After its winter hibernation my 1978 XJ12 went to the garage to have its headlights replaced, it drove fine to the garage, then back to my house and then to where i keep the car, 15-20 miles in total, on arriving at my storage the car started running very lumpy, down on power and spitting and banging, we managed to get it into the unit and turned it off, after a while we fired it back up and it was still running rough.

My mechanic looked at it and suggested we replaced the HT leads, we done this and the dizzy cap and rotar arm at the same time, come to start it up and it just won't fire, mechanic came back and discovered the fuel pump wasn't giving out a decent flow so we replaced that and still no go, a new set of plugs and fuel filter also hasn't cured the problem and i think hes running out of ideas.

It is seemingly trying to fire now, its not just turning over anymore but it won't catch, i don't like the stuff but a few squirts of easy start up the air trumpets allows the car to run almost immediately but it quickly dies once thats burnt off.

It has a decent spark at the plugs and plenty of fuel getting to the fuel rail but it just won't catch and run. Does anyone have any suggestions for anything else it could be?

Thanks everyone

 

Air filters clean? Exhaust clean? Have seen mice nest in these areas that disperse when started and plug the runway. Had an XJS with 5lbs of dog food in mufflers. Slowed car down very well.

 

yeah i've had both air filters out and they were both looking fine. I can't say i've noticed anything unusual coming out of the exhaust when it was first started and she fired up fine everytime before it suddenly started playing up after a couple of days of first being used

 

Mmmmm, PreHE.

The NEW rotor has the magnet in the heel???????

This magnet is used to trigger the switches in the trigger board to activate the injectors.

MOST, nearly ALL aftermarket rotors do NOT have that magnet. They are hard to find, and the last one I needed was $90.

The fact it runs with Ether, is a sure sign of that missing magnet.

BUT,

If the magnet is in place, well done, then the trigger board is all that is preventing the whoosh juice entering the cylinders.

There are 2 versions af the trigger board.

1) 3 wire unit. The original, and imbedded with unreliable reed switches.

2) 4 wire unit. Imbedded with Hall Effect Sensors, and much better. The 4th wire is for connection to a 12v Ign supply.

I would check that rotor first, and if it is magnetised, count the wires on the trigger board, and come back.

 

Hi Grant, thanks for the reply, it does sound like it could be the rotor arm, the part we got listed in the SNG catelogue was JLM9624, and its listed for pre HE and HE to 1989

Part search results from David Manners Ltd - JLM9624

which was neither hard to find or that expensive so would suggest it was the wrong one, will get it out and compare it the one that was in the car, luckily i kepted all the old parts.

While trying to investigate this problem i think i've found another one, when you turn the ignition on, the fuel pump comes on like its always done since we've owned it, but reading online its supposed to cut out after a couple of seconds once its pressurised the system, and then come back on when you start cranking, mine never cuts out while the ignition is on, it just runs constantly. The car has always been hard to start when its been sat for awhile so has this been causing a long term problem?

 

Well done.

That number sounds wrong, but thats my memory saying that.

Some V12 listings for that rotor quote the E Type V12, which with carbies has NO magnet, and is the same rotor as the HE. Confused??????, nah, its a Jaguar.

The fuel pump timing circuit doing that is not uncommon. The most common "fix" was to earth the fuel pump relay terminal to a close by earth, instead of via the ECU circuit. Those old D Jetronic ECU's are bullet proof, and have few issues.

Memory again??????, that fuel pump relay is the 2nd one in from the right hand end of the units mounted on teh radiator top panel, but I might be wrong.

Hard starting etc is usually related to the old 3 wire trigger board, they really were that bad.

Rotor magnets losing their magnetism is also getting common now due to age and heat.

The next issue was the Opus fiasco, but, you are on a winner, ya got spark, the Ether proves that.

 

Thanks for all this help once again Grant, i don't think we would of ever picked up on this idea without you. It was starting to get slightly baffling as we had a good strong spark at the plugs and fuel getting to the rails but no firing.

Looking at the old rotor and the ones in the parts listing under that code are clearly different. Hopefully the magnet in the old one will still be ok and we can just clean it up and pop it back in because i have no idea where we'll find another proper one.

 

DO NOT clean the tip. Leave it as gungy as it is.

Test that magnet with a steel nail. It is NOT a strong magnet, not needed, but will still raise a 2" nail. I have had a few where the magnet was quite weak, and they still worked fine, albeit with the 4 wire trigger board. The Hall Effect are more magnetic sensitive than the 3 wire reed switches.

 

Time to Google up "how to remagnetize" !!!


At one time devices existed to do that to magnetos, that were once popular as ignition voltage sources.


And on most if not all one lung engines...


Carl


Carl

 

im pleased to say it looks like the magnet in the old one is fine

 

Well done.

 

Now, does it run?

 

. . . a fortnight and no news is poor forum etiquette Ryan . . . and given the prompt expert help you received, hitting the "thanks" button to Grant's posts would have been warranted, don't you think? I figure it's just an oversight, as we all do our best to keep these forums as friendly and courteous as possible.

Regards,
Ken.

 

BUT,

He is in the UK, and the damn thing is probably running so well he has driven it off the edge of the island, oops.

OR,

Is still in the pub celebrating.

My 2000km drive home with the XJR recently, would have found the edge of the UK for sure, didnt see him?????

 

sorry for the slow reply, i've been out of action for the last week and half or so, so hadn't had a chance to work on the car.

We did get over today, finally, and replaced the original rotor arm with the original, connected the battery and turned the key. Success she fired almost straight away. Left her running until the temperature gauge got up to normal and she seemed to be running fine.

Didn't have time to take her out for a run today but its meant to be decent weather tomorrow and monday so hopefully we can take her out and check the rough running doesn't return.

Did notice when i turned the engine off we have a small steam leak coming from somewhere around the near side top corner of the radiator, if its not one thing its another it seems at the moment

video of it running

http://www.youtube.com/watch?v=-SpxT...ature=youtu.be

 

Hey Ryan . . . well done . . . and big kudos for taking my tap on shoulder comments with good grace. This issue of matching rotor arm, not only physically to match dizzy, but also to triggering efi, is a trap that many of us have fallen into . . . usually when replacing worn or damaged parts.

I won't comment specifics on rad steam leak as I am unsure if V12 rad matches same year XJ6, or XJ-S, or neither. Generally though, I would remove rad and get rad specialist to pressure test and repair as required. Bonus is that they can clean out any clogging at same time. IMHO, not really a DIY job and I never trust the Bars Leak type of fix.

Cheers,

Ken

 

Well done Ryan.

Your round at the local, whenever I find the UK, and travel there, HAHA.

The PreHE EFI radiator is a BIG sucker, and the "tinning" at the end plates is the weak point.

If and when you are stooging around and find a spare radiator, the S2 Injected V12, EARLY S3 V12, and ALL XJ-S PreHE radiators are the same. The cut OFF point in 1981ish. The later HE (1982iah onwards) radiator will fit, TRUE, and simple to do, but a fan blade change is recommended, OR, like mine Efans, and not for discussion here at this moment.

The early Carby V12 radiators are different, so be careful.

 

Forgot, I do that.

Have a close look at the bundy tube small pipe, that travels from the RH side of the radiator to the LH side, and has a small hose attached just above the LH top radiator hose.

That bundy pipe rots out quickly, and may be the reason for that steam.

That bundy pipe is UNDER the rad top panel on the S2 V12 cars.

 

Thanks Grant . . . I knew it (bundy pipe) but couldn't think of it for all the tea in China. They really did rot out, but were well hidden. What I did not know (as admitted in my post) is that all the injected S2 & S3 XJ12s and all pre HE '79 -'81 V12 XJ-Ss all shared the same rad. Drat . . . that means my '79 XJ-S has same weaknesses . . . more things to check!

Thanks for info, Grant,

Ken

 

Ken,

Find an old school radiator shop, should be easier in your area, and get them to double tin the thing, then NEW OE radiator mounts rubbers, 4 of them, good as made.

The S3 V12 I refer to is the early PreHE versions, just to be sure.