My xjr feels a bit sluggish/flat sometimes in certain gears or in hot weather.

When I plugged in the scan tool, the reading on "WOT" only ever reaches 83% (with the peddle depressing the kick-down switch as far as it goes and in non sport mode).

Does anyone know if this is normal? I have had the TB off a couple of times in the last year; anyone know how to restore 100% throttle?

BTW the throttle cable is adjusted as stated in the manual.

Cheers

Alex

 

Did you carry out a hard reset after adjusting the throttle?

I've found mid to high 90's% is as good as it gets even on the later AJ27 tb's. 100% gets you a limp mode, I've seen it and done it, it must exceed the sensors and trigger this state.

Hot weather with a supercharged car is bad news, the ignition retards to stop detonation, and this is why its sluggish compared to a cool damp air filled spring morning, a big difference.

Mods to help and some special engines have killerchiller cooling to combat the power losses.

 

No, I don't believe I did. I didn't adjust the throttle as such, I just removed and reinstalled.

Please remind me how to perform hard reset.

So do you think 83% is abnormal? Or am I barking up the wrong tree?

 

Bump up the clip on the throttle cable 1 or 2 settings and retry. I got mine to 97% and stopped there as I didn't want my idle rpm much above 600rpm..

 

check your kick down switch under accelerator as well. may be misadjusted.

 

[QUOTE=xjral;1024962]No, I don't believe I did. I didn't adjust the throttle as such, I just removed and reinstalled.

Please remind me how to perform hard reset.
/QUOTE]

That simply means removing the battery cable for a few seconds then re-attaching.

 

Thanks chaps.

The question is, is it worth bothering with tweaks to get the thing to say "95%" throttle, or is it more likely that it already delivers "full throttle", but just doesn't say it on the scan tool?

Could I be imagining my cars lack of performance because I've had it so long?!

 

Is the 99 throttle cable operated like my XK8? If so you can check by having someone push the pedal all the way with the engine off and check for additional movement at the throttle body.

 

On many cars (incl. my STR) the PCM watches to see the highest ever TPS and regards that as in effect 100% i.e. as WOT. You never get 100% on the sensor and it doesn't care.

I guess there's a value it does have to exceed but don't know what that is.

(It also watches the min value, which again rarely is 0%.)

(To be more correct, it watches the APP sensor(s) but think of them as TPS for this!)

 

You may like to do a simple thing like rteplacing the air cleaner with a fressh one or replace it with a K&N panel replacement...if you are hell bent on extracting that last nano ounce of 'performance'.
What oil do you use?
Preferably a high quality low friction full synthetic 5 or 10W40
Whe did you last attend to the plugs?
Make sure none of your brakes are dragging including the hand brake.
Change super charger oil and belt if necessary.
Any thing esle that is a power sapping impedance.
Always check the simple things forst to remove any power sucking impedance ;o)

 

Brakes, oil, air filter & plugs are all good.

If jagV8 is correct, then I am barking up the wrong tree, and the car is effectivly delivering 100% throttle (and fueling correctly for 100% throttle).

I was concerned that it was reaching 100 % throttle opening but only delivering 83% fuel!

What about a failing coolant circ pump for the intercooler? Has anyone experienced this and the associated symptoms?

 

When you turn the ignition on you can hear the intercooler pump running, it's located on the lhs from the front of the car on the subframe quiet low down.

The pedal percentage is nothing to do with fueling, it's just a means of monitoring.

Has it posted any codes along with the loss of power? Try it last thing at night or first thing when the air is cooler, charged cars with (H)Eaton run hot anyway, I've explained why hot weather puts a blanket on power.

 

No DTC's, apart from from the occasional can bus error or TC/ABS failure.

I suppose if I can establish that the pump is working, then I guess everything is as it should be!

Just so I can understand this: the ecu doesn't use throttle position at all to calculate fueling, so just uses maf?

 

My 98 XJR uses a throttle cable directly to the footpedal. I popped off the intake boot and the throttle blade was clearly not opening all the way, like 70% id say. I bumped it up a clip or 2 as stated and my car shifted down like it was supposed two and redlined all of which didn't happen before. Obviously I had a lot of slack. This is way too easy of a task.. Go mess with it for 5 minutes and see what happens..

 

+1 I mentioned that earlier, but not as concisely, not being familiar with the XJR engine.