I have a 1991 XJS that was running fine. After filling up with gas,the car would not start at all. The starter cranked,but the engine would not run. After sitting for the night,I went out and it started right up. The engine ran a little rough,but then smoothed out and ran normally. Any ideas where to look? Is there a sensor somewhere I can check out. I would think if it was the fuel pump,it would just stop working all at once. Any ideas or direction to inspect would be greatly appreciated. The distributor was generating a spark,but is that a part that can work and then not work?

Thanks,

Don Verrico

Submitted by DVerr94100@com… on Sat, 06/21/2008 - 16:55

Good day everyone. To Don Neff, I appreciated your help in helping to determine that my car's problem was the RPM and CPS sensors. Do you know or does anyone know a good online source for purchasing these sensors( and other parts)? I've looked intermittently but have not been able to find them.
Thanks,

Don V

Submitted by neffd@msn.com on Wed, 05/28/2008 - 16:56

> After sitting for the night,I went out and it started right up.

It would be a great help if you'd include information about the engine in your XJ-S. My info here is for the '91 marelli V12 engine.

Check the resistances of the Crankshaft Position Sensor at the front of the engine and the RPM Sensor at the rear of the engine. They become heat sensitive as they age and give the symptoms you describe - runs well when cold, fails when hot.

The sensors are indentical and should have 750 ohms at any engine temperature. If one is bad, replace both since they are the same age so the other may fail soon too. About US$75 each.

Don Neff
1991 XJ-S Conv. V12 5-speed
Novi, MI, USA