Hello, great forum! Been lurking for a while now picking up great info on these cars.
I've been trying to help a friend of mine get his Dad's XJS working again. Car's been garaged since before last winter and when tried to start in March nothing.
Not a daily driver so I could spend the odd couple of hours trying to get it working.
Bottom line is there is no fuel pump operation when turning on ignition. I've read all I can about this including AJS engineering pages.
Fuel cutoff switch operating as expected
attempted to replace relays for both main and fuel pump - no joy
Replaced fuel pump (old one would run with direct feed from battery though) no joy
tried removing fuel pump relay and ground the orange wire from pin 87 - no joy
So I suspect ECU is at fault and last night removed from the car expecting to find a 6CU but it already has a 16CU!!!
So now I'm a bit stumped - should I go back over everything again?
Is there anything I've missed or got wrong?

Cheers

 

First and foremost, welcome.

OH boy.

Remove the 2 LARGE spade connectors part way down the +ve battery cable. Clean them, get a torch, and reconnect PROPERLY. By that I mean ensure the male spade actually slides INSIDE the female section. These 2 Brown wires are the battery +ve supply for the 2 relays you are messing with, and are well known to go hissy.

If the new pump fails to operate with a live +ve feed, and a seperate earth wire, you got a dud pump.

That Orange wire is the Earth for the fuel pump relay, you know that already, so if that is earthed seperately, the ECU is no longer doing the earthing, so the ECU is out of the equation.

Alongside the battery are 2 EARTH studs, remove ALL the wires, clean with Lemon juice, rinse clean, grease and reconnect. These earths are for numerous items throughout the car.

Then comes the electrical section of the ignition switch. These die, age related, and there is NO ignition power supply to the cars components. They are removeable, not easy, and can be opened up and cleaned, and relubed, thus rebirthed. Takes about 2 hours.

Lets know what you find.

 

Thanks for the tips, I've checked those brown spades already but won't hurt to double check. The old pump was working with 12V applied directly but I didn't try starting the car.
I hadn't quite realised that grounding the orange wire would take the ECU out of circuit, knowing that convinces me the issue will be wiring related so I'll double the efforts in those areas.
Would ignition switch problems inhibit the fuel pump circuit? The car does turn over although I haven't cranked it much as the pump never runs so didn't see much point in that.
The car is 6 miles from me so I can only get there a couple times per week, and the owner is out of town this weekend but I'll report back later next week on the progress.

thanks again

 

As you know, the pump should run for 2 seconds with the ignition switch on (dashboard warning lights illuminated), but not not in the start (engine cranking) position.

The ignition switch circuit therefore does activate the pump for 2 seconds. The ECU detects if the engine is turning over and only if it is should the pump keep running. If the switch is playing up, it could stop the pump running for those 2 seconds or the engine cranking. However, if the car is cranking, it is not very likely the switch is the trouble. More likely the wiring fault to the pump is elsewhere. Try hot wiring the pump and cranking the car and seeing if it will start. But do not drive it like that!

If it does start, then next thing is to see if the pump relay is receiving volts for a couple of seconds when you switch on the ignition. If it is, and the pump is not running for those two seconds, you know the fault is not with the switch. If it is not, then you know the fault is somewhere in the circuit operated by the ignition switch that runs the pump for two seconds.
Greg

 

So an update....
Went over to the car last night and refitted the ECU, cleaned the earthing points and checked through the wiring again - no joy. In keeping with checking everything, I took the original relays for the pump and main and applied 12V to pins 85, 86 and got the click and short circuit on pins 30 to 87 for the pump relay but nothing on the main! I made sure the polarity was correct as the main relay has a block diode to prevent wrong polarity connection.
So bought a replacement 30A relay from Maplin and put it in there and no joy???
On closer inspection to old relay had its own circuit diagram and pin 87 is doubled on the output, the version I bought had 87a and 87!
After a bit of head scratching, I put the good pump relay into the holder for the main, and bridged pin 30 to closest 87 wire AND bridged the two 87 wires of the pump relay holder and reconnected the battery, THE PUMP RUNS!!
Had an assistant sit in the car and reconnected the battery and tried to start - two turns and it fired up, purring like a cat should.

So I now need only to get the correct relay for the main and I can get on with trying to bleed the coolant system! This is what I set out to do some 5 weeks ago after repairing the AAV valve. a couple of months ago.

No doubt I'll need to post about the best methods to get all the air out of the system - I understand its a long process sometimes?

thanks for all your help guys!!

 

Keep it simple if the fuel pump is running then check for a spark.
The easiest thing to check for a spark, forget voltages at the coil and plug wire testing pull a plug wire off a plug any plug use a spare spark plug any spark plug hold it with pliers or a rag against the engine block or head get someone to turn over the engine do you have a spark??????

 

Well he did say it started up and was purring like a kitten, so it sounds like he got it figured out! Glad you got her running again. I love that feeling of victory you get when you hear it fire up!

 

Oh yeah, its running pretty sweet, just haven't taken it out on the road yet.
I'm expecting delivery of a replacement Bosch main relay complete with block diode this morning. Didn't fancy driving with a permanently running pump!

I had previously repaired the throttle linkages and the AAV on this car so she idles very well and responds to the throttle pretty sharp for such a large motor.