My 1998 XJ8 will accelerate to red line but only with a little pedal input (I think it's about 15-20% of the pedal travel.). If I floor it it revs to around 4-5K RPMS hesitates and then the rpms bounce up and down between 3K and 5K.

Any ideas? I've already replaced the fuel pump and filter, spark plugs, MAF sensor (with a used one) checked for vacuum leaks and reset the computer.

Oh, and there's no fault codes.

If needed I could post a video of the problem.

Thanks,
~Valiant

 

Maybe a throttle position sensor?

 

If this is in park or neutral that is because there is a rev limit of 3k in park and neutral to prevent killing the engine.

 

It does it whether it's in drive, neutral or park and whether or not the engine is warmed up or not. I have cleaned the connector on the TPS and checked the voltage. At idle it was 0.91 and WOT it read 3.67 volts. I checked this using a digital multimeter and went very slow on the pedal and it only climbed. From what I read this means it should be good but I could be wrong.

I read somewhere that there is an APP (Accelerator Pedal Position) sensor on some models. Can anyone tell me if the 1998 XJ8s had one? and does anyone now of a way to test it?

Thanks for the input guys I'm looking forward to getting this thing on the road.

~Valiant

 

Check the air trunking you took off again for leaks.
It is easy to get a kink in the flexible part downstream of the MAFS (I only know about XKRs though)
If your Throttle Position Sensor (TPS) was bad you'd be in restricted performance with loads of error codes.
Where did you measure those voltages?
Have you cleaned the throttle body?
I'm not saying this will fix it but, since you've done a reset, it can't hurt to reset WOT settings.
https://www.jaguarforums.com/forum/x...connect-74146/

 

Well, I've just cleaned the throttle body and load breather. I've followed the instructions for resetting the WOT don't know if it worked.

I took the car out and attempted to get red line while in gear. I selected 2nd on a empty road and tried to carefully control the pedal to get it to 7K rpms. It would only go up to 5100 RPMS before it would just stop accelerating. I even set the cruise control and used the plus button again it would go up to about 5000 to 5100 RPMS and then just drop.

It seems to have good power at the low RPMS.

Steve I tested the ground to the TPS and then found the wire that fluctuates according the pedal travel (I think it was the green wire second up from the bottom of the plug).

What I find so strange is no error codes... Oh and I've checked the air intake duct for leaks there are none.

Any help will be greatly appreciated.

Thanks,
Valiant

 

Is it worth checking the fuel pressure?I know you've changed the pump but I believe your MY has a regulator on the line - but I'd think that you'd get lean mix error codes.
There have been one or two posts where a bad MAF sensor or bad connector/leads have caused problems so there's a couple more things to check.

 

Well, just got done checking fuel pressure at the rail... 41PSI engine running.

The other day I was looking at the vacuum lines and noticed one that was deteriorated, so I replaced it. After I went to test drive it and it died within a block and continued to sputter at Idle and die.

I just don't know what to check next. Still no error codes!?!?!

Any more Ideas?
Thanks
Valiant

 

Here's a thread on fuel pressure
https://www.jaguarforums.com/forum/x...-99-xj8-51682/

What code reader have you got? Can you see live data like fuel trims?

Have you done a propane check for vacuum leaks?

 

I've got a Auterra Dyno-Scan laptop version and I can see live data. I'm going to be very busy for the next few days. But when I get a chance I'll get screen grabs of the fuel trims, oxygen sensors and anything else I think might be useful and post them up here.

So is the fuel pressure supposed to be lower at Idle? It was still at a high idle (1000 RPM) when I was reading 41PSI as I didn't let the engine warmup.

Thanks again for the effort to help me it's much appreciated.
~Valiant

 

Alright so here is some live data from driving around the neighborhood up to 30MPH.
















And this one is from earlier on in siting in park engine warmed up I revved it a few times and it seemed perfect red lined quickly and stayed there just fine. But by the time i got back home it was doing the stumbling and hover @ 3000 - 3500 RPM in park or Driving it.





Let me know what you think of the graphs. What should I check next?
Oh and I checked all the vacuum with a vacuum pump and gauge.

Thanks
Valiant

 

Make sure the EGR is not clogged, that requires removing the TB again. Once you take the TB off, you will see the EGR.

You will know how to take it off just by looking at it.

SGB

 

The car is fixed see my post here: https://www.jaguarforums.com/forum/x...52/#post571512