Howdy folks.

Just for some history, last week I did all four 02 sensors on my 04 XJ as it's been throwing cat efficiency codes for a while now. The job was quite easy, btw. Now when I went to clear the codes, I also found a P0191 hanging out like it had nothing better to do. I cleared them all but lately, the car has been hesitating slightly, usually under part throttle.

I tested fuel pressure simultaneously with a mechanical gauge and a Bluetooth ODB on my phone and they were pretty close to each other. The ODB was reading higher by 5psi than the one on the rail. Rail was reading around 45, or so.

So what I'm trying to figure out is, pump or sensor? I couldn't get the car to hesitate(Yet!) with the gauge hooked up because cars are spiteful, but I did notice one odd event. I saw a spike on the mechanical gauge where the needle swept to 80 very quickly 3 times. It happened so fast that I never saw whether it was on the phone, as well. I also didn't notice whether there was a stumble or not. If so, it was imperceptible.

I'll do another test run tomorrow and see what that brings. In the meantime, I figured I'd see what the brain trust thought so I don't have to throw parts at her. Out of all of the European cars I have(4 Audis, 2 BMWs, and VW), this and the VW have been very reliable. It's my wife's car so I'd like to keep her happy!

 

The reason I like WDS/IDS Datalogger is because the readings 'scroll' on a graph like a heart monitor or a 'lie-detector' on TV.

The 'spikes' would show and remain on the screen for a period of time. (or in the playback)

Hope you are watching the next time something happens with a sensor monitor event.

 

I'd love to run WDS but it doesn't seem like a viable option, at least not when I briefly looked into it a few years ago. I already run the BMW and VW/Audi group specific ones. The Jag is the odd man out.

I did notice that the rail pressure bled down to maybe 10psi overnight. Not sure if that's normal with this system or not.

For now, I'll try to catch it acting up live so I have an idea of which way to go.

 

Possibly dirty connector or pressure sensor failing. ECU sees low pressure occasionally and ramps the pump up. When it gets better signal it goes to normal. This could have triggered your original cat efficiency issue as well.

 

That makes sense. I'm just hoping that it's more possibly a sensor than a pump. As to the cat codes, I'm fairly certain it was the O2s as that not only did eliminate the codes but has started to considerably settle down the fuel trims.

 

If your pump can jump to 80 psi it is not the pump!

 

easy way to check is output state controls and push the duty cycle up

you can do it with an ids or a launch

 

I didn't know if maybe the pump, or the check valve in it, was maybe on the way out.

 

I'm not really sure what that is exactly. I'd love to have IDS but I have no clue how to get that up and running. I have the factory diag programs for BMW and Audi/VW and I assumed it would be just as simple for the Jag, but alas.