Crossflow missfire

[andy oliver]

During a race my car developed a bad missfire at anything over about 3000 rpm under load. Out of gear it revved freely. When missfiring the tacho would flick to zero. The battery is fully charged. The engine is pretty standard with Lumenition ignition. Any suggestions gratefully received.

Thanks.

[ECR]

I know this might not sound likely but trust me it is. What you have described is exactly the symptoms that I experienced with my crossflow setup (including the tacho problem). Remove and clean the 3 wires to the back of the alternator and make sure the connection is good. These wires are part of the ignition circuit (at least they were on my 1990 car)

Try it..

Good luck !

 

Ex Chairman Roger

 

Edited by - ECR on 14 Sep 2008 19:12:34

[andy oliver]

Many thanks, I'll give it a try.

[Roger King]

Yes, the alternator connections are prime suspect, particularly as the tacho is misbehaving at the same time.

 

You can prove this by disconnecting and bypassing the alternator to run on battery only for a few minutes.

[Peter T]

Also check the engine earth strap, as this can cause similar problems that you have.

 

 

[ncm]

Hi Andy, I have experienced the problem described by ECR. In my case one of the connectors came adrift whilst the engine was on full song....tacho died completely , closely followed by the engine. Unfortunately it was the battery connection that came off and subsequent investigation revealed that the tacho, fuel pump ,alternator and several other less important items had fried

One other possibility, that happened on a track day, is a plug electrode burning off. Engine started perfectly even when cold and ran fine at low revs but attempting to boot it brought back the missfire. That one was eventually traced to a brand new distributor having too much advance...after it had destroyed the freshly rebuilt bottom end ☹️

Brian.