Hey guys, I couldn't find a post about this so I figured I'd ask. I have a 2003 XJR that recently began having some issues. A week ago the car began giving us a "restricted performance light" intermittently however I could get no error codes from the car for some reason. For about 5 minutes at a time every few days the car would kick in the rev limiter at only 3,000 RPM, then the light would disappear and everything would go back to normal. I kept driving in an attempt to figure out and the other day it died completely.

The issue was beyond my rudimentary understanding of automobile inner-workings so I took it to my mechanic. He found that the ECU was not grounding the fuel pump (can't remember if primary or secondary) for some reason. He grounded the relay attached to that pump and the car started right up and ran fine, although it still had the "restricted performance" light. We thought everything was going to be fine but then when test driving it the rev limiter again kicks in around 3k RPM.

Has anyone seen an issue like this? Does this require replacement of the ECU or can it be "reprogrammed" somehow?

Thanks for your time guys!

 

One of your two fuel pumps has failed.

During startup and normal driving they use secondary and primary respectively.

The descriptions for the sequencing and testing can be found in existing threads.

 

Take your OBDII reader and plug it into the car and drive, when the car goes into RP the code reader will capture the temporary code. You are having a temporary fault that must occur 2 times in a given period of time to set a real code for you to read. This is a common issue with failing knock sensors. The RP is initiating the rev limiter.

 

The previous owner stated that he replaced both pumps shortly before I purchased the car. Obviously that could be a fallacy but he seemed irritated about the cost, so I doubt it.

Additionally I do believe the mechanic tested both and they were fine, save for the fact that the secondary pump was not allowed a ground by the ECU.

Does this normally happen when a fuel pump has failed?

 

Is it possible the RP is caused by manually grounding the secondary fuel pump relay without the ECU's "permission"?

If I'm understanding correctly, any time the RP light comes on, regardless of reason the rev limiter kicks in yes?

 

Yes the rev limiter kicks in when RP is activated the other about the pump I do not know. Plug in the OBDII reader and find out the real reason for the RP.

 

Thanks for the help!

 

Please let us know what you find.

 

Omni, I had a similar issue with my RP coming on for a minute or two and then going away. Over the period of about a week to ten days it got worse until it finally popped a code. The fix was a bad coil on #6. It had to fail almost completely before a code was set. It was still drivable as it would cycle back and forth but it was getting to the point that even a short run to town might cause it go on and off 3-4 times in about 5 miles.

 

I am not sure we will ever know. So often we get questions we provide input and never hear from them until another opportunity crops up. I hope they will come back with an answer.

 

It was actually the primary fuel pump. This is something the mechanic should have caught initially but he got thrown off by me telling him the pump was changed recently. So basically he worked around the issue by grounding the relay to the secondary pump. The car was running off the secondary pump (I think) after that, and that is why it was running, but running with the RP.

I do appreciate all the help, I told him to revisit the pump and that's when he found the issue due to your responses.