I own a 1985 Jaguar XJ6 Vanden Plas and Ive got an issue that I just cant pinpoint. Before I get to the problem, here is what has been done recently. I had both tanks cleaned and sealed, new fuel pump, fuel filter, starter solenoid, etc..
My Issue is that I can start the car up just fine and it will idle all day long but if I try to drive it, after a few seconds 5-10 sec, it will start studdering and loosing power like its out of fuel but will start idling fine again once I let go of the gas. Any Ideas?

 

A fuel pressure test would be really useful here. Do you have a gauge?

Cheers
DD

 

Agree with Doug 100%...
Did you change the fuel filter after cleaning the tanks?
And, if so, sounds like the fuel pump... You using an aftermarket or original Lucas?

David
EverydayXJ.com

 

I replaced the fuel pump b4 I knew the tanks were bad. Got the tanks Cleaned and sealed and replaced the fuel filter after I fixed the issue. The fuel pump came from a local parts store. It's the only one I could find that actually works for my model. It's an aftermarket. I don't have a fuel pressure gauge but I know there's pressure on the lines because I can open the filler cap and it quickly sucks in air. Hope that helps. Thanks

 

If the tanks were badly contaminated/rusted the new fuel pump could've been ruined by the crud in the fuel. It happens.

I'd buy a fuel pressure gauge and check the actual regulated fuel pressure at the fuel rail, which should be 36 psi. The whoosh when opening the gas caps is a different issue and doesn't prove that the engine is being feed at the correct fuel pressure.

If you wanted to replace some parts on a hit-n-miss basis I'd go with a fuel pressure regulator or an air flow meter. Better to check fuel pressure first, though. It's really a fundamental thing when diagnosing fuel injection problems.

Cheers
DD

 

I've seen some very similar things happening with either failing or all together wrong fuel pumps..
When one of my Lucas pumps started going bad, I put a fuel pressure gauge on it. At idle it was reading 33psi... I thought it was ok. But I got a longer fuel line so that I could watch it going down the road. Under load it was only pulling about 10psi... and the car would stumble badly...

Another guy called and said his car would run fine at speed, but would cut out badly during stop and go traffic. We had to trailer it to my house, and we found out that the aftermarket fuel pump he had purchased was really rated at 75psi... So at speed and even throttle the car could keep up with the amount of fuel being delivered. But when he stopped it was overfueling and cutting out.
We put the proper fuel pump on it and it's ran fine ever since...

As a friend on another forum told me a long while ago... It's not fuel presence that matters, it's fuel pressure.....

David
www.EverydayXJ.com

 

I'll check the fuel pressure and get back with you with the results.

 

In case you don't have a manual.....

Disconnect the hose to the cold start injector from the fuel rail and use the now-vacant nipple on the fuel rail to attached your pressure gauge

Cheers
DD