VHPD Misfire

[clarkey]

My SLR has developed a misfire at 7000rpm, first noticed at Donington on friday. It got worse, and was pretty violent (as if it had hit the rev limiter).

 

I changed the plugs today (Champion RC7YCC) and it appears to have improved it a bit, but it is still there.

 

Compression test showed 220-210-235-225 psi, so no huge problems indicated, although there is a tiny bit of sludge in the header tank. Water temperature is fine, oil pressure is fine too.

 

HT leads, etc, all look fine. Any other ideas? It needs to be in top shape for Curborough.....

 

Thanks for your help.

 

Edited by - Clarkey on 22 Jul 2001 13:54:34

[Roger King]

Obviously, you need to check all the usual things on the ignition and fuel side, but if it always occurs at the same point in the rev range regardless of how much throttle you are using, you would be well advised to check that you don't have a broken valve spring. This may be nothing to do with your problem, but is definitely worth a look. If this is the cause, major damage can ultimately result (dropped valve, etc).

[clarkey]

Thanks Roger. As it happens at 7000rpm, I tend to be using full throttle......

 

Looks like the head is coming off then. What fun.

[Roger King]

Point taken about the throttle at high revs, but it might be worth trying to get up there with the engine running idle on less throttle. If the problem is related to throttle opening the misfire will probably not occur under these circumstances.

 

Have a look at the springs as best you can before you remove the head. I'd hate to be responsible for a load of unnecessary work!

[TorAtle]

On my K there are two wires going to battery negative, one large 30cm directly to chassis and one small (both black).

 

Now the small one is ground for the ECU, check that connection before you do anything else. A bad earth can give misfires like you describe.

[simonpa]

A dirty/faulty/badly connected crank/flywheel sensor can give bad misfires. This is common on higher mileage Ks.

I doubt a head-related problem would cause your sort of misfire (in my limited experience...).

 

I'd also try another ECU, if possible, to eliminate that avenue. You could try to borrow someones M3D to test this.

If you're near Fleet, you can try mine, if you like.