I have an '84 XJS that i recently aquired. Read through many articles on this forum for helpful advice. I purchased the car a month ago and have been soaking in all the reading material i can find before trying to tackle some of the issues i am having. Car sat 3 yrs. I have gone through the ignition and got her running but am still having a few issues. I have freed up the mech advance and made sure the vac advance was good. I am experiencing what seems to be a fuel issue from time to time as the engine will sputter on acceleration as if is running out of fuel and on occasion will pick up and move on out. Noticed that the longer i run engine, the worse the problem presents it self . Finally it gets to the point where it sputter/cuts out on rev-up in park. I have removed the pick up from surge tank and checked sock which was clean. I have also heard heavy air in fuel tank as if someone shot a blast of compressed air into it ( bubbly sound). This happened as i had a helper cut ignition switch on as i was checking fuel pump operation sound. Also noticed that the fuel filter didnt have any fuel to hardly speak of and when fuel line was removed from inlet side of fuel filter, there was alot of air followed by fuel coming back from the fuel rail supply line. The battery was removed when i removed the fuel line. New fuel filter. Anyone have an idea as the whats this is pointing to?

 

My thoughts from experience down here.

NO particular order.

Fuel pump is lazy, COMMON.
The RH fuel regulator (dummy reg) is jammed, I remove it, as the LH Fuel reg is the actual pressure regulator.
The CTS (Coolant Temp Sensor ) is flaky, also common.
The TPS (Throttle Position Sensor) is also flaky, common now with age.

A fuel pressure test at the rail is mandatory in my opinion.

Have a look under car on each side, you will see metal pipes that are the supply (RH) and return (LH). These are easily crushed, and that will reek havoc.

The list is MUCH longer than the above, but that should get it running for as long as you want it to without cutting out.

 

As well as Grant's list, it might be worth trying to run her with the fuel cap off, in case the pump is trying to vac the tank because the air inlet valve is blocked.

Greg

 

My RH fuel regulator was leaking fuel into the vacuum line. I removed it and didn't replace it with anything and the car runs fine. Maybe not pertinent to your issue, but it's one piece you can literally remove from the equation without harm.

Along the lines of what Greg is saying, after running it as you described, is there a huge whoosh of air rushing into the tank when you remove the gas cap? If so you may have found the problem. I ended up drilling a small hole in the center of my gas cap the equalize the pressure. I do wish I could get the fuel venting system working properly, but at the moment it's a bit far down on the list.

If you've got a decent digital VOM, you can measure the resistance of the coolant temp sensor as Grant indicates and compare it to the book values that are in the engine performance guide. That should give you an idea of if you need to replace it or not. If you've not yet looked at the engine performance guide it really should be mandatory reading for anyone working on one of these. I can't remember where it's at, but it's on the site here and someone will chime in with the location. Save it as a PDF, it's good stuff to have handy.

Good luck with it!

John
1987 XJ-S V12
63,000 miles

 

Thanks for all the replies. Today as a work day off, i removed the fuel pump, filter and hoses. Removed the supply head from the surge tank and inspected tank. I am going to have the pump checked out (walbro) and install all new rubber hoses in the boot. I inspected the supply and return metal lines as Grant suggested and found all good. The fuel cap is a loose fit as the gasket is worn. What would be the simplest way to eliminate the rh regulator and would a simple cap off of the vacuum line to it be ok? I am wanting to get things sorted and inspected before performing a fuel pressure check. I am kinda leaning towards the fuel pump as before i removed it, i started the engine and listened to the pump. The pump was making several different sounds as the engine was running. Kinda noisy on start up and then after a few seconds was quieter but sounded like it was not pumping or was pumping air.

As far as the throttle pot, i am sure it has internal issues and being a electrical forklift tech i am sure i can come up with a simple pot retrofit.

Thanks everyone for suggestions and ideas. Will post on future findings.

 

I had a 85 that had a stumble off of acceleration once, and it felt just like a bad accelerator pump feels in a carburated car. Turned out the vacuum advance was bad. Fixed that, and my problem went away.

 

Today i reassembled fuel system in the boot and installed a fuel pressure gauge. Removed the right side fuel pressure regulator and started engine. Pump was putting out 40 psi at idle. Could increase rpm and quick rev engine and discovered pressure would fall to 28 psi. This pressure would not increase until i shut down engine and restarted. This would get pressure back up to 40 psi. This would hold until i revved engine. I could remove vacuum hose from left regulator and fuel pressure would rest at 46 psi. I am thinking the left regulator is sticking or has gone out. Are the 2 regulators the same? If so i will swap and see what happens.

 

Spec is 36 psi as I recall. Lower vacuum should result in slightly higher pressure, higher vacuum should result in slightly lower pressure.

If I'm understanding you correctly I agree that your LH (outlet) regulator is on the blink.

LH and RH regulators are not the same

Cheers
DD