Hello,

I am new to this forum and I greet you guys

A friend of mine bought an 1981 XJ6 iii 4.2L Jag (on ebay,from the US) and after getting the car we found the engine has some problem running (igninte and stop, rough idle, hard to accelerate, hard to raise revs etc..)

the problem sort of come and go so its hard to describe..
- We replaced all 6 injectors to new ones.
- We checked the air flow meter and it seems ok (reading the output voltage)
- We found the Air flow meter's input voltage is about 10.2V on its harnes.

I would appreciate any help or hint with this

Regards,
G

 

Rust and crud in the fuel tanks and supply lines maybe ? Have you changed the fuel filter ?

There is a lot to go wrong on such an old car, but I expect our expert on Series 3s, (Doug), will be along soon to point you on the right road.

 

Hi Mitchel,

thx for your reply.
I forgot to write about the fuel tanks, the right-hand side one had a blockage at first, we blow the pipe with compressed air and the fuel now flowing freely.
and yes, we replace the fuel filter.

Doug sounds like a hope for us

Thx

 

Pull the new fuel filter and empty the contents into a clean container. What you see will determine your next steps :-)

Cheers
DD

 

Doug,
thx, will check it and will write back here.

Thx

 

Hi Doug,
I performed your test and the fuel was very dirty, with some rust but the filter was still able to pass the fuel.

do you think small parts of dirt are passing the filter and make all the troubles?

Thx

 

Possible.

More commonly the contaminated fuel A) doesn't ignite very well and B) damages the fuel pump.

The fuel system needs a thorough cleaning, fresh fuel, another new filter, and possibly a new fuel pump.

One option is to remove the tanks (big job, by the way) and have them professionally cleaned. Or remove them and attempt do-it-yourself cleaning. Or leave them in place and attempt do-it-yourself cleaning. Many owners go the DIY route with good sucess.

It's advisable to install a fuel filter between each tank and the pump....thus protecting the pump from any contamination that may be remaining. I know one fellow who used this method to let the system clean itself, so to speak. The first pair of filters clogged in just a couple days. The second pair clogged in about a week. The third pair took about a month to clog. He went through 6 or 7 replacements before all the loose contamination was finally captured. Not saying this method would work in all cases, mind you.


Cheers
DD

 

Doug thank you for your detailed answers.

I am thinking of "bypassing" the system to eliminate other causes of trouble by mounting new external fuel tank + filter and a replacement pump and check it.

what do you think? will a replacement pump do the job? (should output 2.5-3 bars if I am correct)

thx

 

Worth a try but you'll need a ump with more oooomph. The Jaguar (well, Bosch) pump will produce about 6-7 bar which is then regulated down to 2.5 bar.

Cheers
DD

 

Hi,

We took apart the fuel system. Connecting the fuel pump directly to a pressure gauge gives ~7 Bar. (pump running smoothly).

Can you tell the pressures we should get on the common-rail at high and low vacuum?
We like to try it with the engine running.

thx

 

The only spec from Jaguar is 36.25psi while cranking.....I'll let you do the metric conversion :-)

I'm guessing a 2-3 psi variance from that depending on vacuum, open throttle vs closed throttle

Cheers
DD

 

hi,
after many trials and checks, it seems that the fuel system is fine,
and the main issue is with the closed loop state.
when engine is cold it is kinda OK, when getting warm problem appear.
will appreciate any lead

thx