I don't have any reason to believe I have any issue with the secondary fuel pump on my 97 XJR, but I've often wondered if there were any indicators of a secondary fuel pump failure and how it is validated?

Seat of the pants, is there any typical abnormal behavior that might have one suspect that the secondary fuel pump is not working correctly?

For example, for the crank position sensor, we know that if the tach doesn't register 200-300 RPM when cranking, that's a clue.... not to mention the car isn't running correctly

Or is there a way to identify/eliminate the secondary fuel pump function, say by removing a relay or checking for current at that relay location?


It's just something I've thought about occasionally that if the secondary fuel pump did fail, what would be the symptoms and how would one troubleshoot.

Any thoughts?


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I might be wrong, but I believe the secondary fuel pump kicks in around 4000 rpm! so that might be a good way to test the fuel pump?

 

Perhaps, but what would be the symptoms if it did not?

Is the extra fuel PSI/volume generated by the secondary pump enough that its absence at that RPM and above cause a "seat of the pants" or other symptom one would notice from the drivers seat such as "stalling" at 4k RPM and not climbing?

Or instead would it only be something one would see via OBD such as an increasing lean condition?


I other words, would one even notice?

That's really what I am curious about, how would an owner know if they had a secondary fuel pump issue/failure?

.

 

I'm hoping the ecu would know there is a lean condition if the secondary fuel pump stopped working. Also as a "seat of the pants" feel, I think there'd be a strong enough feel if fuel cut happened.

Does anyone know if the secondary fuel pump, pumps exactly the same amount as the first pump?

 

I believe that the secondary fuel pump 'primes' the system on start up so if the pump was faulty there would be a non start situation. Not sure on the flow rate of the pumps but pretty sure both pumps are the same.

 

See my earlier posts in the X308 section.

It sound like the fuel pump strategy is the same.

I have a little jumper that can be used to jump the
relay circuit with the car off so I can hear if the pump
whirs as expected.

 

The secondary fuel pump relay and control is located just on top of the battery, you can easily remove the relay and with a jumper wire power up the pump it is the same as the primary pump, with both pumps running the pressure is the same as its regulated its the volume of gas that increases as the engine consumes more gas.
A tip is to switch the wires in the harness above the tank so you use the secondary as the primary because its not run as much and rest the primary pump as its worked the most during normal driving.