High Knock Counts When Engine Cold & Part Throttle, Low RPM Knock - Datalogs

[Ski Bum]

Since I got my datalogger I have gotten the engine to the point where during 3rd gear pulls at WOT I amnot getting any knock whatsoever. To do this I brought the boost down to 14psi. For now I figure thats ok, at least the engine should be safe.

Something else is going on. When I start the engine cold and drive (slowly, not hitting boost or going past 3k rpms) the engine surges and lacks any power as if I'm intermittently pulling a trailer. After this started happening I hooked up the datalogger to see what was going on. When the power loss happens the knock counts rise to 50 counts, while the timing is pulled down sometimes to -10. Again I want to state that I'm only at partial throttle not exceeding 3k rpms. Once the engine is fully warm, 2-3 minutes of idling and 2-3 more of actual drving, the surgin goes and away and the engien feels normal. In fact after the surgine stops I can log WOT 3rd gear pulls and have 0 knock all the way to 7k rpms at 14psi.

Along with the cold driving knock I get "seemingly" random knock. It usually occurs at partial throttle <30%. For example I have seen 11 knock counts at 21* timing advance at 1750 rpms at 29% TPS. Another occurance was 36 knock counts, 0* timing advance, 41% TPS at 2781 rpms.

What could be happening when cold to cause such extreme knock and power loss? It only started recently, and not in conjunction with any new mods?

 

[andymoraitis]

I would inspect the knock sensor and look for any goo around the back of it. If there is, it's toast and needs to be replaced. As a matter of fact, if you're still on the original, it's time for a new one. If you find no evidence of any seepage around the sensor, check it to make sure that you have proper torque. These are basically microphones and if they're too tight or too lose, they won't register properly.

Let us know what you find,

Andy

 

[Ski Bum]

Ok, I went to have a "look" at the knock sensor today after finding it is located directly beneath the intake mani. How do you get at it without removing the intake mani? I can see a harness that may be the knock sensor plug but I'm not sure. The service manuals I have all show the knock sensor location with the intake mani removed, probably of an engine on a stand

There is also a dissconnected plug taped to the harness just next to the plug that may be the knock sensor, what is that?

 

[Ski Bum]

I would inspect the knock sensor and look for any goo around the back of it. If there is, it's toast and needs to be replaced. As a matter of fact, if you're still on the original, it's time for a new one. If you find no evidence of any seepage around the sensor, check it to make sure that you have proper torque. These are basically microphones and if they're too tight or too lose, they won't register properly.

Let us know what you find,

Andy

If the knock sensor was in fact in need of replacement would it cause the cold operation issues I've been having? Could the microphone be hearing something when cold that it interprets as knock?

 

[Ski Bum]

How do you get at the knock sensor to even inspect it? Isnt it directly beneath the intake manifold?

 

[megadan]

Get it from under the car.

 

[Rex2342]

The knock sensor can pick up anything and display it as knock. Things like lifter tap, an exhaust leak, and even a blown strut have been know to register as knock. To check the sensor you shouldn't have to remove it. Just trace the wire to the back of the sensor. The sensor is packed with silicone or something from the factory but if you feel a sticky mess at the end of the wire it needs replaced. Mine was so bad the slicone was gone completely and there was nothing sticky left. Changing it is a PITA because of it's location but it can be done without removing the manifold.

 

[donmagicjuan]

This thread's 5 months old, fellas. I would hope he found it by now.

 

[Rex2342]

I didn't even notice!