BlackCar

Ditto. Exactly the same problem. One shop used aftermarket belts. I was getting cels that read as misfire codes, while the engine was running fine. Took it to Bill Boys at Possum Hollow Motorsports in Phoenixville...just north of Philly He upgraded the pulley and put on factory belts. Problem solved.

hkate

Same here. I had the exact same problem. Drove around for months before I read a thread about the belts. I was so happy to see the darn light go out I even started a post here about it. TELL ONE TELL ALL - OEM BELTS ONLY!!!

AOW162435

I recently installed a new set of Porsche belts but just can not get my head around this issue. Why on earth would our car's be so sensitive that non-OE belts cause CE lights? Seems ridiculous to me.


Andreas

Amfab

It is my understanding that the non-factory belts tend to slip slightly, and this slight slippage is just enough to cause a very slight change in load on the crank, and this is perceived by the sensor as the very slight stumble of a misfire.


If the belts were dusty, the load would be much higher and there would not be such confusion

cabrio993

It seems ridiculous at first, until you observe it and think the whole thing through and then it makes perfect sense.

This is what was observed, and this is my conclusion, mileage may vary...

Since the non-oem belts are a bit wider, but they need to fit into the same V pulley, the v-belt doesn't go as deep into the pulley. This make the non-oem belt side surface not to be in full contact with each of the pulley halves as it tends to grab/pinch the outer, wider section of the belt. You could see that the top of the belt between the pulley halves had a dimple, or a slight "U" cross section. This make for and uneven distribution of the friction with the belt and the pulley.

This also explains why the CEL wouldn't come on unless the engine was revved over 5K rpm. We revved the engine while watching the belt, and you could see deflections, and/or undulations of the belt at those rpms. As the rpms rises, the centrifugal force would make the belt to tend to go outside of the pulley, relieving the tension on the top part of the v-belt and changing the friction load toward the inner part of the v-belt.

So, at higher RPMS, the deflection and undulations of the non-OEM belts would make slight slips and grabs of the pulley and a very high rate, creating variations on loads on the crank that would be interpreted by the crank position sensor as possible misfires. This would cause the ECU to adjust ignition to try to fix the false misfire condition making everything worst.

We observed the OEM belts at the same rpms and they were smooth throughout the whole range, without any deflections, undulations and change in v-belt cross section profile.

That's my story and I'm sticking to it.

AOW162435

Well said.


Also, well said.


Andreas

fast_freddy

I have a Conti belt on mine with no problems whatsoever. Oddly enough a local auto part store had one. Perhaps it's down to the car being OBDI. Who'd have thunk?

cabrio993

Good point!

JeffC

Hi folks,

I am changing my belts to OEM and am having difficulty determining which belt drives the fan and which belt drives the alternator. There are 2 part numbers 99919234350 and 99919232850. Which one goes where?

Thanks,

Jeff

Edward

Hahaha ...I am so lame! I thought the orig thread was about using OEM seat belts ...like WTF? How would OBDII sense seat belts?!!!
I should never surf pre-coffee

Edward

C4SJOHN

I think you should have started a new posting to get your answer faster. The outside belt is 99919234350.....

EckFe1

Hello guys,
I have Porsche belts on all 3 but will change to an aftermarket one for the alternator. Porsche states 9.5x760. I bought that one and I had to pack over 1/8 of shims in between. The belt is so far down between the pulley halves that the alternator spins like crazy. It looks like it's actually making contact with the shims. I tried the 9.5x776, which is used for the fan but it slips and is loose.
So I purchased 10x770 and hope to get rid of most shims, plus make the belt ride higher. The angle of the V should still be as the 9.5, just a bit wider. If it doesn't run all the way in the groove at the crank, it shouldn't matter because the newly replaced AC belt is now much wider then the old stock one. It is a Porsche belt but the old style isn't manufactured anymore. It was a bitch to install it because the 4 slots to tighten the AC compressor is at its shortest position and it's already at the right tension. If you have to do that on the side of the road, forget it. I had to have a 2nd person to hold down the compressor with all the weight he had. The fan belt however fits just right.
Any thoughts on my idea? I won't be driving for another 6 weeks but I'll have everything ready.

JeffC

I am kinda lost here ... is the outside towards the engine?

C4SJOHN

Outside= Back of car away from engine

2ndof2

Was doing some light reading on causes of misfires. My car had Conti belts installed about 7000 miles ago but I haven't had a misfire code since my motor's top end was redone about 5000 mi ago with all the plugs, wires, etc replaced including my clutch - that is, not until Saturday. Anyone had Conti belts work for a while and then start causing a misfire code? With so many convinced that non OEM belts are causing troubles and all of the work done on my car, I'm beginning to think this may be the root cause for my misfire codes.