It's been a while since I thought aobut it but what are the normal LTFT values? Mine are 14.8 to 15.0. Isn't 10.0 more like it?

I was looking at mine because this afternoon my 2000 MY 85,000 mile XK8 began starting hard after it sits for 20 minutes or more. It catches, but won't maintain idle and will stall unless I feather it for a while.

The last time this happened it was the fuel pressure regulator which I replaced. I'm going to check the fuel pressure at the rail and see that the leak down is... Maybe it is a failing fuel return check valve? Fuel pump? (it's original).

As always, thanks!

 

hell no your fuel trims are way out. youre running lean from vacuum leak. low fuel pressure etc..positve fuel trim that high shows its adding fuel to base fuel mapping to maintian acceptable air to fuel ratios. check for vacumm leaks first. i cant believe you dont have CEL on. but look at the intake bellows between the MAFS and throttle body. Check part laod and full load breathers hoses etc.. do a hard battery reset to clear LTFT and start diag again after these first checks

 

Thanks Brutal, good advice as usual.

No CEL signal yet. Haven't had any troubles of this sort for a year or so. In fact, it's been a really reliable car through the winter.

I'll report back after I take a look.

 

I posted some charts from AE yesterday in another thread, it showed my short term and long term fuel trims at idle and 2500 rpm.

My LTFT are right around 8.5%

 

I took some to go over the intake this morning and didn't see anything unusual. It started fine and ran well - LTFT's are below 10. Importantly, it staerted without hesitation just fine each time when warm.

I doubt the issue is permanently resolved, but for now, there's nothing esle to do.