I drive my 1990 xjs at least once a week and never had a starting problem till now.
Turned the ignition and motor spin did not feel or sound right, not as fast as usual, so I thought low battery, battery charger not working.

I took the 900 cranking amp battery out of my Mercedes, that I know is fully charged because I backed it out of garage and drove it over to my other garage that the xjs is in.
Installed the 900 amp battery in the xjs, turned ignition and still does not seem to spin as fast as usual and still no start. I bought a new charger and Mercedes battery read 100% charged,
The xjs battery read 42% charged.
Does not sound like starter drag.
Before I start mucking around thought I would ask for members help that have much more knowledge than I have.
Thank you for any advise.

 

Does it change if you prime the fuel rail (key on pump buzzing) like 4-5 times?

 

no, i drove the car 2 days ago no problems, parked in garage, now wont start. motor does not spin as fast as usual.

 

Start checking grounds would be the first recommendation, make sure the engine has a decent ground particularly. There could be a break or disconnect that occured whilst driving that wouldn't impact much but a starter pulls a lot of amps, I believe that the V12 will in some cases use the accelerator cable as a ground but that may not be beefy enough to get things going , if a battery with a 900 CCA rating is the same as a discharged then my money is on grounding.

 

Also if youv fiddled with batteries make sure that + cable is pushed together theres a inline split and socket about 8 inches back from the cable end. It may just be coming loose.

Thats of course assumong your car is still sporting that stupid plug in 96'

 

Thanks I will check cable, 1990 XJS convertible

 

I just read-------Grant Francis Sticky No start of a HE V12.
I think maybe a little above my know how.
I guess first see if it is getting fire to plugs, if so then check fuel delivery,
If not getting fire, I don't know what to look for.

All help is welcome.

 

I will run jumper cables from engine to frame.

 

Is a pin out table the same as a fuse box ?

 

OK,

Its what is known as a Mareli car, just to keep on track.

The fact you drove it 2 days and all was well, it will be something simple I reckon.

Some of this may sound STUPID, but I am NOT going there:

It has fuel in the tank?
The fuel pump "whirs" for about 2 seconds when the key is switch to Ign ON (Position 2 in some languages)?
That covers the "bang juice" basically,

The lack of rotation speed:
Alongside that battery is the MAIN EARTH connection, and a 2nd stud with other earth cables attached. Make sure they are A) CLEAN, B) Tight. dont just look at them, undo them, clean them, refit with a smear of grease, and tighten accordingly.
Check the +ve battery cable, ensure it is secure at that silly junction just downstream from the battery end. ALSO, the 2 wires that plug into the spade connectors under that plastic cover. They have a habit of coming loose on those spades, and sometimes, falling out when battery fiddling takes place. Fitting a charger, etc etc.
The 42% battery is not good, but the Merc monster, and nothing changes, oops. That is where I head for EARTHS, as mentioned already a few times. The engine earth fiasco is fickle on a good day. Attaching a jumper cable, engine to chassis is the quickest by-pass.

I am still in the "used it 2 days ago, all OK, now its NOT OK" thought track. No need to re-invent the wheel at this stage of the issue.

Just for the hell of it, and it worked once on the X300, and the Black S Type. I used the foib, locked the car, and then unlocked again, and they started straight up, so I was informed that RARELY the Immobiliser has a hissy and does not "release" then car, NO idea on a 1990 XJS, if your market has such a thing, BUT, its pretty simple to lock/unlock and give it a shot.

If the car has an aftermarket system, they are reknown for reeking havoc, just saying.

 

Thanks Grant, Battery post and cables are clean and tight, I will check the cable plug connectors and put jumper cables engine to frame. The fob is a jaguar fob, I did the lock unlock several times the other day.
A week and half ago I filled up 91 octain 100% gas and has about a half tank gas now. I have owned 10 years now and always 91- 100% gas. In the ten years never had a starting problem.
I have a profound hearing loss so will have Wife to listen for fuel pump.
I did read and print your write up on ( no start ) and when it gets to electrical, kinda confusing for me.

 

Good, good, good.

Me with one eye, and one leg, we will sort this critter.

I am maintaining the "slower spinning" as the root cause of the no start, something is "robbing" voltage, and Earths are #1 on any car.

One step at a time, electrics are not hard, as long as you take it slow and work systematically. Once the "slow spin" is sorted, we can move on if need be, to the next suspect.

 

This is not easy to look at; but I think it is important to check the positive thick lead from the starter motor to the firewall post. The car has to be in the air to do this easily. It is not unknown for the positive lead where it attaches to the starter motor to become dirty or oil saturated and make bad contact; particularly as the lead from the alternator is siamesed with it.

Secondly, I would run a dedicated extra earth strap from the motor direct to a bright-metal earth on the frame rail.

Thirdly, if not already done, I would examine the point, alongside the RHS of the battery tray, accessible by removing the cover over the relays etc, where the battery earth strap actually earths to the frame. These often corrode and have the same effect as a poor negative battery post connection. Again, clean the strap and the frame attachment point to bright metal, attach the strap and spray some grease over the area.

 

Looking at all the pictures I've taken of mine I can't see any kind of earth / ground strap from the engine to the frame - seems odd - there has to be one somewhere, if you don't get a good ground on any aluminium block then galvani corrosion is 100% guaranteed especially within the cooling system - I'll be hunting for mine again come weekend. If I don't find one I'll be following Gregs 'secondly' myself - probably a strap from the top of the engine mount to 'somewhere' to be decided. Don't earth to the front subframe that the engine sits on as it is pretty well isolated by rubber mounts.

 

If I knew how to post, I would take video of engine spin with sound.
Im thinking, starter drag would cause slow spin and voltage drop, will get Wife listen to starter and fuel pump.

 

I made some ramps awhile back that sets the car 2 feet off the ground but no way to get it on the ramps.
I will check battery ground.
Thanks Greg

 

Let me know where you attach to frame, for now will use jumper cables.

 

Today I have to mow our acreage and do some tree limb clean up, tomorrow, mow Dad's yard.
Will give me time to mellow out and come back fresh.

 

Worst case find a way to get a good ground between the engine to the chassis too - just a temp solution - that will either prove or disprove the engine grounding as an item - a jumper cable from one ot the engine lift points (pretty robust looking brackets)

Maybe the locations ringed below - clean them a little before clamping - don't go too mad as they're coated and you need them clean but the zinc coat to remain intact.

 

Ben
The OEM earth strap goes from the bottom middle left side of the sandwich plate to the subframe and from there to a bolted earth fixing on the LHS lower chassis rail. Lots of chnaces for loose bolts and poor earthing.
Grant always recommends an extra strap direct from an alternator bracket bolt direct to the frame. Which I have done as well as cleaning up the OEM earths.