Hi

Having ongoing issues with my X300 XJR.

The symptoms are hesitation/surging when throttle opened to 3/4 then if you have the throttle on the floor the car kangaroos along the road and then eventually stalls if you let your foot off the gas.

I have checked the TPS output at the ECU pins. It is 0.62V at idle position and incidentally I have no idle issues, this does increase in a steady fashion as you open the throttle but at WOT it only reads 3-3.1V.

Would I be correct in assuming this is wrong.

The car has covered 126k miles and I have already ruled out coils and air flow meter (changed).

 

The symptoms are hesitation/surging when throttle opened to 3/4

then if you have the throttle on the floor the car kangaroos along the road and then eventually stalls if you let your foot off the gas.I'm interest in knowing what you finally figure out as your root cause.

 

Thanks for the suggestions, pretty sure the injectors are ok as my xjr runs lpg as well and the fault is the same running on that too. I forgot to add the TPS does have the correct 5v reference voltage just a little suspicious as I don't have any fault codes either

 

So does anyone have any advice on replacing the TPS on the supercharged beast? I tried taking the oil filter off earlier but still couldn't really see it any help would be greatly appreciated as I'd like to avoid removing the charge cooler etc etc

 

Aaron:
The voltage you cite seems low. Be sure your linkage cable is actually opening up the throttle plate before you tear into it!
And, although some folks say they did not need to do it, be aware there is a procedure to calibrate the new TPS that requires the dealer level software.

 

I can see what you're saying but 99% certain throttle is physically fully open and this issue did start out as an intermittent one but has now decided to fault all the time which has helped diagnose it easier

 

I agree with Ross, the TP output seems low.

0.62v at idle is fine and you say there are no idle problems.

At WOT the output should be around 4.8v as I recall? If the ECM is only seeing 3.1v and the throttle plate is truly wide open, I imagine the ECM would be having a hard time reconciling the MAF with the TP and perhaps this could cause your symptoms?

Have you tried measuring the TPS output at the the TPS connector? There may be a wiring issue between the connector and the ECM. Doubtful but cheaper than replacing the TPS

 

Ok getting somewhere as got a day off. Checked signal in the loom just above tps, same. Then re checked whilst operating the throttle by hand from under the car and hey presto! Smooth increase all the way up to 4.97v at WOT! So guess I need to adjust throttle cable somewhat?

 

You should have two cables: pedal to traction control unit and traction control unit to throttle body. The adjusters are on the cables themselves. You'll see 'em.....just follow the cables themselves.

Someone has posted the official adjustment procedure but I've never been able to get my head around it. I just slacken the adjusters and then tension them until most of the free play is removed. You'll know you've gone too far if the engine speed increases.

I've long been suspicious (but never really investigated) that an old/worn/malfunctioning traction control unit itself can cause a drag/interfernce/loss of motion on the cable to the throttle body. I've had to adjust mine a couple of times as excessive slack develops...almost as though the cable are stretching.

Years ago I was battling a high idle problem (which can have several causes) and fixed it by slackening, exercising, and readjusting the cables. I *think* the TC unit was somehow sticking or binding.

Cheers
DD

 

Right I found the bulletin adjusted the cables and now I have the full range on TPS now which is good, 0.62 - approximate 4.54v.

However I still have my fault so was barking up the wrong tree. The car still try's to stall when you put your foot down but I believe it is when the first stage of the kick-down kicks in and the gearbox goes to grab a lower gear so now believe I have gearbox issues. I had box issues over Christmas and have changed the fluid a number of times and all seemed ok for a while

 

The ECU retards the timing at the moment of each gearchage....I wonder if there's a glitch in that function?

Also, is the problem rpm sensitive? The #2 fuel pump turns on at 3000 rpm. I not sure what would happen if it doesn't. A lack of power would be expected, at least. Not sure if such a fault would account for the specific symptoms you're experiencing.

Just spit-balling here. Others will chime in with better advice

Cheers
DD

 

Perhaps, perhaps not?

The ECM communicates many things such as throttle position and engine speed etc to the TCM, perhaps they are now out of sync in some way? It might be worthwhile trying to do a 'drive cycle' and see if that improves things.

drive cycle.pdf

If not, then you might want to disconnect the TCM and inspect/clean the pins. Also might be worth checking that the kick down switch under the accelerator pedal is working correctly.

Doug makes a fair point about the 2nd fuel pump though I wouldn't expect that to cause a stall at speed but who knows?

 

Boy would it be nice if the X-300s had a fuel pressure test port, wouldn't it!

 

That would have been nice!! I ended up making my own test fitting with an assortment of bits and bobs Works fine on my XJ6 and XJS.

 

Well later thy day I actually got some fault codes and related to shift solenoid B being jammed, so now have on order from the US a pair of shift solenoids, not using the car until I've put them in, on the plus side work have supplied me with a hire car for my longer work related trips and getting by using my lovely little 1970 mini in the meantime!