Hi Guys, I have a 2001 XJR sadly do not get to drive as often as I would like. The common not able to start syndrome happened and after various reads here found out the fuel pumps had given up one for sure long ago then the second causing the problem to come to light. After replacing both pumps and the car starting fine i did notice that when I pulled the relays while on tick over the buzz from the pumps revealed they were actually both on! My question is, is there something else that I have got to replace that sorts out the starting changeover form primed to run to switch off the the second pump and only connect it on heavy load? Many thanks for any input.

 

I understand that you have pulled the pump relays one by one. Which one did you pull first?

Otherwise, the pumps work as follows: on ignition switch "on", the second pump runs briefly to prime the system; during cranking, the first pump runs and continues to supply fuel after start-up; during driving, the second pump comes on as required by the demanded engine power. This, including the change-over to the second pump if the first one fails, is all controlled by the ECM (it directly operates the pump relays) so there are no other parts involved (other than the pumps and the two pump relays).

 

Hi M Stojaovic thanks for the swift reply :O) to hopefully clear the post up. The way i thought the pumps were supposed to run is turn ignition on on second pump primes... start .. first pump takes over second pump cuts off untill you need more fuel as when a greater load i e a hill or revs above 3000 then both are then operational...in my particular case the new pumps which i will add are actually ford Modeo same specs same era as when car was in Fords hands so I presume Ford fitted this version that was stock (these i bought from a local spares shop here in South Africa where Jaguar prices are through the roof and were quite frankly a tenth of the price R1008 for both less than 50GBP ) and after fitting noticed there was a slight difference in tone, so when I pull the one relay whilst ticking over the number one pump stops replace that relay pull number two it stops put it back both are running seemingly at the same time. So is there a unit maybe that would be reading the condition that has possibly suffered a malfunction or is it the ecu that determines when conditions require both to run in tandem. From the threads that I have read it seems most members who have had issues in the past say a better alternative is to fit a switch using pumps alternating whereby using both alternately so as in my case both seem to be running at the same time will this cause a problem at the engine end, Once again thanks for the reply and hope my long reply does not cause even MORE confusion :O)

 

First, I have to correct myself regarding pumps running at ignition "on" (before cranking) - it is the Pump 1 that runs for ~ 2 sec. and stops; during cranking, Pump 1 will run again and continue providing fuel after engine start-up. Pump 2 will only be switched on during driving and at higher fuel demands or when Pump 1 fails. This is all controlled by the ECM (engine computer). The pump relays are as shown on the drawing:

You said that, while the engine was idling, you pulled one relay (presumably the Pump 1 relay, see diagram) but you did not say whether the engine stopped running or not. I have not done this test but, if you pull Pump 1 relay out (engine running) the ECM will immediately switch to Pump 2 and the engine should not stop. If you pull only the Pump 2 relay, the engine will, of course, not stop. In both cases, you should see "Restricted Performance" warning.

Why do you think that both pumps were running on your car while the engine was idling? If the ECM makes immediate change-over to Pump 2 when you pull Pump 1 relay out (the engine does not stall), you will still hear the pump buzzing but it is now from Pump 2 and not from Pump 1.

 

Hi Mike. Just a quick note to say thank you. Have checked all that seems to be linked and have come to the conclusion the problem is with the ecm. Get different readings befor and after clearing fault codes which leads me to think the next step is take the car for a good run then check again. I did do a hard reset while trying to track down no start so the brain is empty I think the car and maybe mine lol. Anyway only one pump at the moment so will drive and then see if any new developments. Yet again thanks for your help D B