I installed two new pumps on my 2002 XJR. The pump on fuse 15 runs all the time when the engine is running. It also turn on for a few seconds to fill the rail when one clicks the starter switch. The pump on fuse 7 runs when clicking the starter switch, the same as the other pump, but then does not run again. I have a voltage meter monitoring the pump laying by the drivers seat and it has not come on during any normal driving. Does the computer monitor fuel pressure and turn it on when the pressure drops below a certain level?

Thank for the information.

 

yes, pump 2 cuts in at higher rpm, I've read either 3000 or 3600 rpm.

 

Have never read 3600, can only remember reading 3000 rpm, which I can also confirm that it does on my car (same ECU basically).

 

Yes, that is just what it does. I took it out on the freeway and when entering the freeway, I floored it and the second pump came on in the 3000 RPM range. Now I am happy as all is well. Thanks for the information.

 

How would you know if one of the pumps isn't operating ? What are the symptoms?

 

Diag for those pumps is not difficult. An understanding of the system is necessary though. Pump 1 is the main pump for engine running normally, as stated. Pump 2 is used to prime the rail and for high fuel demand situations. Diag of pump 1 would show up as a start then stall condition. Since pump 2 primes the rail but pump 1 doesn't operate, then the engine may start and stall. Failure of pump 2 would show up as a hard start but otherwise normal running engine until a high demand situation. Pump 2 is not able to prime the rail but once the engine turns over, pump 1 is turned on. I believe there is a way to get pump two to run as pump one by switching the big black connectors that are against the fuel tank in the trunk. Follow the wires down from the top of the fuel tank (where the plug goes into the white flange assembly) down to the next connector. My memory is a little hazy with the specifics but I did have a failed pump one in a car and drove the car into the shop on pump two. Once you have determined the failure, REPLACE BOTH PUMPS and filter socks! You can find them cheap enough through the internet that replacing only one would be silly.

 

I'm wondering if this could be my problem. My car runs and drives, but when I start the car the car turns over a few times before it turns on. Makes me think that the 2nd pump is not priming the rail now that you explained how it works, or is it normal on the XJR since the compression is lower?
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Either engine should start up quickly. the lower compression, in my experience, does not make a difference on start-up.

 

On the later cars ...(AJ27SC)

Either pump can be forced into action as the only pump by the ECM if it is able to detect the need to do so.

So ....

Pull relay 1, if car starts and continues to run, the pump on relay 4 is good.
Put relay back in.

Pull relay 4, if car starts and continues to run, the pump on relay 1 is good.
Put relay back in.

During single pump operation, "restricted performance" is displayed as a result of the relay coil not showing a current draw to the ECM. The ECM can only detect that a relay *may* be bad, not that the pump is bad.

 

See the test above describing the pulling of relays.

If you do not hear the pump priming, it is because the secondary pump is not priming the rail. That leads to a slow start.