Engine Misfire

[cjspindler]

Hi,

I have a problem with my Williams with it misfiring under part load conditions. I've just had the following changed, so can only think that it could be fuel related now.

Spark Plugs
HT Leads
Dizzy cap
Rotor arm
Ignition Coil
Crank sensor

The car drives fine on full throttle, but is a pretty bad misfire on light acceleration and now some constant speed.

Does anyone else have any similar experiences of this and could point me in the right direction?

The car has a adjustable fuel pressure regulator, which i have adjusted and it has improved it slightly, but still not fixed.

Cheers

Chris.

[Wobba]

Can you identify which piston has the misfire?

Is there a constant fuel pressure at the fuel rail? No leaks?

Possible dirty injector, intermittent ECU fault, fuel leak or loom issue maybe.

Why do you use an adjustable FPR out of interest?

[cliokiz]

Check your injector plugs aren't loose

[Wobba]

Also, when did the problem start? Could be cam timing as well, but probably something much simpler.

[chip]

Spec of car?

could well be a lean spot in the fuelling at that point causing a misfire, maybe due to the map not being right for the mechanicals, or maybe due to a sensor fault putting you on the wrong point on the map.

[chip]

PS

Have you monitored the AFR when it is happening?

[ratboyvalver]

check your earths buddy,

[cjspindler]

All,

Thanks for the replies.

That gives me something to work with over the weekend.

But to answer some of the questions:

No, I havent identified which piston the misfire is coming from. Is this an easy job?

I will try and put a fuel pressure tester on, and see what happens when it misfires

The car had a FPR already fitted when i bought the car.

The problem has started after i filled the car up with fuel - it had a very slight similar problem previously, but this happened once in about 50miles. Now it's everytime I try and maintain speed and apply light throttle.

The spec of the car - well...the car was used as a hill climb car, and now I use it as a track day car. The engine has had gas flowed head, Kent cams, ECU re-map, full Devil exhaust, and lots of other bits and pieces, but last time it was dyno'd it was running 170bhp

The car has been checked with diagnostics, and the only fault found was the crank sensor, which i've had changed and doesnt seem to have made any improvements.

Does anyone think it could be fuel pump?

[Wobba]

Two things I would do as simple tests are a compression test and swap the ECU over with a spare if you have one.

[dimma]

Check the wiring loom along where it comes out of the relay box on the passenger front inner guard in engine bay. I had a similar problem where the loom rubbed through against the body and had corroded some injector earths.hope this helps I know it's nasty when your trying your best to fix something and no matter what you do it doesn't work.