Misfire Problem

[Scott@FP]

About the only other thing I can add is possibly severe fuel rail pressure pulsation if it is being batch or semi-sequential fired injection, that RPM range is about where you usually see that, and its very specific in its frequency range, if you accelerate rapidly you don't see it as bad, but steady state or slow accel it goes crazy. I'm going to assume this car is full sequential, but its worth mentioning anyways. Did the fuel rail plumbing change during the rebuild? Some V-6's fire the injectors 1-2-3-4-5-6 which has the potential to set up some feed problems. FP regulator pressure source same? FP regulator diaphragm leak? They leak (breached diaphragm) in weird ways at times, only at certain positions and pressures etc. Just throwing that out.

[Martin]

Injectors are the same and so it the plumbing and rails. Strange thing is that the misfire is not load related but RPM.
Fuel pressure regulator situated on the connection between the 2 rails.

Firing order same as other V6`s (1-2-3-4-5-6 down on the crank) but cylinder numbering is different (Consecutive on banks)

Yes its fully sequential, pressure source same.
I Havent stripped the regulator but this is the pressure in the logging......

[Scott@FP]

Note the slight rise (~2 PSIg) in FP but no corresponding rise in manifold pressure just prior to the first misfire event on La2?

May not mean anything but might be worth looking into.

[Martin]

I see what you mean, ill have a look at the regulator, thanks

[AaronM]

Hello Martin,

If this was happening to me I would watch what the rpm was reading on the screen when the problem occurs. This will tell you how good the crank reference is. Run the engine into the misfire and hold it. Disconnect one injector at a time and see which one or if all have an effect. Sorry if you have already done this. I am looking through this very quickly. What do the plugs look like? any a bit off?

Cheers

[MSIMARD]

Do you have any abrupt changes in the 'injector timing' table?

[Martin]

Hello Martin,

If this was happening to me I would watch what the rpm was reading on the screen when the problem occurs. This will tell you how good the crank reference is. Run the engine into the misfire and hold it. Disconnect one injector at a time and see which one or if all have an effect. Sorry if you have already done this. I am looking through this very quickly. What do the plugs look like? any a bit off?

Cheers

Aaron,
Checked the RPM, and there is also no Diagnostic errors. The plugs look good, Iev tried 3 different brands, Resistive and non resistive.....Ill have to check the Injectors like you said.

Do you have any abrupt changes in the 'injector timing' table?

Nope, its all good. Ive tried changing INJ timing aswell, and running totally flat timing for injection.

[Martin]

Found the problem.........


Its was an incorrect current setting on the injectors. I just dont understand why it ran like this for years


Thank you for all the help and recomendations.

[ElectronSpeed]

Martin,

Do you have any thoughts on why this is more of an RPM dependent thing than a load dependent thing (or am I remembering the problem wrong)?

thanks,

[Martin]

Yes you are remembering correctly, it is only at certain RPM`s time and time again if you ramp it on the dyno.

I dont really know why this is the case since the voltage is not fluctuating a lot. Another thing that baffles me is that it ran for years like this, no misfires.

I inccreased the injector current from 2 to 3 amps and all the problems went away. If I increase it to 4 amps it shows a peak error. Beacuse there is such a fine line between misfiring and a peak error I decided to make it -3 amps to extent the Saturated mode before PWM starts on the injector.

It runs well now and is back to original power figures and its a smooth graph.