Why does my truck shut off randomly?
June 28, 2009 5:51 PM   Subscribe

Why does my truck shut off randomly?

I own a 1997 GMC Jimmy. About two weeks ago, I filled up at a local gas station and began experiencing some problems related to what I believe was water in the tank. I dumped a couple bottles of Heet (a “DryGas” type product) to get rid of the water and stop my sputtering. It seemed to work, but since then, more problems have arisen.

Every now and again, with no rhyme or reason, my car will shut off. Not stall. Not sputter. It just shuts off. The speedometer and tachometer will zero out and the radio cuts out. The dummy lights come back on and I put my car in neutral and start it up right away. From this point, I will usually put it in Drive or Reverse (depending on which direction I was going to begin with) and continue. Sometimes, however, the car will shut off again. This “shutting off” usually happens when the vehicle is traveling slowly (ie: braking or just taking off).

An item of note:

I have a remote-starter unit on it and am unsure if that is causing problems. I haven’t the money to have it removed properly.

I know you guys aren’t my mechanic, but hopefully you can send me in the correct direction to get this issue fixed.
posted by DonSlice to Travel & Transportation (7 answers total)
I'm not at all a mechanic, but several of my cars have shown this sort or behavior with bag egr (exhaust gas recirculation) valves and/or faulty oxygen sensors.

I'd start to coast up to a light and the engine would cut off. Sometimes it would start right back up but others it would sputter and stall out a couple of times before it would catch. Eventually it wouldn't restart and I'd need to have it towed in for the repairs.

I have no idea if these parts are even relevant for your Jimmy, but the problems symptoms sound familiar...
posted by Barnsie at 6:06 PM on June 28, 2009

I've seen aftermarket remote start units case problems on GM vehicles. Usually, there'll be some indication like "Security" (or other immobilizer warning) illuminated on the dash, if it's the culprit.
You can probably remove it yourself. If you have the tools (it'll either be phillips head screws or some small 8 or 10mm bolt, if anything) and time (15 minutes) to take down the panel under the drivers side dashboard, just look for the obvious splices into the stock harness. Many remote start set-ups use connectors that sort of "T" into the existing harness that clamp onto a wire and break through the insulation. They'll be pretty easy to spot. Just don't touch the yellow wires. They're for the airbag system.

Is your check engine light on and did it come on during your 'bad gas' episode? If your check engine light is on, go to Autozone, get them to scan it for free and tell us what the code is.

Is your car ever hard to start? The V6 Jimmy/Blazer has a fuel injection unit installed inside the intake manifold that is the source of many hard starting and poor performance concerns. The fuel pressure regulator and injector are integrated into one unit and both elements are subject to failure. I've traced quite a few engine performance problems back to that unit on the Jimmy/Blazer and it's pretty notorious.

There are a few things that can cause sudden shut off. A bad crank position sensor can cause this, too. If the engine computer can't keep track of the engine's rotation, it'll die immediately, especially on earlier OBDII cars that don't have a redundant signal for engine speed.

Also, have you done anything with your battery recently? Bad battery connections can cause a sudden shut off. If your battery tie-down is missing or damaged, the battery will be subject to sudden jarring and vibration and can short out or aggravate a poor connection.

If the car isn't sputtering, shuddering, or being sluggish, we can rule out other engine performance failures (generally) like vacuum leaks, EGR failures, and throttle position sensor failures. Those failures typically have additional symptoms (check engine light, lack of performance, etc) and don't manifest in a "sudden" shut off. I would also be reluctant to condemn an ignition coil unless you're getting misfires in addition to stalling.
posted by Jon-o at 6:16 PM on June 28, 2009

Hey Jon-o. Thanks for the thorough response. Here's what I can answer:

There is no check engine light, nor was there during the bad gas episode. I wish this wasn't true- a visit to get it scanned would save a lot of time.

The car isn't hard to start, but there is a slight delay (sometimes up to 5 seconds) between the time that I turn the key to the "on" position and the dummy-lights coming on. If I try to start the car before the lights come on, the engine will just turn and never fire.

I have checked the connections on the battery. Both seem to be free of corrosion and are in there firmly. I'll have to check on the tie down.

Your list of sudden shut off causes make me curious and more informed when I can get this looked at by a mechanic.

posted by DonSlice at 6:22 PM on June 28, 2009

Diagnosis time: if the car dies because of some engine thing, the radio and the gauges would still work. If they die at the same time as the engine dies, that points to something electrical. I would check for loose battery cables first, but most likely it's either a loose cable or failing ignition switch.

A remote starter, installed properly, shouldn't cause issues like this. It just adds a different circuit to start the car. It just piggybacks onto the normal wiring. Unless your car is starting for no reason, there is probably nothing wrong with it. (If it was installed improperly, all bets are off.)
posted by gjc at 6:26 PM on June 28, 2009

When you check the battery tie down, check the ground strap connection where it bolts to the body/frame. That's also a critical connection.
Right next to the battery, on that car, is the ECM. It's the black box with the heat-sink fins on it with all the wires and connectors going into it. Inspect those wire harnesses and make sure they're not damaged. With the car running, give those wire harnesses a firm wiggle. This is more of a long shot, honestly. But I have seen some wild problems revealed by a lucky wiggle test.
posted by Jon-o at 7:20 PM on June 28, 2009

If the radio goes off, that means an electrical problem. You may have checked the battery connections but what about the connections at the other end, in particular the connection of the ground cable to the chassis. Another possibility is a bad ignition switch.
posted by JackFlash at 7:24 PM on June 28, 2009

I had this exact problem. I don't know if my experience will be relevant, as it was a different car and brand new, but I'll share anyway in hope that it might help somewhat.

The car was a 1990 hundai scoupe. Thought the problem was was electrical, in addition to all the things you mentioned, the power windows and locks wouldn't work. The windshield wipers also stopped. All at the same time.

It happened frequently, but at random times so it was impossible to replicate for mechanics. The amount of times it was in the shop in the first year added up to the equivalent of 7 months. It didn't happen to the mechanics till the last time it was in the shop. A few days later they solved the problem, it was a defective or cracked o-ring.

I don't know if this story will help you figure it out because I honestly couldn't tell you what an O ring is, or where one would find it in the engine. I also don't know what the repair process is like. While they said it was easily repaired, by then, I was already 3/4 through the lemon law process and the next time I went to the dealer, it was to pick up my refund, not my car.
posted by necessitas at 7:36 PM on June 28, 2009

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