Need Help With Diagnosis - Misfiring Problem

[Jebu.32]

Hi,

I need some help with diagnosing an irritating misfire problem on my car (R32GTR)

The car misfires/currently cuts out at about 4000rpm.

I've already done the usual checks and replaced/tested these items and they have turned out to be ok.

- AFMs ok

- Ignitor - swapped with known good unit

- New coils

- CAS - swapped with known good unit

- No tears, leaks in hoses and piping.

Im currently using PowerFC and no errors are reported on the sensor/sw check screen.

I'm suspecting that it might be an injector leak or injector failure?

Just thought I'd run through you guys first and see if maybe one of you have experienced this before.

Anyway thanks in advance for the help.

[Jebu.32]

Sorry i forgot to add that the knock reading on the PowerFC is 1.

It NEVER changes on rev or idle.

Could it be related to a knock sensor problem?

Are the symptoms similar to what I've described?

Any thoughts appreciated.

[Luciano]

spark plugs are known to cause this sort of problem.

When was the last time you changed the ones you have? and if you did recently, did you gap them?

[Jebu.32]

hi,

I've already changed the plugs and gapped them.

I've done this today and so far still no improvement:

1) Changed injectors

2) Swapped TPS

3) Swapped fuel regulators

4) Removed boost controller

The problem is still there.

I tried to slowly accelerate, it seems to be fine until about a 5-6k

But if I try to gun the throttle, if misfires immediately.

I honestly don't know whether its fuel related or sensor related.

It doesn't seem so bad when the car is cold, but as i drive it longer, it gets worse.

One more thing that I haven't tried is the O2 sensors.

According to the PowerFC reading, the O2 sensors at idle are:

O2-1 = 1.2v

O2-2 = 1.2v

But when I WOT it gives me these readings:

O2-1 = 0.6 - 0.8v (roughly)

O2-2 = 0.6v

Could the O2 sensors be on the way out?

I'm pretty certain other parts are ok.

Just want to narrow down the problem areas.

[rob82]

hi,

I've already changed the plugs and gapped them.

I've done this today and so far still no improvement:

1) Changed injectors

2) Swapped TPS

3) Swapped fuel regulators

4) Removed boost controller

The problem is still there.

I tried to slowly accelerate, it seems to be fine until about a 5-6k

But if I try to gun the throttle, if misfires immediately.

I honestly don't know whether its fuel related or sensor related.

It doesn't seem so bad when the car is cold, but as i drive it longer, it gets worse.

One more thing that I haven't tried is the O2 sensors.

According to the PowerFC reading, the O2 sensors at idle are:

O2-1 = 1.2v

O2-2 = 1.2v

But when I WOT it gives me these readings:

O2-1 = 0.6 - 0.8v (roughly)

O2-2 = 0.6v

Could the O2 sensors be on the way out?

I'm pretty certain other parts are ok.

Just want to narrow down the problem areas.

02 sensors wont cause a missfire at full load - unless there is a dodgy PFC tune which enables 02 operation at very high loads. To check try turning o2 feeback off within the PFC. Have you check your base timing? If your 02 sensors aren't f**ked then it looks like it may be lean. To check the pump remove the return line from the rail, place the hose into a measuring device and start and run car for exactly 30sec - then measure. You should have around 1.5L as in 3L/min of fuel flow.

[The Dan]

It's not your O2 sensor.

Do what rob said, flow test the pump. I would be more inclined to check it before the injectors though. Bridge the fuel pump relay and time the flow into a 1L container.

Have you replaced your fuel filter? A block fuel filter is a known likely cause of missfire under load. Can sometimes be mistaken for coilpacks.