R33 Gtr Impossible Missfire

[JBRPerformance666]

Hi

Thanks to anyone who has taken the time to think about my cars issue.

Below are the mods done to my car in a little more detail but firstly im asking if anyone has experienced a similar issue to me and what you have done to resolve it.

Secondly if anyone has any suggestions on the next step in the process then im also interested to hear it!

My car has developed a misfire, actually its more like a hard cut rev limiter at about 5200rpm if under load. At idle or lighter load it can rev higher. The wideband indicates the AFR is not changing when the problem starts. The plugs all look fine. Fuel pressure is available (checked while under load on dyno). Symptoms are the same no matter what gear its in.

Already Tried:

Checking Plugs, replaced, and gapped them progressively tighter until getting as low as 0.3. Replaced with Iridium plugs at .8, then refit new copper at .6 - No change.

New Coil Packs - No Change

New Leads - No change

New injectors - No Change

New Crank Angle Sensor (checked with timing light to top dead) - No change

Disconected turbo compressor from intake to test with no boost. - no change

Some more details about the car.

built motor, T04Z Turbo - no maf sensors

Haltech Platinum 2000

Ls1 Coilpacks

huge fuel system

Im sure ive left out some key info however ill come back and add anything the moment i remember it.

[Hadouken]

Wow now that is interesting. Does this happen in all gears?

[Hadouken]

Are you still running the ignitor for the coils? I think that is the only thing that has been left out...

[MrStabby]

What was the last thing you changed before the misfire started?

What dwell are you running on the coils?

[GTRPSI]

I had something similar on our GTR, turned out being the ignitor module.

Also check your earths to the engine, ignitor module has one on the R32 GTR's on one of the rear bolts holding it down, unsure about later R33 GTR models.

[JBRPerformance666]

Hi guys thanks for the time.

It sure is an interesting one!

The ignitor module is no longer in place, LS1 coils have an ignitor built in. All have been replaced.

Dwell time on coils is supposed to be 3.2ms @ 13.8v. Ive altered the ecu as low as 2ms right up to 5.5 and it makes no difference to the issue.

Prior to the misfire a wideband afr was fitting approx 1 month beforehand.

And yes, happens in all gears on dyno and all gears ive tried on the road.

[JBRPerformance666]

the sensors are also all functioning and displaying valid parameters on the ecu interface.

[kaneryan]

hey dude i had this problem
i had a haltech and my tuner had set up a fail safe setting that would set up boost cut. if the boost spiked above a certain psi it will boost cut.
i could rev past it if was on light throttle but if i punched it in 4th gear from low down like 3000rpm and waited and waited and waited then bang full boost would come on hard at 5500rpm and it spiked a bit it would hit the boost cut and almost throw me through the windscreen haha. for example boost was set at 20spi and when it came on boost like that it would spike to 21psi and the boost cut was set to 21psi and then it would boost cut... maybe this is your problem

[kaneryan]

i also had a similiar problem when my fuel pickup line had a split and the fuel wasnt quite making it all the up to the top of the tank before a bit was spilling back into the tank. once again on full boost the haltech registered that the engine was leaning out, so it would boost cut. maybe it is a fuel issue, but then you said that the AFR's arnt changing to hmm its a tough one

[JBRPerformance666]

Both ideas make sense but one thing I tried was disconnecting the turbo compressor from the intercooler so the engine would run without any boost at all. Still the exact same proplem.

Also ive checked the fuel pressure with a gauge while on the dyno, not fuel pump or pickup related as the pressure in the rail does not drop.