No start problem on my 2008 n/a XJ8. It will crank and crank, but will not even try to fire. I'm getting a P0121 error and so I suspect that the ECM is shutting everything down because it thinks it's not getting a good reading. Isn't that how the safety features work on these drive-by-wire cars now? So, a couple of questions:

1) Is the TPS replaceable on the X358? It looks like it it riveted on which would be a simple issue to drill out and remove the 4 rivets, but that usually means they don't mean for you to mess with it. Also, I can't find a replacement part # listed anywhere, so that seems to confirm my suspicion.

2) Does anyone have a part number for the TPS? If Jaguar doesn't intend for me to replace, is there another Ford part for instance that will swap in for those bold enough to drill out and remove the old one?

3) Can anyone confirm if your TB moves when you step on the accelerator with the key on/engine off? In other cars, I have tested the accelerator position sensor by turning the ignition to "run" without starting, and then stepping on the accelerator pedal to watch the readings on my scan tool. Sensor D and E (I think those are the 2 on the pedal) are usually something like 1/2 of each other. I can step on the pedal and watch the 2 values go up and down to see if they track together and if they are smooth. But I can also usually hear the throttle body opening and closing with the pedal. I do NOT hear or see my throttle body moving right now on this car when I do the same. Is that normal for a Jag?

4) Speaking of the accelerator pedal positions, can anyone confirm their proper relations? On a Ford, for instance, one is usually 2x the other. Checking this car, that does not seem to be the case, and I can't make out a steady relationship. So, maybe it's the pedal and not the TPS? Anyone got a part number for a new accelerator position sensor?

5) If the TPS is the culprit, and if (as I fear) the TPS is NOT replaceable individually, then can anyone give me a good source for a rebuilt unit that is not $1,000?

THANK YOU ALL for anything you can suggest!

(By the way, I'm sorry to ask for part numbers if this is something I can find myself. I'm new to this Jag, all my old ones were X300's, and I can't really find good resources to check. If there's a link to a good parts list, I would be thrilled to do the work and look them up myself. THANKS again!)

 

throttle is a unit. buy used


on old 32bit ecm APP1 3.418V APP2 .664 at idle. APP1 2.212V APP2 3V at WOT

when i get into my 06 i’ll tell you how that reads.

 

So, there's some kind of inverse relationship? One goes up and one goes down? That's unusual.

 

They're trying to detect failures, to throw codes rather than risk such as unwanted acceleration.

 

O.K., does anyone have a source for rebuilt throttle bodies for a n/a '08 4.2 XJ8?


Yes, of course that's how it works. But on most cars, app sensor E is some constant multiple of sensor D. That way the computer can compare then to verify good data. If the signal from the two sensors report something that does not agree, then the cpu realizes that one or both signals are bad and shuts the engine down so that the car doesn't accelerate out of control. My questions is: do you know what that relationship between D and E is supposed to be? Is it E = D * 2? That's pretty common, at least in Fords for example.

Looking at my live data, the two sensors D and E do not appear to be moving together. If I knew what that ratio was, then I could use that info to confirm if the app is bad. But, if Jag uses some other more complicated formula, then the weird sensor tracks may just be a function of that unique solution.

Thanks!

 

If you don't have app codes then it must be OK.

If you do have codes, it's bad.