Earthing Points and Electrical Faults Roulette

(Skip to the end of this post if you want to cut to the chase)

Ah yes, that perennial favourite of the aluminium bodied Jaguar owner. That game that we all play at least once in our ownership cycle. And that game is the ever enjoyable "I wonder what intermittent electrical failures I'm going to have today?" Perhaps we should have some sort of scoreboard system so that we can each rank how serious our electrical system failures are? This might be words that come back to haunt me, but I haven't yet had any big scoring failures. I just score big points by the sheer number of failures that I get to enjoy. It's just a little something that makes Jaguar ownership that all the more.... interesting shall I say?

So far I scored;
Almost constant misfire
I've been locked out of the car
I've been locked in the car
My windows won't go down
My windows won't go up
The alarm won't set
The alarm keeps on going off
My bonnet is open even when it is shut (according to the dash)
My DSC sometimes doesn't work (according to the dash)
The door mirrors won't fold in
The door mirrors won't fold out
One door mirror folds in
One door mirror folds out
Both door mirrors get stuck half way out.
And today's brand new fault, I had an absolutely empty fuel tank, (range 0 miles) when I put 30 litres (about 5.75 gallons) in the tank less than a mile before, (false reading on the gauge and the trip computer)

Today I unscrewed and cleaned up all three earthing studs behind the headlights, (G1, G2, G3?), and BC1, BC3 and G23 by the battery in the boot, plus G25 under the CD Changer in the boot. I did this by unscrewing the aluminium nut, giving the stud a scrub with a brass wire brush, then giving the stud and the electrical connectors a blast of contact switch cleaners before nipping them back up again. None of the earthing studs that I have come across have looked particularly nasty, just an ever so light white / grey dusting on them.
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I've tried doing a few searches on line about earthing stud locations, and most of them appear to only show the studs in the boot / trunk, and those behind the headlights. Before I mess about jacking the car up, am I correct in thinking there are further studs behind the front bumper or on the front subframe? Also where abouts is the main (G4) engine block ground? Is it worthwhile me unluging all electrical connectors I can safely reach to give them a blast of contact cleaner?

In advance fellas, many thanks.

 

Do a hard reset to see if some of the issues clear up.

I agree with cleaning as many grounds as possible.

pull up on some ramps at the front end. Check ground straps between the transmission and frame.

 

Thanks Mike.

it goes into a local JLR Indy tomorrow for a full diagnostics and reset, then to a mate of mines place on Wednesday to see if any more codes have come up.

In the meantime I'm going to continue cleaning as many earthing studs as I can find.

Does anyone know where the main engine earthing stud / strap is? Or is that the one you were on about by the trans tunnel Mike?

cheers

 

Update;

I've had the car up an axle stands today, removed the front two undertrays, couldn't find any earthing straps or studs behind the front bumper, (is there any, or was I just imaganing that there was?).

I then spent the next few hours in very cramped conditions trying, but failing, to get the two side undertrays off. I did find a couple of very chunky earthing straps under there, specifically the one that runs from the altinator to into the depths of the right hand undertray. From a visual inspection there was nothing to cause any alarm with the other two earthing straps that I found. Due to this size of them and the lack of ease of access I didn' want to go disturbing them if they 'looked in pretty good condition.

Tomorrow morning the Moneypit is in with a local JLR Indy for an hours diagnostics, reading and clearing of the fault codes and an ECU reset.

As unlikely as I am finding it that the vehicle could develop all of these various faults at once, it can' e ruled out. Besides a dodgy earth somewhere, is there anything else that could be causing it? I'e had the battery checked and that' ok, so what else is there? All of the earthing points that I have located have checked out pretty good.

However, if it's going to end up being an expensive job then I'll be breaking the car for parts.

In advance chaps, thanks

 

The underside cover are taken off rear one first. 4 bolts on rear, 2 nuts in middle, and 3 at the front which attach to the front cover, and then 2 hidden screws through the access holes that attach it to the front crossmember. Then remove the front cover. As far as the engine to body ground, it is on the right under side close to the area where engine and transmission mate.

 

Thanks Box.

The two front covers were removed no problem this time, (I made some mods to them last time I had them off). It' the two side covers I'm struggling with. Some of the recessed 10mm's just spin and spin and spin without coming off. I'm going to have to fix both sides with an angle grinder, but I don't want to tackle that job until I've got a replacement pair. The only problem with that is I'm not paying £90 per side + 20% VAT. I'd rather wait until I can find a decent second hand pair for £60 all in plus shipping.

I've just taken it out for a 5.5 mile run around my local area. The occasional misfire is still present, but no other problems. Well, except for uneven ride height, but that happened last time I had it up on axle stands but righted itself after a couple of days anyway. Of course saying there have been no electrical dramas in a short 5.5 mile run is nothing to write home about as all the faults, besides the misfire, have all been intermittent.

Would anyone care to take a bet on what they think the fault is that is causing the misfire?

Would anyone like to take a bet of whether or not an ECU reset will fix the intermittent electrical faults tomorrow?

Would anyone like to take a bet on the source of the electrical faults?

I'm going to go out on a limb and say....

1; Damaged injector, (I dropped one from shin height whilst cleaning them, but I can't remember which one).

2; No.

3; I'll be told by the JLR Indy that I need one of the ECUs replacing, ("that will be £1763 +VAT please sir").

 

The electrical guide (wiring diagrams, earth point locations plus much much more) and other relevant documents can be downloaded here;
https://www.jaguarforums.com/forum/g...r-index-50609/

 

Good luck today, hope it isn't as bad as you fear.

 

I am sure a search on the internet will show pictures of the locations for most earth points. I have found most of mine (2004 XJ8 base) anyway. However, I do not think you can really tell how good the connection is without using a tester or actually removing and cleaning the connection with a brass brush. A visual inspection will not really do much especially on aluminum. Using a multi-meter may work, by checking the wire to the chassis or body, but I do not like to pierce the insulation if it can be helped (I have done it though). They need to be taken apart and physically cleaned and inspected. I have had the connection look good but be broken inside the wire itself. That condition did not reveal itself until I physically jiggled the end of the connection.

I won't take any bet on your problems. Just expect it to be expensive .

 

Fortunately I have never had a problem with the undertray fixings but I have thought

about how to circumvent it.Use a hole saw to cut around the spinning nut and a large

washer (could make a plastic one) to replace tray after repairing original fastener. That way you can use existing tray.

Simples?

BTW bonnet and alarm problems are both due to dodgy switch located

under one of the bonnet latches.

 

Door mirrors can suffer from extensive corrosion of alloy hinges and need cleaning

and lubricating.

Fuel tank senders can also suffer from corrosion of the contacts.

The senders clip onto the fuel pump housing and can be cleaned or replaced.

 

Evening all. Another update.

I didn' have a misfire although the symptoms were very simular. I had an air leak causing the engine to run very, very lean.

The cause of the air leak was located to a damaged nipple where a hose meets the pipe the runs between the airbox and the throttle body. As a temp solution this was reglued with aroldite.

The stuttering may also be caused by low or very dirty trans fluid. It' going into my mates workshop tomorrow do I'll investigate further with that.