Ok so I have a similar problem. Ran fine then the pump stopped. Wiring all checked out ok. Started up a few hrs later but stopped again then nothing. Had the ecu checked by aj6 and they said it was fine, had them upgrade it anyway. Plugged it in and it run lovely. This weekend the pump did not come on with the key so I flicked the key a few times and it then worked, got a mile down the road and it cut out. If I ground the orange wire the pump runs but won’t pressurise so the engine won’t run either. And ideas???
Edd,
I see that you are new to Jag-Lovers. Welcome.
What is the year and model of your Jaguar and what engine does it have?
Paul
Hi Paul,
I’m afraid I just have the engine of one of the fine beasts. It was an xjs v12 5.3 but the car was beyond repair so I kept it british and put in in my mk2 Ford Zodiac.
Edd
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A Jaguar V12 in a Zodiac, Edd …?
Fair enough, but the car wiring would differ…
Welcome on board - we’ll solve it…
Frank
xj6 85 Sov Europe (UK/NZ)
Thanks Frank,
I used all the running gear as well so its more jag than anything else 
.
We used all the looms so it is as close as possible. It did run fine but it seems to be a semi intermittent problem.
Edd
Edd,
I suspected that there was more to the story from your post. AFAIK Jaguar never used orange wire for fuel pumps. That made me wonder.
If you were having this problem in an XJ12 or XJ-S I would suspect a bad ignition switch or a failing fuel pump due to fuel tank debris. I have no clue what it might be in a Ford Zodiac and I had to look at images on Google to find out what one looked like.
Paul
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I assume then that all wiring looms and components were transferred in toto, Edd - and the engine did run properly before ths problem occurred?
On the V12, the fuel pump is activated for two seconds as the ign is turned ‘on’. With an intermittent problem, sometimes no pump action when the key is turned ‘on’, the fault may be the ignition key itself, the relay or the pump…
Grounding the orange, as you did, should indeed run the pump if the fuel relay operates. Then it gets a bit murky…
Did you actually check fuel pressure with the pump running? And did you check that the injectors were clicking while cranking? If you have an ign key fault or a faulty main relay; the ECU may be unpowered - and will not operate the injectors…
The V12 set-up is somewhat complicated - but for sure; if the pump operates it should give pressure, and this should be verified. An intermittent, or weak pump, may do what you describe - a fuel pressure test may clarify matters. The point being that a fuel pressure test is unambiguous - removing some uncertainties…
And a V12 in a Zodiac is well worth the lists attention - to be dealt with as a V12 problem…
Frank
xj6 85 Sov Europe (UK/NZ)
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The pump is ok (jag pump, I used everything I could) it’s something that switches the pump.
Pictures required, that one of the more unusual swaps.
OK, I’ve only briefly scanned this thread. But a 1982 V12 will have a 6CU ECU, and the 6CU is known for failed fuel pump relay circuits. In fact, it would have been unusual for it to have operated this long.
Two choices: 1) you can take the orange wire from the fuel pump relay coil to the ECU and connect it directly to ground instead. This will enable the fuel pump to run whenever the ignition is on. Car will run fine, but you lose the safety feature that the ECU will shut off the fuel pump if the engine isn’t running. Like, if you crash the car and the crash manages to stop the engine.
- You can ship the ECU off to Roger Bywater for repair. Or, of course, just buy another one. If you go the buy another one route, it is suggested you buy the later 16CU. It’s a plug-in upgrade.
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If so, Edd - why no fuel pressure with the pump running…?
The ECU may be the culprit as Kirbert says, even if it checked out OK by the ‘aj6’ people - with an intermittent fault one never can tell…
The ECU simply grounds the orange fuel relay wire to run the pump. It is easily checked, with the orange wire disconnected from the relay - 2 seconds ground at ign ‘on’. And indeed, with the relay separately grounded - the loose end of the orange wire should show ground with the engine running…
This function should be irrelevant to the other ECU functions…?
frank
xj6 85 Sov Europe (UK/NZ)
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Hi Frank,
This what I don’t understand… what tells the pump to stop when it’s at pressure? It’s got to be electrical as it ran fine with the re programmed ecu. If it was a mechanical issue then it surely would be faulty or not??
No pressure involved…
The ECU will switch the pump on.
It will keep it on as long as the engine is running.
It will switch it off 2 seconds after it detects that the engine has stopped.
The pressure is regulated at the fuel rail and the excess goes back to the tank.
For safety, the inertia switch should do; but probably no flooding protection if you forget the ignition for a while. I‘d do 1).
Ok. So there is another issue somewhere. If I ground out the orange wire the pump runs but the engine won’t start. Frank sensor is sending a signal so I know that’s ok. Tried a new pump relay before so it’s not that.
you can also put the car in reverse, open up the air flap in the Mas Air Flow Sensor. I’ve used a screwdriver handle side inserted to hold the flap open. T hen turn the key to the on / run position. You should hear the fuel pump run.
What you’re essentially doing is faking out the car that it is going backwards. The fuel pump only runs when the engine is running or starting the car.
Have you checked the fuel pressure at the fuel rail. should be between 26 & 36 psi.
If you’ve done all of the above, then carry on.
Hope this helps
No you can’t on the V12. I wrote that too but caught it😅
Hmm… I missed the V12 bit. Oh… I see it now. Of course frank nailed it. Actually Frank is the one who taught me that trick. Credit goes where credit is due.
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That was what’s puzzling, Edd…
The orange is connected between the fuel relay and the ECU. Which grounds wire internally for two seconds in ign ‘on’ and continuously while the engine is turning (cranking or running - induced by the ign amplifier).
This function should not interfere with starting/running - but, in principle, the orange wire should be disconnected from the relay, and the relay grounded separately. (I’m not sure how the ECU will react with external grounding of orange ?). The ECU grounding function can then be tested separately by checking ground on the loose orangeend…
Assuming that the fuel pump pressurize the rail, as David explained - a functioning ECU should run the engine with the fuel relay grounded. However, since the problem is intermittent a fault may not be confined only to a faulty fuel relay grounding outlined by Kirbert? There are unknown nooks and crannies in the ECU.
To test ECU; listen to the injectors clicking while cranking - signalling that the ECU is operating. If they do, and there is fuel pressure - the engine should start. But verifying fuel pressure may be pertinent…
An intermittent fault can only be pursued with the fault present - and as long as the engine is starting/running; the fault is absent…
Frank
xj6 85 Sov Europe (UK/NZ)
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If I understand correctly:
Your ECU is not turning the pump on but even when you run the pump manually the engine will not start ?
I guess next step is to check your fuel pressure and pressure regulators.
If you have pressure indeed, and you know your ignition works, I suspect a massive ECU failure.