Knock issue

[mylittleblackbird]

So I've been trying to diagnose a source of knock for my S2 3800 N/A. In my efforts to find the source of this knock, I have noticed something that I think is unusual.

With the histograms, and watching the knock counter, my knock counter runs constantly. It counts up at roughly 4 counts per second.

What I find even more unusual is is that this counter continues to tick upward at the same rate with the key on, engine off.

I've unplugged the knock sensors at the PCM, and it still continues to count.

I confess that I do not have a perfect understanding(not even remotely) of how the knock sensor counting comes to play, but given that I've pulled the pins for the knock sensors at the pcm plug, and it continues to count upward, would this indicate that I have a faulty PCM?

Any thoughts, suggestions, or input is welcome.

Thanks,
Doug

[5FDP]

Do you have a scan of this??

I guess I don't 100% follow what is going on.

[mylittleblackbird]

morning scan.hpl

I have many scans. I will gladly provide you with one.

My question/concern revolves around the 2nd histogram table. When set to count, rather than average or last, it constantly adds. It has been a long time since I used this program, and the last car I was scanning was a 97 SE. I don't remember the knock count going bonkers when scanning that car, unless there was knock to be detected.

Thank you for taking time to look at this. I appreciate it.

[Russ K]

The counts are how many times that cell was hit. Nothing to do with knock. The counts can also be seen on the spark advance histogram.

Russ Kemp

[mylittleblackbird]

That puts my mind at ease about one part of the equation. Thank you for that. The other part is the large amount of knock I get when just driving around. I've removed timing across the board(5 degrees) and it still has KR. I don't understand where it's coming from....

[5FDP]

From doing tuning on my GTP and just watching stuff on our other GP GT, the GT will just get random knock and heavy knock at WOT when using 87 pump gas. Switch to 93 and it came down a few points just with that. Doing something exhaust wise such as a 3in downpipe might take the rest away but as it's my sisters DD we arent doign anything to it.

Perhaps post the tune aswell.

Have you done anything to the motor or ever touched the knock sensors?? Sometime if they are over or under torqued the readings will be wrong.

[mylittleblackbird]

The engine is 99% stock, with the exception of a home-made intake insert. The cat is "free flowing" if you take my meaning. It's actually in a Bonneville, so there is no u-bend to contend with. I'm not concerned about the high rpm knock, so much as I am about the 15-20 degrees of knock at 1600-1800 rpm under highway load. I've pumped in 89 octane fuel, I've pumped in 91(They took away our 93 octane), I've put in colder plugs, I've pulled 5 degrees(add -5 to all cells, right?) of timing from the stock tables, and almost magically experienced MORE knock.

I have not done anything with the knock sensors.

Next time I have my laptop handy, I'll upload the tune I'm using for the guru's to look at.

Thanks.

[xtremesilvy]

which spark table did you pull from? my impala 3.8 had a good amount of knock stock, i changed the downpipe/cat delete/u bend delete and ran 91 and it got way better ,than i did some tuning to the knock sensor table to shorten up decay time and limit max knock as to eliminate phantom knock, so far most i see on stock timing tables is 2*, and knock sensors will pick up vibrations and such so make sure the motor mounts and such are good

[97AutoXVette]

which spark table did you pull from? my impala 3.8 had a good amount of knock stock, i changed the downpipe/cat delete/u bend delete and ran 91 and it got way better ,than i did some tuning to the knock sensor table to shorten up decay time and limit max knock as to eliminate phantom knock, so far most i see on stock timing tables is 2*, and knock sensors will pick up vibrations and such so make sure the motor mounts and such are good

Curious how you modified your knock sensor decay time tables.. Without units for decay values, I was tempted to change that as well, but didn't know what to change to. Any help would be great. Thanks!

[mylittleblackbird]

I changed both high and low octane tables -5*. There is one other thing worth noting. All gas in the area is E10, so my stoich AFR is set to 14.13. The car runs better, but I still get that vicious buildup of knock at 1600ish rpm.

Here is the exact tune I am running now. It is not the -5* tune.

99 stock timing e10.hpt

[mylittleblackbird]

Here is a scan using that exact tune, taken just 5 minutes ago.

I would really like to think that most of this KR is false KR. I'm certain that some of it is not, but 15-18 degrees cruising on flat ground????

[ ATTACH]45400[/ATTACH]

[mylittleblackbird]

I've concluded that the major knock is being caused by the steel ring inside the downpipe. It rattles like a crazy.

Does anyone know a good source for a 2.5" downpipe that will fit an H-body? ZZP seems to sell 3", but that's too big for me.

[xtremesilvy]

they do sell a 2.5" catted or catless DP, i swapped my DP and noticed nothing over 2* on stock tables anymore

[mylittleblackbird]

Sadly, they do not offer a 2.5" for the H-body anymore, it seems.

I guess I'm stuck with making one. Who knows how long that will take.

Thanks for the assistance, folks. If I ever get this next attempt to find the cause of my KR complete, I'll report back.

Thanks,
Doug

[Dr. Nopps]

Check this out, may help may not.
http://www.hptuners.com/forum/showth...cks-Guide-quot