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Discussion Starter · #1 ·
I went to the 'strip on Friday night. The car seems to pull well 1st through 3rd and then when I put it in 4th it just seems to not pull as hard as it should, and the exhaust sounds kinda funny... rough sounding, almost like the ECU is pulling timing or something???

BTW my car is a stock '02 Z with the only mod being a Halltech stinger intake, but I had the same problem the last time I took it to the track before I put the intake on. 30k miles (50k kms) on the odo, and was running 115 MPH traps (114 before the Halltech went on).

If I'm in 4th on the street it seems to pull fine... I've only noticed this problem at the track after running WOT through 1st, 2nd and 3rd. Coolant temps are about 192 at the start of the run and about 200-202 at the end of the run (according to the DIC).

Any help would be appreciated... the car just feels like it's lying down when I put it in 4th and go through the traps... it just doesn't "sound" or "feel" right when it goes into 4th...
 

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My stock 03 does the same thing, except sometimes going into 3rd too. I run WOT and bam, go into 3rd or 4th and it hesitates for a split second like the fuel pump cutsoff...help!
 

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Traction control maybe? Were you running in Comp Mode?
 

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Discussion Starter · #5 ·
I constantly have the traction control barking at me on the street as the car can spin even going into 4th gear sometimes...!...but the problem I'm describing is not traction control. When the traction control comes on during a hard gear change you'll experience an almost total loss of power for less than a second while the tires hook up, and then full power is restored.

My problem comes at the track running in "Competitive Driving" mode, so I know that it's not traction control.

This problem persists in 4th gear as long as I have my foot to the floor - if I was to keep accelerating long after the traps had gone by the car would still feel and sound very sluggish. Like I said earlier, the best way I can think of to describe the problem is maybe that the ECM is pulling timing for some reason - the rough sounding exhaust is why I think that may be the problem...

Carbon deposits? Faulty plugs? Wires? I really have no idea what's going on since the car runs stellar right through the top of third, and as soon as I put it into fourth it just doesn't pull and it sounds really bad...
 

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hey, my 02Z does the same thing in 4th gear and 5th gear...1st to 3rd are awesome....but if i am crusing in 4th gear at around 3500rpm and go WOT...i get that similar slight hesitation and bog...

keep us updated... maybe its the plugs or wires, i have to get this checked as well.
 

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Make sure are your plug wires are firmly in place ! could also be a fouled plug !

Rob
 

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Discussion Starter · #8 ·
Well, I was talking to a buddy of mine over the weekend. A friend of his took his car to Agostino Racing for a dyno-tune and they told him that high-rpm misfires are a common problem on Z06s. He also said that this problem could easily be tuned out...

I will be looking into this and updating accordingly...
 

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I have this problem with my 02 as well. It has a noticeable miss in 3rd at about 6200. In 4th it starts earlier at about 5000. It's definitely load dependent. I've changed plugs and wires. I have hptuners and am experimenting with different a/f ratios and timing. I'm starting to believe that its detonation and not a faulty component. Perhaps a hot spot in the combustion chamber.

I'll let you know if I find a combination that works.
 

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It's your torque management.
The stock table for example at 5200 rpms allows a max of 453 lbs of torque.

Intake air temps will pull timing also starting at 98 degrees depending on the manifold air pressure.
 

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Discussion Starter · #11 ·
Update: My contact that said the prblem was a high RPM misfire was corrected... apparently the high RPM misfire problem is only common on cars with exhaust work done. My exhaust is stock (for now).

91twin: Your description is dead-on! The only thing I have to add is that mine seems to be engine temperature dependant - the higher the coolant temp the sooner it starts in 4th, and it even starts at the top end of third sometimes, just as you've described. My gut feeling is the same as yours - a hotspot in the combustion chamber causing mild detonation and causing the knock sensor to pull timing.

FRC Tom: IAT shouldn't be a factor since all of my track outings so far have been on nice cool evenings. Torque management? My engine makes nowhere near 453 ft.lbs of torque... is that at the wheels? My car is stock except for a Halltech Stinger intake, and this problem plagued my car even before I installed that...

If there was a hotspot in the combustion chamber, could it be caused by carbon build-up? If so, could the "decarburisation" process (where you spray that can of stuff into the throttle body while running) help to clean the engine out???

Thanks all! :drunken:
 

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Hey Lance it's Doug. I'll give MISSILE my autotap for you to try next time he comes down. You'll be able to monitor LTFT and a bunch of other things that may be able to help track down your problem. Or go to or call ARE and talk to Peter.

Those are some decent times you're running too :jammin:

You damn southern ontario guys and all your good tracks.
 

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Discussion Starter · #15 ·
Hey Doug! Congrats on the Z! And I thought I got a good deal on mine...

Is the Autotap similar to the OBDII tool that the Uxbridge brothers have?

LTFT? What's that? We Southerners ain't much fer book lernin...

JCO forever...
 

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Blue Angel - I was finally able to get on a clear section of road for 4th gear. Here is a scan showing detonation at just below 5000 in 4th. You can see the KR in red.

http://www.z06vette.com/gallery/data/500/8230SCAN3.jpg

FRC Tom - Thanks for the tip. I increased torque managment but it didn't help in my case. I can see where that might cause problems in modified cars.

I'm going back through old scans to try and find optimum a/f ratios, timing, highest dyn/cyl fill and injector rates for different IATs (writing a program to help with this).

The decarb procedure looks interesting. I might give that a try.
 

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Blue Angel said:
My gut feeling is the same as yours - a hotspot in the combustion chamber causing mild detonation and causing the knock sensor to pull timing.

If there was a hotspot in the combustion chamber, could it be caused by carbon build-up? If so, could the "decarburisation" process (where you spray that can of stuff into the throttle body while running) help to clean the engine out???
Unquestionably. GM has a top-end decarbonizing treatment. Have your Dealer do it. The car smokes like a mo-fo when you do this and it stinks to high heaven. You're family and neighbors will thank you for not doing it in your driveway.
 

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Discussion Starter · #18 ·
Wow... what would the public do without the internet???

That's AWESOME 91twin... thanks alot!

Notice that the ECU pulled almost 2 degrees of timing at the top of 1st gear, then she ran like a champ through 2nd and 3rd only to get a big-ole bitch slap halfway through 4th to the tune of 6.6 degrees... this is EXACTLY what I feel while driving my car, and like I said at the track I got it to fall on it's face through both 3rd and 4th gears, but 1st and 2nd felt fine...

Which program are you using to collect this data?

This forum is terrific! :z:
 

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Blue Angel - I'm using hptuners scan to record this data.

I suspect many Z06's have this problem, but of course you have get over 100 mph to feel it and not everyone has to suffer with 91 octane. What octane are you running?

It would be nice to be able to set gear parameters for spark advance but I don't see a way to do that. Anyway i'm still working on it.
 

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Discussion Starter · #20 ·
91twin...

I'm begining to wonder if this high RPM misfire problem is related to oil intrusion from the PCV system.

Based on info from another thread, early LS6s are subject to a problem where the "baffles" in the PCV breather come un-glued from under the valley cover; the baffles are designed to strip the oil out of the air flowing into the PCV system. When the baffles separate from the valley cover it allows an oil/air mixture to enter the PCV system and travel directly through into the intake manifold.

Having oil vapor in the intake manifold is bad; apparently oil vapor will effectively reduce the knock resistance of the air/fuel mixture.

Upon hearing this I checked my car out... the floor of the intake manifold is wet with oil, and the PCV valve/hose assembly is oily as well...

Is there any way you could block off the PCV hose and re-try your 1st-4th gear blast with your HP Tuners on and see if there's any corelation between PCV flow and Knock Retard?

The only thing I see wrong with this theory is that there's no manifold vacuum at WOT to draw air/oil through the PCV system. Although, any blowby gasses would increase crankcase pressure, and that could force air/oil through the PCV system... just a thought.

I'm replacing my valley cover/PCV system this weekend, and I'm also gonna try that decarbonization process as well if I have time.

Another idea someone had was to place a "catch-can" in the PCV line. Not a bad idea...

You're right - most people will probably not notice this problem. I'm stuck with 91 octane as well, although Sunoco sells 94, they just don't have many stations that are handy to get to around here.

I just read an article on HPTuners last night (Chevy High Performance mag., I think) and it sounds pretty good. How do you like it? What was the cost (roughly) to buy the system? Seeing that Diagnostic chart you posted got me all fired up!
 
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