Hello all,

I bought my grandpa's '86 XJ6 about two years ago. The car sat for about five years without being driven, with the tanks half full; needless to say, the tanks rusted. The sump filters failed and the rust-gasoline mixture fragged the pump and the injectors. After several hundred dollars in a new pump and injectors, hours and hours of running kerosene through tanks/draining them, and pulling out rust from the tanks, the car is now running mediocre. It will gladly gain speed gradually, but putting the pedal to the floor leads to some consternation. The car will lurch forward, the engine will then violently hesitate several times, and will eventually even out, only if I let off the throttle and then push it back down. Every so often it will hesitate around 20 mph, then even out, and then hesitate again around 59 mph, and even out after hitting 61 mph. Top speed right now is at 86 mph. I know that the performance should be much better than this. When the weather warms up, I plain on draining the tanks again and cleaning them/the filters. Any other suggestions on what to do next? Thanks!

 

It definitely looks like fuel supply as the engine runs OK albeit when running although not on full power and is often hesitant. If it was ignition, I would be looking for backfires and unburnt fuel smells.

Does the engine start and run nicely at idle ? Does the fuel pump run steadily and quietly ?

You have cleaned the tank pickup filters, changed the pump, presumably you have changed the in-line fuel filter and checked/cleaned the fuel lines too and replaced the injectors. That must have cost a tidy sum so you must be very disappointed in the results. DOn't worry, I have been there and know what its like !

All the work you have done means clean petrol should be supplied to the fuel rail. There is a check you can do to see if this is so: -

Disconnect the fuel line flexible to the fuel rail, arrange for the flexible pipe to feed into a jam-jar or something, put the transmission into Drive, and then turn ignition key to the Start position for about a second or so. Being in Drive the engine will not be turned over by the starter motor, as this is inhibited, but the fuel pump should run. It helps to have an assistant holding the jam-jar to make sure you don't squirt fuel all over the place. You should hear the pump start and then stop. The petrol in the jam-jar should be nice and clean. ONLY ONE or TWO SECONDS MIND YOU, its a powerful pump ! If you're nervous, extend the pipe into a jerry can or similar away from the engine compartment.

And NO SMOKING or any naked lights or flames anywhere near, and have a fire extinguisher handy.

If petrol is clean, you may need to check the fuel pump relay contacts in the MAF box. Inside the black top are two very small contacts that keep the fuel pump relay closed. The air flow flap in the MAF opens these contacts when the engine is not running, but as the flap moves on engine start, the contacts close to keep the fuel pump running. A bad contact could cause intermittent fuel pump running. In my case total failure until car was restarted.

YOU can check the fuel pump volts supply by rigging up a couple of quite long leads with a small 12v bulb at the end, connecting these to the fuel pump contacts, bring the leads back into the car so you can see the bulb whilst driving the car, (better to have an assistant), and check the bulb stays alight whilst you are driving. Any bulb flickering means the MAF contacts (or the fuel pump relay of course), is suspect.

Other thing that may need attention is the injector wiring loom. On the six cylinder cars which use Lucas-Bosch L-Jetronic, the injectors all fire together once per engine revolution. Switching is done by earthing the injectors via the ECU. Bad contacts here can also cause bad running

Have a read of this internet site too

Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

There are other people more expert than me so wait for them to post before actioning anything. Remember, take the cheap cure first !

 

With rust and scale coming off the walls of the fuel tank(s), it will be difficult to avoid having the fuel filter become clogged repeatedly.

Did the shop performing the work on the injectors test the fuel pressure once the various parts were replaced and the tank(s) cleaned? Did they also replace the fuel pressure regulator located on the engine fuel rail? It is entirely possible that there could still be fuel starvation occurring at higher rpms and road speeds.

NBCat

 

Thanks for all the help!

@Fraser: As soon as I find time this weekend I will test the pump relay. The car runs pretty rough at idle, and the fuel pump squeals a little. I'm worried a chunk of rust got sucked in it.

@NBCat: We did all the work at home. We didn't test the fuel pressure or replace the fuel pressure regulator. Do you think it's possible that the rust has caked around the sump filters, blacking gas flow?

 

Fuel pump should not squeal, it should quietly whine away. Fuel pressure regulator is a favourite failure, (it failed on my Series 3). Filters at the bottom of the tank collect muck as the car runs along, because there is quite a high fuel flow, and the return fuel stirs up the muck near the inlet filter.

So sounds like its time to, (yet again !), check the tank filters. Also you might care to check the pipes that pass fuel to the changeover valve, and the changeover valve itself maybe; these can jam at inconvenient times, as with me going up a long hill wanting to change over !

Essentially you have got to get to a situation whereby clean fuel at the correct pressure is present in the fuel rail. Once that is done, then other diagnostics can be done. You might care to check the integrity of the connection from the ignition coil to the ECU, as this is the timing source for the fuel injectors.

 

Drained the left tank & pulled out about a cup of rust caked around the filter. Cleaned the pick-up/filter (which was perfectly intact), started the car & took it for a drive. After going about 300 yards, the engine sputtered hard at 20 mph. Now it shuts off completely. Praying the pump didn't suck in any loose rust, although it is making about the same squealing noise as before. When I find more time, I'll disconnect the pump and run some carb cleaner through. I'll also look into getting a new pressure regulator. Any other suggestions? I appreciate all the help!

 

Quite honestly, unless you enjoy working on the fuel system of this car, you probably should consider replacing both fuel tanks along with the fuel pump, fuel filter and pressure regulator. The amount of scale and rust present in the system will prove problematic at the most inconvenient of times and will eventually leave you stranded somewhere, probably far from home!

In addition, you may want to have the fuel injectors serviced by a reputable shop since they may be scored or otherwise contaminated.

NBCat

 

I have a 86xj6 vdp i ran a tank of gas with rust / destroyed my fuel pump now my engine idels rough but top end is ok just don,t have any good take off! i did not check my fuel pressure regalator butr did change filters.

 

What does your oil look like. I put rust/crud through my system. After replacing pump, filters, lines, cleaned up the fuel rail, it still was acting funny. The oil was horrid. I changed the oil and filter, it ran totally different.
My oil pressure gauge seemed normal, but the oil filter was so bad it lead to hesitation and erratic performance.

I also changed up my fuel system to have 2 parallel filters BEFORE the pump.
I don't recommend this for everyone as some cars will explode

 

Ummm another thing. you should test the tank's ability to release gas. Disconnect from the changeover valve. If gas freely flows out, its likely not he tank/tank filters. If you can suck on it without any give, you are jammed yp and 300m is how long it takes to make a vacume in the line.

Ive also heard of a single large chunk jamming at the changeover valve stopping gas well.