fuel problem
 

I have a 1979 XJ6 with fuel injection, it starts and runs but every time I try to go somewhere it conks out .. when I start the fuel runs back to tank well but when it starts acting up I notice that fuel only spurts back in tank...not full flow as it was...engine spits ..sputs and backfires through exhaust, have cleaned valves and they seem ok to me..any help appreciated

Welcome to the forum holiday,

I've moved your question from General Tech Help to XJ6 & XJ12 Series I, II & III forum. Members here with the same model will be able to help.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some info about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

Usual suspect for an engine that starts but wont sustain revs is a blocked fuel filter. They arent that expensive and a good thing to replace of you arent sure of the existing one, before you start looking further. If you do it replace any fuel lines that you work on as you go, they age and can fall apart internally.

I have tried everything I can think of...I am now concerned with the fuel pump relay ... car acted up last night but I did get it home ... now after hooking up fuel pressure guage I can not start car and find that I do not have voltage to fuel pump when I try to start ...I have been finding that I could start car but after 10-15 minutes it would act up --missing --not running right --and that return gas flow to tank would be good when started but when problems started the flow returning to tank would be very minimual I am wondering if this relay might be my problem 1979 XJ6L

Could be, at the very least you arent going to get much further with problem determination until you have reliable power to the pump.

Use a long jumper wire from the battery to apply 12v to the fuel pump . Does anything change?

Cheers
DD

PS- I'm assuming this is a 4.2 engine with fuel injection

Spare batteries are of great assistance. Even the side post ones
with patched - terminals.


Ok to ask.


Carl

new development with problem ...put on pressure guage 32 lbs when I start but as engine warms up pressure starts going down ,when it gets to about 15 lbs the engine starts missing and acting up ...12 v ok on pump ,,very little gas flowing back in tank ,,,checked pressure regulator and when I pull vacuum hose pressure goes up as is supposed to and hose is clean not wet, do I have restriction in line (new filter) and why only after a while ??

Which proves the regulator is not leaking internally but doesn't prove that it is operationally OK

Possibly, yes.

The *purpose* of the filter is to capture crud


Crud in the tanks

Pull the filter and empty the contents in a clean jar. Your next steps will be dictated by what you see!

Cheers
DD

Thks for all the help ....I have been able to get car running ,,,crud in tanks seems to have been problem ...both tank units were not working so have replaced with new, guage reads low as to fuel in tanks and in checking voltage on sending units it varies between 5 and 6 volts ...is this normal ? should it not be 12volt ?

1. Great, it is running. But, more crud in the tanks to mess up the new parts? Drain and flush???


2. Electrickery not my strong suite. I struggle with it mightily. But, I do win more ties than I lose. I think your fuel sensors are doing what they are supposed to do. Vary the voltage by the variable resistor. The guage senses different volts and reads accordingly.


You might wish to "calibrate". Run one tank down to where the guage shows empty. Fill it, about 12 gallons, I think. Did it take close to 12?
Does the guage now read full? If that works, OK!!


Repeat with the other tank.


Albeit, eccentric, the twin tank thing is intriguing...


Reminds me. I need to visit the gas station in the Jaguar on Monday or so. Both tanks down to just under 1/2.


Carl

Carl is spot on. The fuel sender is essentially a variable resistor with a float that changes the resistance according to fuel level.

Tip for those who have non-working or jammed fuel senders.
The two senders I took out of the coupe were encrusted with rust and crud. One would not move and the other wasn't reading any resistance across it's travel.
I had a bucket of citric acid and water I often use for de-rusting bits. So I chucked them in there for a day or two. The rusty crud had all gone, in places where the original plating had failed there was a coppery colour. But both now worked! That is they gave the same readings of resistance from low to high.
Don't know how long they'd last or if I'm ever going to use them myself as I've got a new one for one side and a couple of others which I hope are in better nick.

I think the twin tank was a good idea as it made the boot much bigger than if they'd fitted the tank conventionally.

thks JagCad and anjum ..I did not realize voltage would be variable ..used to old Model A's and 50's Fords where things were pretty basic ..anyway with your help I am making progress and learning , running good on both tanks, will drive for awhile and then drain and flush tanks again ...going to check out couple other things over winter so will probably be asking again , Denton

Denton:


I date back to those days and before!!!


1. T Ford. No guage at all. Look in the tank or use a yard stick!!!


2. A Ford. Glass lens in the middle of the dash to see the float in the tank.


3. 50's. among the first of the variable resistor in the tank. I am a bit
fuzzy there. The one in my black 49 Mercury coupe worked and I had no need to fix it.


4. I expect bureucrats would fuss at Jaguar's two tank system. Jaguar
"fixed that by a single tank in the boot, but up front.


Carl

well I thought I had it made and NO ! 2 new sending units installed in tanks ...full of gas ...left reads just over 1/4 and right reads just over 3/4 ...what next ??

Just a couple of thoughts. You can check that the gauges go full scale by earthing the non black wire at each sender, they will probably be OK but good to eliminate.

The senders are left and right handed, are you sure they are in the correct tanks? if not they might be binding or rubbing internally.

I guess the last choice is to drain or run down the tanks and pull the senders again, check that full movement of the arm does give matching gauge movement.

On a general note. All the XJs that I either know or owners I have discussed the fuel level thing with have the "reads just over 3/4 when full" thing happening. With new senders though it seems reasonable for full to read full at least for a while.