Loss of power

[JeffTurbo]

Hi
Driving my XJS today and I experienced a loss of power. Didn't feel like it was missing but it was doing 5mpg and ran like an 1,000cc car. Would it be a plug etc, fuel or electrics. Lasted for 4 miles then cleared. It then came back intermitently. Not sure what this could be as i've not experienced this before.
Can anyone help me please.
Thanks
Jeff

[kelsham]

Hi if its a Marelli ignition system check the distributor rotor for tracking and burn through. they are known to short circuit down to the distributor spindle. Best not drive it until you check it takes one bank out of operation. regards Kels.

P.S. This can damage the catalytic converter and in extreme cases catch fire to the car.

[JeffTurbo]

Hi if its a Marelli ignition system check the distributor rotor for tracking and burn through. they are known to short circuit down to the distributor spindle. Best not drive it until you check it takes one bank out of operation. regards Kels.

P.S. This can damage the catalytic converter and in extreme cases catch fire to the car.
Don't yet know what ignition system it is. 1989 V12, would it be a Marelli?

[dhdove]

Jeff Turbo

Don't know about the 5mpg bit - presumably as reported by the computer?.......
....but the symptoms fit blockage by rust debris/suspension matter in the fine nylon filter in the swirl/fuel pick-up tank under the battery.

I had this a couple of times till I diagnosed it, when I drained the system and cleaned the tank it was 1/4 full of crap - rust from the main fuel tank that was collecting in there. Apart from the big bits the rest was almost like treacle, very fine particulate matter in suspension.

The nylon filter in there has a very fine mesh and will eventually block, restricting fuel flow.

I ended up changing the main fuel tank due to corrosion.

Good Luck

DH Dove

[JeffTurbo]

Thanks Guys
Check the easier thing first before the petrol tank change.
With the distributor rotor possibly tracking, how do I check this? If I change the rotor arm would this cure it or should I look at replacing something else?

[kelsham]

Hi to help diagnosis, if the car is down on power because the rotor arm is shorting down this usually takes out only one bank and the car will typically run smoothly on the remaining bank. Syptom is down on power. The rotor should show signs of tracking/ burn marks, when removed and examined. A second point regarding fuel starvation caused by blocked filters, when I experienced this the pump became noisy as the fuel cavitated round the impellor. You have two filters, one is in the sump tank near the battery. You can clamp off the feed pipes to it and remove the sump tank, then remove the filter without draining the main tank. Take care with spilt fuel. Remove the battery first for safety. if this is the fault the car will usually start and as the sump filter picks up the loose debris it will begin to run badly. My 1986 car has a second replaceable filter under the bonnet. Hope this clarifies things Regards Kels