A little bit of backstory...

I drive a 2001 S-Type 4.0, about 127k miles on it at this moment. Everytime I've started the jag, it usually misfires lightly for a few minutes but always quits after the engine warms up (I always wait for it to stop shaking the car before driving). I say "misfires lightly" because the RPMs don't bounce much, and when I had an ignition coil go bad a year ago, the misfiring was worse...just putting that into perspective.

Anyways, about a week ago I took it to go out to eat. Got back in the car, and when it started, it was misfiring extremely rough. As in, the RPMs were bouncing b/w say 450 and 1000 at idle and whenever the RPMs fell to the low side, the low battery light would briefly flicker on. This continued for a few seconds, shaking the hell out of the car before the RPMs fell too low and the engine stopped. The jag doesn't start, and my buddy's OBD2 scanner shows no codes, no check engine light, nothing.

I suspected this would be something like a bad crank or camshaft sensor that caused the misfiring, but this shouldn't prevent the car from starting. So I'm at a complete loss on what the issue could be. Have any of you guys experienced something similar and/or have any advice on what the issue could be?

Thanks,
Austin

 

Austin,

Ever change the tensioners, timing chains? If not your engine may be done.

Read up on the 4.0 tensioners - lots of threads on it.

Good luck

 

Wouldn’t there be horrendous crashing noises with a timing chain failure and pistons meeting valves?

 

Connect a fuel pressure tester to the schraeder valve on the fuel rail and see if there is any fuel pressure. The fuel system specifications are shown above. If there is sufficient fuel pressure, remove the coil units and check for oil in the spark plug wells and on the coil units as they may be shorted.

It is also possible that one of the secondary timing chain tensioners has failed and an exhaust cam has jumped two teeth. Do you hear a rattling sound whilst starting the engine when cold?

 

I don't currently have a fuel pressure tester on hand, but I'll try to see if I can't get my hands on one soon. In the meantime, I'll check out the coils.

I'm unable to get the car to start; however, it does crank when I try to tart it. I don't hear any sort of rattling sounds while cranking it

Thanks

 

Not necessarily Karl

 

Turn the ignition key to run. Listen in the rear passenger side for a whoosh sound. (That's the fuel pump priming)

If you hear that find the Schrader valve. Stick some towels there after turning ignition on to run stick a small screwdriver in, while wrapping cloths around. You should get a strong pulse of fuel. (Fuel pressure gauge would be better)

If you get a dribble or worse yet nothing your fuel pump is suspect. Check fuses, etc.

 

Sorry I haven't been keeping up with my progress, but I have since fixed the issue. I thought I would include what I did on the off chance that someone else has the same issue. I would like to thank NBCat for the suggestion to check the fuel system.

I had found a while back that there was no fuel pressure on the fuel lines (from pressing on the schrader valve near the engine), I attempted swapping a relay to check if that would potentially fix anything - no dice, and the fuel pump fuse wasn't blown either. A week or so later i turned the car on again (I wasn't attempting to crank it), and I heard a loud pop, which was the fuel pump fuse. I suppose that at some point after the fuel pump failed, it became internally shorted. I purchased a new fuel pump assembly (delphi brand i think) and installed it, and she started right up.

Thanks for the help guys!

Austin

 

Austin-

Thanks for coming back to give us a update on your issue. From my short time here I can tell you that is not as common as it should be.