Hi all
After owning my XK8 for three weeks and having some slightly hard transmission shift someone suggested I collect some fuel trim data. Today I collected the following at both idle and at 1500rpm. Parked up at operating temperature after a drive.

Idle
Bank 1 STFT 0.78%/LTFT 7.8%
Bank 2 STFT 6.25%/LTFT 0%

At 1500rpm
Bank 1 STFT 10.9%/LTFT 1.56%
Bank 2 STFT 6.25%/LTFT -0.78%

These look a little odd to me (not that I've seen any before). Can someone more experienced help me with understanding these readings?

Thanks
Phil


Reply

 

The bank 1 LTFT is a little high +/- 5 preferable, indicating a air leak on that bank. But that should have no impact on the transmission. What year is the car? 4.0Lor 4.2L?

 

just an FYI:

when collecting data above idle speed, the engine needs to be under a load, moving down the road. Preferably going up a slight incline. Not just revving in Park or Neutral. Revving the engine without a load tells you nothing.

This applies to all ICE's, no matter whether they are fuel injected or carburetor fed.

Z

 

See if this link helps

Link JagRepair.com - Jaguar Repair Information Resource

 

You should be looking at the LTFT not stft when doing this test...
And they look good..... Bank 1 slightly high but nothing to worry about...
A smoke test may be in order to locate the small leak/leak's affecting Bank 1...

 

How do you justify that?

Dozens or hundreds of people across the forums on here have found the opposite.

 

I justify it by direct observation during 50 + years In the transportation service industry.

Z

PS. : At an identical rpm, the trim numbers change dramatically when the engine is under a load vs, “free-revvjng” in neutral or park. Obviously, the gas consumption under a load is going to tell a much more complete story during problem diagnosis. This is methodology taught in every factory seminar I’ve ever attended, from 1970 onward.

 

Hi all
The car is a 2005 4.2K xk8.
everyday is s learning day. Yesterday I knew nothing about fuel trims. Now I know something.
Thanks everyone,
Phil

 

OK, well never too late for you to learn that simply revving a hot engine when parked easily reveals if there is an air leak. You can read it all over the net or even try it for yourself after you create a small leak.

 

your attitude is learning me a lot more than just fuel trims. Disrespectful posts regarding my knowledge and experience are more telling about you than they are about me..

i stand 100% by my posts. Yes, an air leak can be detected without driving a car. However, there are a multitude of fuel trim issues, including air leaks, which can be intermittent , which are best revealed by driving a car and examining the data stream log from an engine under a load. Don’t take my word for it, the SAE guidelines for trouble-shooting will say the same thing.

But what do they know ? Why rely on experience when there’s Google ?

Z

 

I'll take a moment to rely on experience. :-)

2002 xkr

My long-term fuel trims are both high negative, averaging somewhere between - 17 and - 20%. and are equal on both banks.

They occasionally trigger p0172 and 175.

I also get code p1111 which I believe is pointing to the IAT sensor in the MAF.

If the intake air temperature is reading a false high, am I right in assuming that that the ECM will think the air density was correspondingly low and that the fuel needed to be reduced to compensate?

 

Early this year I was getting the same error codes and the attendant negative trim numbers, though not quite that high.

The XKR MAF is much pricier than the XK8 version, so I was not especially anxious to replace it. It took 3 separate cleanings before the cleaning was effective enough to solve the issue. I admit, before the 3rd cleaning, I was about to give up and buy the new part.

So even though the MAF may look pristine, another round of spray cleaning may be in order.

additionally, with the engine running, try wiggling the MAF
connector. If the idle speed / quality changes, then a little adjustment of the connection is in order. Worked for me.

Z

 

Thanks. I've only cleaned it once. I'll give it another good dousing.

 

I have not disagreed with your new statements, but note that I did (and do) disagree with your claim that "when collecting data above idle speed, the engine needs to be under a load, moving down the road. Preferably going up a slight incline. Not just revving in Park or Neutral. Revving the engine without a load tells you nothing."

As I pointed out, that is wrong.

BTW no need to resort to insults even if you can't bear being corrected.