woodstock21

Hi guys, been a while.
After getting my car back together, gm hot cam, ls6 springs, a little porting on the heads, and custom ecm tune from HP tuners.
My knock sensors keep retarding timing, most noticeably in second gear.
In an attempt to go wide open, or anywhere close to that, the timing is VERY noticeably retarted. even noticable in normall driving, almost always in second gear.
Driving around with my tunning guy and laptop hooked up confirmed its the knock sensors pulling timing.
I replaced both sensors with ACdelcos, and a new wire harness for them. It is definitely not pinched under the intake. Same problem.
There is an exhaust leak behind the left side cat, tuner guy said that could be the problem, effecting o2 readings. But i think its something besides that.
any ideas, i appreciate the help

woodstock21

Come on' nobody???

redbird555

iTrader: (14)

I mean you're question is a little vague.But no an exhaust leak will not trip the sensors. Any type of metal to metal contact like the exhaust banging or rattling can though. You could also see if the knock is false by draining the tank of fuel almost all the way then go and get 5 gallons of 100 octane and throw it in and drive. If the knock is still present its most likely false.

The tune could also just suck. Go put a stock timing map in it and see if it knocks.

woodstock21

Hey great advice thanks. I added some octane booster and it ran great. I guess I'll start running the 110 octane pump gas, and tweak the tune a little.

2MCHPWR

iTrader: (10)

what year is the car? 1998's have the sensors set to very sensitive and I had to desensitize them via the tune to get rid of the KR.

Chevy406

iTrader: (12)

If you run leaded gas (most 100+ octane race gas is leaded) you will kill your O2 sensors pretty quickly.
Are you throwing any check engine light for the knock sensors? If the ECM senses either sensor is failed, it will pull the maximum KR degree that is set in the tune. This is a fail safe to protect the engine. Ask your tuner if he has deleted the CEL codes for the KR sensors. If you have a code then you need to keep troubleshooting to find the cause.

If there isn't a KR code then you may need to reduce the knock sensor sensitivity along with burst knock sensitivity. But just be sure the sensors aren't actually picking up knock. Is your engine stock?

Fix the exhaust leak too. Any exhaust leak, especially near the O2 sensors will let the O2 sensor show more oxygen and the ECM will throw fuel to that bank. Exhaust leaks and lazy/dead O2 sensors will hurt your fuel mileage.

woodstock21

The car is a 1998 yes, the engine is fully rebuilt, the only things I changed from factory is the gm perf hot cam (225/225), LS6 springs, and gm perf high volume oil pump.
The tuned deleted the CEL for the knock sensor code, because it was coming on. I also had him turn down the sensitivity as much as HP tuners software would let him.
I replaced both sensors with new ac delcos, and the harness, and it's not pinched under the intake.
I know I can't run the leaded gas long term, but the higher octane is the only luck I've had fixing the problem. Not sure what that means?
The tuning shop is a well established shop. (Carilona dyno, Wilmington NC) but maybe a bad tune?
This was an issue before and after I had it tuned.

Chevy406

iTrader: (12)

So that tells you that you have a wiring harness problem (assuming that the new knock sensors aren't bad). Talk with the guy doing your ECM calibration. You can either continue trouble shooting the wire harness from the knock sensors to the ECM and get them operational without any CEL codes or else just turn the knock sensors off entirely (i.e. enter zero for max knock retard). If this is a daily driver I would highly suggest fixing the knock sensors so you have that protection for your engine.

Once again, just to clarify. When the ECM senses a failure with the knock sensors it will trigger the check engine light. While that CEL is current, the ECM will pull maximum knock retard anytime the conditions for Power Enrichment (PE) mode are satisfied (throttle pedal position, MAP, coolant temp, etc). This is a protection mode that is "hard-wired" in the ECM.

Black89Z51

iTrader: (2)

Valvetrain changes can cause false knock signals as well (it's in Greg Banish's books). The valvetrain could be causing noise at the same frequency of knock causing the KR.

woodstock21

This would make the most sense, because the valve train can be noisey. In this case I'm assuming turning the sensors off would be the solution. Although my tuner said he turned them down "as much as he could" is it possible to turn them off completely with HP tuners?

Black89Z51

iTrader: (2)

Yes they can be turned off.

woodstock21

The tuner tells me he has done all he can to disable the sensors. Apparently he is wrong in that statement. But I don't know enough about ecu tuning to argue... I've been running 93 pump gas plus a royal purple gas stabilizer / octane booster and it seems to run well. Could their be any negative effects of running that mix long term?

woodstock21

Gas didnt do the trick actually. still stuck with the same problem.

woodstock21

"When your suspension "loads" while strapped to dyno, under those conditions, there may be now grounding contact somewhere in exhaust or x member that under just idle/rev/street driving does not show because the suspension is not loaded in a heavy hit, clutch dump situation. So if you find an area that is close...look carefully for any witness mark from grounding against something"

I read this in a different thread while doing some research. What exactly happens when an exhaust is grounded at some point?
Is it literally the electrical "ground" of the exhaust?

The cat back on my exhaust is simply welded to the "frame", (rush to finish my car)
Could this possibly have an effect on the knock readings?

Im trying to nail it down guys. bear with me here... thank yall. haha.