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Discussion Starter #1
Took my car to the dealership because I have a strange misfire occuring at around 40mph in 4th gear. It isn't terribly bad but enough to be incredibly annoying in city driving. Dealership concluded that there is a slight misfire... this problem has been occurring for a while now and no cure. Replaced my plugs, wires, and coil pack. It seems worse when I am coasting. no engine trouble code is present which is why the dealership could not help. Anyone have any idea?
 

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I'd love to know too. I had a misfire in all 4 cylinders and since no other code, dealer sent me home.
 

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Took my car to the dealership because I have a strange misfire occuring at around 40mph in 4th gear. It isn't terribly bad but enough to be incredibly annoying in city driving. Dealership concluded that there is a slight misfire... this problem has been occurring for a while now and no cure. Replaced my plugs, wires, and coil pack. It seems worse when I am coasting. no engine trouble code is present which is why the dealership could not help. Anyone have any idea?

Year, engine & mileage?

I have no simple answer. First step with solving a misfire issue is to find out exactly which cylinder/s are misfiring. And if you discover that the misfire moves around between different cylinders that's a helpful clue as well. With no codes to help, you need a proper scan tool that can read the misfire counts per cylinder. Any mechanic has one. You can get a PC based scan tool for around $200. Without gathering evidence, all you can do is throw parts at it which almost always is more expensive then a proper diagnosis would have been in the first place. Infrequent & random misfires are generally the most difficult to track down. There is always the option of waiting until it gets worse: i.e.-more frequent, less random & sets a code.

You can buy a basic code reader for twenty bucks that will read & erase codes & save you the hassle & expense of driving to AutoZone.
 

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I had the dealer scan mine and they told me it was a misfire on all cylinders. They didn't really give me a solution, just sent me on my way because there was no code that was logged. Just the flashing cel that lasted for about 10 seconds. It's not really a big issue and only happens once in a blue moon. But when it does happen, it happens when the cruise is on and going uphill or when I'm coasting (completly out of the gas). Happens more with the cruise on and going uphill tho.

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I had a slight misfire around 45000 miles. So slight that you could barely hear it in the exhaust. I drive nothing but highway, about 100 miles a day, so at high RPMs it was barely noticeable. It finally threw a code (misfire..duh) around 50K. I checked the plugs, all looked clean, etc. So I brought it to the dealer. The number 3 cylinder was misfiring. Cause was a clogged injector. But that is was just the beginning. The reduced fuel into the cylinder brought the temperature up in that cylinder. The temperature got so high that the valves and head started to deform. I ended up needing a new head (too deformed to machine the existing one) and valves. Probably some other things too, I don't remember exactly what. I believe them because they showed me everything. The main concern GM had was that the Ethanol in fuel may have contributed to the increased temps. They wanted all the parts sent back so they could research it.

Then came the 'who pays' part. The injector was the ultimate cause and was not covered by the power train warranty. But the car is a PZEV and I live in one of those states that requires those vehicle to replace anything that would cause an emissions rejection to be replaced under warranty if I am the original owner. So I didn't pay for it and have no idea how expensive it would have been. Also got a free rental for the week it took to get done.

Hopefully your issue is a bad plug or one of the coils.
 

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I had the dealer scan mine and they told me it was a misfire on all cylinders. They didn't really give me a solution, just sent me on my way because there was no code that was logged. Just the flashing cel that lasted for about 10 seconds. It's not really a big issue and only happens once in a blue moon. But when it does happen, it happens when the cruise is on and going uphill or when I'm coasting (completly out of the gas). Happens more with the cruise on and going uphill tho.

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That is my exact story i had this weekend, same results at the dealer as well. I do notice at times my rpm idles around 1100-1000 when the car has sat for a few hours then runs normal after a few blocks. Do you get random hesitation and fluctuating gas mileage like i do?? On another note, i almost only use 100% gas.

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That is my exact story i had this weekend, same results at the dealer as well. I do notice at times my rpm idles around 1100-1000 when the car has sat for a few hours then runs normal after a few blocks. Do you get random hesitation and fluctuating gas mileage like i do?? On another note, i almost only use 100% gas.

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My gas doesn't fluctuate but I do get random hesitation like it doesn't wanna kick down a gear or it'll hesitate from just taking off.

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Discussion Starter #14
Holy crap after everything, I have taken my car to three different dealers, two transmission places and two general mechanics... no one could figure it out. Everyone kept saying it felt like a misfire. Well I put the car up on blocks and was checking the cvs thinking maybe that was the case, but when i turned the wheels I noticed the engine and transmission shook kind of funny when I reversed the spin on the wheels... So I looked at the engine mounts and transmission mounts and they were fine, but then I saw on the top of the car there is a snubber (basically an engine mount strut) and it was broken... I asked mechanics to check the mounts and they all claimed they were fine... clearly they werent. the shaking I was getting that everyone thought was a misfire was actually the snubber not dampening the torque...
 

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Holy crap after everything, I have taken my car to three different dealers, two transmission places and two general mechanics... no one could figure it out. Everyone kept saying it felt like a misfire. Well I put the car up on blocks and was checking the cvs thinking maybe that was the case, but when i turned the wheels I noticed the engine and transmission shook kind of funny when I reversed the spin on the wheels... So I looked at the engine mounts and transmission mounts and they were fine, but then I saw on the top of the car there is a snubber (basically an engine mount strut) and it was broken... I asked mechanics to check the mounts and they all claimed they were fine... clearly they werent. the shaking I was getting that everyone thought was a misfire was actually the snubber not dampening the torque...
Did any of these "mechanics" actually check the misfire data? That takes about 2 minutes to do.
 

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Also fyi ...... Chk engine light came back on and read codes p0171 and p1133. Maybe we have the same problem?

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Dealer just told me i have a clogged cat. Loving that warranty. You probably have the same problem. I first noticed my car having problems long before my cel came on. EvEn though it shows the signs evidEntly they cant change the cat until the light comes on

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