large KR at 2600RPM near no load...

[3400-95-Modified]

Ok, so I've been fighting this issue for two years now... best solution I've been using so far is just unplug the knock sensor when I'm not at the strip. But the issue I have is on the highway at 75mph converter locked in 4th if I'm just cruising with nearly no load the KR meter will start to climb and pull timing like crazy, it will pull up to 18* of timing and leave me at 10* advance... Talk about pulling a few pony's out from under you.

As soon as I crack the throttle just a bit more and increase the load the KR begins to go away at the recovery rate... slightly higher speed 80mph it doesn't seem to do it... So I'm assuming this is a sound from SOMETHING or interference due to that specific condition thats causing this KR to apear... With the knock sensor unplugged you can't hear a thing... and I know if it was pinging enough to pull 18* I would be able to hear that. The red beretta I had was pulling 8-9 degrees on the high way once under load and I could HEAR that even when it was pulling the timing.

Slightly higher octane fixed my old car's ping I could hear, but running 93 in this thing doesn't make a difference. I've also dropped that spark advance area down from 34* to something in the 25* range and it still pulls exactly the same amount of timing, which is why I think its an interfering sound of some sort.

Does anyone have any ideas on how to isolate that noise from the knock sensor other than putting that damn wire on a toggle switch?

I've swapped wires and that didn't fix it, I'm going to swap coils today to see if that changes anything, and then I have an ICM I can test as well.

There is only one other thing that I can think it may be... Due to the fact that I have the intake spacers the top of the coil bracket does not bolt to the upper... I'm wondering if thats rattling in some way to make a noise its picking up. I'll have to see if I can bend that bracket enough to make it to the holes and line up so I can bolt it down.

[robertisaar]

using a PCM that has a removable knock filter?

[3400-95-Modified]

No, this is a 97 Venture PCM and to my knowledge the filter option was only on the 95 and 94 OBD1.5 ECM's uesd in my application.

[robertisaar]

according to alldata, the 97 venture PCM also uses a knock filter, but after 97, they were removed/replaced...

but since it's from a 3400 already, that shoots down my original thought of "try a 3400 knock filter".

[mickaz]

well I heard some had problem with the earlier BIN they started with.If you use a Bin from a more recent car, maybe it could solve some of the knock?

[3400-95-Modified]

Only other choice I have is a 97 Monte, and I didn't have this problem all the time, thats why I wonder if it's interference from another component, or possibly an engine noise from a rattle that its picking up somehow.


Some info I found on ZZPerformance

Q:What is REAL KR and what is FALSE KR?
Real KR is KR that grows with engine RPM and engine load. It depends entirely on detonation, which is dependant upon throttle position, MAF, MAP, engine load, engine temperature, and RPM. As RPM and engine load increase, the chance for KR (or higher KR) increases. As the vehicle shifts to the next gear, KR will usually make a small jump up as well due to the higher engine load.

False knock is characterized by a sharp spike to an immediately high value of KR followed instantly by the KR Recovery Rate. It doesn't grow with engine RPM or load, it jumps to a high value on throttle input and then recovers to a low value, or zero perhaps, as engine RPM continues to increase. Note that this is exactly opposite to the characterization of REAL KR. Remember, knock is simply specific noise detected by engine microphones. Because it happens to fall with in the frequency of real KR does not necessarily mean that it IS real KR.

Q:What can cause FALSE KR?
Outlined below is a list of things that can cause false knock.
Sway bar hitting exhaust downpipe - This happens typically with the downpipe of headers because that configuration puts the downpipe in very close proximity to the sway bar … much closer than the stock downpipe. The banging noise from the two metal objects hitting may resonate through the frequency band that the PCM detects as knock through the knock sensors. The solution to this is to flip the swap bar over. Because of the curvature of the sway bar near the downpipe, flipping it will allow the sway bar to curve AWAY from the downpipe rather than toward it.

Transmission oil stick hitting exhaust crossover pipe - This typically happens with the crossover pipe of headers due to their large size and proximity as opposed to the stock crossover. The banging noise from the two metal objects hitting may resonate through the frequency band that the PCM detects as knock through the knock sensors. The solution to this is to carefully bend the trans oil stick away from the crossover pipe so that the two do not touch.

-Anything loose in the engine or outside the engine may cause noises that drift through the frequency range that the PCM detects as KR. Carefully check your engine! This is very vague and is intended to be vague because just about anything loose in or out of your engine that is making noise could cause this. This includes loose or noisy components in your transmission as well.

-Loose knock sensors, or knock sensors that are too tight. Double check that your knock sensors are torqued to spec (14 lb-ft).

The description of false KR is DEFINATELY what I'm having so hopefully I can find out the root cause of it.

[Joseph Upson]

Could it be a bad sensor?

[pocket-rocket]

The thing with it being consistent at a certain RPM and not all RPMs/loads has me believing John is on the right track with the ICM bracket since engine harmonics would be different between high load vs light load. I would pin the bracket down. It's a cheap fix costing all of a little time and a couple bolts, assuming that's it. And if it isn't, well at least you know the ICM is now pinned down and that eliminates it as the problem.

[robertisaar]

ICMs don't like vibration anyways, so it's definitely a good thing to do regardless.

[3400-95-Modified]

Swapped sensors and still had the same symptoms.

I tossed in some rubber feet I found at work between the bracket and the upper intake and hopefully that will stop the noise, I went on a quick ride and didn't see any KR on the highway but had some WAY down lo at say 1800 rpm putting through a town... that I can almost accept as Bog knock or something of that order, but when its pulling 18* on the higway thats just not acceptable. I'll see how it goes on the way home tonight to see if it pops up with anything.

[3400-95-Modified]

Rubber feet didn't solve it. It was back on my way home. So I swapped out the coils with an old stock set I had from something. after that I got nothing on the highway on my way home... so I'm not calling it solved yet but there is a chance. Stock coils I tested and were showing up with 5.6k on the secondary side and 0.7 on the primary side, all the same.


Don't assume that all coils are created equal... out of the three I had on my car before, 2 matched and one was an odd ball... The one odd ball matched the GM coil specs exactly... The two others had a resistance of 8.5k-8.6k on the Secondary winding... and the GM ones as noted are only 5.6k all the primary windings ohm'd out at 0.5-0.6 so similar to the GM ones.

And so far I have not been able to re-create this KR symptom... I hope to god this was it. 1 trip home last night, 1 trip to my parents 1 trip to work, and 1 trip to the hardware store... nothing yet. And I was getting the KR at 2k yesterday on a regular main road not highway.

Some say failure starts in the 10k-14k area of the secondary windings, but at the same time they say values can varry from application to application, so I'm wondering if simply having that miss matched setup was causing some interference somewhere... I wonder what else this could have been doing to my setup.

[AleroB888]

For false KR, try packing Permagum around the knock sensor, works for me.

[3400-95-Modified]

Well so far there may not be any need... I have not been able to get the same issue to repeat. This am right when I got on the highway I got some which appeared to be false due to the spike nature and drop off, BUT it only happened twice, NEVER as bad as before and then vanished when the car was warmer, so I almost can atribute that to some noise when the engine is cold. I'm also going to put my stock plugs back in for now since I'm not spraying and just using the car on the road... I have the TR6 plugs in there which are about 2 steps cooler than stock. That plus my cam sure isn't helping down low.