My wife and I just completed a road trip in our 2001 Z06 that covered 5500 miles in three weeks. The trip took us from near Houston, Texas to Palm Springs, CA, to San Diego, San Francisco, to Utah, to Grand Junction and Breckenridge, Colorado and back to Houston. The drive was great with a lot of cruising between 80 and 85 mph. And the roads, particularly Highway 1 in California and Highway 12 in Utah were a blast. These are great sports car roads. Too bad most of the traffic on them is SUVs and trucks.

Issues: I have always run 93 octane gasoline in the Z, with no complaints. Starting in west Texas, the best gas available was 91 octane, and the Z was not happy. The engine would clatter with preignition under part and full throttle. Same story in New Mexico and Arizona. California was even worse. While their gas is also 91 octane, it contains 10% ethanol. This was regardless of gasoline brand. I tried Shell, Arco, Chevron, and Mobil. In California, the Chevron was not quite as bad as the others.

The Z continued to clatter on the gasoline in Nevada, Utah, and Colorado. In Grand Junction, CO I put the car in for some Goodwrench service. The dealer checked it out and told me I had spark knock. He said the system was 100% normal and OK for use.

The clatter continued through NM until I got back to the 93 octane gasoline in Dallas.

Questions: Who else is having this problem? I have read about it before on the forum with other 2001 Z06s. Has anybody succeeded in having GM address the issue? Has anyone fixed it themselves?

I thought the engine control computer used a knock sensor to retard the ignition when this occurred? If so, why isn't mine working?

BTW, gas mileage on the highway averaged over 28 mpg between TX and CA. Of course the average went down to about 17 mpg in city driving. Gas mileage on the return trip averaged 29 mpg on the highway. This was with 91 octane gas. For some reason, when I got back to Dallas and changed to 93 octane gas, mileage dropped off at least 2 to 3 mpg.

The dealer in Grand Junction insisted on charging me $45 to diagnose the spark knock, despite my GMPP with $0 deductible. I think this is BS and will be taking it up with the General. If the General will not cover diagnosis when he agrees the car has a spark knock problem, what is the value of the warranty, anyway?

Maybe I misunderstood the way the program works and am supposed to just drive it until I have holes in the top of the pistons, so the General can install a new engine.

I do have a buddy in California with a 2003 Z06, which does not clatter on the crappy CA gasoline, so I know the problem is solveable.

 

We've been running our 2001 Z06 on this "wonderful" CA gas for almost three years with no problem, & no apparent knocking. Is your PCM program stock?

 

I have experienced this problem in my previous vette, 99 FRC.
When I would take a road trip from Charlotte to Atlanta or something similar... the car would ping badly after a few hours of highway cruising. Once you drive normal again and put your foot in it, the ECM re-learns and the problem goes away. Your car runs most efficiently right before it pings. The ECM learns and adapts to changes, but it takes a bit of time for it to map the conditions.
The gas was most likely not the problem.. Others have experienced the same thing and this was explained to me some time ago by the C5 tech on this forum.
mike

 

Another thing... your knock sensors are fine.. Knock is a different sound that the sensors are tuned to. As I mentioned before, slight pinging happens when your engine is running at peak efficiency. A small amount of ping is not harmful and shows an efficient mixture. These cars usually run rich in order to prevent knock and pre-ignition. On Hwy trips the ECM keeps the timing advanced when low engine loads are present for better mileage.

mike

 

The vettenet CA - yes the PCM is stock. the car is unmodified except for Vortex inlet/filter. The dealer says the engine has spark knock at partial and full throttle (this was on 91 octane Colorado gas). Other gasolines and states with less than 93 octane sound identical.

If this is not what the knock sensor is supposed to control, what good is it? The car runs like crap under these conditions and I certainly will not keep my right foot in it.

 

For those of you who think this is an isolated (one off) problem, you might have a look at the messages from Z06JOE, GMSZ06, Z06LS6 and Saving41. Teh big question is, has the General recognized and found a fix for the problem yet????

 

TSB 02 07 30 024--All it takes is a reflash of PCM with new program

 

Had my 2001 for 1 year now and absolutly NO problem with the 91 Calif gas, in fact it never pings or knocks.

 

Sounds like a really great trip.

My wife and I went to NCM for Museum Delivery in June 2001. To get back to Houston (via Warren, MI) was 2,350 miles. Until we got back to Texas (our first stop in Texas was near Dallas), the best we could find was 92 Octane. Once back in Texas, we changed to the 93 Octane. I haven't been forced to step down to 91 octane and I have never suffered the issue you are describing.

At the dyno, another Z06 (exactly like mine except for color) charted with 25 fewer HP on the rear wheels. The first thing the dyno operator said, "You haven't been using premium gas."

dave

 

Z11409 - That TSB number is incorrect. It is for a cracked transmission casing. My dealer says the only TSB which may apply to my condition is for corroded knock sensor terminals on cars where the owner washes down the engine. Not likely for my car as the dealer in Grand Junction Colorado says he already checked the knock sensors for correct operation.

Powermad - it was still a great trip. Beware of sub 93 octane. It is closer than you think. I found only 91 octane premium in parts of west Texas and only 90 octane premium in the panhandle.

Mine runs so good on 93 cotane that I never suspected this problem. I never tried 92 octane or any regular in this car.

 

No problem here with CA 91 octane fuel.

 

Z.06, try a lower octane in your regular in-town driving... I bet you wont have a problem..
mike

 

Hi Z.06 -

I have never heard a ping from my car - although I did have to put in some questionable fuel at one fill up on the way to Tampa last year.

I would not think you should hear pinging from gas that has only two RO points less than your normal fuel - I would think that is a potential problem...

good luck!

best regards -

mqqn

 

C5 Missle,
I will try some 89 octane intermediate grade and let you know how it goes. If gasoline octane rating means anything, I will have a problem. But I will try it and also give Mr Goodwrench a listen. I think I will have a problem. I could be wrong but I have over 4000 miles of experience that says you are wrong.

 

My 2002 does this as well using 91 octane, the car is stock . It runs fine other than the distrubing clatter during WOT in 2nd and 3rd gear between 5000 and 6000 rpm. No codes are thrown. I took mine into the dealership last summer (5 hour round trip) and was told the car is fine. They suggested that there may be a bit of carbon buildup that could be removed with a fuel additive.

 

I've not had any problems with my Z in two years burning 91 octane fuel in Utah. I was told the lower octane is allowed because cars require less octane at higher elevations. I think it's because it's cheaper to refine and the elevation issue, while true, is a good excuse to maintain a higher profit margin.

I have do have some pinging at times in my old 79 L82 on the 91. Again, none in the 2002 Z.