Trying to sort an irregular stumble in a 1989 xjs that looks to have the Marelli ignition. PO replaced crank sensors front and rear, ignition switch, cap, rotor, plug wires, plugs and coils.

When I put a noid light on an injector plug a get a bright pause with the stumble. I don't know if this is just a prolonged period of illumination for the little incandescent light or if there is a voltage jump. I don't have an o-scope.

Any ideas would be appreciated.

 

check fuel pressure, and check ignition timing

 

Can't hurt to take a good hard look at the injector harness. Unless yours is a rare exception the insulation will be cracking off the wires in multiple areas....and bares wires might be shorting

Cheers
DD

 

Lol...you are spot on. All of the injector clips were broken so I replaced those first. Ignition timing is good. I haven't done fuel pressure yet but the on/off nature of the stumble screams electronic to me. I am currently trying to find all the grounds and verify them but that is a bit like searching for a needle in a haystack.