Hello all,

Recently bought a XJ6 VDP 86. I am working on getting this model running optimally but am having some difficulty. First, it is idling roughly and will sometimes die if forced to idle for extended periods of time [stop lights/signs]. Most notably, the idling is not just "too low" but it waivers unsteadily (between 3-700, usually starting at 7 and working down to 3 in a pendulum style 7,6,7,6,5,6,5,4,5,4,3 etc). The car also takes just a slight amount of gas to start properly. I'm unsure if these factors are related to my main question here but I wanted to provide that as background info on the car's current running condition. I won't bog down the forum here with repetitive "engine idling rough" solutions.

Now, when I do get it started with a little gas it operates, while it idles rough, the engine does not die when being fed even slight acceleration. However, once I turn the vehicle off, while underneath inspecting for leaks, I saw a steady but very fine stream of fuel dripping from the ride side of the engine bay (between the engine and air flow meter somewhere but not visible from atop). This leak is NOT active while the engine is running nor when starting it but ONLY starts to leak when the engine is killed and the key turned off. The leak starts strong (thin stream) and gradually becomes a few drips and then nothing. I left an old flat canister underneath to ensure it was not a small continuous leak but I only ever got fuel in the container immediately following turning the engine off.

Any help identifying the culprit as to this mystery warm engine leak would be greatly appreciated as I do not think it is wise to leave small gas puddles everywhere I happen to turn off my car.

 

It probably is leaking when the engine is running but not clear to see because the engine is shaking off the drips. I'd suggest a jumper wire too power up the fuel pump and pressurize the fuel system in a static state so you can use a bright flash light to find the leak.

 

I agree about pressurizing the system to aid in the search.

Remove the fuel pump relay (on the firewall....the one with white/green wires) and use a jumper wire to apply 12v to the socket/terminal associated with the white/green wires. This should make the fuel pump run. You'll hear it.

There might be two sockets in the relay connector with white/green wires. If one doesn't power the pump, the other will.

However....

Is there any chance that the gasoline is actually leaking from the area of the right front wheel?

In front of the wheel is the vapor cannister. There are some conditions.....I'd have to do some mulling to remember the details...where the tank venting/purge system can malfunction and raw fuel be drawn into the cannister. It fills up and overflows.

With the engine running some of this fuel might be drawn into the engine...which might explain your running problem.

Cheers
DD

 

Thanks to everyone for the cursory steps.

The fuel pump does run properly both when doing the jumper wire test as well as by activating the flap inside the AFM manually and I can hear it activate but unfortunately doing this does not make the source of the leak any more apparent to me. I have checked all the fuel lines coming from the injectors to the fuel rail. I am getting a little very tiny drip around the little brown clip near injector #3 with the tiny T fuel line split where 1. the longer line (about 1'6") which runs to the right/front side of the fuel pressure regulator and 2. the short line plugging into the small nipple on the engine bay itself.

Both of these hoses had deteriorated and basically deformed in my hand into goo as I pulled them off to replace them. However, even after replacing them, there is still a very small drip right around the brown connector before either of the small dividers. I cannot find what this little brown clip is or what it does according to the parts guide that I have. This is definitely not the blue cold start injector. It is to the left/cab of the vehicle compared to the cold start injector.

However, Doug, you might very well be right. I do have the customary "woosh" in the fuel tanks but have not heard any of the characteristic clicking/popping/cracking into place. I will be depressurizing the system, disconnecting the canister and investigating the situation. I have the annoying pressure valve (CAC3101) on order so I will replace that when it arrives in the mail. I think that you may be correct that it is this fuel canister as that would describe why I can only see it when the car is shut off after having fuel running through it. However, I don't have much experience dealing with this canister. I don't know where the lines from the canister are going. Mine has two lines coming out of it that go directly into the wheel well towards the engine bay but I have no idea where the lines emerge. Perhaps I need to pull the fuel rail and AFM and intake manifold in order to work on these lines? If it is the case that it is spillover from a malfunctioning canister set-up, what should my next step be?

Also, if anyone has a comprehensive fuel line map or chart that would be phenomenal. Replacing fuel lines is pretty simple for me but making sure that I have exhaustively checked all lines is much harder since I don't conclusively know the location of every fuel line. As this is a relatively new purchase, I honestly wouldn't mind just replacing all hoses simultaneously but I don't want to do that unless I can actually replace EVERY hose - I'd hate to miss one, only to have that be the culprit of a highway burst/breakdown.

The leak is generally falling downward in a straight column slightly to the right and front corner of the oil pan. As I can hardly crawl under the car while its dripping gasoline to look up and find the leak, other than operating the fuel pump (which doesn't seem to visibly cause the leak), are there any other means by which I could detect this leak?

Thanks again for all of the information!
John.

 

Update:
I drilled a small hole with a 1/8" bit in the valve between the tanks and canister after depressurizing the system. I then changed the fuel filter and shook the air filter clean. I also disconnected, cleaned, and reconnected the battery terminal connections. Upon restart (with slight accelerator assist) engine shook far less, accelerated more smoothly and most importantly, stopped dying after long idles. The idle is still somewhat rougher than ideal but at least the car is operable on streets and capable of stopping and starting without impediment.

After my first successful test start upon reconnecting the fuel relay and turning the key, it started rough, I heard a very soft 'thud' somewhere to the right part of the engine bay and then smoothed out almost immediately. When I turned it off this time, it leaked as I described before (small stream to eventual drop to the front/right corner oil pan between engine bay and AFM). This leak however, was substantially smaller in overall quantity of fuel from those I previously reported.
Deciding that I would just take a spill container with me for when I turned the car off, I decided to go for a test run. Upon completion (up 65 mph, some in town driving, multiple stop signs/lights) with some success, I stopped at a store, put the container in place, and killed the engine. There was a very small series of single drops (6-10) and then nothing. Then I started again, drove home and repeated. Nothing came out this time.

While I hesitate to say that I have 'solved' the problem, the idling has evened out majorly or at least it has stopped killing the engine at stoplights and the fuel leak appears to now be intermittent and/or smaller and/or solved. I will post updates in the future if this problem crops up again inexplicably but for now, I am hopeful.

 

Also, if anyone could help me out with that small brown clip or the fuel line diagram I mention above, that'd be great as there is still a very very tiny gas leak near whatever this brown clip between the injectors and to the left of the cold start injector. It is brown an screws into the rail.

 

There's a fuel temperature switch that screws into the fuel rail. It's brown and has two vacuum hoses. Is that what you're talking about?

It shouldn't leak fuel, obviously. In fact it shouldn't even touch fuel. The hole it screws into doesn't actually go through the wall of the fuel rail. If it's leaking, remove the switch and determine why. Maybe the hole had a thin spot and broke through?

More later

Cheers
DD

 

I believe that is the part I am talking about. It was these vacuum hoses I replaced but they were indeed covered in a light spray of fuel from the brown connector. I have taken both hoses off in replacing them but I have yet to unscrew the brown connector piece (fuel temp. switch I guess) from the fuel rail.
If as you say fuel shouldn't get here, I suppose the usual thinking would go that I could remove it without depressurizing the fuel system but in this case, since I know fuel to be present, would it be better to depressurize before removal?
If there is a hole, should I seek to repair or replace the part or will it mandate that I replace the entire fuel rail?

Thanks again for all for the help so far!
John

 

i dont know how you ended up getting on here but to be honest, any fuel leak, no matter where, when and under what circumstances should be fixed before driving at all. there is no guarantee that this mysterious leak the only appears when the engine is stopped wont turn into a leak that pours fuel all over a hot engine on the freeway all of a sudden. i think you are on the right path with the charcoal canister but your system, being later and on a us car that has much tighter emissions standards then an english or australian car will be very different from what mine is.

do you have a factory manual? i have one at home but wont be there till Thursday night (Australian time) but i can see if my manual has the updated diagram and if so i can post it if you still want it. if you dont have a copy ide recommend buying a factory series 3 manual in paper form. it may cost a little more but having it all on paper in front of you is worth the $50.

jaguars are bandits for under bonnet fires and im paranoid about it to the point i carry a fire extinguisher in the passengers seat (of all my cars). sometimes i even get frazzled if i drive by a petrol station in my xj6 without realizing and smell petrol lol


regards jay

 

I do have the factory manual and using that the good advice of others here I have largely determined it to be caused by one of two things. I intend to replace both suspect systems in one fell swoop and see where that gets me.

1. The Fuel pressure Regulator is broken (maybe?), causing the excess fuel to be drawn in through vacuum lines not designed for the fuel injection pressures. I have a working replacement part but the nut is unbelievably stuck (thus my other thread to which you already replied).
2. The fuel changeover valve in trunk and/or return valves in each rear wheel well.

The changeover and return valves are a pretty hefty expense (the set for all 3 runs for ~250$USD at Welsch Enterprises ( Welsh Enterprises, Inc - Jaguar XJ6 Series III (80-87) Fuel/Emissions Fuel Tank, Fuel Delivery & Return Parts - Fuel Return Valve Kit )) but I trust that the added piece of mind and cleanliness in these old fuel systems even only at points certainly can't hurt.

Currently working on testing the changeover valve in trunk to see if I need the kit or just the ones in the rear wheel wells. From all I can gather these jobs are just disconnect battery, depressurize, clamp, disconnect, remove, refit, ignition. Are there any tips, suggestions or cautionary tales from anyone out there pursuing or who has pursued this same remedy?

and jay, after I saw my first engine fire in person on the highway next to me, I bought a fire extinguisher and keep it in cabin at all times. It's not being paranoid once the fire starts!

thanks.
john cook.

 

The FPR can fail a couple ways. First, the diaphragm can leak allowing raw fuel to be drawn into the vacuum hose and thence into the engine.

I suppose it might leak in such a way as to allow pressurized fuel to be pushed into the vacuum hose but I'd have to mull that over. Not sure.

Or, even if not leaking, the FPR can fail to correctly regulate pressure. A pressure gauge is obviously the best way to check. Normally, if the pressure was too high, the fuel would be pushed (too strongly) thru the injectors causing over fueling





Not really sure how the changeover system would cause a leak at the engine....unless *both* return valves were closed....in which case pressure would indeed build up on both sides of the pressure regulator




Sounds right


Here's a bit of reading that might or might not be helpful
Fuel Tank Switchover Checklist, Series III XJ6

Cheers
DD

 

how did you go with removing that fuel pressure regulator?

recently i was driving down the freeway and found a car up against the barrier and on fire. all it needed was a blast from an extinguisher or even a liter of water but instead it was totaled, seems a waste. after that i bought 3 x 1kg fires extinguishers from a garage sale, 1 for each car for $15 all up, seemed pretty good to me!

regards
jay

 

Doug,

As to why I think the fuel changeover system is related, there are two reasons:
1. is this which I saw over at jag-lovers:
"FUEL CHANGEOVER SYSTEM: If the fuel changeover malfunctions there is a possibilty that one tank may become overfull. If this happens, excess fuel can be drawn into the fuel vapor cannister (in front of the right front tire) and, from there, is drawn by engine vacuum directly into the engine. A fuel drip in the area of the front wheel is an obvious indicator. For diagnosis, the vacuum line from the cannister to the air inlet tract can be removed and checked for signs of raw fuel."

2. Selecting the right tank before I kill the engine causes the drip to go away. Staying on the left (my primary fuel tank) before I kill the engine causes the drip to be present once the ignition is killed.

For those two reasons, I surmise that the left fuel tank return valve has become either clogged or otherwise broken causing the lines to become overfull and leak near the front right of the gearbox just to the inside of the right wheel well (as described in the jag-lover quote above).

Anyone care to weigh in? I am planning on simply replacing the left return valve and fuel pressure regulator now unless someone else here strongly suspects a different culprit. Thanks for all of the input thus far.

 

Concluding notes:

On 5/1, I replaced the original lucas fuel pressure regulator with a GP Sorensen FPR part no. 800-157 as well as the nut and washer holding the FPR bracket to the fuel rail.

This completely resolved my leak after shutting the engine off. Fuel was being drawn in to the vacuum hoses on either side of the fuel temperature switch as a result of the faulty FPR. Removal after FPR replacement shows no signs of fuel where before fuel was leaking out of the (unclamped) connectors to the FTS (obviously, as they are neither the right grade nor clamped to deal with raw fuel).

It also resolved some rough starting/idling issues I had been having (aided of course by the installation of new fuel and air filters, an oil change, AFM adjustment and cleaning and replacement of the coolant temp. sensor). Problem solved, now onto the recharging the A/C with R12a and redoing the front brusing and upper/lower ball joints to get the handling back in shape).

 

Good job !


Cheers
DD

 

Evening John, I believe this file I have shows the fuel injection components and their full tubing and housings. I will send the file posted here