I am currently trying to sort out the Starting/Ignition system on a 1988 XJS V12. It turns over freely but it seems like it isn't going fast enough for it to actually fire up. I am starting to think that there must be a boost coil for the starter to fire up the 12 cylinder beast! Is there anything I am missing or should know ?

 

Assuming a fully charged battery the first thing you should do to address slow cranking is ensure that the battery cables are clean and tight, the main grounds are clean and tight, and the "+" voltage junction posts on the firewall are clean and tight. If the battery is good and all the connections are OK then your starter itself might be ready to give up the ghost


No, there isn't.

Cheers
DD

 

Do what Doug has suggested, then do it again, as there are so many +ve and -ve (EARTH) connections to check through.

Take a voltmeter, probe the +ve terminal of the coil, turn ON the Ign, note the volts, should be close to battery volts. NOW, crank the engine, observe the voltage reading as its cranking, should not drop any more than 1V. My reasoning, is that maybe?? the electrical section of the Ignition Switch is way past needing a clean out.

The MAIN earth straps, yes there are 2, are at the LH engine mount area. One is engine to cradle, the second is cradle to chassis, they break, are missing, get tired, and then what you have happening is guaranteed.

Test for spark. Unplug any easy plug lead AT the spark plug, attach ANY old spark plug in the end of that lead, and earth the spark plug anywhere it basically lands, and crank that engine, You are looking for a FAT BLUE CRACKER of a spark, NO GOT that, NO GOT start of that engine, simple.

Read my sticky at the top re "no start.........". If there is more you need, ask, please, we will all help.

These are simple engines and system, neglect, and age is now at your front door, and once sorted, more reliable than a Toyota.

 

Hi

Minor hi-jacking of thread: How long are these ground cables approximately ? I want to go shopping before going under the car, i.e. on my way home from the office...

I remember my ground cables at the engine/front cross member to be in bad condition, and I'm not even sure both were present when I re-installed front cross member. My car runs well, so I thought it could just be fixed at a later point.
This thread made me think that may be now. I have a car that actually spins the engine well when starting, but it does not exactly start at first turn, and it sounds like this could be at least part of the reason. I also think I have leaking pressure regulator or fuel pump check valve as priming does help

 

Leo,

Memory, HAHAHA, about 8" each.

I remove them, and go for an eye to eye Battery Spec cable from a sump bolt to the V mount chassis bolt, one each side.memory agin, they are about 14" long, and maybe too long, but stretching them to fit, and clear exhausts etc, is a no no.

 

Sounds like a good way to do it, and redundancy is always good. Thanks for a fast reply !

 

Like this . LH side shown, RH still pending...

 

I had the same issue with my 91. Ran a ground from the engine to the frame. Solved the problem.

 

Than you Sir, Sorry for the delay in responding. Makes sense that the grounds could be the issue and when I inspected them on teh weekend they were all in rough shape. Battery is in decent shape but the rodent population had a little field day with the wires under the bonnet!

 

Well found.

SIMPLE cars these V12's, only made complicated by overthinking.

Have a Beer, you earned it.

 

Just found this tip from one of the Jaguar Enthusiasts Club Technical Advisors. Seems a really good tip and not one I'd heard before! In summary:

Take a voltmeter and set scale to 20V DC
Attach one probe to engine or cylinder head and one probe to the car body / chassis / battery negative terminal
Get someone to churn the starter whilst you monitor the voltmeter
If you get a reading of over 0.5 V then you have an earth leak

As we know, it's easier to run a second or even third earth strap than to try and work out the leak.

Cheers

Paul

 

Here is a update on the '88 . Have spark, and fuel to the injector rails but nothing past the injectors. The Lucas box was fried and we had to jerry rig it to make it work. the spark is weak and we have great compression indicating 150psi with a not a great seal on the tester. I am truly in need of a hard copy manual. The main issue I think that is since it was stored over the winter at a storage yard near a farm the field mice got to many of the wires. already found a few that have been repaired.

Thank you all for your time. and so sorry for the delay in updating everyone. Within the last week was the first real time I have been able to spend working on the big kitty and I am starting to make progress for it to fire!

 

OOPS.

A couple of things,a nd its after Midnight here.

1) The shielded wire from the AB14 Ign Amp is NOT sending a pulse to pin #18 of the ECU, hence NO Injector activity.
2) The weak spark is NOT good, as that engine needs a FAT BLUE CRACK of a spark to even get even a fart out of it.
3) The mice have eaten the EFI loom, that's the one in the bottom of the V, AKA Death Valley. That loom is 98% the cause of HE running issues from age alone without the rodents.
4) Have a read of my sticky at the top "No start of a HE......."
5) Drink beer and contemplate anything but the V12.

 

The EFI loom is our thinking as well ad that is what is mhat my next job will be after I get some front tires for it. Its just around noon hour here and beer o'clock is coming later on!