www.jec.org.uk

Hello, My jag starts first time all the time, until today.It just turns but does not start. Can anyone point me in the right direction. Thanks Phil

Sorry I should have said its a V12 6l 1993. Damm!

Irisphoto

I had exactly the same problem on my 3.6 Coupe a few years ago.

I checked the spark - OK, checked the fuel - OK, but it would NOT start.
It was the first time I had ever known where a car with a spark and fuel would not even fire!

I then suspected the crankshaft sensor........it was trailored off to my local jag specialists and it turned out "the brain" (ECU) had failed.
They fitted a secondhand unit and........... back to normal - started first time every time.

DH Dove

Duff immobiliser?

Thats sound bleak thanks mates i will look into it

How about my make shift imobiliser! on the drivers door frame is not in wrong position.

What do you mean? mrb39

Irisphoto

Not too bleak I hope - Don't despair

If it is the ECU, from memory they're about £250.00 new and about £100.00 secondhand. But my 89 3.6 had one combined ignition and fuel ECU, I believe the later cars have two, with the functions split.

Can you check yourself for spark and fuel? Basically take a plug out/ turn it over, observe and smell. If you haven't got one or the other that's a place to start.

Where do you get your car serviced - are they a Jag specialist? If all else fails can the car be trailored there by a breakdown service?

Do let us know how you are getting on, we're all here to help

pjts - would it be the immobiliser? wouldn't that stop it from cranking?

mrb39 - I had to think about that post too! , I guess you mean the accident/fuel pump cut-off switch? That could well be the culprit if it's had a knock

Irisphoto, there is a small oblong box on the passenger side (on my car) directly inboard of the A post at knee height with a hole in the top - if the button has popped up, push it back into the down position. You can remove the clip on (?) trim to get a better look at it.

DH Dove

dh,

A couple of good ideas there.

Most of the aftermarket immobilisers cut the fuel and ignition circuits but allow engine cranking. That's how mine works, and it's usually the reason why my car won't start - I've forgotten to disarm it!

PAul

Hello, Know you said it (cut off thing) I know what you mean. This sound pretty stupid be how do I check the fuel and spark. With spark do I just pull a HT lead from the Plug itself? I sort know the answer, I feel a bit thick at the moment. Thanks Phil

Hi Phil if you disconnect a plug lead and hold it with a pair of insulated pliers about 1/4 of an inch from the engine you should see a spark. The spark should be blue not yellow.
To check for fuel listen for a click from the injectors while the engine is being turned over. On the early engines it is possible to make the injectors click by turning the throttle pedestal fully open with the ignition switched on. Probably still applies to your car. report back. so it can be determined if its fuel or ignition. regards Kels

Irisphoto

Hope this warning doesn't come too late...........

If you are unfamiliar with checking the spark - either by bridging from the lead to the plug top or by removing the plug and holding it to earth...........

............Modern electronic ignition systems work at VERY high Voltages- say 30,000 volts? (I'm not too sure exactly) tho' the current is small they will give you a real belt! Enough to endanger life if you have a dodgy heart/pacemaker

If in doubt enlist experienced help

DH Dove

Thanks Mate, Im going to give it a try in the morning. Let you know how I got on. Phil

Irisphoto

OK, as long as you feel confident. Be careful that your "insulated" pliers have sufficient insulation for the voltage and do not have the insulation split at the bottom where you are holding them

BTW If you find you have a good spark but no fuel/aren't sure, try the old tried and tested method.
Take out several plugs, tip a SMALL amount of fuel down the plug holes - say 5-10cc. Replace the plugs and leads and turn the key - Be VERY careful not to crossthread the plugs, a little copperslip does no harm (don't get it near the electrodes). If it fires and tries to run you definately have a fuel problem, if it doesn't and you're sure there is a good spark it's probably the ECU or maybe crank sensor.

DH Dove

ok, thanks, I have another question for you. Can you tell me where the crank sensor is? 12 V6 1993 Cheers !