I have a 1996 Jaguar XJS with the AJ16 engine.

I enjoyed a long period of time when the LTFT was at zero. Then it crept all the way up to 10.2 before I did something about it.

First I replaced the camcover gasket without any change.

Then I tightened the intake manifold gasket bolts. I found one, maybe two that seemed to be less torqued than the others. I got the LTFT down to 7.6

I just ran both TPS Reset and Oxygen Sensor Reorientation and now I'm down to 4.8

Besides the fact that I didn't think the oxygen sensor reorientation did anything other than tell the ECU which of the four oxygen sensors is attached to which plug, I found a hairline crack at my rear exhaust manifold. (Bolts were all tight)

The odd thing here is that both my LTFTs match, however as I watch the STFT constantly change, I have noticed that Bank 1 STFT never gets as low as Bank 2. At best they are equal for a moment, but I never see any points in time where Bank 1 readings are lower than Bank 2. I have been watching this for days now. How could the LTFTs continue to be equal?

 

Hi Vee - I can't help with your problem but I do have a question. I was under the impression that the LTFT readings on these cars were "less than accurate".
I remember that you have a PDU. Is that how you're getting accurate readings? No matter what I use to read mine it's (the LTFT) always up through the roof.

 

Vee,

I'd also read that Jaguar never got the LTFT readings working right under OBDII on the AJ16 XJS. I remember looking at mine many years ago on an OBDII plugin with an app and the figures didn't seem to make any sense so I just forgot about them.

Cheers

Paul

 

Think of LTFT as a coarse setting, and STFT as a fine setting. As long as the STFT does not go over a threshhold set by Jaguar, LTFT doesn't change. Minor differences in STFT aren't of concern.

 

What is the STFT set by Jaguar? I have never been able to make any sense of my 1996 trim figures.

 

That seems to be true for the 95 MY, the 96 works differently, apparently.

 

STFTs should be changing all the time...maybe less so at idle. While driving, they should constantly be changing. I figured that as long as they are moving around, the oxygen sensors are doing their thing. If they are flat, then there's a probelm.

 

Well…after replacing my fuel filter and the camcover and spark plug gaskets, my LTFTs have been dwindling. I’m at 1.8% now, and while I’m happy with that, I’m sure I’ll be at 0% soon.

I’m not sure which one fixed the problem, but the STFT ranges still differ between banks, and I haven’t sealed the exhaust manifold crack, but here we are.

I do want to add that I believe used too small diameter section of the orings at the fuel filter. Maybe that played into this? I used an A011 size last time, which is 9.25x1.78. This time I used the A110 size which is 9.19x2.62. (Viton)

 

Went in to apply the Thermosteel patch...and wouldn't you know it...the glue inside was dry. It was old. I couldn't use it. No one near me sold it, so I ordered one and was ready to put the car back together again...

While there, I did manage to find that one of the two exhaust manifolds...the one that had cracked, had gotten loose. The bolts were not tight, so I tightened them. I'm sure the STFTs will probably be more consistent now. Will report back.

 

My LTFTs crept back up to 10 again.

But I'm back to a LTFT of zero!

I believe one of two things helped the car get back on track.

1. I disconnected the camcover hose from the engine entirely. The hose from the camcover goes straight to an oil catch can. There is a baffle in the catch can, and the outlet hose simply points down in the engine bay. Before there was an egg separator that drained oil back to the engine via the dipstick tube, that has been capped off and abandoned. The vapor was also sent into the intake manifold. That path has also been capped and abandoned. The hose no longer connects to the intake elbow either. Basically that camcover hose basically vents to the outside air now. (through a filter)

2. I unplugged the TPS, when the engine was hot and running, and plugged it back in before the engine died.

One of those two activities seemed to have driven the LTFT for my car back to zero.

Thought I would share that here.