Speeddemon777

Hey Guys,

Im stumping people left and right with this one. First off I have a 2006 C6 Z06 with 22600 miles completely bone stock. So about 2 weeks ago I noticed at WOT above 4500rpm I get a hesitation. So far here is what I have tried to solve the problem:

-New Spark Plugs and Wires
-New Battery
-New MAF
-New MAP
-Fuel injector cleaner
-A compression check(Temp Warm 170F) High 207.5psi and low 200psi (higher psi probably caused from the block cooling down)
-Leak Check No loss of compression after 5min on any cylinder
-Fuel Pressure check (gauge mounted on fuel rail) 60-65 psi at idle and at WOT when problem occurs.
-Tech 2 was connected today and showed the car went very lean almost instantly at above 4000rpm. I may not be 100% accurate as I am not an expert in this area but from what I understood from the technician. The Tech 2 reported advance time above 50 degrees and -1 air flow from MAF and no knock retard again this only occurs at WOT. (ZERO CODES???!)
-Per recommendation from Tech. I had the computer reprogrammed with stock tune from the dealer.

So far none of these has improved or affect the problem at all. I will try and get the data log from the tech 2 tomorrow. My next step is to try a new computer. Any thoughts or ideas are appreciated. Thanks!


FINAL VERDICT

So after throwing ideas back and forth with my tuner all day today as to what it could be. The conclusion we came too was the alternator. Basically at high rpm the voltage would become sporadic for some unknown reason. This sporadic voltage cause major detonation and in turn the car running extremely RICH. The theory is that the fan blades hit the windings causing the car to lose voltage intermittently. This sporadic voltage was too fast for the car DIC to pick up except for a few times. So I tracked down a gen II alternator and put it in as per the request from the tuner. Now she back to her usual old self and this nightmare is finally over. NOW TIME FOR A RETUNE!!!!

I really gotta hand it to you guys though. The ideas kept the juices flowing and allowed me to both learn a lot about advanced troubleshooting and about the car itself. You all inspired me to keep going. I cant thank you all enough.


SIDE NOTE: If you stumble across this and want to do a test to find out if this is your problem too. I would recommend hooking up a high end meter to the alternator(the DIC does not update the voltage fast enough to catch the drops in voltage, neither will an HP Tuners or other OBDII style diagnostics device) and put the car under load. Hope this helps save you time and money. Good luck!

zali0104

If possible get a print out of fuel trim vs rpm and post.
Having said that, sounds to me you have an air leak. Remove the hose between MAF and throttle body and inspect closely for cracks.
Next step would be to smoke the intake manifold for possible cracks or a leak in the PCV system.
It cannot be the intake manifold gaskets, that would result in a miss fire and accompanying codes.
You will need to take it to a repair facility that has a smoke machine for this procedure.
Good luck.

Joe_G

Did you check to see if one of your carbon pads in your air cleaner came loose and is flopping on the MAF at higher RPM?

Pics are gone but here's a thread on the issue.

https://www.corvetteforum.com/forums...with-pics.html

Free to check....

Speeddemon777

Hey Guys sorry for the delayed response!

Here's an update. So the computer was replaced and did not fix the problem. According the the technician the data log on the tech 2 can not be transferred due to a unknown problem with his tech2. -__-

I have checked the air duct and intake for cracks. Nothing visible at all. I have also checked the carbon pads prior to all of this they are snug as can be. One last thing I checked on the MAF was that I have a solid 5V at both signal wires for the MAF and AIT as well as a good low reference voltage(GND) and GND wire. (Note: these were checked at idle.)

Possible hint to the problem: When the car is first started up and allowed to warm up the hesitation is either none existent(pulls strong as hell) or hardly noticeable. After one pull maybe two she begins to hesitate and sputter at 4k-4500rpms. No idea what that could mean though.

Thanks for the ideas guys. Im running out :/, but still determined.

Joe_G

There is an acceleration based rev limiter that shuts down the party when you accelerate too quickly but it normally only kicks in for cars with 4.10 gears or sometimes in very cold weather where cars have more power...doesn't seem to fit your issue as its summer and you are bone stock.

https://www.corvetteforum.com/forums...gear-only.html

There is another rev limiter for neutral or clutch pushed in. Check your clutch pedal to ensure its all the way up when this happens. If the clutch pedal isn't hitting the switch or the switch is faulty this would cause your problem as the car thinks the clutch is pushed in. Your cruise control wouldn't work either if the clutch pedal isn't closing that switch at the top of the pedal mount.

Check that and I'll keep thinking.

zali0104

Smoke the intake.... Remember, lean condition over 4000 rpm.
As engine heats up the leak gets bigger due to expansion. smokee smokee.

Joe_G

Lean condition will lead to p0174 code. Are there any codes?

zali0104

P0174 = Bank 2 too lean

Speeddemon777

The car hasnt thrown any codes, which kinda sucks. I will try and find someone to do a smoke test on the intake system on monday. Unless you guys have suggestions for a DIY version? I saw a few on the internet, Im just not sure how effective they would be.

Just out of curiosity if there was an intake leak wouldnt it have shown up on the tech2? The reason I bring this up is I originally thought maybe I had weak value springs the technician that helped me said that according to the tech2 my vacuum pressure was good(I didnt get a value) and that it probably wasn't valve springs.

Btw side note the technician wanted me to pay 650 put the car on a dyno and to diagnose there. Any thoughts on how successful this would be? He seemed pretty convinced it was tuning, but I feel as though a stock car should run perfectly fine with a stock factory tune. Thanks again.

Speeddemon777

Also, the tech 2 reported that banks 1 and 2 went way lean at 4k. Still no codes and there was no knock retard reported either. Just thought I would add that in there. Sorry for the double post.

Joe_G

Stock tune is fine for stock car. If you had an intake leak it would set a po172 and 174 code.

Did you check the clutch switch?

Speeddemon777

I checked the clutch pedal this morning. Everything seems to be fine. I put the car in second gear with cruise control on didnt seem to disengage cruise control till the clutch pedal was depressed an inch or so. Then I put cruise control on again in second gear and stepped on it watching the DIC for disengagement of cruise. Everything checked out fine.

zali0104

At WOT pcm goes open loop and operates of stored fuel and ignition maps, no fuel corrections are made hence the lean condition. Same reason no codes are set. Drop off wot and she goes back to closed loop, real time fuel and timing adjustments and running monitors.
Looking at the tech 2, you may see elevated fuel trims.
What air box are you using?

Speeddemon777

Stock air box. Stock paper filter. I read some where that at 4k the pcm also switches to the MAF and TPS for air fuel ratio calculations. I ohmed out the TPS last night here are my results just for note purposes.

TP Sensor 1(Pins D and E) 2.09kohm at idle and 1.05Kohm at WOT smooth transition
TP Sensor 2(Pins F and E) 2.49kohm at idle and 3.18kohm at WOT smooth transition.

Image of Pins:
http://puu.sh/iGf5Q/bd7a9e7caa.png
Pins Legend:
http://puu.sh/iGf8t/a8aae251c0.png

c5racr1

By chance did u use anti seize on the plugs?

zali0104

Not that I recommend it, but would like to know why you're askin?

Speeddemon777

I would love to know why it would matter as well, but I did not use anti seize on the new plugs. The plugs didnt seem to affect the problem any how. Just a heads up. I got a OBDII Diagnostics scanner with live monitoring and recording similar to the tech2. I will post the data very soon.

Speeddemon777

Here is the data log from the scanner tool. I have more data but didnt include it such as the pedal position sensor, cat temp,....if you want me to add those I can. There is no export all feature so I am having to make these manually. Let me know what you think. Thanks again.

zali0104

Is your car automatic? I have a tsb. Argh it's a Z06

Speeddemon777

Nope C6 Z06s only came in manual I believe. why?