Hi guys,

First time on this forum, and sorry to say I'm having massive electrical difficulties with my Jag.

I began a few weeks ago with a christmas tree dashboard (after the car had been sitting in a barn for a couple of months) - every warning light on the dash came on. A mechanic friend found the code P1793 - and after recommendation I bought a new battery. I have also checked the alternator, which seems healthy.

The code is now intermittent, but I still have an odd 'pulsing' as the lights dim rythmically with the engine, both at idle and speed. And fuel economy is awful.

I have checked some of the earths that I can see - maybe I'm missing some vital ones.

Is there anything else I can check?

Cheers guys,

dan

 

meant to say its a RHD '97 xj8 3.2.

 

Check all the power leads as well. My 98 had a loose power cable by the ECU. There's also lots of rely and fuse blocks in the car, it might be worth looking at the cables feeding those boxes, for tightness and corrosion.

 

Do as suggested and clean the connections first. This might help http://www.gusglikas.com/AutoRepairElectrical.htm

 

Cheers guys,

Where is the ECU and TCM housed. Is it under the glove box or in the engine bay?

Thanks,

Dan

 

Dan, I wonder why you need to know where these are?

I'd follow the suggestions on here about cleaning and checking every connection you can see under the bonnet, armed with wire wool, a bit of dielectric grease and a methodical approach might just sort it out. Leaving these cars any long period can let verdigris in, that green oxidization at connections.
The fuse box on the passenger side, check the heavy cable connection, clean the maf and throttle body/part load breather, fresh gas, new battery, give the car the chance to settle down. Once this bit of work is carried out, you can maybe look further if the car isn't running any better, post what you find after carrying out the cleaning work. I'd also look at the JTIS/Wiring diagrams, this can be found in the sticky in the XK8/R forum....

 

Ok guys,

Spent another few hours on this morning.

I checed the TCM and ECM, all seems ok and swapped a few of the relays around.

Checked every earth I can find - but I'm not sure where the main engine block earth is. Any ideas?

Anyway, fault is still there but slightly different. At first the P1793 code was back - BUT the engine was running fine, smooth and no pulsing on the dash lights. However I started it again, this time no fault codes but uneven idle/pulsing dash lights were back.
Very puzzling.

I will clean the MAF and breathers tomorrow, but I'm not convinced they're to blame.

More advice welcome!

Cheers,

Dan

 

If you go to my link I provided you it has the entire electrical wiring diagram for your car. It also has the locations of all the connections. As for cleaning the connections my recommendation is to use a toothbrush and not the wire wool in any area where the residue could short out between contacts creating additional problems. Using a good contact cleaner (CRC) then the dielectric paste (CRC) sparingly.

 

the engine earth is from body to block on the rhs in front of the gearbox, underneath the car, this is another one to check - can't miss it, thick braided cable.

I only suggest cleaning the MAF etc with regards to crappy fuel consumption, not your electrical issue, (the throttle body connection, clean that also).

Relays rarely go wrong so I doubt it to be one of these, maybe a dud connection.

 

Ok,

Again checked all earths I could find. No joy.

But then I found acid coming out of the end of the battery, which I bought 6 days ago.

So what's causing this. I guess a f***ed alternator??

Thanks again guys,

Dan

 

Fortunately, that is easy to check. That would match up with the symptoms you describe.

 

underdog:
Do you have a multi-meter? If you get a meter (and learn how to use it) and a schematic diagram, we can go step by step through some basic tests that will indicate ground or wiring problems. If it is a module going haywire, it will probably NOT be found with only a meter.