Knock, knock.... grrrr

[Formulaboy95]

Okay, this problem is driving me insane. I noticed my car bogging (almost like me letting off the pedal) somewhere after the 8th mi. At first, I thought it was a limitation of the stock heads/headers not being capable of flowing that well in the upper rpms. So, I got the SLP shorties, and catco cat.

Problem didn't go away, but I trapped much higher. Definately a noticable difference, but still the same bog at the 8th to the traps. So, I got the pcmcomm logger. Everything looks perfectly normal, but every single time, it gets to 93mph at 41xx rpms in 3rd gear.... it takes out 6+ degrees of timing, and it gradually comes back to 36 degrees slightly after the trap.

I always use 93/94 octane, and occasionally a few gallons of 100 mixed in when I go to the track.

Opti was recently replaced with the MSD SC8.5mm wires, Blaster coil. Plugs are NGK TR-6's gapped at .035, but were previously NGK (55's?) stock gap.
I removed the IAT resistor also, still the same prob.

I then replaced the knock sensor with a factory gm one, and changed oxygen sensors. Still same prob again.

So, next day at the track I made another knock pass, then added 2 gallons of 110 to a third full tank, ran it for 20 mins. Same prob next run.... THEN.... Knock went away for 2 runs...

Took it out for a run about a week after that, and knock again.

So, I put in the Walbro 255... andddd same exact thing 93mph 4175rpm. arrrrggghhhh


SO, I am on the weather to put the new NGK TR-6's, Pressure Master Header gaskets and stage8 locking bolts on. Going to inspect the wires, mabey opti again while it is down.... Need some serious help on this one, because I am running way short on money trying to solve this problem.

Where should I look next... I think it has to be a miss, fuel or spark. I doubt it is mechanical, lifters/valves/rings. Not throwing any codes for opti, but mabey cap & rotor aren't getting good contact at that exact rpm possibly. Or Digital ignition time??

This one has me baffled.... Anyone wanna take an eduacted stab at this one. Okay fingers tired from typing, sorry for the long post.

[LS1 TA]

Sorry dude, it sounds like you've done everything. Whenever I have a problem like that and replace everthing under the hood, it usually ends up being a fuse or vacuum leak. Sorry I couldn't help but I feel your frustration.

[Formulaboy95]

yeah.... I am lost, and running low on funds.

[Craig 94 TA GT]

Maybe I missed it, but what about the knock module? I'd say the LT4 is worth the $35 to try (if you don't already have it)...especially since you have the headers now.
So it only happens at 4100 in 3rd, not in any other gear, correct?

[Formulaboy95]

Got the LT4KM, no difference.
Once or twice, I got knock from doing a big burnout. Rare occasion
Always seems to occur at 93Mph 3rd gear. Not close to 4th gear...

[Craig 94 TA GT]

Do you have a the log file handy? Is the knock retard reading 6 degrees, or is possible it's pulling 6 degrees, somehow, somewhere else?

[Kevin - Blown 95 TA]

Sounds like false knock. Make sure the knock sensor wire isn't burnt or rubbed thru. Make sure the exhaust isn't hitting the crossmember. Other than that, if you know a programmer, maybe you can get him to program out the burst knock feature and see if the knock retard goes away. You will still have the regular knock retard to protect your engine, but it won't be anticipating knock and pulling timing when you stab the pedal.

I had a little bit of that going on at random and it turned out to be the cat came unglued inside and the brick was rattling around.

Another thing about my car is that I used the plastic valve covers which seem to work better for absorbing sound from the roller rockers.

[Formulaboy95]

It is pulling ~6 degrees due to knock. The one I am looking at has knock retard degrees at 5.3 when it occurs at 93mph. Spark Advance goes from 36 to 31 degrees.

Strange thing is it is constant... I rarely ever get knock, but I can count on it at 93 mph if WOT. I think if it was exhaust, it would seem more likely that it would be random.

[Craig 94 TA GT]

Only other thing I can add is...is the motor fully warmed up when you make your pass(es)? I used to have a weird false knock problem too after the 1.6 RRs, stock valve covers, and the motor being cold. At idle, it showed 0.1 to 1 degree of retard due to knock. It would show up to 4-5 degrees of knock retard during any driving condition. However, as the motor warmed up past 180 or so, it went away. Several months later, I'm not seeing any knock whatsoever...even when the motor is cold. It just gradually disappeared...somehow

[Joe 1320]

It would be interesting to see the fuel map along with the spark rate....... There could be something with the fuel volume. Have you checked pressure at WOT? What are the fuel trim values when knocking?

[Injuneer]

Have you ever had anyone review your pcmcomm logs? If you can send it to me in an Excel friendly format (.csv) I'll be glad to take a look at it.

I've seen a few of these kind of cases. The fact that you only get it at the 1/8-mile point seems odd, but it the high loads in higher gears that trigger misfires on a weak ignition. I've seen at least one case of a high voltage plug wire being too closer to the knock sensor wire, and another with a loose motor mount.... if you replaced the KS, you're aware that it is right next to the motor mount boss.

Send me the data log if you want.

[Formulaboy95]

I am going to get a spread sheet together. When I had it dynoed last fall before the headers and fuel pump the air/fuel was 13.9-13.2 throughout the run, but I didn't have pcmcomm logger at the time.

Motor mounts are probably shot. Which brand should I look at for those.

Last run I took on the highway the log showed that it went lean on the pass side. This is because the header bolt loosened up on the #1 cyl, and burnt the gasket. Air is getting in, and the 02 on that side thinks it is running lean, and dumps fuel in to compensate. But, the other logs show the knock at 93 before the headers.

I doubt I am maxing the injectors out, but don't know if it is worth flowing them, or upgrading.

If the opti isn't throwing any codes, I am guessing the optical section should be fine and it has no idea if the spark is getting there. I plan on eventually doing the LTCC, so an ignition box would not be worth the $. Tested the impedance of the msd coil yesterday, 4580 ohms on all terminals. Going to look at OVC wires, to see if that will help at all. When I redo the header gaskets, I am going to put an 02 bung in, and borrow a friends Innovate LM logger again.

Any chance this could be from rotational noise? At 4100 rpms in a lower gear there is no knock, but at 93mph without fail it comes in. I can't hear any physical knock.

[Joe 1320]

Last run I took on the highway the log showed that it went lean on the pass side. This is because the header bolt loosened up on the #1 cyl, and burnt the gasket. Air is getting in, and the 02 on that side thinks it is running lean, and dumps fuel in to compensate. .

Bingo. You won't hear audible knock when the computer pulls out the timing. I believe you've found your culprit.

[Formulaboy95]

Well, I replaced the leaky header gasket, bolts and plugs on the drivers side. Replaced the motor mount on that side too. Checked wires on that side with a digital meter, looks like they are okay. Cleaned the air filter, replaced the fuel filter.

Went out for a ride today, to see if there was any change since the leak is now gone. NOPE... but I did find something out. Knock happened again, but I didn't really open the car up. Between 4000-4200 it gets knock @ 56mph this time. So I guess it isn't so much mph, but rpm.

I copied the section out of the log and attached it this time. With the header leak gone, the O2's values are real close to each other like they should be.

I am on the weather to do the pass side stuff, then I am going to do the Taylor wires OVC.

Any other ideas???

[Formulaboy95]

Here is the same log about 5 minutes later. Not sure if I let off the gas or what.