i do have a 85 XJS in absolute original condition that was running flawless - until it suddenly stopped after i got it from the winter storage and was driving on the highway. Since then it might start normal and run smooth for a while - or not. if it does not start right away - it will not start even after several attempts. if it runs it accelerates normal and can be driven like it used to be. i thought that it might be the cable from the pickup coil to the ignition amplifier because the engine stopped when i wiggled it a little bit and therefore it replaced it. i also replaced the ignition amplifier (i have two identical cars and can just swap parts). the strange thing is: the engine always starts for a few seconds before it dies off again. i assume that this is due to the cold start injectors. the fuel pump is fine. the fuel filter is brand-new. i assume it is some weird electric contact failure....where should i search? should i go ahead and replace the pickup coil? better suggestions?

 

The "could be" list is pretty long.

Deteriorated/loose/brittle/corroded wires and connectors often cause problems.

Next time it's in "no start" mode check for spark. Knowing "has spark" or "does not have spark" is a good first step and will go a long way towards narrowing down the "could be" list.

Cheers
DD

 

...it has spark and the engine revs always up for a short period before it dies.

 

The could be list is shortened by one item. There is no cold start injector on your engine. Check fuel pressure and watch it as the engine dies. If it remains steady then move onto other things.

 

i think that the fuel pump preloads and shuts off and does not restart if the engine does not run but if it runs the pump is running totally normal....until it dies again. the engine does not stumble nor is the acceleration different from what it used to be before the problem occurred. i noticed today that the electric auxiliary fan stops when the engine dies but all other electric devices are fully functional - including the ignition lights etc. in the dashboard. i cleaned and reconnected all mass-connections to make sure the problem is not caused by that....no effect. i cleaned all contacts on the resistor pack without any effect. would;t it be a easy explanation if the ECU is not getting the trigger signal from the distributor trigger unit/ignition amplifier and therefore does not initiate the injection? the engine and exhaust does not smell like gasoline. however....thanks for your answer so far.

 

Mmmm, I agree with all suggested so far.

The infamous "shielded wire" from the ign amp TO the ECU is pretty high on my list.

I would bridge the fuel pump relay socket (the black one in the boot), and that will have the fuel pump working whenever the ign is ON, so be aware please. It will remove the ECU from the fuel pump control circuit.

The CTS (coolant temp sensor) in the rear section of the LH thermostat base is another pretty high up. The sensors can go flaky and the wiring INSIDE the plug is also well documented as an issue.

HOWEVER, the fact you "wiggled" the wires to the amp recently, has me pondering those wires where they actually go thru that rubber grommet in the base of the distributor, THEY BREAK, inside that grommet. A very frustrating thing to find the first time.

I would get a timing light, attach it to any convenient spark plug lead, tape the trigger in the ON position, run the engine, and note the flashes as the spark plugs fire, and when it dies and splutters to a stop, is the light still flashing???, or NO flash. You will need to be quick to see it, but it will eliminate the spark as the root cause.

Loss of 12v to the +ve terminal of the coil is another issue, and directly related to the electrical section of the ignition switch having a hissy moment, which is common now on the "older" cars.

Thats enough for now I think.

 

Good Morning.
Tank you very much.....will try the search in the order you suggested. I am a little bit upset with the car: it usually starts right up whenever I was hanging over the engine for hours to exchange a contact or something - not always easy actually - and makes you think: yeah.....I got it right! Then you drive down the road and the next thing you get is the laughs of the rest of the family after you walked home! These cars are a little bit like divas: one day grand style - next day total disaster.......but I like them.

 

...btw.: how do you tape the trigger to "on" position....the one in my car does not have the wheel with the small magnets on it. it has one that looks more like a sprocket with....i assume...a hall sensor as a pickup. all my manuals....even the original for the xjs HE....are not describing this type but the version with the small magnets. my second 85 xjs has exactly the same trigger unit - so i believe that these were factory installed and not some strange aftermarket types. both have the same resistance.

 

He means the trigger on the timing light.

 

@tfl

It would be much easier to understand your posts if you used real sentences and punctuation. I am struggling to understand what you are trying to say. Your posts look like a teenager's texting.

How about a clear concise coherent description of the complaint? Let us know what has been tested so far. Any recent work that you did prior to this? All clues are helpful.

 

Good morning,
No - there were no major repairs or exchanges of any parts done recently. As I mentioned earlier: the car is complete original with no alterations or modifications. It just reached 70000 miles and was always running flawless. I unplugged and reconnected the temperature switch(LH) a few times after the car did not start on the first try. It started after this "repair" right away and was running smooth. I drove it up and down the road a bit....no problems. I am looking forward to drive it this morning - and hope that your advice helped to fix it.
Thanks so far!
Tfl

 

OK, I have kinda worked out the goings on here.

One thing to firmly implant in your mind (DO NOT TAKE OFFENCE), is that "simple old age" is now creeping into these machines at a very fast rate.

That "fix" is a very common fix, and may last minutes/days/years, who knows, its female, do the maths.

The wires that actually attach to the plug are flimsy at BEST, and when they seperate, the engine is DEAD. The wires will be brittle inside the boot, and I would strongly suggest repairing this area at your earliest available time. Solder joints only here.

 

tfl

Thank you for the much clearer writing. Looks like maybe you cleaned a poor connection. If that seems to have fixed it you need to, as Grant said repair that wiring. You will find that just about every wire under the hood is brittle and starts to deteriorate when touched. Just be real careful and systematic when you do the repairs. Otherwise you will end up with more problems than you started with.

 

Good Morning,
The car started right up yesterday morning and driving was as smooth as it could be - thank you very much for your help.That connection and sensor would probably have been the last one I would have looked at because it is not obvious that it can actually "kill" the engine if you take a look at the ECU wiring diagram. I have to admit that I do not really understand why the engine was always revving up for a short moment during the starting process. Doesn't matter - I hope the fix buys some time to enjoy the car - although it will take a bit until it will gain my trust again: I do not like to be stranded on intersections.
Thanks for e help again!

 

well...i think i was right questioning the fix for this problem:
it started right up this morning....and then died again. the temperature probe trick did not help anymore. back to zero - i would say. btw. the cables under the hood are not looking too bad. they are not falling apart and are not "stiff". all switches etc. work as they should. i will check everything again from the fuel pump to the timing pickup. frustrating - at least.

 

No significant improvement so far: iit runs well-if it runs - and does start for a short moment of it does not. The machine manages to drive me a bit crazy: after every "repair" it starts up right away and runs great. Would be easier or figure out what is wrong if it wouldn't do that. I can't denie that I start to believe that the ECU might have an issue. I will just exchange it and see what happens.

 

While you in that area, REMOVE all those earth wires on the bolts/studs alongside the battery, CLEAN them WELL, apply some grease/whatever, and reassemble and tighten properly.

Among that lot is one of the earths for the ECU???.

 

Thanks for the hint.....but I did that as one of my first "search" actions as it seems to be a known cause for problems like my car has. However - did not help at all. Nevertheless - thanks for the help again!

 

More thoughts, a tad slow, I know.

The "main relay", the one in the RED socket may be tired. It switches the ECU ON, and the fuel pump relay ON.

Also, on the main battery +ve cable, just down a bit from the battery post, are 2 large spade connectors, protected by a plastic cover. These can loose contact, and then there is the issue of "re-plugging" them, as it is SOOOOOO easy to slide the male spade down the side of the female, instead of inside as it is meant to be. These supply 12v to the main relay, and other items that I forget at the moment.

Of course the ECU may be hissy, but that is rare in the big scheme of things, BUT, the '85 originally came with a 6CU ECU, and these were unreliable in the fuel pump "ON" circuits, and most have already swapped them out for the later 16CU units, which are significantly better, plug and play, and also process data about 5 times faster than the 6CU unit, and mine was swapped waaaay back, and is as reliable as expected.

 

.Just be aware the 16CU from a marelli is not compatible with the Lucas according to the book. Looking at the diagram there is communication between the injection and ignition ecu.