Have been data logging my 94 and found that I’m getting some pretty wild KR.

What I know for certain from the logs:
-temps never exceed 200
-any time it is at 100% tps it pulls 7-8 degrees KR. Regardless of RPM.
-under steady cruising its usually at 0 KR
-any amount of throttle to accelerate seems to instantly cause 5 degrees KR which slowly decays down
-sometimes at idle it’s pulling 1-2 degrees

Sometimes knock counts are increasing when it pulls timing. Other times not. Does this sound like low octane mode?

the car is modded:
-94 6sp, 4.11 gears
-LE Ported heads/intake
-Comp 502 cam
-1.6 RR
-short tubes, stock cats and exhaust
-LT4 knock module
-PCM for less tune
-LTCC with LS1 coils
-MSD vented opti, set to 0 degrees per MSD instructions.
-Injectors and fuel pump are original to the car
-knock sensors are original to the car, recently
-remove but torqued per FSM specs
-fresh Citgo 93 in the tank
-BLMs a little low, ~120, sometimes split

Regarding the MSD opti, I set it to 0 per MSD instruction. I then retarded timing on it to see if it would impact the KR. I retarded it by as much as what should be 4 degrees and it had no change on KR, it behaved exactly the same, though I felt a reduction in engine power with the opti dialed back, especially at higher rpm

Any thoughts on what to try? I don’t have anyone who will touch it on a dyno to tune.

 

when i went to get my lt4 tuned it started to go crazy at about 4500 and was on-off up till the 6000 mark. the tuner thought it might be the icm going crazy but by the time we got back to the hotel it had a knock in the lower end.
thought that engine was toast.
six months later i was taking off the rack and when i went to get the balancer off the hub, it almost fell off. tightened the balancer to hub bolts and everything is fine a year and a half later. check your balancer bolts. 2 cents deposited.

 

Will check them. I did have the balancer off this winter so I suppose it is possible.

I’ve tried a few things and it’s rather inexplicable.

I disabled low octane KR by zeroing the vs coolant table and then reflashed the pcm. Still does it.

Using EEhack, I retarded the timing by 5 more degrees. Still does it. Even at idle the knock counts are climbing and it’s pulling spark.

The only thing I can think it might be is either the knock sensors are junk or it’s picking up false knock from the roller rockers or maybe the DMF? They do make some noise but nothing abnormal for a RR and the pcm does have an LT4 knock module.

Do knock sensors have a finite lifetime? These are 26 years old... considering just replacing them to eliminate as a possibility but last thing I want to do is fire the parts cannon. I torqued to spec when they were removed/installed over the winter. 14 ft lbs if my memory serves.

 

Knock sensors DO Fail. We have seen a few of them here on the Corvette Forum C4 section.

My C4 was running very poorly and would not accelerate like it was supposed to. I checked the Knock sensor and it was indeed "bad" sending retard signals to the ignition control module. I changed the part (and the coolant) and the car felt totally different. It was once again able to spin it's tires.

If you have an overactive knock sensor I would replace the sensor and not change the software. On the older L98 engines have a roller cam and they don't trigger false knocks very often. If it was an L98 (not in '94) I would start looking at the EGR system as when the EGR fails the car will have higher combustion chamber temperatures and have the potential for knocking.

If your engine has some deep metallic noises coming from something being loose or whatever that could trick the knock sensor. With knocking at Idle you clearly must have a bad Knock sensor. According to RockAuto your Corvette uses two knock sensors...(?) They cost $26 each for the AC Delco parts at RA.

Good Luck!

 

Thanks for the replies. I guess I’ll go ahead and replace both the KS. As mentioned earlier, sure the roller rockers make typical noise but nothing wild. Given how much spark I pulled out of it and saw no change in reported knock (as in still way high) I’m fairly settled that it’s false knock.