Not my car but on friends car with similar mods ( 98 SS LS1 M6 )

Start it up and it idles good. Put it in first and give it even the slightest throttle and the car loads up, like it is dumping fuel. The car will hesitate but above 3krpm it seems to smooth out. At first we thought it was drivetrain realted because the car felt like it might of broke the gears but we checked that and they are fine. It's like the car is out of timing but how would that be possible? It all started on the 3-4 @ WOT. The car had been cutting out at 6k + rpm before so it might be the fuel pump but why would it dump fuel at part throttle?

What we have checked:
Plugs ( dark, rich, with a little green on top from the race gas )
Swapped MAF sensor
Swapped MAP sensor
Fuses and Relays for fuel pump
Grounds on the back of the cylinder head

What we are going to check:
Fuel pressure
Injectors ( maybe they are hanging open to long? )
PCM
valve springs

Could it be the crank or cam sensor? What else should we try? TPS sensor? Anyone run into a similar problem?

This is fustrating, everything was runnin fine before..

Thanks,
Justin

 

ttt - if we can figure this problem out with his car in Hammond, I'll see about getting the car up to work sometime this week. Let me talk w/ Geoff first.

I'd definitely check fuel pressure when you get some time.

 

i know it sounds stupid but might want to check for bad plug wires or coil pack. when a plug wire goes bad and starts to misfire, the car will buck at low rpm's and surge, then will smoothen out about 3k rpms and above.

 

My car is doing the same thing.It startted after changing the plugs and unhooking the AIR tubes to do so. Ataped the car to check for misfire and there was none aslo checked KR and LTerms, every thing seemed fine. Replaced gaskets on air tubes, Changed fuel filter and ran some injector cleaner, still didnt solve the problem.The only other thing i can think of is a vacume leak some where.A friend said that if you take WD40 and spray around places like the AIR tubes and where the EGR tube goes into the manifold the engine will rev if there is a leak. I'll try this tomorrow and let you know what I find out. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
, justin ( also <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> )

 

My guess is a bad plug or plug wire... You can't tell by looking at the plugs. It's easy to diagnose with an O-scope. I'd start by changing the plugs. Still exists, change the wires. My 2c's....

 

Thanks, we are going to swap plugs and stock wires to eliminate that possibility. Also going to swap coil packs.

Justin

 

Should of pulled the #8 plug the first time around <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

<img src="http://bellsouthpwp.net/j/s/jsears8/000gap.jpg" alt=" - " />

<img src="http://bellsouthpwp.net/j/s/jsears8/000gap2.jpg" alt=" - " />

Justin

 

Plug gap is a little tight isn't it Justin? <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Bruce

 

<img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

 

His fuel pump was cutting out so I guess that's why it was detonating so bad, but why just #8? It's hard to tell from the pictures but there are small gashes on the tip and outer edge. We did a compression test and the cylinder is fine and it is not smoking.

At least it didn't look like his last one
spark plug <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" />

Justin