False Knock

[MCHdrivesan86GN]

I happened to have to change my alternator and while it was off I replaced my serpentine belt. Once alternator and belt were replaced, I took it on a long drive primarily to monitor voltage to make sure the alternator was functioning properly.

So after I confirmed alternator was functional I took my car for another drive and I noticed immediately that the spark was retarding, I was not building boost or driving fast, just normal driving. I did check the fuel rail pressure it was ok. I also checked all the mount points for the alternator, and mounts for the alternator brackets, to make sure they were torqued adequately and they were.

Let me also state this, there was rattling/vibrating noise from the engine prior to me replacing the alternator and serpentine belt, but there was never any knock under "normal" driving conditions. Now under very heavy acceleration there was, but it was minimal at that. I think it was false knock as well, because I have alky injection, ramp rate set to max, and I added more fuel up to the max of 20% and it would still occur but once at max boost they was none. I have turbotweak chip with matched injectors.

When I replaced the alternator and serpentine belt, this issue popped up. Please note that at stop or idle in park there is no spark retard. It only takes place once I'm driving or I rev it in park and yes there is noise rattling/vibrating noise coming the engine. So I believe the knock is being caused by excessive engine noise and it got worse with a new serpentine belt and I do not believe that it is the ESC or knock sensor that are malfunctioning. I will confirm the latter, I just need to get the correct leads for my multi-meter to probe and determine signal integrity from the ESC and knock sensor.

So it sounds like I have it all figured out, excessive engine noise correct? Well the only problem is that I can't audibility locate the source. My best guess is that it seems to be coming from the lower pulley on the engine, the one with the fan mounted to it.

Any thoughts? I'm going to hoist it, jack stands, and check and see if there is anything loose in the exhaust, motor mounts, etc. I've also considered using my camcorder and recording it and posting on utube to see if anyone else finds the noise familiar. Again, any thoughts or suggestions are greatly appreciated.

[kenmosher]

Try a belt that is one inch shorter ... it very well might be the tensioner "bottoming" out when the motor torques over, rattling against the accessory bracket.

[MCHdrivesan86GN]

Thanks.

I will definitely look into this, because it started immediately with the new belt. My wife threw away the old one, otherwise I would have stuck that one back on it.

Since I can cause this while in park and reving the engine I will have someone rev it for me and try to see if I see anything visually.

[Keller]

GM used a lot of belts that have metric sizes that don't work out to even inch sizes. The aftermarket usually sticks to inch sizes. Sometimes, that fractional amount can make a difference. Also, if you use an underdrive or RJC pulley set, an inch shorter belt can help. I've found that the alternator pulley used in the RJC set is small enough to be aided by this smaller belt.

It isn't hard to determine the length of a smaller belt. A Genuine GM belt for a Pontiac GTP app I have sitting here (anyone want to buy these? The guy sold the car... ) is labeled 6PK2330. That means 6 ribs and 233.0 mm. That would translate to 91.732". In inch terms, if it was 92", it would be labeled depending on the manufacturer. In Dayco it would be 5060920. Kelly-Springfield or Drive-Rite would call the same belt a 920K6.

That is the great thing about standards. There are so many to choose from.

As for the TRs, the recommended size the parts stores list is a 64". (i.e. 5060640 or 640K6) However, the factory belt listed as P/N 10105307 is supposedly 1619 mm. That equals 63.74"...

Ooops.

This may be a situation where the 63" works better than the 64". Actually, a 63.5" would be fine, but that may be hard to find. In theory, they do make belts in half-inch increments, but good luck finding them. Note the Kelly-Springfield 635K6 P/N in the listing.

[87geeinn]

Going back to the original problem at hand...from the detailed description that "MCdrivesan86GN" gave, it could possibly be the belt tensioner going bad or at the end of it's travel. Although I've never had a problem with mine, some attest that the tensioner does have the ability to set of the knock sensor when they start petering out or the belt slips. That said, a while back, I went from a 64" belt to a more stock-sized 63.5" belt (they are available at most parts stores, although it will probably have to be ordered) and the belt started squealing like hell. I went back to the 64" belt and all was fine. As long as there is a decent amount of tension in the belt and the tensioner is not bottoming out or at the end of it's travel, I've found that a 64" belt does just fine. FWIW, a too long belt, or if the tensioner is at the end of its travel, the tensioner pulley could be tapping on the A/C compressor bolt located just behind the pulley, especially if the bearing is shot.

If all of those suggestions pan out, you might need to dig a little deeper (i.e.-torque converter bolts, etc.) Keep us posted.

[MCHdrivesan86GN]

If all of those suggestions pan out, you might need to dig a little deeper (i.e.-torque converter bolts, etc.) Keep us posted.

Most definitely. I appreciate your input.

[MCHdrivesan86GN]

Originally Posted by 87geeinn

Going back to the original problem at hand...from the detailed description that "MCdrivesan86GN" gave, it could possibly be the belt tensioner going bad or at the end of it's travel. Although I've never had a problem with mine, some attest that the tensioner does have the ability to set of the knock sensor when they start petering out or the belt slips. That said, a while back, I went from a 64" belt to a more stock-sized 63.5" belt (they are available at most parts stores, although it will probably have to be ordered) and the belt started squealing like hell. I went back to the 64" belt and all was fine. As long as there is a decent amount of tension in the belt and the tensioner is not bottoming out or at the end of it's travel, I've found that a 64" belt does just fine. FWIW, a too long belt, or if the tensioner is at the end of its travel, the tensioner pulley could be tapping on the A/C compressor bolt located just behind the pulley, especially if the bearing is shot.

If all of those suggestions pan out, you might need to dig a little deeper (i.e.-torque converter bolts, etc.) Keep us posted.

The best I can tell, there doesn't appear to be an issue with the tensioner pulley or any others. I have also removed the "trans shield" to look at the torque converter and flywheel, everything seems snug there.

In listening to the engine and reving it, the best I tell, it appears the noise is coming from the crank shaft area. I'm not saying that is what is setting off the knock the sensor, but the noise is there. Someone else suggested that I take a look at the timing chain. I might be pulling it off anyway, because I wanted to upgrade my CAM, with help of course. I hate to pull everything apart and get a new CAM only to have the same issue.

BTW, does anyone know of good engine guy for these cars located in southeast MI. I have already had it to Aggressive Auto and they weren't able to tell me where the noise was coming from, it was at aggressive for two months total. They couldn't figure it so there is no point in taking it back there. Just in case someone suggested that I take it there.

Any other suggestions?

Thanks,
Charles

[MCHdrivesan86GN]

Originally Posted by 87geeinn

Keep us posted.

I had a chance to get my car out this past Sat. and as I approached a stop sign there was a clunk and my car stalled. Couldn't get it started, appeared to have a loss of compression. I was close enough to push my car home. Noticed a little oil leaking. I put it up on jack stands and I didn't really see anything. I drained the oil and I seen some shrapnel coming out while draining. I dropped the oil pan, I don't have clearance to get it off completely and it appears that I have a broken rod and maybe some other parts on the rotating assembly.

Looks like an engine rebuild is underway - Merry Christmas.

Thanks everyone's for your input.

[Keller]

Originally Posted by MCHdrivesan86GN

it appears that I have a broken rod and maybe some other parts on the rotating assembly

That would not be false knock then...

[MCHdrivesan86GN]

Originally Posted by Keller

That would not be false knock then...

My theory is that excessive engine noise/vibration was setting off the knock sensor. As I stated in previous post. Unless my car was so out of tune that under normal driving or revving it while in park that denotation was present. I have been very conservation on the throttle, in trying to figure out was going on. Not boosting it at all. Noise kept getting worse and worse.

Bare in mind, I blew a head gasket last oct and I once the gasket and heads were replaced my car was never really the same. Never ran smooth.


Engine is in for a rebuild and I managed to fry the harddrive on my work laptop. My end/new year is just grand!