For the first time since I bought her, my XJ-S won't start.

Cold (drove last week, no issues), starter cranks like a champ but the engine won't even start to catch. I'm assuming it's either not getting fuel or spark but I'm not sure which.

It's probably beyond me to fix but can anyone give me some ideas of what to check to narrow things down a bit?

1989 model year but with a Lucas CEI distributor- think: '88 but with ABS.

Thanks in advance,
Rhett

 

I always check spark first. Pull the coil wire from the distributor, and place the end close to something metal, and reach in a spin it over. If you have a constant blue/white spark, its not your ignition. Put that wire back in, and pull one of the plug wires. Put a phillips screwdriver in the wire, and do the same spin over. If you get a spark to the plug wire, most likely not the rotor or cap. Then things get a little tricky. You should hear the fuel pump run for a few seconds when you first turn the switch on. If you don't, then you have to start investigating why. If you do hear it, I check fuel pressure. That requires some tools, gauge. You need at least about 30-35lbs of fuel pressure to run. If you are decent with a digital volt meter, I can put you on a couple of other things, but check your fire first to see if your ignition is any good.

 

Make sure the coolant temp sensor that goes to the ECU didn't become unplugged. It's the sensor on the left front coolant manifold. If it's unplugged, the engine will crank but not start.

Thanks,

John
1987 XJ-S V12
63,000 miles

 

I would also check the inertia switch.

It may have tripped, or is having a Lucas moment.

It does/will cut the fuel pump circuit.

 

Toggled the inertia switch but no change. Put the old smart phone in the trunk and turned the key and it sounds like the pump is running.

 

Have you tried jump starting off another battery?
I've had 5 XJS's and only one failed to start one day (strangely enough the youngest one).
The battery was using all the juice to turn the engine over so there was nothing left for all the electronics.
Because the engine did not fire first time it basically flooded so there was no chance of it lighting up.
As I vaguely recall you basically have to purge it and start again.
Turn it over to make sure that there is fresh fuel in there.
Pull the inertia switch up to disconnect the fuel pump (much easier than fannying around trying to find fuses).
Crank the engine for 10 turns.
Go away, make coffee, invade another country or whatever and leave it alone for at least 30 minutes.
Push the inertia switch back down and go for launch.
It should fire within 3 or 4 turns (don't touch the throttle pedal at any time, let all the bits breathe and do their own thing).
It worked for me and I got that from this forum.

 

Hilarious!

I'll give it a try.

 

Maaaaaate, rule #1 of V12 ownership

THE MOST WARPED SENSE OF HUMOUR YOU CAN MUSTER.

Failure of that will have you drink more JD than me, and they simply dont make that much of the stuff, HAHA.

Another little assist to start on some of mine has been to turn ON the ignition (NO start position, just ON), press the gas pedal, you "should" hear the injectors fire (click. click, click) as the pedal is pressed. If you do, good, you are getting a pulse of sorts, and also giving a squirt of fuel from the injectors.

DOWNSIDE, if as mentioned above, the engine is in fact flooded, you just made it worse, so drink something, toss a coin, eat a meat pie, make a decision. One of mine simply was a mongrel to start after a heat soak shut down, and a quick stab of the gas pedal before going to the start position fixed that issue every time.

 

Be Buggard! Never heard of that before on any car, just goes to show you learn something new every day. Must try that on mine, will make one hell of a backfire when it starts.

I was going to say if you have fuel and spark it should fire but hell what a way to see if your wiring to your injectors are working, big two thumbs up on this one. I've found the biggest trouble with these cars is the wiring, especially the injector harness, if its anything like mine it only belongs in one place the A.C.T Landfill, that's where mine now lives permanently. I just rewired the darn thing and get rid of that two coil system on the Lucas ignition, go with the new single coil.
Good Luck

 

The PreHE and the HE all have that feature.

No idea why, I found it by accideant a very long time ago.

One of my PreHE was a fair bugga to start cold, and by simply pumping the gas pedal once after the prime cycle, amd then going to "start" had it fire almost instantly.

The HE got hissy in 46c temps after a short shutdown, so I instinctively did the same, and fire it did.

My initial thoughts was that this was going to save that Lucas starter motor significantly.

My other thoughts is that it also indicates that the TPS (HE), Throttle Switch (PreHE) are actually talking to the fuel ECU. It proves little else as far as I can figure.

Backfires are generally EFI loom issues, which we all know are now sooooooo unreliable.

 

My 1994 XJS (6-cyl) does the same thing occasionally. Starter turns okay, the fuel pump runs and everything is doing it's thing. But, I wasn't getting any sparks from the ignition coil. Replaced coil, distributor cap, ignition amp, flywheel sensor.Turned out to be the fuse (F7) for the ECU.
Fuse F7 on the fuse panel passenger side under the dash.
Don't know if it is the same for the V12.
10 Amp fuse.
Most fuses blow and have big gap you can see most of the time.
But these had really tiny gaps. An ohm meter detected the first
and 2nd ones that blew.
The third time it was visibly open.
I carry a couple of 10A fuses now. My wife knows which one to replace now.
No more "Honey, I'm stuck at the parking lot again. The car won't start!"
Now it is, " I replaced the *#%^ fuse today! When are you going to fix it for good?"
One day I'll find why that fuse is blowing.
I think it may be a Ignition amp module.

 

Stupid question but I've read that you can fry the ECU if you don't jump the car properly: is there a preferred grounding point for the negative jumper cable? Or some similarly obvious yet not immediately apparent dark magic?

 

Never had a problem jump starting an older car but not sure about modern stuff.
At the end of the day if you are jumping off one car then its battery terminals are just a connection point between the alternator on the jumper car and your battery so it shouldn't be a problem.
I think?

 

Sorry, but still confused. On the XJ-S: hot cable to + on battery, cold cable to ...? Trunk/boot latch? Negative post on battery? Some other ground point?

Growing up, I always used the negative post on the battery but I was told that will fry the ECU on the XJ-S. Sorry to be daft but it seems like every small step that would be a no-brainer on a regular car has special rules on the XJ-S

 

I always used the negative post on the battery with my XJS. Never fried anything.

'Tis getting the polarity crossed that you have to be extra cautious about

Cheers
DD

 

Thanks for that. I followed the steps outlined above and while invading a small country was in fact deeply satisfying, the car still won't start.

 

Have you tried this approach?

 

Getting there. Had the car towed to the shop where it started without hesitation. :-/

Beyond the frustration, I am thinking that points towards an electrical connection problem of some kind and away from a fuel delivery problem. Thoughts?

 

Be Buggard!
Ok you have bought it down to an electrical problem! My thinking now is this is going to be mighty hard to knuckle down, I believe it's simply a loose connection, I would personally would start with the earth wires, rusty loose or simply corroded and badly crimped or burnt out more than likely, what works well is you can buy a $3.00 light tester test circuits this can test either earth or active cables. Auto Circuit Tester 6V 12V 24 Volts Voltage Gauge CAR Test Voltmeter Light Bulb | eBay
If I had to start I would start from distributor/coil cables then work back from there. If Ok, look at the wiring in the boot, they normally rust out there on the earth side, if still no luck just start chasing cables to see if you can come across it. I realise its vague but it could be in so many places.
I would just simply try to narrow it down by cleaning every connection and check it, then place a piece of tape around them so you don't double back, just keep going your bound to find it.
Good luck

 

My money is on a low-tension problem. I suggest you renew all the connectors to the coil and take it from there.

Greg