Any idea what could cause this on my 04 XJR? I've had the problem for a couple of years. A variety of codes have come and gone, and currently I'm showing just P0231. I have replaced the fuel pumps, filter, fuel pressure regulator, plugs and wires, coils, O2 sensors, and this week the secondary fuel pump driver module. Nothing makes any difference.

 

I'm unable to play your .avi file on my phone. I will try again later at the PC, but from your title, are you saying your engine is rev-limited to 4500 rpm?

I havent seen this symptom before, but P0231 is indeed a secondary fuel pump code. You have obviously checked off most or all of the potential source of failure. Do you get put of range measurements for fuel pressure and STFT LTFT?

Seems to me if pressure numbers are in range, and with all of the system component replacements, perhaps you need to focus on PCM and sensor input, Cam and Crank position sensor inputs etc. I apologize for such broad strokes, but that's sort of the point I am making. Zoom out your view, cast your net a bit wider to include what the PCM is doing. If the fuel system is working as designed, and the 4500 rpm is truly hard limited, it might be worth widening the scope.

As I recall, the rev limiter is around 4000, unless the transmission is in drive.

 

Thanks, I'll check the sensors next. This whole problem started with the fuel pumps about 4 years ago. The car died and wouldn't start, and I couldn't get any pressure on the fuel rail. I replaced the pumps and it cranked right up, but anything more than a couple of seconds of full throttle would cause massive detonation and misfires, with the check engine light flashing. I did more research and discovered that the XJR doesn't just have two 3.2 bar fuel pumps, but two 5.1 bar pumps. I replace them with the correct Pierburg pumps but the problem remained. Over the next year I replaced all those other items, but no change. I parked the car in January, 2019 because I was moving away for a year. I started working on it again recently and now the problem is different. Now it's limiting to 4500 rpm, but no CEL, no misfires, no detonation.

 

You could connect up a decent diagnostic reader to see if you can get live data to see if there is anything obvious at fault, fuel trims etc. That might provide you with some clues. Has the P0231 fault code now gone for good?

 

I think I might have solved it. Yesterday I removed, cleaned and replaced the crank sensor, then test drove it. No change - increasingly sluggish as the rpm climbs, and it chokes out around 4200. I tried unplugging the O2 sensors, no change. I plugged them back in and got the old result - almost immediate sputtering, detonation, check engine light blinking like a pinball machine, restricted performance indication and the car almost quit. That run gave DTC's for multiple cylinder misfire and misfire rate cat damage. I started thinking that whatever the problem is it must be something the PCM doesn't monitor. Just for ***** and grins I removed the upstream O2 sensors, leaving the exhaust open, and tried again. It ran like a scalded dog all the way to 6,200 rpm. No hesitation, no misfire, no codes.

I think I need cats.

 

Maybe the upstreams sensors are faulty. Maybe try replacing them first incase it isn't blocked or faulty cats.

 

They were replaced with OEM two years ago, and unplugging them took them out of the equation.

 

I replaced the cats today with a pair from some company called Davico. The best thing that can be said about them is that they're cheap. They have the worst looking welds I've ever seen, and the left one doesn't fit to the downstream pipe because of the angle. I got it in a little way and clamped it, and it's not leaking at the moment but I don't expect that will last. I'll take it down to Midas and let them straighten it out.

Other than that the car runs great. No more problems, DTCs or anything else. All the power is back, right up to redline. I think what I had was a series of cascading failures starting a few years ago with the fuel pumps and ending up with the cats, maybe because of all the misfires. Anyway, it's finally fixed.

 

I am glad to see you hitting the upper stratosphere once again; it must be a joy after all the pain you describe. Those were the cheap CATS? Ouch! Hopefully most of us won't experience something like this during ownership. I am curious about "Cat-cleaner" fuel additives; often sold as a shortcut to pass emission tests. I imagine they could help a partly clogged CAT, - as long it it isn't crumbling internally.

Did you consider, or try any of this stuff? Can't imagine it clearing a converter as blocked as yours must have been. It could even make things worse by breaking down carbon at the front of the converter and blocking the honeycomb further. Then again... You could have tried THIS LUNATIC's solution. He puts a gallon of lacquer thinner in the fuel tank and tell people to "drive 150 miles" - Ok, sure. Maybe on a 1988 Corolla with 392k miles and so much rust you can stop the car using the Fred Flintstone method. But on an XJR... It takes an "interesting" mindset to do $#iT like that. Or soak converters in laundry detergent. They can be brutally expensive though, so people will be people - and try stoopid stuff - LOLOL

<- This guy obviously has fans. I am not a member of that group.

 

LOL. My usual fix for cats is a big spade bit in my drill. They perform well when they're hollow. A couple of anti-foul adapters for the downstream sensors and everything is good. However, that method depends on having a straight shot through the cat for the drill, which the Jag does not.