Misfire

[Adam Southgate]

Hi All,

I've got an irritating misfire at high revs (above 5.5k in 1,2,3 and above 5k in 4th and 5th) and at full throttle under load. Have tried a load of stuff to cure it without luck, so if anyone has suggestions for what can cause a misfire (or a pre-ignition)? Please let me know so I can sort out an organised test day where I go through all the options to try and fix it!

Cheers,
Adam

[Porsche917]

Dang Adam - if you had any luck at all it'd probably be bad...I've done a huge amount to my car but can't say I have experienced a misfire (yet). Rebecca had the problem at Brands - she has an ex Paul Bravo car as raced by 'the Stig' last year - they cured the problem by 'brimming it' with fuel - RJ did it at Brands and it worked....just a suggestion, sorry I don't have something more clever to contribute.
Cheers
Geoff

[Adam Southgate]

Any suggestion is a good suggestion

Getting used to the bad luck now - very close to hiring a car just to get myself racing!

[A.Kirkham]

Well I suppose I'm the bloomin' expert on misfires by now (wish I wasn't though!) - last 2 seasons have been affected by misfiring - I suppose the 1st thing to do is assertain whether it's fuel or ignition. A spark tester of some sort like an in-line firing light would be a good idea - if the spark is breaking down under load try swapping coil/leads etc - then dizzy and whichever type of amplifier/transistor box you have? Are you bosch electronic ign/ lumenition or points ign? If it's fuel then you're into swapping all the obvious stuff like pump/fuel filter etc - if you can get onto a rolling road before Snett that would be ideal of course! Best of luck with it Adam.
AK

[A.Kirkham]

Btw, if you're considering hiring a car why not ask about one of the black Flegg flyers?

[JB31]

Adam,
I used to have exactly the same problem with my car. We finally traced it to the engine not getting enough fuel.
We discovered this by measuring consumption in testing. 2 cars running round together at the same pace, and mine used 40% less fuel! 2 things sorted it. We swapped the complete fuel metering unit for another one. Both appeared to be identical, but the second one made a huge difference and it would rev cleanly to 6k through the gears. The second thing was (and here I'm straying into techy stuff i don't really understand) that the secondary pump in the tank (I think it's called) wasn't working. When tested on its own it worked fine, but installed in the car it wasn't running. This was down to a fuse having blown which wasn't readily apparent.
Hope you manage to sort it
John B