False Knock (???) any suggestions

[Matt68]

I am working on a 01 Vette on a chassis dyno. Car has Patriot Heads, Cam, shorty headers, 42lb/hr injectors.

I did the autoVE and MAF tuning and everything was coming in good. When going into the higher RPM's (>4000) on the MAF tuning we were getting KR above 4000. It wasn't the normal saw tooth, it just shot up to 9.9deg. The actual timing in that range after the KR reduction was in the 12*. I went though and removed 2* across the board and still had it. We pulled plugs and everything looked fine, AFR was sufficiently rich. The valve train is a little noisy, so we were wondering if it was setting off the knock sensor. I logged several of the EST_XXX_DMA.pids and it looked as though the Brake Torque Management was removing timing during that same time in the logs. We tried changing settings in the tune to eliminate this. You can see it in log 006_1 and we removed it in 0016_1 but the KR is still removing timing.

After several hours of trouble shooting we decided to try and increase the timing and see what happened. Added 2* of timing in the loads above 4000RPM and we picked up torque. Added another 2* and continued to pick up torque. Went though this until we have about 30* of timing at the upper RPM's and continued to make power. The car went from about 330ft-lbs to 377ft-lbs and power went from 319 to 395.

Are there any ideas as to what could be causing this? Also, we have been searching for ways to adjust the impace the KR has or eliminating the knock sensor, and can't find a good setting that makes an impact. My concern is that we are just "tricking" the computer right now, and if whatever is making the KR appear gets repaired then there will be problems.

Thanks,
Matt
Spark_00016_1.efi
Spark_0006_1.efi

[WeathermanShawn]

Matt, I agree that is not 'real KR'. Usually in PE Mode (which I will assume you are in) KR is limited to 4 degrees..Plus I have never seen a KR pattern like that. Its false.

The only suggestion I can think of is comparing to a stock tune to make sure all Knock Sensor calibrations are in the Tune File etc..You can either do that yourself or post up your Tune if you want someone else to double-check.

If its not some glitch in the Tune, must be a mechanical/electrical issue with the knock sensor?

Thats a good one. Must be driving you nuts huh?

[Matt68]

I was real nervous about bumping up the timing, but I felt pretty confident in the checks we had done. I am just glad we were able to use a dyno to validate the results.

I did compare it to a stock 01Vette tune, and there does not seem to be any differences. If I get a chance I will post what I have (it will show quite a few changes trying to solve this issues now).

[WeathermanShawn]

It seems like the culprit would be in the Knock Sensor Voltage. I.E., mechanical/electrical..Thats a little over my expertise level, but perhaps replacing the KR sensors?

I agree, I would leave the Tune alone. Reducing the amount and duration of KR is always possible, but not smart for the street.

Good luck..

[joecar]

While on the dyno, listen for knock using a knock headset.

Check the knock sensors, see if they are rusted, if so replace them.
(how many miles/years on the knock sensors...?)

30° seems a little high, but if there is no actual knock, and depending on the DCR it may be ok.

What are the specs of your cam...?

[joecar]

Also, MAF seems ragged at higher RPM... what MAF plumbing do you have...?

Do you have any MAF logs where the pid channel count is no more than 24 (to get fastest sample rate)...?

What intake manifold and what throttle body do you have...?

As your RPM goes up your MAP drops by about 6kPa over the range, this is a significant drop (your heads/cam are outflowing your intake).

How much HP/TQ is your combination expected to make...?

[Matt68]

While on the dyno, listen for knock using a knock headset.

Check the knock sensors, see if they are rusted, if so replace them.
(how many miles/years on the knock sensors...?)

30° seems a little high, but if there is no actual knock, and depending on the DCR it may be ok.

What are the specs of your cam...?

Getting specs on the cam right now. The plan is to supercharge this car down the road, so the stock TB and airbox are used. It also has the LS6 intake.

The motor has about 77K miles on it, but I have an LQ4 motor sitting out in my barn that I could steal the knock sensors off of. Doing a part search, it looks like they are the same.

Motor has a new cam, pushrods, but the lifters are stock. We were discussing adjusting the preload to try and quite down the valvetrain noise.