Hi all! For the past months I have been hard at work on my next xj-s project. This time it's a black 1984 xj-s V12 with biscuit interior.

The car was in such shambles from the interior to the paint to the electrics that I tore it down pretty extensively. All the exterior trim was removed in preparation for a repaint.

I just finished rebuilding and installing the rear suspension assembly and went to start it for the first time since February. Alas, no start... I could hear the fuel pump relay click, then click again a few seconds later as it should when the key is in the "on" position but the fuel pump wasn't working. But I tested the fuel pump and it is fine.

So I hotwired the fuel pump and sat in the trunk and simulated what it does under normal operation while my assistant cranked the car. Because it is still not starting I assume there is no injector pulse?

Any ideas what is going on? The relay is working but the fuel pump isn't. Are there grounds/fuses I can check that might result in such symptoms? Also is there something that could fail which would result in no injector pulse or fuel pump operation?

P.S... I have confirmed spark so I know I'm on the right track with the fuel delivery issue.

Thanks in advance

 

Actually, no.

If you turn the key on the relay should power up the pump for about two seconds. After that nothing else should happen unless A) you turn the key to "start" or B) you cycle the key "off" then "on" again.



"Fine" as it makes noise or "fine" that it actually delivers fuel pressure ? :-)





Assuming the pump is working and you have fuel pressure, yes, I'd say lack of injector pulse is a good possibilty. A noid light would be really helpful in verifying this....only a few dollars





Power TO the pump relay AND the fuel injectors comes from the "main" realy....so that's one place to look. It'll probably be right next to the pump relay and it has the following wires:

Brown 12v constant voltage
White 12v key "on" voltage
Pink/black 12v output to injectors and pump relay
black ground

Cheers
DD

 

Not sure about your particular year of XJS, but I recently replaced the fuel pump in my '92. I had power to the plug at the top of the fuel pump access cover, but the pump wouldn't run. I ordered a pump, and upon disassembly, discovered that the wiring and plug on THE UNDERSIDE of the cover was burnt to the point that it failed to make connection. Kirby's book discusses how to rewire it using some bolts placed through holes drilled in the cover, which I had done. My old pump was good, but since I'd already purchase a new one, I replaced it anyway as cheap insurance.

howlinowl

 

Have a look at the battery +ve cable, about 4" down from the terminal, and you will see a connector crimped around a bare section of cable. Inside that plastic cover are 2 terminals, which should have heavy Brown wires attached. These Brown wires are the +ve juice to the "main relay", and the "fuel pump relay", and they do fall off at times.

The relay "clicking" indicates that the ign is supplying a signal to the relay coil, and the ECU is supplying a timed earth path for that coil, so the relay "clicks", which is the contacts closing. Now, the 2 other terminals on that relay are (1) the Brown +ve juice, and (2) the wire TO the fuel pump. Soooo if the relay closes contacts (yours is), and there is NO juice in that Brown wire, the pump will not work.

Look carefully at the socket that the relay plugs into, as I have had the wire going TO the pump slide out of that socket as the relay is plugged in, and not enough to fall out, but enough to be clear of the spade on the relay, so nothing happens when the relay closes.

Injector pulse is a different issue, and Doug has mentioned the basics so far, but many items come into play here.

 

Development: In addition to the non start issue, I had smoke! The cluster of relays on the passenger side engine bay (the one with the starter relay), and the cluster of relays in the trunk were smoking profusely and smelled of burning insulation whenever I turned the key to "2".

For some reason, I popped in my 16cu spare ecu to replace the 6cu unit that was in there before. No more smoke and it fired right up. go figure.