Greetings all. It may be April Fool's day, but this problem is no joke and the biggest fool so far is me! The vehicle in question is a 1996 Vanden Plas, 4.0 NA, LWB, LHD, US Spec, at 146k.

Scenario: Occasionally, perhaps after 20-30 successful starts and proper running, I get a no-start situation which simultaneously has the fuel pump quitting, all BRAKE lights not working, and reverse lights not working. That's it!

Everything else works:
OBD system is clear and fault free
Central locking, key fob, and alarm system work properly
Trunk lights and release work
Wipers, headlights, running lights, turn signals, windows, mirrors, seats all work fine
The car has a new battery, with solid connections.

After much fiddling, she will usually come back to life on her own. Fiddling means pulling and swapping the relays, disconnecting the battery, looking for bad connections or wires, testing with a test light, etc. When she decides to cooperate, the fuel pump pumps, and all the brake lights work properly, as do the reverse lights.

Tonight after arriving home, the same symptoms reappeared for the first time in two weeks. During those weeks I have been frequently testing and all was well until now, again: Key on. No sound heard from fuel pump prime. No brake lights (although there IS still the click at the shifter and the P glows red). No reverse lights. My noodle is baked!

As you may know, I also own a 96 XJ6. Great car, 145k. Two weeks ago when the symptoms appeared, I swapped the Body Processor Module between the six and VDP. Symptoms remained at VDP. XJ6 did fine with VDP's BPM. Double checked, and not the problem. I also physically checked lots of wiring and connectors. Found power supplies at the fuse boxes under the hood to be loose. Checked and cleaned all the car's main power connections. No other loose wires or grounds found. No blown fuses.

Tonight, just for fun, I swapped the Lighting control module between cars (since some function of those lights is controlled there). No change. Symptoms persist. Pulled & replaced relays, no change. Checked fuel pump cut-off switch, not tripped.

The only commonality I can come up with is that the fuel pump relay and fuse, the high mount brake light relay, and the light control module are all located in the boot wiring box. No visible or tested evidence that anything back there is amiss.

I have full service manuals on cd and a scan tool. I consider myself to be experienced with these cars. However, my willpower is waning. So here I am, open to all ideas. What do I do now, XJRengineer, Doug, etc?

A sincere THANK YOU to all who dare to involve themselves in another dreaded intermittent situation!

Cheers.

 

Wow at least im not the only one with this problem.
I found today my alternator is now dead aswell.
Have you had any charging problems?

 

Hi Triple 6, I see you are in PHX area too,

No charging problems whatsoever. I replaced my very old battery recently because it was run down by cranking, while attempting to start the car during one of these episodes. It was time for a replacement anyways, and it had to be ruled out as a contributing factor. That day in January the car got to ride home on a flatbed!

I've checked the connections at the starter and alternator too. It is strange how the car will start and run perfectly every time, usually for several weeks, before the sudden failure to restart. Also it seems more likely to happen during a hot start... but not always!

BTW, next morning she started right up like nothing happened! Still doing fine now, but will be on limited use. I don't want to be stranded again.

Maybe its an intermittent control module, like security/locking, with fuel cutoff?? But I don't think that would explain the rear lights not working.

Good luck to you, watch here for updates!

 

My latest thoughts:

I am going to focus on why the fuel pump is suddenly quitting. If I can correct that problem, the rear lights should automatically work, right?

I neglected to do a check of the fuel pump power supply last time I had the fail. I only assumed there was no voltage getting to it. Could it be that the fuel pump is intermittent?

I'm also considering swapping the ECU between the six and VDP.

I saw in the circuit diagram that the reverse lights are tied in to the corner brake lights, which explains the simultaneous failure of both (but not the cause). I suppose I should check the brake light switch, although the shift interlock still functions during the fail........

 

I sure hope someone comes up with the solution. I think this might be the cause of the sudden stalling, for about a second, that a lot of us have been having.

Come on guys with the great solutions. Chime in.

 

check the positive stud that passes current thru the firewall on the passenger side of the engine compartment next to the exhaust manifold if you can wiggle it the insulation needs to be repaired. it was the culprit of my intermentant no start

 

Thanks!

I checked and cleaned that terminal a few weeks ago. It is in good shape. I also cleaned and cleaned the terminals on the left and right, and tightened up the connections at the fuse boxes at that time. No difference... same problems. However it is always good to have tight, clean connections.

I believe I will replace the fuel pump. It sounds louder than the other car, and maybe not as smooth either. It might be intermittent. Who knows if that will make a difference, but at least it won't cost much to do.

Stay tuned.........

 

Maybe the lighting and starting issues are co-incidental but not the same. I had intermittent starting but without the lighting effects that you describe. Every time I took the car out I never knew if I was going to get home again. The car would crank but not start (due to no fuel supply). I thought it was a security issue and spent ages trying to get to the bottom of it. When it wouldn't start it could start again 5 min later or it might take hours before it would start. It would then run perfectly again for weeks. Eventually around 8 months ago in desperation I replaced the crankshaft position sensor and so far starts every time. I was dubious about doing this at first as I always had the "rev counter reading on cranking" indication when the car wouldn't start and the general advice is that this is supposed to indicate that the crankshaft position sensor is OK. Also I thought there would have been an error code if the sensor was faulty. During the many occasions when the car would not start it never once raised an error code on the diagnostics. I have since tested what would cause a no start by disconnecting some of the sensors and found only two - the crankshaft postion sensor and the ECU temperature sensor (not the temperature gauge sensor although this is close by). By the way neither of these raised an error code either when disconnected before trying to start. The technical data tells you that if the crankshaft position sensor is defective then the car can start and run as the ECU can use the camshaft position sensor signal to deduce the crankshaft position after a bit of trial and error during cranking but I didn't find that on mine - much to the amusement of onlooking bystanders it just didn't start at all no matter how much it was cranked. The sensor is not expensive and might be worth a try or as you have two cars you could swap them over and see what happens.

 

Thank you so much, Man!

Very interesting, very similar situation. Unfortunately, I have already been through the CPS swap. At first I thought it was successful, but then was disappointed a few weeks later. Glad to hear that your replacement was successful!

On Monday, the car was in "failure mode" when I first went to start it. After testing for voltage in various locations (good +v at rear relays and fuse box), I went to key off and retry to test the fuel pump voltage during the key-on prime. Of course then it worked! I drove the car three times in the last three days (round trip, no restart needed), and it started and ran perfectly. Warm-restarted just fine each time, after arriving back home.

Going to test that fuel pump voltage supply during the next failure mode!

P.S. I still get the starter 'click' intermittently (but not yesterday!!). So far I believe that to be a separate issue.

Thanks again all, for bearing with me here...........:-)

 

The Vanden Plas is doing better lately...

I tightened the single white wire at the starter terminal, which was loose. A real bear to reach. The starter is not original, and the connection apparently was not done up properly. It is the fifth loose electrical connection I've found under the hood so far. Loose connections = intermittent faults.

It has been about three weeks since, and with almost daily driving, I've had no more fuel pump issues or failures to start. I did not replace the fuel pump since I was not convinced it was the culprit.

It seems as though the ECU wants to see that circuit connected at the starter, and if not (open circuit), then no fuel pump!

However I still get the occasional click from the starter. But when that happens, the fuel pump and brake lights are still operational! The starter will engage at the 2nd or 3rd attempt.

Her future is looking brighter. Knock on polished burl walnut!!

 

Great news!

If you go and pull the blue relay out of the right side heelboard fuse bus, you will get exactly the same symptoms I was experiencing. Seems that my relay would act up every so often, even though I tested it repeatedly.

So simple, right? Yes indeed!

Yesterday, I looked at the wiring diagrams for the brake lights again, and traced the power input to the Light Control Module for the brake and reverse lights, to the RH heelboard fuse box. Also, the fuel pump relay has a fuse in that location, as does the center brake light. It didn't fully make sense at that point, but I had an idea...

I went out and pulled the RH heelboard relay. Keyed on, and the failure symptoms appeared! No fuel pump, no brake lights, no reverse lights. Everything else worked normally, as it had during the many failure incidents.

The items that failed are the only ones actually routed through that bus relay!

However, many other components are powered from that fuse box, so I had assumed that if the relay in that fuse bus was bad, none of the items powered from there would work. Incorrect! Most of the other items fed from there are powered when the key is in position 1 (or off), and are not controlled by that fuse bus relay!

Notice that the brake lights don't work if the key is at position 1 or off. Same with the fuel pump, the rear fogs, and the wiper high speed position! Other items supplied from there do work, such as the seats and windows (position 1), and the interior lights (key off).

MORAL OF THE STORY:

We should pay more attention to the relays at the five fuse locations!

I discovered that my symptoms were ultimately enough to identify the problem, once I studied certain information and understood it well enough! Persistence paid off.

THANK YOU to all who replied, contributed, and pondered on my behalf!

CASE CLOSED.

 

Great news.
Congratulations on getting to the bottom of the problem - a lesson to us all.
With the benefit of hindsight you can see the common factor :-) but these systems are so (un-necessarliy) complex it's often not obvious where to look for a problem like this in the first place.

 

Excellent sleuthing !

Cheers
DD

 

Great work! I have a similar situation, but after purchasing a new relay it seems my fuel pump is no good. With 107000 miles I'm lucky it lasted this long!

 

WOW! I've had the intermittent-starting issue in my '00 XJR, but not to the extent many of you mention. 83K on the clock, had it checked by my Jag only mechanic several times but he can't replicate it. It has started consistently now for months but on a recent trip from LA to Vegas, a hot start condition saw it crop up again. Several twists of the key in succession cleared it and it started on the third try. A beep accompanied each previous try. I had my GPS plugged into the cig lighter and I unplugged it. Voila! No starting problems since. I will remember the kick panel fuse box remedy, however, for future reference. Thanks, JagSkiGuy