Engine misfires on Bank B...

Sasha · Postby **Sasha** » Mon Sep 24, 2007 4:02 pm

Hello everyone,

Someone I know has a 1991 V12 XJS fitted with the MARELLI ignition system . The car developed a
misfire on B Bank , which is the 6 cylinders on the passenger side . The misfire blew the intermediate exhaust box right off . This suggested straight away that unspent fuel had
reached the box , expanded & ignited with the heat .
Since then the following have been changed , with NO CHANGE.
CRANK SENSOR , BOTH COILS , SPARK PLUGS , PLUG LEADS , DISTRIBUTOR CAP
ECU , NEW EXHAUST
Wiring has been checked , engine timing checked , Distributor checked over
Compression , injectors & injector seals
She still won't run without the misfire PLEASE PLEASE PLEASE can anyone help ?

regards,

Sasha,,

poprivet · Postby **poprivet** » Mon Sep 24, 2007 6:31 pm

There's lots of info on the Marelli problems in Kirby's book. Click on Technical above for the link.
Sorry I can't be more specific, the 6 cyl engines are more my thing.
Pop

ptjs1 · Postby **ptjs1** » Mon Sep 24, 2007 6:34 pm

Sasha,

Maybe a silly question, but did you change the rotor arm when you changed the dizzy cap?

From what little I know of these Marelli systems with the dual dizzy cap arrangement, failures on one bank are often down to failures in the cap or rotor arm.

Also, put decent quality genuine parts on, not pattern items.

Good luck,

Paul

Postby **davidr** » Fri Oct 05, 2007 9:21 pm

Sasha,
I agree with Paul. It sounds just like a problem I had with my V12. The carbon brushes on top of the rotor arm wear out and no longer contact the distributor. As the Marelli system is effectively 2 separate 6 cylinder systems going through one distributor this only knocks out one side only. Try changing the rotor arm and hopefully that will cure it.
Sorry if it turns out to be something so simple after you've obviously gone to alot of trouble and expense changing components so far!
I'd be interested to know how you get on
Good luck!