Could a bad drive pulley or belt cause a misfire?

JWaldz

JWaldz

Moderator
So, recently I've been chasing down a couple misfire codes. A P0300 and a P0303 (misfire #3). I checked spark plugs (as they are less than 10k miles old) , replaced all 6 injectors with freshly flow tested and rebuilt OEM ones, replaced wires, and swapped coil packs #1 to #3. Still getting the misfire with a cruddy stumbling idle from cold start. Otherwise drives just fine.

I'm curious though, could a bad drive belt or pulley cause a misfire?

The reason I ask is because I've had a rather large constant belt squeal on startup that lasts a few seconds. Simultaneously, the stumbling idle will occur and then begin to clear up once the squealing subsides. Eventually, after a few seconds, the stumbling idle will clear completely and then I'll be on my way.

I have a suspicion that I have a pulley going out, as I can hear, what I can best describe as, a running outdoor water faucet sound. Especially louder on cold startups.

I've done light reading on drive belts/pulleys and misfire correlations. It seems to be a less-common cause than the typical ones, but still could very well be a cause. With the common ones troubleshooted, I'm trying to think outside the box here, especially since I seem to have a drive belt or pulley acting up.
 
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JWaldz said:
So, recently I've been chasing down a couple misfire codes. A P0300 and a P0303 (misfire #3). I checked spark plugs (as they are less than 10k miles old) , replaced all 6 injectors with freshly flow tested and rebuilt OEM ones, replaced wires, and swapped coil packs #1 to #3. Still getting the misfire with a cruddy stumbling idle from cold start. Otherwise drives just fine.

I'm curious though, could a bad drive belt or pulley cause a misfire?

The reason I ask is because I've had a rather large constant belt squeal on startup that lasts a few seconds. Simultaneously, the stumbling idle will occur and then begin to clear up once the squealing subsides. Eventually, after a few seconds, the stumbling idle will clear completely and then I'll be on my way.

I have a suspicion that I have a pulley going out, as I can hear, what I can best describe as, a running outdoor water faucet sound. Especially louder on cold startups.

I've done light reading on drive belts/pulleys and misfire correlations. It seems to be a less-common cause than the typical ones, but still could very well be a cause. With the common ones troubleshooted, I'm trying to think outside the box here, especially since I seem to have a drive belt or pulley acting up.
Click to expand...
Sounds like a cracked head or heads. Especially common if it's a supercharged motor.
 
Well, there is no way a slipping belt or bad bearing on an alternator, A/C compressor, or P/S pump can cause a misfire.

The timing belt is cogged, and if it squeals, in general, it's a death throw. The one exception is the water pump. It is driven by the BACK of the cogged belt. A seizing water pump might well cause those symptoms. I'm not sure if that can result in a misfire by some effect on valve timing, but it is the best bet for a connection.

The other thing you should rule out is a loose crank bolt. That can be very bad, although I am doubtful if it could result in a squeal plus a misfire. But maybe...

I still think they are more likely to be independent problems.
 
TheDurk said:
Well, there is no way a slipping belt or bad bearing on an alternator, A/C compressor, or P/S pump can cause a misfire.

The timing belt is cogged, and if it squeals, in general, it's a death throw. The one exception is the water pump. It is driven by the BACK of the cogged belt. A seizing water pump might well cause those symptoms. I'm not sure if that can result in a misfire by some effect on valve timing, but it is the best bet for a connection.

The other thing you should rule out is a loose crank bolt. That can be very bad, although I am doubtful if it could result in a squeal plus a misfire. But maybe...

I still think they are more likely to be independent problems.
Click to expand...

Thanks for the insight.. I don't think it's the timing belt squealing. I think if it was, I'd be up schits creek by now. Plus, the timing belt and water pump are 30k old and OEM.

I just want this to be fixed already... sheesh
 
Loose crank bolt/pulley is the first thing that comes to my non-mechanic mind but as stated, not a mechanic.
 
So this is what you have been chasing down for months correct?

I'd now perform a coolant pressure test and then a leak down test to check for a cracked head.

Ever check fuel pressure on a cold engine?
 
LittleCaesar said:
So this is what you have been chasing down for months correct?

I'd now perform a coolant pressure test and then a leak down test to check for a cracked head.

Ever check fuel pressure on a cold engine?
Click to expand...

For a little while yes.. It hasn't gotten any better, yet it hasn't gotten any worse. I did a block tester to check for exhaust fumes but tested negative for fumes.

Haven't done a leak down test. Never checked the fuel pressure when cold.
 
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