On a stock setup with the one-way fuel system, 55psi is what you get all the time? or will it go higher under load?

Having problems with my XJR, detonation and hesitation above 5000rpm.

Connected up the SDD and monitored the fuel pressure, cruising around it was pretty much 55psi. Holding it in 2nd a full throttle from about 4000rpm the pressure climbs up to ~70psi, from 5000rpm it drops off to ~60-63psi and it starts pinging & hesitating...do two runs 4000-6000 back to back & the pressure doesn't get over 60psi and it pings even worse.

Just trying to figure out if my fuel pumps / regs / valves are on the way out....

More info here Fuel starvation and massive detonation - Jaguar Forums - Jaguar Enthusiasts Forum

 

Read through your other thread, I'll post this there as well.

On an OBD meter (or SDD) it should read 55psi at all times. The sensor has a manifold reference and the system varies the pump speed to hold a 55psi differential against he manifold pressure, either vacuum or boost.

If you use an external gauge you will see 55psi + manifold pressure, so something in the range of 40-70.

I have no direct experience with an XJR but I have done some fiddling with the pressure in the 4.2 XKR.

My guess would be that you have a bad sensor. Located on the right side fuel pressure rail near the front. Held on by 2 bolts, easy to access without removing anything else from the car.

My reasons:
70psi is not a high enough pressure to cause the injector not to open, so pressure too high and fuel starvation don't make much sense together.

You got an error that is pump PWM too low, meaning that it could run slow enough to get back down to 55psi. This should not be a problem, unless the sensor is lying and says the pressure is higher than it actually is.

What to check:
Fuel pressure with an external gauge. This one can be difficult. Most cars any more don't have the handy dandy schrader valve to just hook up a gauge so you might need to invent something.

Fuel trims at idle. Are they way high as if it's compensating for low fuel pressure?

Pump PWM drive. This should range from about 20% at idle to near 50% at 6000rpm. If the drive output is much less than 50% at WOT, then that is likely the reason for fuel starvation.

The raw O2 sensor output. The stock sensor is actually a wideband O2, and there is a lot of useful data in there, if you know where to look. You can't see fuel trims at WOT but you can log the raw O2 ouptut in mA and convert that to AFR. If there is a lean condition, you'll see it.

 

On my 2004 XK8 I had a rash of bad fuel pumps, the first bad pump, original to the car, was losing pressure under load. With my OBD reader, I could watch the fuel pressure while cruising with no driveability issues, and the pressure was normal, at around 55 as I recall. But push the pedal half way to the floor or more, pressure would drop to 10 psi, and the engine would bog down. Now, this is not the point I want to make, but for informational purposes, I never had a pinging problem during these times. Fast forward to 5 replacement fuel pumps later, all done by the dealership, all due to malfunctioning check valves in the new fuel pumps. Again, that isn't the point of my reply to your post. But because I was very concerned that ethanol in the fuel was causing these check valve problems with these new fuel pumps, I decided to use ethanol free fuel. The only ethanol free fuel around here is 89 octane. This worked out fine for me for about 1 year. I never had any pinging with the 89 octane. But after about a year, I started noticing some slight pinging under load. This gradually became more consistent and bothersome, to the point where it changed how I drove the car, slower, lighter throttle trying to keep the pinigng quiet. Then, after some time like this, maybe a couple of months, I occaisioanly noticed an extremely slight surging on the highway at a steady speed. This was so slight that I really wasn't sure if it was my imagination, but over the course of a few months 3-6 or so, this surging gradually got worse, and my wife even noticed it as a passenger. The pinging was still there too, but to minimize the pinging, I started using 91 octane fuel, which does have ethanol, so I added stabil for ethanol to try and prevent the ethanol issue. During this surging period (it would not do it all the time), I recorded Fuel pressure, ignition timing, short term fuel trims, throttle position, MAF, etc, every sensor I could think of. Never did I see any strange readings. The surging progressively got worse, and then one day I finaly got a MIL light and RP. Code indicated TPS/throttle body. Cleared the code, was ok for a hundred or so miles, got another code. Cleared, ok again, but quickly the issue was more and more frequent to the point the car literally was not drivable. I bought a new Throttle body, and all has been perfect since. After the new throttle body, I went back to ethanol free fuel, absolutely no pinging ever. And the engine has much more power and is smoother then I recall it being in a long time. I knew afterward it was low on power during the pinging and surging period. So, this is my experience with pinging. I wish you the best with yours.

 

Steve, you make a great point ....Its been two years since Ive messed with this , the problems are slowly coming back ...every once and a while I will have to crank it to start and I have noticed the pinging at times when I first get her out of the garage until I run a few tanks of fresh fuel through her ... I would drain your tank and start with the best fuel I could find ....before I went into the whole thing again ...the newerblended gases are no good for these older cars ....Good Luck