Hey Gang, I have an 1984 XJ6 mk3. I was leaving school and it started but as I was pulling away it died and would not restart. I had it towed back home and this is what I'm on about. When I move the key to the ON position every morning I can hear the fuel pump pressurize for 1-2 seconds and then stop, I don't hear the sound of the fuel pump prime the system before first startup anymore. I think if I found the cause of this problem it would run again! If I hold the MAF flap open, with the key in the "ON" position the fuel pump will run. I have replaced the fuel and main relays and rebuilt the diode pack. I also went to a junk yard and picked a part, what is that green Lucas relay box by the fuel pump? Changed the green box and still nothing? What could it be?!? Thanks for your input everyone.

 

Very odd that you ever heard it as the "prime" capability was not designed into the 4.2 fuel injection system. On the V12 cars, yes....but not the XJ6s.

I think you were hearing something else.....or a PO has altered the circuit in some way.




I suspect so, yes.



Ok, good, at least "run" half the circuit is operational. I think you're missing the branch that powers up the circuit when the starter is engaged.....the "start" half of the circuit.

This should help...but all bets are off if someone has modified the circuits.

Fuel Pump Circuit Checklist



That's the antenna timer-relay

Cheers
DD

 

Thanks for your help Doug, I also have no voltage to the pump during cranking. I have also checked the ignition pinout and the inertia switch both of which are operational. Anybody have an idea of what that sound is when the key is moved to the ON position? Thanks

 

Maybe your hearing the climate control servo initialize with the key "on"? It makes a whir sound. Just a guess.

For voltage to energize the fuel pump relay when cranking, power comes from a white/yellow wire off the starter relay to diode pack terminal #3, thru a diode, and out to the f/p relay on terminal #5.

Cheers
DD

 

Pump starting when moving the MAF flap proves the correct operation of the fuel pump relay and pump. This is the mode when the engine is running, and is bypassed when starting. When you crank the engine the pump volts supply via the MAF is bypassed by the ignition switch until the engine starts, when the supply via the MAF takes over. So it sounds like somebody before you has made some modifications you know nothing about. As Doug says, the pump should not start until the engine is cranked, and only continue running whilst engine is running.

 

This, right here, was worth the cost of membership. I had a DPO wire the fraking fuel pump right into this relay.

Seriously.

 

simple way to check if the fuel pump runs:

First, make sure the a/c Mode switch and radio are OFF. Total silence required.

Second, place the shifter in 1st gear, turn your right ear to the rear seat as you try to start the engine, you should hear the fuel pump charging with every turn of the ignition switch.

 

DPO ? Sorry. I'm not up to speed on this US slang, although suspect it is not complimentary !

 

PO = Previous Owner
DPO = Dumb Previous Owner

:-)

Cheers
DD

 

Thanks Doug, I shall keep it in my lexicon for future use !

 

I like the idea except the sound stopped happening the day after the car died.

I hooked my Multi meter up to it and cranked and no voltage at the pump. Ill do a wiring check this weekend and get back to you.

Does and one have an xj6 1984 ish year that hears this prime sound on after the car has been sitting a while when you move the key to the ON position? Thanks

 

mine does it everytime, it was built Sept. 1984, it sounds like a "mmmmuuurrrrr" for about 2 seconds.

and I can also force it to make the sound by placing the shifter in 1st gear and turning the ignition switch to Start. The pump cuts out by itself even if you keep the switch in the Start position.

this is an old principle, Jaguar used it since 1962 in all twin-tank models and maybe in single tank models too; My '65 'S' type also has twin tanks (but it has twin pumps) and it does it too. I assume it's pressurizing the system. In the 'S' type, the sound of each pump is a very fast "clook-clook-clook-clook", maybe I have a chicken in there?

 

Acronyms can lead one astray. PO could also mean present owner and following that logic, dumb present owner. - -

When I was in the mist of surgery on my 83, I thought I was hearing the pump whirr. Naaah, it was the antennae going up. radio was on, but volumn way down.

That is why I like test lights and multimeters.

Captainjaguarscathouse is an excellent source of schematics. This is an absolute in dong electrickery on these cars.

Well, the d... water company said the hedge in front of my house occluded the meter. They wanted me to cut a huge hole in it. 6'high and 60" in diameter!!! With the help of my local county supervisor, I got them to comromise. Still a big hole, though. One green recycle can and cutting. Next session includes my chain saw.

Carl

 

that's why you should never turn the engine off leaving the radio on. If you normally put a cover over your car, and one day you decide to go inside the car and start it with the cover on, guess what will happen to the antenna?


I treat it like a 747: All Systems OFF before shutting the engine off.

while driving, change tanks every 15-20 miles to keep the "wings" balanced.

 

Jose:

My Jaguar doesn't see a car cover. It is comfortably housed in the garage. I do switch tanks at about a 1/4 at a time. But, how much gas goes in depends on fuel pricing at the time!!

My Jeep is in the weather, But, it is very hardy. Well over 200k. Clean, tight and strong. Paint looks as good as ever, Not a sign of clear coat burn. A tribute to it's forebear.

Yeah, when I wired my creations, I made everything hot with key on and dead with it off. Not so fussy with present beasts of burden.

Carl

 

So I held the MAF flap open with the ignition on and opened the end of the fuel rail and A LOT of bad gas came out on the other end. Pritty nasty stuff. So I drained the left tank clamped off the right and put another gallon of farm fresh 87 into the left tank and pumped it through up to the fuel pressure regulator it'll it ran clear (although I will still get a few drops of water in the bottom of a gallon at the end of the rail. I can't seem to get it all out.) I checked for spark and test lighted the injectors.

With the maf held open for fuel delivery, spark and injectors I still can't get it start! Every so often ill get what I think is a spudder but its short lived? How is a car with spark, and fuel not starting?

 

And are you getting a nice fat blue spark or a puny orange spark?





Can you be a bit more specific as to what you did here and what the result was?




To clarify, are you trying to start the engine with the AFM (not "MAF", by the way) held open?




Having fuel at the fuel rail is a good sign but it has to be at (at least something close to) the correct pressure, and the injectors have to be commanded to open and close correctly. From what you've posted I'm not sure we're there yet.

One quick-n-easy trick: unplug the coolant temp sensor and use a paper clip to jump the terminals in the connector. Now try starting the engine. Report back if anything changes.

Cheers
DD

 

When I say "test lighted" I just mean I put a 12v light to the injector connector and cranked the engine and I have volts at the injectors with the AFM closed during cranking. Since then I removed the injector and during cranking w/ the AFM opened and I have a healthy spritz of fuel while cranking. The cold start injector isn't working however, no voltage at the injector connector. Also no fuel pump voltage durring cranking UNLESS the AFM is held open. (Im cranking with the AFM open, i have no voltage to the pump under cranking if it AFM is closed) The spark is orange. I tried your coolent temp sensor trick but I read an artical you wrote and saw that I should leave the plug off to get a rich mixture. No luck having it start but I should check to see if the cold start injector opens with the connector off. I was getting 0.5kohms at room temp which is the 160 degree impediance. What should my next step be? The engine doesn't even struggle to start. Thanks Doug

P.s. also noticed fuel in the vacuum lines of the fuel pressure regulator. I'm sure it's not normal but can it be the cause of the problem or do you guys think it can wait till later.

 

Good!



Good!




Fixable, but in and of itself would not cause a "no start"




Most likely a faulty diode pack and/or the diode pack not getting voltage from the starter relay





No good! Needs to be blue. Weak ignition coil is a likely possibilty





Keep reading......



If there's raw fuel in the vacuum line (singular) to the fuel pressure regulator then the regulator is leaking and raw fuel is being sucked directly into the engine and is surely causing some degree of over-fueling...from mild to severe.

It's apparent that you have a stack-up of problems so you'll need to start fixing 'em one at a time. Personally I'd begin by replacing the fuel pressure regulator and then investigate and repair the orange spark situation.

For the purposes of getting the engine started you can bypass the fuel pump control circuit so the fuel pump operates while cranking....and leave the proper repair of that problem until later

Cheers
DD

 

Thanks for all your help. To anyone just joining us let me get you up to speed. My car stopped running after which I took it to a seedy shop who reassembled it...poorly. It isn't running. To get fuel to the engine the AFM must be held open, the pump has no voltage during cranking. With the AFM open I have fuel and spark but it won't start.

In trying to get it started ive:
1. fixed the orange spark by replacing the coil
2. tested the fuel pressure, I'm right at 32psi after cranking and it holds pressure.
3. Drained both gas tanks and cleared the lines of water.
4. Checked injectors to insure they are opening durring cranking.
5. Rebuilt diode pack and replaced starter relay. I haven't checked for continuity between the too yet.

I think it's a timing issue. When I took my car to that shop the mechanic was messing with the reluctor and pickup in the distributor, maybe he set it out of wack. The air gap is correct and the injectors are opening so I assume the pickup must be working. The distributer shaft is not loose and the vacuum advance seems to work properly.

Can you adjust the reluctor position relative to the rotor or is it notched to a fixed position on the shaft?

If yes, Can this type of a mis-timing of the fuel injectors causing gas not to enter the cylinder?

I would like to add my cold start injector is fouled up and I have no voltage going to it as well, I'm waiting for parts

Thanks in advance to all that reply. This car means a lot to me and my wife. We took it to St. Augustine for on our wedding day so we won't let it go easily. Cheers