My 1992 xj6 runs like 10 minutes,- then dies. When that happens fuel pressure drops, very erratic, put a fuel gauge on the fuel pumps up to 42 psi & drops, when cranking, after a few seconds shoots up immediately to 42 and drops after a few seconds,- repeats itself- basically no fuel when cranking.
Also when this happens,- checking spark ( pulled a wire and grounded it to see whats going on) the spark is erratic
some times none, sometimes weak white, some times good bright blue spark, it will be consistent but at times "erratic".- Let it sit for a while and cool, will start and run fine for a while... Can anyone tell me where to start looking? Anybody have any ideas-Thanks-Jimmy

 

Hi Jimmy,

Welcome to the Jaguar Forums! It's great to have you with us!

Your symptoms are definitely curious. My first question is not meant to be offensive, but how long has it been since the engine had a good tune-up (plugs, wires, distributor cap & rotor, air & fuel filters, gunk cleaned from the air intake plumbing, idle air control valve (IACV) cleaned, throttle position sensor (TPS) cleaned, electrical connectors and ground points in the engine bay cleaned including the engine ground strap, checked your drive belts, etc.)?

A few other possible contributors come to mind:

1. Low battery voltage can cause all manner of difficult-to-diagnose gremlins. How healthy is your battery?

2. The crankshaft position sensor (CPS) can cause weird misbehavior when it begins to fail. When its signal becomes erratic, often when the sensor gets hot, the engine control module (ECM) will have no timing reference so it will discontinue spark. Many Jag owners have learned to replace their CPS and keep the old one in the trunk/boot as an emergency spare.

3. Could your fuel pump or fuel pump relay be failing intermittently? If your fuel pump relay is the standard "ice cube" size, you can temporarily swap one of the less-important relays (radio, horn, etc.) for it to see if things improve.

4. If the fuel pump is failing and the fuel pressure regulator and/or fuel check valve have failed, the pump may not be able to maintain adequate fuel pressure.

5. Stalling after 10 minutes could indicate a clogged catalytic converter - the engine runs fine until backpressure builds up and stalls the engine.

I'm sure there are other possibilities - it's late here and my brain is tired, but hopefully others will offer additional suggestions.

Cheers,

Don

 

Thanks Don...I'm in the process of running down the checklist now, The car was bought from a car hauling firm, lots of things toasted...Lighting module,- body module,- ign. amp,- seat belt issuesalmost all fuses. It's the shops daily driver now.
My body shop's mechanic has over the last 30,000 miles has yes- done belts-filters-oil changes-and a gasket or 2....
Pretty much trouble free for over 30,000 miles, car had 91 or 92,- now is like 127,000 it needs all that.
The throttle pos. switch tests out ok, What is a good way to clean out one of those?? car did have a 17 code but ran fine.
The cps wasn't sending a tach signal ( the 200 rpm deal) so I pulled one from another car(a good runner-it was in the yard) started and ran good for a couple miles...same thing...cools off - runs great! The battery voltage dosen't drop below10.9 or 10.8 when this is going on. Batt is good almost new. Now the grounds were all nasty, I do not think have ever been touched unless while something else was getting fixed...I'm picking away at it... So thanks again Don-Jimmy