I’ve been driving my xj12 occasionally for a year now and never had a problem with starting the engine even in winter conditions. I’m fairly new to the v12 and all its features, so I’d really like to hear an advice where to start looking to fix the issue I’m experiencing.

I recently washed the car, which I would be scared to do again
After a good clean it started without any problems, then drove it for a while and everything was just fine. I parked the car, returned after few minutes and the engine wouldn’t start. It cranked, but didn’t start. I managed to get it running once after a long struggle and it ran fine just as usual, but it was only once.

I opened the fuel filler cap and noticed there was some water above the little flap. I figured that more might have got to the tanks and fuel lines, so I drained both tanks, unplugged the feed line to the fuel rail and using a compressor blew the rest of fuel from the system. Indeed there was some water in the tanks, not too much though.
I then put fresh gas, changed the fuel pump, as I was having a new one anyway, but it didn’t help. Today I managed to start it once more (without air filters) and again it ran without any issues, but tried once more and again no response.

I am not sure whether water in fuel system was the reason of this behavior or just a coincidence.

Simple checks: I’ve got spark, battery fully charged, fresh fuel, it runs to the fuel rail.
However, I pulled one spark plug, and it wasn’t wet, which I believe it should be after cranking for a long time.
Could this be the injectors that were somehow broken by the water?

One more thing, I suspected air in the system so I checked the air bleed valve. Is it normal that when I took off the upper hose fuel poured out of it?


Where should I start to diagnose and fix this?

Any help would be much appreciated.

 

OOPS.

There is a stickie at the top of teh XJS section that I wrote on NO start a while back, might help a tad.

Water in the fuel is not good.

I am assuming you washed the outside of the car, and NOT the engine bay??????

Fuel filter should be changed, if you have not done so.

Then locate the EFI resistor pack, usually bolted inside the engine bay behind the RH headlamp area. Remove its multi pin plug, CLEAN it, and the resistor pack section, then CLEAN it again.

Remove the distributor cap, wipe the inside dry, it probably has some condensation inside, NOT common, but what the hell, worth a look see.

Check the carbon brush contact, dead centre inside the cap (under the centre HT post). They do burn away, fall out, generally reek havoc.

Remove the coil HT lead, and ensure the hole, and the HT lead end are clean, and NOT green with gunge.

The list is looooong, but there is a starter.

 

Thank you for your reply, I will check the thread you mention.
I washed the outside of course. I never even come close the engine bay with water, especially with old cars. The rubber gasket on the filler caps was the reason of all of this, I will definately change them.

Ht leads and distributor cap are new, I changed both when I got the car. Checked them already, everything looks fine there.

I've already ordered the filter, will change it as soon as it arrives.
I will check the resistor pack and see what happens.

What about the the air bleed valve. Should there be fuel in the upper hose? Isn't it just for vapor release?

 

OK.

Not sure on teh hose you are asking about.

The fuel enters the rail on the RH side, and then exits on the LH side via the FPR (Fuel Pressure Regulator), thr FPR thing on the RH side is NOT a pressure regulator, and can be deleted with no ill affects, they even run better without it.

Fuel is ALWAYS present in any fuel hose, either pressure side, or return side,

There is NO bleeding as such, as the system "self bleeds" by fuel circulation. The pump can and does, supply about 4 times the flow of fuel that engine will ever demand.

The top inlet of each injector has a SMALL, FINE, bucket filter screen fitted. They are trouble free, UNLESS dirt or water is ingested. Water will eventually evaporate, dirt will not, So, when its running, leave it running, bonnet shut, for at least an hour. The heat generated will boil away any stray water in these pockets, and that running will also circulate a good amount of fresh fuel to all thr components.

Each FPR unit has a small vac hose in the end. If fuel is present in either small vac hose, that related FPR is toast. As I said, the RH can be deleted, but the LH is the actual pressure regulator, and the RH and LH are different and NOT interchangeable.

 

A non-start situation in a V12 really has only a small number of causes: assuming that the fuel pump is functioning properly the list of suspects is the following, roughly in order of suspicion
1) the GM module inside the ignition amplifier (on top of the manifold) - this is especially to be suspected if cold starts are normal but warm/hot starts are difficult or impossible. This sounds like the situation in your car. 2) if the car will not start at all, suspect that rodents have damaged the pink wire found in the V of the engine, under the cruise control bellows. The rodents LOVE this wire. 3) the coils if there are two - with one on the radiator rail; the very late V12 (up to 1992) had only one coil and some earlier cars have been converted to the single coil form. The single coil tends to develop cracks on the underside (unseen, therefore) which allow resin to escape. The coil eventually fails. Again, a problem with hot starting is an early indicator. 4) occasionally the pickup inside the distributor becomes faulty - rare but it does happen because it happened on on 1992 of mine. 5) finally, there is a shielded wire running from the ignition amplifier to the ECU; inside there is a wire whose coating often cracks permitting grounding. When this happens, the engine will not fire (see photo)
If the fuel pump fails to run, the two principal suspects are the silver-topped Bosch relays on the radiator rail (see photo - upper centre) - beside the red cylindrical fan relay (this is assuming that the car has the original relays). One of these is the pump relay proper, and the other - which looks identical but has different circuitry and a red diagonal slash on top, is the "main" relay - and this relay powers the pump relay in turn. If either of these are defective, the engine will not fire.

 

Thank you so much for all the advice, I begin to understand this engine a bit more.
I will check all the vital components this weekend and gladly report to you the effects of my attempts.

 

 

Good, the Bugga.

Establishing what goes AWOL when it dies, is critical here.

Some of the common are:

On the rear section of the LH thermostat housing is a Temp Sensor, with a 2 pin plug on top. This is the Temp Sensor for the Injection system, and is the PRIME signal for running. Example: running V12, unplug that sensor, dead V12.

The sensors are OLD, and should be replaced, easily obtained, used on many EFI cars, and a Bosch part. I ahve the Australian Bosch number somewhere on file if its needed.

The wires inside that plug, and about 6" up the loom do fracture, again, age related.

Unplug that sensor, take a paper clip, shape it to suit, and bridge the 2 terminals IN the loom plug. This will "trick" the ECU into thinking the engine is AT operating temp, and if that stops the stalling, then the Sensor is toast.

The EFI resistor pack terminal clean, mentioned before, MUST be ticked off the list.

INSIDE the Ign AMP is a small metal cylinder in one corner, secured to the casing with a single PK screw, REMOVE it and trash it. It is a noise suppressor, and age now has them "leaking" to earth as they heat up, and killing the SPARK.

Thats some ideas until you can identify it its Spark, Fuel, Injector Pulse, thats drops out and kills the beast.

 

substitute the ignition switch, if you don't know its history.