Pekka_Perkeles

This is a 2007 Z06. Totally stock. No mods, nothing done. And it surges at light throttle.

See here (note that log parameters are scaled, i.e. rpm are between 1150...1250 etc.):



(Wideband sensor not attached in the log.)

So far I've tried:

- new plugs
- spark wires
- coils
- injectors
- throttle body
- PCM

Furthermore, I've tried to:

- run open loop (closed loop disabled)
- run VE only
- run MAF only
- mix of those

No change. It just surges at light throttle.

Checked fuses, obviously, as well as grounding point near PCM.

No error codes, except occasional P0300.

I'm totally lost on this one. Please help.

Function Racer

Have you cleaned/replaced the MAF? Have you cleaned the throttle body and applicable sensors (Specifically the TPS)?

Those would be the first two culprits to check when dealing with a light surge. Perhaps check the incoming from the TPS and see if it changes % during surging.

Also, FYI with the LS7, small surging at light throttle under 3k RPM seems to be normal throughout the Camaro z/28 crews. No bucking, but almost like a fuel shut-off when the big 7.0 is trying to breathe down low in the RPM band.

luka2sb

you clearly have some sort of a interface. if it's HP Tuners, why not record an event and post the data here?
I'm assuming you have something since you were able to run VE only and MAF only.

Pekka_Perkeles

Here's HPTuners data log.

C5 Diag

So this is a stock car and you're running a wideband O2 sensor ??...looking at this log (more used to looking at a scan tool) I can see quickly your long terms are running almost -10%....what do your O2 sensors look like...if you are pulling fuel the O2 are probably seeing a rich condition...I like to look at MAP(BARO) with key on...should be around 103 KPA at sea level...so have for checked for any DTC's ???...as was mentioned I would clean your TB and if you can get your hands on a bidirectional scan tool I would do a fuel injector balance test...are you still getting P0300's ??...your MAF sensor value (12.9 grams/sec) seems a little high for 1200 RPM)...an "over reporting" MAF can cause a rich condition.

Pekka_Perkeles

Thanks everyone for suggestions.

This is indeed a difficult one.

I do have wideband part of the HPTuners channel configuration for E38 PCM, as I mostly deal with cars having some sort of power adder or cam or so. That's why there is AFR PID, but wideband has never been in this car, as it is with a stock engine.

1. MAF

This was my first guess as well. But it does surge similarly also without MAF.

It does not matter if I physically disconnect MAF cable or if I set the PCM to run Speed Density (ie. with Virtual VE).

That's why I haven't tried new MAF with this car.

2. O2 sensors

It does surge with or without them. No change if I run it open loop or closed loop.

3. Throttle Body

I tried another one with of course another TPS sensor and no change.

4. DTC's

Typically none, except sometimes P0300.

5. Injectors

Tried other set, no change...

6. Coils, plugs, spark wires, no change...

7. Maybe LS7 is just surging a bit in a stock form?

Maybe, but so far all LS7 engines having small or moderate aftermarket cams I've been able to tune to run silk smoothly. And this one is stock!

I can make this car surge more with tuning, but not less.

luka2sb

i dont see anything wrong in the file. could it be something mechanical , like worn out torque tube bushings?
it kind of looks like you're at such a low torque level that you are going back and forth through trans gear lash?
if you're accelerating just a little bit harder, to put a positive torque on the gears so that you're not in the lash zone, does it still surge?

something keeps triggering your torque management spark retard, that's kind of odd.

i'd add LTFT, knock retard and accel pedal position to your recording.

Pekka_Perkeles

It did have noticeable backlash in halfshafts, so both of them were replaced. It actually helped a bit, but the surging was still there.

With a bit more throttle, surging does go away, though. So it is there only on light cruising situations, but easily noticeable on normal driving.

Also, heads were removed for valve guide replacement. Nothing special there, just worn out guides.

BrianC6Z

How's the intake? Filter clogged at all? If it's a nice day (e.g. no concern of getting crap pulled into the engine), pull the intake filter off and drive around for a minute to see if the problem persists. It drives very differently with the extra air and it could be that you're getting turbulent air at that speed under the hood and it's causing it to enter the filter sporadically. I wouldn't expect it with the stock setup but if it was dirty/clogged at all, that could be a possibility.