jerkyboy

C5 guy here with an ls-7 conversion. Took awhile to get a good tune but found a great shop, got it done. Car was running great. Parked it, went out a few days later and when in 6th and a I feed it a little throttle, it just kind of rolled flat whereas the few days before, it would steady build speed. As I drove it more, it was doing this in most gears. Also, when I lift off the throttle, it would almost surge a little.

So at a C&C, someone had HPTuners and we datalogged. He said the computer is pulling 9.9* of timing everywhere that I gave it throttle. HPT was indicating a knock sensor error. This error does not pull a code on my DIC nor do I hear noticeable knock and the motor sounds the same as it did after the tune was done.

So I took the vette back to the shop that installed the motor and associated wiring harnesses thinking maybe it's a wiring issue or bad KS. I'm assuming he has a tech II or something similar and says there's no timing being pulled that he can see. Could HPT see something pulling timing where the shop's scanner is not?? Attached is the datalog from HPT. Can someone look at it and give me some ideas where to look? I don't have HPT to see the file. Very frustrated at this point. Sorry for long post

Motor: Made (549/545
New crate short block
WCCH stage II heads
dragonslayer crank
Forged manley rods
Diamond pistons
stock TB
Stock intake
1 3/4" Kooks LT's
custom grind cam: .630 int .631 exh lift 232 int 244 ex duration on a 112 lobe sep
Conversion harnesses (using LS-6 style drum style knock sensors in stock LS-7 locations on either side of block)

realcanuk

It is pulling timing everywhere. The reason is it showing knock retard at those spots. As to why that is something impossible to tell without seeing the actual tune. Even harder since its not a stock setup. Could be a tune issue, or wiring, or the sensors.

Unreal

Determine if it is real knock and go from there. Anything banging around can cause false knock. When my lifter was dying my knock count was constantly 8-10 degrees until the lifter came fully apart. Loose sensor, loose part, anything banging can cause that. So first step if finding out if it is a mechanical issues or real knock. Adding a few gallons of 100 octane and see if the knock goes away is a good way to find out of it is real.

And as the crazy Canuk said, hard to diagnosis this online. Post up a log is the first step for help around here.

jerkyboy

I wish I had HPTuners so I could see the log I posted above. I might suck it up and purchase the package and start teaching myself to tune. At the very least I can use it for data logging. Unfortunately there is no reputable tuner within 3 hrs of me. If the shop that has the car cannot find a mechanical issue, I guess I'm dragging it back to the tuner. Would HPTuners pick up knock codes that a typical shop scanner (I'm assuming tech II or the like) wouldn't pick up?

realcanuk

That's what it shows.. all over.

realcanuk

You can see the KR cooresponds exactly to the timing pull.

Unreal

I would bet on a mechanical issue. Unless your tuner is a nimwit and attempting to run 60+ degrees of timing, that is way too extreme to be normal knock.

jerkyboy

Thanks guys. It ran perfect right after the tune and for a week after. I'll keep looking for the obvious

Unreal

In that case, something is coming apart or loose.

schpenxel

Anyone can download hptuners software for free and view logs/tunes. You can just can't edit or save tunes.

So--download it and play around if you want to look at logs.

http://files.hptuners.com/VCM%20Suite/VCM%20Suite.msi

KM177122

Thanks! Good to know!

jerkyboy

Well I stopped by the shop today and spoke with the gentleman working on the vette. He said that he took it out a few times and no timing was being pulled and the car ran like a scalded ape. He took it out another day (which was warmer outside) and it pulled timing everywhere. Even when sitting at a light and he revved the motor, it pulled the timing. All wiring checked out and he said both sensors ohm'd out ok. I called the tuner and he said that in this situation he has just "thrown parts at the situation" I guess meaning he just replaces the knock sensors until it stops pulling timing. I'm using the old LS-6 style drum KS's that normally go under the intake on an LS-6 but now relocated on to the side of the block. Could they be more sensitive than the newer style knock sensors? I've heard that you can desensitize the sensors in the tune. Is that my next step. Boy this is frustrating!!!

KM177122

I hope you get this solved! I know one of my frustrations during my build has been dealing with my tuner and builder and they point fingers at each other when an issue arises and I end up trying to fix it myself. I guess tuners aren't mechanics and mechanics aren't tuners.....go figure.

Chevy Guy

Thanks for this link!! I wasn't aware of this!!

0Tampa Tuning

Im thinking your picking up a mechanical rattle. Check your exhaust to make sure its not hitting the frame of heat shield.

www.TampaTuning.com

548chevelle

Does anybody disconnect the knock sensors?

schpenxel

No.

548chevelle

Does the LS7 engine use a resonant type knock sensor which is supposed to respond only to the pinging frequency versus the older type which responds to any kind of mechanical noise?
It's easy to determine. Just remove the connector on the sensor, hook up a voltmeter on the AC scale, tap the engine with something hard like a wrench and if you get a voltage on the meter you got the older type. A resonant type will show no reading.

schpenxel

It's supposed to only pick up the frequency that knock happens at

548chevelle

The knock calculator says for a 4 1/8" bore that would be 5.5 KHz