www.jec.org.uk

not sure where to put this but the title is self explanatory

one of my manual 300 XJR's fails to crank 9 times out 10, and will lay dormant now for days on end before inexplicably springing into life at the turn of the key. The dash pack lights up as it should with the ignition on EXCEPT the check engine light will extinguish when it should stay ON. I am told this is an indication of an ECU fault, however three known to be good ECU's from other cars have been tried and the same result. Today I have swapped out the security module and exciter, wrapped my key in foil to blank the transponder off, then with the matched key off the other set of modules strapped to my key tried to crank the car, nothing. To prove a point I did the same test with my modules in another car and we got a crank and fire first turn. My ECU also runs other cars

I now have a limpet of an XJR stuck outside annoying the neighbours and in the way

Any ideas or thoughts most welcome, but not the gallon of unleaded and a box of Swan Vesta my local garage suggested earlier today

Poor connections on starter solenoid, Rob?

I often see this type of fault on boats which have been dormant for a while and the engine which lives in damp conditions grows a nice layer of corrosion on various electrical connector/contact points.

Worth perhaps crawling underneath and checking those points as well as other high loads connections generally.

Only wish I could come up and help......

Mike

make sure the engine ground wire is in good condition , corrosion can get between the strands causing high resistance , preventing the engine from turning over , it may even be broken ??

just a thought

BB

Have you got a code reader to try on it, just in case. to rule that out?

I guess you could try connect 12v directly to the starter?

not sure of the significance of the CEL not being on when it should.

Rob,

Don't know if this is any help (because you know more than me!):

I had a problem with an XJS (many moons ago) that had a dodgy earth strap (block to bodywork) and it turned out that I'd shorted out the crank sensor - but it earthed (to the cylinder head, near the front /l/h area) through one of the small wires that went round the block to the sensor (from memory).

There was no sign of insulation damage, but you could see that a 'flash' mark on the cylinder head, where the weakest point must have been.

The significance of the CEL staying on is that the ECU, security module and body processor have given a "permission to crank" signal

if the solenoid was bad at the starter, the lights would dim showing a drain, this is not the case

however after a long conversation with our Mr Marks tonight, he on the wiring diagrams and me nodding like I know what he is on about, we have found a wiring link between the ECU/Body processor and CEL

so tomorrow, job 1 swap out body processor, job 2, pull centre console and look for a chaffed wire behind radio which is where this link runs into a 48 pin connector

wish me luck, will report back

HI Rob,
Hopefully the wiring diagram that I gave you at Western day will have been of some help. Good luck getting the car started.

Let me know if I can be of any further help.

just an update, car has now gone to XJK in Stoke courtesy of the RAC as it has baffled every one, Andy, XJK have the wiring diagram too

well, looks like we may have success, XJK spent four days on the car, they too could not get a check engine light to stay on with ignition on, this is the signal that the ECU has "permission" to crank. It was discovered that the ECU had no power so was not switching on and hence no signal to crank, hence no check engine light

Now to find out why

Ian Kelsall, essentially went through the car checking all power and grounds, and found a dodgy connection on the inertia switch, this has been remade and the car has been fine since, it is still with them for an extended test period just to be sure

All I have to do now is work out why my other manual car will not even energise the dash pack!, oh and work out the "vehicle too low" on a devil juice 350, not sure if that will get done before or after I look at a 350 Super 8 with the dreaded "restricted performance"!!! such fun on a wet November Sunday

better than wallpapering and building wardrobes,...............







keep at it

BB

It was wet n wild weather wise yesterday, but still somehow managed to wash the XJ40 in between downpours and fit the CD unit. At the risk of complete thread derailing (sorry!) I will share a slightly amusing story about the latter fitting.

As some will know, the XJ40 CD brackets are somewhat unusual and unique. After much phaffing around I found it much easier to actually climb into the large boot to gain better access to fit the rear screws whilst supporting the CD unit with the other hand. It started to spit with rain so my well-meaning partner looked out of the kitchen window and just saw the Xj40 with its boot open (you can see where this is going - right?). Anyway the next thing I know is that the boot lid is coming down on me whilst I'm still in it!!! Fortunately my cries for help (or rather my WTF exclamation!) were heard and I was released within moments. So my top tip - if you are in your boot for whatever reason, make sure you have a mobile phone or have told someone!

Ta, Rich

Love it, been there when checking for leaks in the boot of a 40

Glutton for punishment Rob. Most would say one jag has more than enough "challenges", then times that by infinity and beyond.

yesssssss, its back!!!, K44 XJR the black stealth bomber is back at The Towers, after a recovery by the RAC to XJK in Stoke two weeks ago, four days of investigation of the wiring by Ian Kelsall, found a poor connection on the inertia switch which was failing and shutting the power off to the ECU, the connections were all remade, car serviced and collected on Monday, the run home across the magnificent and deserted A7 was a blast, these 300 R's where you have to move a stick thing and a third pedal are down right awesome on a road like this, no silly unwanted up and down shifts, perfect power control and an endless supply of torque and power. Thanks again XJK