96LT1TX

Hey everyone, I have had this problem for now a year and a half and it is still driving me crazy. I don't like trying to tune without a working knock sensor. I have replaced the wire to the knock sensor, replaced the knock sensor itself, and checked for plug wires near it. There does not seem to be a wire anywhere near it. I still have the shorty headers, and the plugs are run basically right on the bottom of the head on that side with factory looming still. It reads 5 deg knock at idle and whenever I am on the throttle, and then the second I take my foot off the gas it reads 0 until I get closer to idle rpms, where it picks back up. Anyone? I am about to just get rid of knock in my tune and get it dyno tuned, so if anyone knows a good place to do that in Houston ( I am thinking HPE? ) I am about to have to do that.

Thanks

sbs

You appear to be using "knock" to mean "retard."

Did you explore the possibility that it is retarding due to actual knocking?

Who did your current tune?

AHARTZ28

Did you put in an LT4 knock module?

Injuneer

The knock retard would logically disappear when you lift off the throttle, since the PCM backs off on the timing, and there is no appreciable cylinder pressure, compared to open throttle. Its either retard due to real knock, or the engine is torquing from side to side based on throttle position, and only rattling on something when the engine is reacting to the coastdown torque of the driveshaft, and moving in the opposite direction. Have you checked the motor mounts for damage or loose bolts?

96LT1TX

Sorry for the confusion, it is "knock retard" that is 5degrees at idle, and the "knock counts" are going up in seemingly random bits. I will look when I get home from work today to see when exactly the knock counts are going up. I have new poly motor mounts I put in with the new motor, and I thought I had them super tight, and have even tightened them a few times in the last year to make sure... almost broke my finger last time pulling so hard I almost stripped the motor mount bolt and the socket slipped off and I slapped my finger on the k-member. I don't see how they could be loose, only problem is I just had surgery on my shoulder less than a month ago, and wont be able to do any 2 handed wrenching on my car for a while (2-3 months). I also dont have any friends where I moved now that like to get dirty with cars, but hopefully I can find some soon. Ya to me it made sense that maybe the car only pulls "knock retard" when the throttle is on, but then again I do not know the facts about knock retard and knock counts. I did see that at idle the knock counts stay the same, but knock retard stays at 5deg. I also saw that it was at idle, and jumped from 23000 to 32000 counts instantly (10ms? I think thats my increments) but I will double check this when I get home. I am not sure what to check next? It does have an LT4 knock module in it.

It does not seem to me or countless other shops I have taken the car to to be real knock. I have had the roller rockers reajusted countless times, and this time I just took it to a local shop (Late Model Racecraft) who does really good work on LSx's and they adjusted them as quiet as I have heard the RR's in a while. They didn't hear any actual knock either, and I think that one of us would have heard real knock by now. I will look also at which direction the motor torques under throttle and clearance whatever is closest to the exhaust when torqueing that direction.

Thanks for the replies

*edit* It doesnt make sense to me that it would happen at idle if it were something on the "torque" side of the motor rattling with it. The whole idea of idle occurances to me means something exhaust almost, but I have checked the exhaust many many many times and it doesnt leak but of course it shakes (like the rest of the car) with the mean cam. Do people with no exhaust (straight headers) run into knock retard issues?

sbs

Everything you describe continues to be about how you have chased false knock, but nothing related to checking for real knock.

Who did your current tune?

96LT1TX

PCMforless. I know I need a new tune, but on the last dyno run I did it was pretty rich, not lean. I am pretty sure the A/F was around 12:1 throughout the power band. Where would you guys go to get a good dyno tune near houston?

sbs

Just wanted to make sure it wasn't tuned by the neighborhood drunk...

Can you scan it to see what the requested spark advance is?

Has it had the LT4 KM the whole time you've had these symptoms? If so, try swapping back to an LT1 KM. A few people have reported bad retard problems with the LT4 KM.

96LT1TX

Ya, I had the LT4KM in there for years now. I will get that bought and cross my fingers. The spark in the RPM/MAP tables is like 28-32 and it usually runs at MAX like 26-27 and then it jumps to like 31 once I take my foot off the gas.

Injuneer

You can get knock retard from the knock sensor without the knock count incrementing, and you can get knock retard from the knock count, when there is no knock signal from the sensor. The knock count is not in milliseconds, and it can only increase. Knock count appears to be a calculated value, based on the engine's operating conditions. It is normal, for the knock count to increment up at startup, for example. But it has no "dimensions". Its just a number that keeps getting added to the number already in the knock count field, and when it reaches the max possible value in that field, will reset to "0", and start all over again.

There's a good thread on the "Computer...." forum that suggests the logic for when the knock retard is dependant only on the knock sensor, and when, after an incident of serious knock retard is encountered, the PCM appears to start paying attention to the knock count reading.

If you are seeing knock retard, and the knock count field is not always incrementing, ignore it.

You typically do NOT hear knock. The whole purpose of the knock sensor circuit is to detect the onset of knock, at a level you probably wouldn't hear, pull a large amount of timing in response to stop the knock, and then feed the timing back in slowly untuil it detects knock again.

I wouldn't rule it out. The motor mount is right next to the knock sensor. It would make a lot more sense to me to see false knock arise from a rattling motor mount, than some noise coming out of the exhaust pipe several feet away from the engine. If the passenger side mount is rattling at idle and under load, when is it going to move in the opposite direction - when the engine is moved in the opposite direction, by the coastdown torque.

I'm not saying this it the case with absolute certainty... just trying to suggest possible alternatives that may explain the scenario. You have the advantage of being able to look at the engine, listen to it, touch it, etc. We are all (probably) thousands of miles away, looking at a computer screen and trying to help you.

96LT1TX

Thanks again injuneer, you always give me very inciteful suggestions. I wish I wasn't a 1armed man, but what size are the motor mount bolts again? 15 and 18? For some reason I felt like I was stripping them last time, maybe they are standard sizes instead? Sorry to ask such a stupid question, I could always just test and see.

AHARTZ28

both the nut is 18 the bolt is 15

96LT1TX

Ok, well, tightening motor mount bolts with 1 arm is kind of a lost cause. I can hold the other arm up there, but when I try and put force on it, the arm does nothing (Just had shoulder surgery). I will try and recruit some help this weekend in tightening motor mounts. Any other suggestions as far as what it could be? I will check all possibilities (that I can) this weekend. I will be buying an LT1 knock module tonight, putting that in, tightening the exhaust EVERYWHERE, checking, rechecking, and checking again the motor mounts... Anyone else have any ideas as far as false knock? Like I said, I have added the race gas (knock doesnt go away), I have pulled timing in the timing tables down to like 15deg at idle (still knock)... So I am like 99.99% sure it is NOT tune related. I have a scheduled dyno tune this weekend and want to have my knock sensor working for this. Any ideas?