Hi all,
I am having issues with my xj6 series 3 which I have owned for 2 months.
The engine is running rough and chugging slightly.I had to get towed home as I could not drive it.

Since this episode I have flushed both fuel tanks several times and the fuel came out brown and lots of flakes also,this was done over a 4 hour period until the fuel came out clean.
I also replaced fuel filter which was full of crap and flushed the hoses to the pump,I do not know how the fuel was getting through.

Now the car is sometimes running great and then starts to run rough again,the tacho occassionaly fluctuates between 750 and 850 with either tank selected.
When I open the fuel tank caps I get pressure releasing,is this normal?

The timing is set as per decal on bonnet to 4 deg BTDC and I have adjusted the RPM to 800 but the allen screw seems to be in too far.

The fuel return to the tanks is working correctly ie left selected fuel returns to left tank and visa versa.

I thought it may be the cannister in the right front guard as the vacuum valve was disconnected when I bought the car,but it makes no difference if its connected or not.

I think the car had been sitting for about 4 years before I got it.

Has anyone got any more ideas of what I could look at.

Regards Felix

 

My XJ12 also has quite a whoosh when I pop the fuel cap on the tank I'm running on; indicative of a venting problem, which isn't good but doesn't seem to cause running issues.

Could be lots of other things. Misfiring cylinder? A stuck fuel injector?

 

I'd check the filter again. What you see or don't see will guide you. You might still have some crud in the tanks. You wouldn't be the first, believe me.

A small whoosh, perhaps. A big whoosh, no. Run with the caps open and see if the engine behavior changes


The air passageway that the adjustment screw goes into in probably clogged and therefore limiting the effectiveness of the adjustments

Cheers
DD

 

Found the purge valve near charcoal canister was not getting any vacuum to open the valve and the EGR valve was also not working due on same tube,
1 of the vacuum outlets on the throttle body was blocked,now cleared and both valves are working.

I removed the check valve near canister to stop the pressure building up in the tank,I thought the check valve was supposed to allow fuel vapour into canister when engine not running.
The check valve is only allowing vapour back into the tank,the orientation of the valve is correct as it is marked Tank and Canister.

The engine is still running rough so I removed the fuel filter and the colour of the fuel was dark brown with fine sediment at the bottom of the bottle.

I am going to order the rubber and alloy seals for the tank drains and drain the tanks again.

 

Hey Man,
Congrats on the new Jag. I dont know what you have done when you say flush the fuel system but if you still see anything but clean fuel you haven't gone far enough. Those tanks likely have WAY more crud than you think. Have you looked into the tank itself. My car had been sitting for about 10 years and the tanks were useless and needed to be replaced- the tank itself was shedding from the inside. I replaced not only the tanks but the fuel filter, canister, 2 electric return valves located in the rear wheel wells, changeover valve and added an inline prep ump fuel filter. This might have been overkills since I had new tanks but maybe as the lines clean up I'll remove it as my fuelpump isn't happy that it has to suck through a filter.. There is also a screen in the bottom of the tank that's hard to see but comes out with a little patience. You can get a good glimpse of the tank through the rear tail light where the senders are with a flashlight. I flushed the tanks like you did and my fuel filter was still filling with discolored fuel. I found it totally gratifying to replace all the components minus the lines and the injectors. Car is running almost as it should..,..almost <eyroll>

 

Good.

After the additional draining.....

One trick is to install fuel filters between the tanks and the fuel pump. This protects the pump and filters out any small amounts of crud remaining in the tanks. Assuming regular driving these additional filters will clog fairly quickly. The replacements will clog at a longer interval. The next replacements an even longer interval. Eventually all the loose crud in the tanks will be gone. Worth a try....and far, far easier than removing the tanks for professional (or even amateur) cleaning.

But, truth is, in some cases, the innards of the tanks are just too far gone and there's no end to the rust and crud that falls into the gasoline. Things might get expensive. The tanks may need professional cleaning and coating or replacement. New tanks are available.

Cheers
DD

 

The above was definitely the case with me. Tanks were past the point of no return. Though I will say replacement was not hard even for a first timer like myself.....I mean....there were a few curses thrown dont get me wrong.....

 

Yesterday while waiting for new drain seals to arrive I removed the sender unit from the right tank and had a look inside tank.
The inside walls did not look too bad but there is sediment around this plastic filter on end of pick up pipe.
I think this filter is directly above the drain and hopefully I can get it out when I remove the drain and clean the tank a bit better.

 

I finally got the new drain plug seals and sender seals.I removed the senders and drain plugs and the sludge was still coming out.The filters on the pickup pipe in the tanks were completely covered in crap,no wonder I am having all these issues.I tried vacuming the tank and using compressed air to clean the tanks but that did not work.I did not want to really remove the tanks so I disconnected the fuel lines to the tanks in the boot and flushed both tanks out with a garden hose through the sender unit hole.The amount of sludge that came out the drain was incredible.The tanks are now clean and I have blown them out with compressed air.I will let the tanks dry a bit longer before assembling it back together.I will keep you updated of the results.

 

I did an inline filter for my 80 XJ6 see:
https://www.jaguarforums.com/forum/x...cement-227225/
post no 9.
It worked very well but there was still so much junk in my tanks they would plug up quickly. I eventually changed both tanks. She runs better than I ever knew. Just need to keep plugging away at the wire problems.

Bobmo

 

I put everything back together yesterday including the in tank filters.I have back flushed the old filter with clean fuel
and re used it temporarily until I get another one.
At least now I have clean fuel going to the injectors.
I also drilled through the fuel tank check valve at the canister with a 1/8 inch drill as pressure was not going back to canister via this valve.
The engine now has a slight chugging at the exhaust pipes,I will see if it settles down this week.
The timing and idle speed is set correctly.
Will report back next week.

 

I put 1/2 litre of metho down each tank just to get rid of any water that might be in the system.
Then I went back to the charcoal canister and left the vent valve for the tanks that I drilled out fitted,and is now venting out through the canister.
I removed the purge valve vacuum hose from the throttle body and blanked that outlet,I also blanked the purge line that goes into the breather pipe.
Timing was still right at 4 deg BTDC but I had to adjust the allen screw to drop the idle speed from 900 down to 800 RPM.
Now the engine is running as smooth as silk.
So I must have had 2 problems,the fuel tanks were dirty and the charcoal canister system.
All I need now is to replace the fuel filter again next week.
Thanks for your help guys.