For starters I am working with an 89 IROC 165 $6E

I am getting a lot of knock retard in mostly the low rpm/low Lv8 ranges. During cruise all is well until all the sudden I get KR. Sometimes up to 6-9 degrees. Here's an example.

Steady state level road .92tp 77Lv8 1900 rpm 29.5* btdc no changes to load or road conditions and then BAM 3.5* KR for 10-12 seconds.

It seems the knock would come in response to some kind of change but none detected. I don't really think I have anything bouncing around in the chassis or really anything I can attribute it to. I am missing something I believe.

Any ideas?

 

That's going to be a tough one to find. Possibilities are a bearing going bad in an accessory, maybe some drive-line slack at light loads causing play to be taken up and making a little noise.

The knock filter responds to a particular frequency and magnitude of the noise.

The other area the knock filter responds to is a sudden change in frequency. So the false knock can be caused by a new noise, even at a low level, to trip the knock filter.

RBob.

 

Is there a forced knock test in that ECM?

 

It does, but the ECM needs to be in in high load (high LV8) and you would see the SA stair-stepping upward. Some calibrations have it disabled.

RBob.

 

Ok, I didn't think about such sources. I figured the sensor was looking for such a specific frequency it wouldn't be fooled much. Thanks. I do have an idler bearing that is making a little noise and some roller rocker which are a little noisier than I expected, but nothing that just jumps out there. And forgive me for being old school, but would it be an appropriate approach to put some high octane fuel (like 110) in it for the purpose of somewhat eliminating the probability of real knock. Then if the knock still persists look for other sources? My spark curve is getting very flat and conservative trying to get rid of the KR. WB says I'm normal to a little rich so I don't think lean charge is a contributor.

And from another angle, should I be attempting to eliminate all KR? If it pulls a few degrees out here and there in certian conditions is that all that bad? That almost sounds like a stupid question asking it but I am serious.

 

I woke up this morning thinking~ driveline noise! Could it be driveline noise? I have a few non-stock situations. First, a steel bellhousing, next a tko 600 and last a 3.70 rear gear. My thinking is this; The rear gear has some whine at min load and when transitioning from drive to coast. When setting it up I worked with the tech at the manufacturer and had him verify my patterns and all. We got it down to a minimum but he thought that it was something I just had to live with. IIRC it is related to the harmonics of a 10 tooth pinion??? It's not a lot but noticable. If the KS is hearing frequencies like this it could account for the KR seemingly coming out of nowhere. (and not showing up on a datalog) The steel bell may not be "filtering" the noise as much as an aluminum one would. This could also account for the KR im getting in low gears on takeoff. The tko is a great tranny but not as refined as the t5 and makes a little more noise. Now, how to isolate it? Maybe I could steady state cruise and pay attention to whether the KR and rear slack correlate in any way. Does it sound like this is worth pursuing? And what if I do determine it is noise, should I isolate the KS via a brass fitting or something along that line? I'm purposfully staying open minded but my spark curve is conservative, CR is not over 10, 93 octane and fuel isn't too lean. I "feel" like it has to be a fantom knock. I don't want to dummy the sensor too much in the event I encounter <93 or some other situation that needs less spark.

 

If pulling timing doesn't get rid of the knock retard, then it is 99% false. In the end you have less power and less mileage due to the reduced SA.

Can check the plugs for signs of detonation. If none, then false, if some, there is detonation, but we don't know if it is that area.

The only down side to ignoring it, is if it is an accessory bearing, it is on the way out and will fail sometime down the road.

RBob.