99 gmc 4.3L dies for no reason

[maeziesdad]

Me and my mechanic are stumped on this one actually just me he is never around when it happens. My truck will just die going down the road seems like it's not getting fuel or air one. The truck is old and has a lot of miles on it. But has been well taken care of. The fuel filter, and pump are new the cat. converters are new the plugs and wires are also new. When it cuts out the more gas you give it the more it wants to die then after it sits overnite it may run fine for a month or so then out of the blue will do it again. There are'nt any engine lights on and when I take it to the shop it runs fine so the mechanic tells me to just drive it cause he needs to be in it when it starts acting up to find the problem. Please help. It does make a popping noise but it's not a backfire and then a funny smell sometimes comes out from under the truck and aat $65.00 an hour my mechanic is killinh me.

[hotrodpc]

Is it not throwing any codes? Are you sure your check engine light works?. It should come on when you turn the key to on position. I had heard of a similar problem on a Ford once, and it turned out to be a crankshaft sensor. How or why, I do not know but go figure, that was a Ford. Sounds as if it could be an ignition coil, but being that you should have 3 coils, you would think if it was that, you would only lose 2 cylinders not kill the whole motor.

[maeziesdad]

Thanks for your reply. Yeah the engine light works it was on until the convertors were changed. That was the only code it was giving. Coils and caps have also been checked .

[leolkfrm]

Does it smell like rotton eggs? It sounds like unburned fuel getting to the cat. Maybe an injector acting up? When the scan tool is on it are any of the reading towards there limits?

[maeziesdad]

Now that I think of it that does kinda smell like rotten eggs. How do I findout for sure if this is the problem? Also is it hard to correct?

[maeziesdad]

Any suggestions will really be appreciated.

[mudseeker]

sorry, i got nothing.

[junior3382]

Originally Posted by mudseeker

sorry, i got nothing.

And yet, you felt the need to reply? LOL....


Anyways, with all the new timming parts, and the new exhaust parts, there is a good possibility it is the cat itself. The smell you are smelling is the unburnt fuel interacting with the honeycomb in the converter.... I personally hate that smell... The random bogging and stalling, even when giving more fuel, is due to increased back pressure. It sounds like you may have a blockage, but it is not severe enough to stop the motor all together.... Now if after all these parts were isntalled, and checked and rechecked, if the timming is off by just a little, it can allow raw fuel to pass through the engine and into the exhaust. It is not a common problem, but it does happen. I am not sure how long it has been since you put the cats on there, but some are stronger then others... With the random bogging, this would lead me to believe that soon, you will need to replace the cats again before the backpressure causes a valve problem and you end up needing more then just a cat.

Now, I only express all of this due to very recent past experiences with my personal truck. Again, it is not the most common answer, but it may explain it. Meanwhile, I could be wrong. It is hard to really diagnose something without actually seeing it act up. Similar to why your mechanic has not caught it. Now the only concern I would see is that if this IS the real issue, normally the ECU throws an O2 code for a missread, or po300 code for multiple cylinder missfire.... so with there being no codes I am just guessing.... My truck did not throw the proper codes to lead us in this direction until the damage was already done.

_____________

Now there could also be a totally different explaination.... Have you ever seen CSI? there was an episode where someoine had put a ping pong ball in the gass tank of his wifes car. Now most of the time those will float, however, with the suction created by the pump, especially when the tank was lower, it would suck the ping pong ball down and block the fuel inlet, and in return starve the engine and cause it to stall. Then after it sits, it starts right back up with absolutely no problems.... untill days, maybe even months later. Now he did this in the hopes that it would stall in a spot that would kill her, and in the show it did, but it took the CSI guys forever to figure out why the car died.....

I am not saying you have a ping pong ball in your gas tank, but wouldn't that be bizzare if that was really the issue? Anyone have it in for ya? LOL.....

I hope some of this helps... good luck.

[bricen]

ICM Ignition control mudule, i believe thats the name of the part, if it runs then just dies with no rhyme or reason i'll guarentee thats what it is, might be called crankshaft sensor

[leolkfrm]

Find a mechanic that knows how to diagnois problems by using the readings off the scan tool