS in yesterday, so that's not it. It was showing 5 lbs pres. @ idle when it quit. New FSD- that's not it. IP isn't very old 10,000 mi, but has been doing this for about 5000. I have the feeling that it's something electrical, but what?

[CareyWeber]

Check:

Battery connections (both ends of each one)
All engine electrical harrness
Check each connector too

Are you getting any codes???

Do some searches here on wiring issues.

Carey

[Dimsdale]

"I expect that under certain conditions of coasting the PCM stops fuel delivery alltogether."

You are correct, although I have only seen it when using engine braking down the backside of a mountain road in low gear. Engine noise just cut off, and then resumed when the accelerator was pressed at the bottom. Sounds like yours is not resuming after the coast.

Ditto on checking electrical connections.

[rjwest]

READ the codes / history,
May be a clue in there..

[donr]

It's a lot warmer today, and the dying is getting worse. I found that if I keep the rpm's over 1000 when coming to a stop,it doesn't die. When it does die, it doesn't restart until it has a blop on the glow plug light, which is usually about 8-10 tries. Talked to Bill Heath today and he's leaning toward the ign. switch. I've already done the grounds and wiring stuff, and there's never any codes that come up. The automatic trans just freewheels when I let off the accelerator, and doesn't keep the engine rpm up, so maybe the ecm isn't telling the fuel flow to restart when the speed gets down low. Baffling, but I'm stubborn enough to stay with it to the end.

[JohnC]

Where are you measuring the fuel pressure? Any chance the fuel filter is clogged? If it were electrical in nature I'd expect it to be independent of RPM.

[donr]

Have a new filter in it and checking lift pump pres. at the drain line, front of engine. Bought a new ign switch today and will know if that's it soon. I'll keep you all informed, as a lot of people are having the same type problems it seems.

[1995Z71]

What happen with your problem? Did you figure it out? I am having similar issues.

[donr]

I got the new ign switch, and started to install it, then thought I'd try one more thing. I have dual post batteries, so made a harness that connected the pos and neg terminals together, then connected the neg post to a clean ground connection on the fender well, by the fuse box. Then ran a ground wire from there into the cab to the 1" tube that supports the dashboard, there's a couple nuts to attach the wire to. 2500 mi and no stall and running great. Still have the new ign switch just in case.