Yes, I agree that a poor connection at this location is a source of no start. I would also like to say a big THANK YOU to everyone for the info!!

 

@ Gus, it did it for me, and it sounds like it did it for lazyj. This area was definitely the culprit, obvious when I looked at the state of the connections and the car's reaction after cleaning them up. Just hope people find this as a fix in the future. An intermittent electrical fault can drive anyone to distraction, I bet even the IDS couldn't find it.

 

Here's an update - feeling no love from the XJ today...

I was just thinking this morning when I was in the shower that I should post an update to let you all know that re-seating the relays in the engine compartment solved the problem since we have had no more starting problems with the car since. Of course, when I went to start the car this morning the problem has returned... Grrrrrr...

I tried re-seating all the relays again - no joy. Checked the power connector going into the relay compartment - perfect. Checked voltage again - perfect. And yet, the starter solenoid gets full voltage for about 1/2 second and then drops to 0v preventing the engagement of the starter motor.

One thing I had noticed before when the problem was occuring is that the little red light on the shifter assembly flashes on then off at the same instant I get the "click" from the solenoid. Unfortunately I have not noticed if that light lights up at all when the car is starting. I'm sure it will start fine this afternoon when I get home from work (because that's when I'll actually have time to diagnose the problem some more of course) so I'll check that light then.

 

Jerry,
I thought I would throw this in. I had a similar problem, though my car would not even click and it was intermittant, maybe 3 times a month, but very inconvenient. Like I say, no click, but dash lights came on. My battery is practically new. I figured it had to be a battery problem or ground, so I cleaned and lubed every stinking ground and post, and still had this intermittant no start, but I could get it to start if I screwed around with the battery posts. So, last time it happened, I almost burned the cr@p out of myself when I touched the ground (neg) post. So, I research a little and found that people had had problems with the braided ground strap and solved it by either replacing the ground strap, or soldering the crimped ends to the braided cable. Long story short (too late now), I took option 2 and did some soldering, and have not had the issue since.

 

Well, sorry it's been so long getting back to this, I gave up trying to diagnose the problem during the cold weather here and just ran a jumper wire from the output leg of the Starter Relay out of the false firewall so I could jump it to the Battery Terminal there. The car always starts fine when turning the key to on and manually jumping the starter solenoid.

Finally about 2 weeks ago on a tip I got from somebody that read this thread and emailed me I decided to go ahead and replace the batter with a new one. This even with a charging system and battery test checking out fine but I was at my wits end.

Magically with a brand new batter not only did the car start on it's own (without jumping the solenoid) but also all of the stupid warnings the car had been throwing intermittently went away. (Low coolant warning when the coolant level is fine, intermittent ABS errors, intermittent traction control error, and a number of other warnings that would display on the panel).

The car was perfect for 2 weeks, no starting problems, no weird warnings, no check engine light, just perfect. Then out of the blue one morning it cranks but won't start, not even a thought of starting. I haven't gotten too far into yet but starting fluid does not even give it a jump so I'm guessing a spark problem, will check that tomorrow...

The weird thing is that the engine sounds "strange" when cranking. Now I have to admit that I have never heard this (or any other Jag engine) turn over for a while without starting before and it does turn over smoothly, it just sounds "off". Can't really describe why, it just does.

Anyway, I'll post back when I figure anything else out new.

 

I think it has already been addressed, but hairline cracks on the fuse block boards can cause all kind of nightmare problems. I have had this happen with a car I had several years back. Countless hours and dollars spent trying to diagnose the problem, and then it turned out to be a small crack in a trace on the pc board. Intermittent electrical problems are sometimes the worst. Best of luck getting to a solid bottom on your problem

 

Swapped all the relays around, made no difference.

Spraying carb cleaner down the throttle body makes no difference.

If I manually hold the throttle plate in the throttle body open while leaving the accelerator at the idle position it tries to start, kicks here and there but still will not start.

If cranked with the throttle all the way (accelerator all the way to the floor) it tries really really hard to start, right on the virge but just won't quite do it.

This seems to me like it's rich, almost like a flooded condition but if it were just flooded it would have kicked over when right on the virge of starting so many times.

Any ideas? Injection system feeding too much fuel?

I would think that a single cylinder (leaking injector or something) would completely prevent it from starting, just make it hard starting and make it run too rich on one bank.

 

Probably way too late for you, but the symptom is suggestive of a dirty throttle body where the plate is sticking closed.