PCM Diagnostics & Tuning - whats the correct way to desensitize knock sensors and still be functional?




bigshoe
08-02-2005, 11:50 AM
I have a ton of KR on my 98, i've done everything i can think of over the years to kill it, and never found the culprit (have new knock sensors, checked alot of other stuff).

anywyas, i need to kill the false knock but would like to still have the knock sensors as functional as possible incase of bad gas etc... I'm currently running in SD mode, which doesnt allow the computer to revert to the preset low octane table (since i'm using a modified low octane table - but you guys know this stuff..). so what is the most correct way to kill the KR but keep it working for detonation purposes (I still havent tuned spark advance yet, so this is important).

I think the only things i've changed were Knock sensor Global Gain vs MAP vs Cyl, Knock Fast Recovery Rate vs RPM, Maximum Knock Retard vs RPM in PE, Knock Fast Attack Gain vs. Baro, and maybe something else, i need to go back and compare what i really changed. but here are some screenshots of it. yaeh, i know they are huge screenshots, i have a dual monitor setup, so what I probably should have done is make it really tall so its scrollable now that i think of it, if anyone requests it, i can do that.

http://www.members.cox.net/milkac/KnockRetard.jpg
http://www.members.cox.net/milkac/knocksensorcal.jpg


jyeager
08-02-2005, 12:52 PM
Ouch that's ugly.

A foundational question here...Do you have any oil consumption at all?

I ask because there's one way that your knock could be real and not false...and that's if you are sucking in oil.

bigshoe
08-02-2005, 10:32 PM
interesting, I didnt think of that, and i dont remember reading about it in my searches, so the oil may be getting into the cylinders and causing hotspots, or baking to the pistons and causing hotspots or turbulent air - is that the right thinking?

and yes, i've always had some oil consumption, havent really monitored it since i put the cam/intake/ls6 pcv conversion on, i'll try topping it off tomarrow and metering my oil consumption. btw, my KR is either around 1600rpm under about 30% throttle, or at WOT, so if my KR was caused by oil in the combustion chamber, wouldnt it be all over the place?


TAQuickness
08-02-2005, 10:38 PM
Could be getting KR only when you suck in oil vapors. oil has much different burn properties than gas

jyeager
08-03-2005, 06:37 AM
btw, my KR is either around 1600rpm under about 30% throttle, or at WOT, so if my KR was caused by oil in the combustion chamber, wouldnt it be all over the place?
I can't say. It depends on too many variables....But yes you were right about how oil contamination results in knock.

Based on what you just said, even if the oil consumption is gone now (perhaps since your PCV upgrades) you still can't count out that there is carbon buildup in the cylinders causing it.
At this point you not only need to ensure that fresh oil isn't being consumed, but do a top engine cleaning to get rid of the carbon.
Someone mentioned seafoam. GM has a top-engine cleaner you can purchase at dealerships for somewhere around $30 a can. Either way, just follow the instructions.

TAQuickness
08-03-2005, 09:06 AM
Not knocking GM, but IIRC, my can of seafoam was ~$5 at autozone

Wet 1
08-03-2005, 09:11 AM
It doesn't sound like the problem to me, but if you're going to try the top engine cleaning TAQuickness is right... Seafoam works great and is cheap.

87GMC
08-03-2005, 10:01 AM
It doesn't sound like the problem to me, but if you're going to try the top engine cleaning TAQuickness is right... Seafoam works great and is cheap.


Co-sign

WS6FirebirdTA00
08-03-2005, 11:03 AM
have you checked the valve train to make sure it is all still in tact? there are way too many variables here that could cause real or false knock. i would want to fix it instead of override it, it may cause you problems with real knock...

bigshoe
08-03-2005, 11:20 AM
thanks guys, i'm buying seafoam today, planned on doing it today, but slept in, and now i have to go to work.

about the valve train, I had KR before and after my cam install, when i changed the cam, i changed to 918 springs and Ti retainers. now, when my old cam came out, i found this:
http://members.cox.net/mikic/badcam5.JPG
and to be honest, i didnt notice it till the car was put back together with the new cam, it was after that, that i looked at the old cam and noticed this blemish. I made a post about it and we determined that it was a bad casting, and it lasted 80kmiles, the lifter that rode on it appears to be ok, the rest of that particular lobe is very smooth just like the others, so it seems that it was rolling over it fine. BUT, this is possibly a source of harmonic noise causing my KR, car runs fine, i really dont feel like changing my lifters at this point.

top engine cleaner will probably be done tomarrow, then i'll take some logs and see where i'm at (i'll put the knock sensor settings back to stock).

WS6FirebirdTA00
08-03-2005, 11:24 AM
good chance you have a lifter thats causing that, whether it looked ok or not. is there any info to log to monitor noise from cyls by the knock sensors?

WS6FirebirdTA00
08-03-2005, 11:25 AM
remember also. those knock sensors are RIGHT at the lifters, so the slightest noise could cause it, and if it was like that before the install i would put my money on that. did the heads come off at all? when i took my heads off i cleaned the shit off my pistons and there was a good bit of it, then that would tell you you are looking in the wrong areas, esp with that bad lobe on the cam!

TAQuickness
08-03-2005, 11:33 AM
SHINOLA! would be a very good idea to replace the lifters and elimnate them as a possible cause of knock.

Wet 1
08-03-2005, 11:44 AM
thanks guys, i'm buying seafoam today, planned on doing it today, but slept in, and now i have to go to work.

about the valve train, I had KR before and after my cam install, when i changed the cam, i changed to 918 springs and Ti retainers. now, when my old cam came out, i found this:
http://members.cox.net/mikic/badcam5.JPG
and to be honest, i didnt notice it till the car was put back together with the new cam, it was after that, that i looked at the old cam and noticed this blemish. I made a post about it and we determined that it was a bad casting, and it lasted 80kmiles, the lifter that rode on it appears to be ok, the rest of that particular lobe is very smooth just like the others, so it seems that it was rolling over it fine. BUT, this is possibly a source of harmonic noise causing my KR, car runs fine, i really dont feel like changing my lifters at this point.

top engine cleaner will probably be done tomarrow, then i'll take some logs and see where i'm at (i'll put the knock sensor settings back to stock).
Ouch! Are you 100% sure about the lifter???

bigshoe
08-03-2005, 11:52 AM
the rest of the lobe on the old cam has PERFECT wear, makes me think that the lifter was just rolling right over it.

now, the new cam was smooth, and has that same lifter running on it, but still doubt thats causing the KR (i'm not ruling it out though), just because the rest of the lobe is good. I understand that at max lift, thats where most pressure is against he lifter and against the bad surface, and that maybe the other areas are so smooth since there isnt as much force running on the lobe from the maybe bad lifter. BUT what could it be? i have a feeling that the surface of the lifter roller is ok by looking at the rest of the cam wear, so what could cause that lifter to be bad and make the noise now? the bearings should be fine, i dont think they were introduced to anything that will cause slop in the roller (but who knows), and then as far as the lifter doing its job with collapsing and all that, i don't know much about how that works personally.

just trying to gain some knowledge of how it could be affecting it. changing lifters.... man, i dont want to do that :(

WS6FirebirdTA00
08-03-2005, 12:06 PM
doesnt matter if it was perfect, the roller could be fine and not leave marks but still make noise, trust me on this one. the bearings could be screwed in it or loose

WS6FirebirdTA00
08-03-2005, 12:08 PM
im almost positive enough about this that i would throw 1000 bucks down on that

WS6FirebirdTA00
08-03-2005, 12:29 PM
i take it the heads were off then if you looked at the lifter. that would have let you know how much build up you had. new heads too or no?

jyeager
08-03-2005, 12:33 PM
i take it the heads were off then if you looked at the lifter. that would have let you know how much build up you had. new heads too or no?
Don't think so. He said he assumed the lifter was OK because the rest of the cam lobe didn't show scuffing from the lifter.

redtail2426
08-03-2005, 12:46 PM
I would not question pulling that lifter,I would just do it automatically.Theres no way those bearings in the lifter are fine after rolling over that thing for 80k miles.if you are getting kr like you say that would be my number one guess.

WS6FirebirdTA00
08-03-2005, 12:55 PM
ah ok i didnt see that he said assumed

gwj
08-03-2005, 12:58 PM
FWIW, I bought a can of GM top engine cleaner yesterday, the aerosol type, it was about 7 or 8 bucks.
My 2000 has had issues w/KR on and off for several years. Usually a can of top engine cleaner works wonders. :)

Viper
08-03-2005, 04:33 PM
He did not take the heads off; we installed my TR224 in his car back in May.

bigshoe
08-03-2005, 10:31 PM
damn, guess i gotta pull the heads.

and no, i've never had the heads off, just did a cam/intake/spring swap, thats the farthest i've been into the motor.

looks like i gotta spend some cash and go into the motor.... argh...