Ignition breaking up once warm

Hi all,
I’ve been trying to troubleshoot an issue I’ve been having with my '89 XJ-S. The car is highly modified with quad throttle bodies, AJ6 super enhanced ECU, headers with free-flow exhaust. The car runs and sounds fine when cold all the way until it reaches full engine temperature and the coolant gauge reads right around Normal.

Once I reach this point the engine always starts to act up and lose power. It sounds and feels like the ignition is arcing somewhere or breaking up. It’s not a misfire but a gurgling sound.

Can any of you shed some light on this? I’ve changed the fuel filter 3 times thinking it’s fuel starvation (it certainly feels like it) but once it reaches full engine temp, it starts acting up again.

I do have 4 or 5 broken injector connectors that are not secured with their wire clip. Although something that will need attended to, that shouldn’t be an issue.

Thanks,

Mark

Have you checked the fuel pressure when warmed up, and under load? Your pump could be failing or losing power. I once had a car that had a bad electrical crimp connection at the pump connector that would work fine when cold, but get high resistance when hot, and the pump would cut out.

If you had a stock ECU, I’d suggest swapping in a different one. Before I got a scope, I chased a similar issue for months, only to find out the ECU had bad solder joints. Swapping in a different ECU solved the problem.

Verify that your temp sensor for the ECU is giving plausible readings when hot.

Marelli? Check the “timing” (alignment) of the distributor.

Thanks for the tips. I will check the pump and connections.

Mark, back in December 2019 when you had a no-start problem (which turned out to be crossed A and B bank king leads), you also reported some running problems when the engine was warmed up.

Several listers, Kirby included, gave you very good leads. Have you done what was suggested (replacing the filter is not going to do much unless the pickup screen issue, if real, is corrected)?

Good luck.

Thanks for all the tips and advice on my running issue. A clogged pick up tube would make sense. I will run a fuel pressure test when cold and hot and see if it does indeed fall off. I will keep you posted.

Thank you,

Mark