Mine is still showing +55 or so, but the mileage is good and it runs well, so I just ignore it.

 

Sorry its been some time but i would like to give you the update. Long story short my indy jag mechanic/shop doesnt have the software to make the adaptions. Although he does remember doing such adaptions back in 95 when he worked at the local jag dealer. I cant find anyone local that has the ability to reset Both the Fuel Mass Flow Rate (FMFR) and the Air Mass Flow Rate. this makes me crazy

 

Hi RJ,

Still concerned about stalling. But it happens so seldom now I haven't worked the problem much lately. Yesterday I decided to get the Ultraguage out and monitor fuel trims. Following that I did a search and found your results which I am responding to. What I found was The short term trims were plus and minus around zero which I think is normal. But the Long term started out at +57.81. After I drove for a while the Long term had jumped to -99.1. After a stop of a few hours the Lt went back to around 58. I would change now and then a couple of tenths. Now all this is on both banks. I really don't understand the -99, but then again I really don't understand exactly how the fuel trims are supposed to work. During all my driving yesterday the car ran great. No stall at all which it doesn't do very often anyway.

My reason for starting to monitor the fuel trims is to see if there is a glitch when a stall happens. I believe the stall that I have is due to a very short term fuel interuption. Maybe the fuel trims will tell me that.

Just thought I'd bring you up to date on what I have been doing.

Bob

 

Purely "FWIW"....

I've convinced myself to simply ignore LTFT readings on my '95 XJR. First, there's some question as to whether or not the typical scan tools are translating data correctly on these early OBDII cars. Next, the '95 OBDII system was apparently not fully developed to begin with. Third, I'm not sure that any of the readings will make sense or be trustworthy without first a full recalibration using the Jaguar WDS (or equivalent) equipment.

If the STFTs look good, I'm happy, happy, happy (apologies to Phil Robertson)

Under the best of circumstances it can sometimes be difficult to get your head around cause-and-effect with OBD systems. When the system is known for anomalies, though, it gets even more difficult.

Cheers
DD

 

I think we have consensus. Many months ago I took my car to visit sparkenzap. He put it on his wds and even that didn't seem to interface very well. My car runs great, mileage is good, but as good as the XK8, and STFT reasonable with the Ultragauge.

 

Hey guys, I think I figured it out. I remember when I first got my scan tool I couldn't figure out why the mileage numbers were so far off. Finally observed that the mileage numbers were off by a factor of 100. The 100 error is probably in the fuel flow measurement and calculation. And, I think that 100 factor error carries over into the long term trim numbers. If you move the decimal two places to the left you get numbers that look pretty good and reasoneable.

What do you think?

 

I'm not clear on what "mileage numbers" are with respect to scan tool readings.

Are you talking about the trip computer readings? I think those are a calculation based on injector pulse width.

LTFT is a measurement of fueling corrections over a long term.

Not sayin' you're wrong. Just sayin' I don't get the connection.





At minimum.....If you're happy, I'm happy


Cheers
DD

 

Your first sentence is absolutely true. You 'think' you figured it out. I've thought that a few times over the years regarding the AJ16 engines we have. Doug has, too. But we always find something 10 minutes later that blows up our theory.
Doug and I have conversed in a number of threads on this matter, but I'm in a unique position as I have all the original equipment Jag put out to work on 'em close at hand. [when I can cajole it into working, which is a challenge sometimes]

A comment was made that maybe the fuel trims aren't that valuable when dealing with the AJ16. That's basically accurate. The comment about the MAF PID seemingly being two decimals off; also accurate.

Anyway, I think I have enough stuff collected to maybe help explain the inexplicable operation of the system. With all that's going on and the weekend coming up, it will take me a few days, but I'll get something posted here that might help.

In the meantime, elsewhere on the Forum there are a couple of papers I wrote on fuel trims. Search 'fuel trim primer +quiz' and they will turn up. Go through them and you will get some idea how trims work. But bear in mind, the early systems in the AJ16 are much more rudimentary than any later car.

Cheers,

 

I too have dismissed long term fuel trims and the Maf as not important as long as short term fuel trims read normal, figured thats just they way things are. Now, I monitored intake air temps and fuel trims because I was going go place a larger lower pulley for my supercharger, my short term go lean the faster I go, bouncing back and forth from 1 thru 13. I decided to replace the maf with a used one I had and short term fuel trims now remain -1 thru -15, now I have plenty of fuel. I cant wrap my mind around the fact my long terms fuel trims remain wacky and dont make sense. but evidently the maf must be good for something because I now have stft that I can live with. BTW I thought the spare used MAF I had was no good because something sounds loose inside it but it works better than the new after market one. Any thoughts?"

 

Doug,

Hey Buddy, I finally got some of this fuel trim stuff pinned down. Ended up posting in this thread here. I still didn't get all of what I wanted, because I'm currently without our PDU. Sorry.

I hope it helps you a bit in understanding your '95.

https://www.jaguarforums.com/forum/x...rs-etc-126997/

Cheers,

 

Ahhh, good info, many thanks. It'll take me a bit to absorb it all, though


Cheers
DD

 

Man, that stinks! Recalibrating the TPS and reorienting the O2 sensors and shutting off the ABS light is probably less than 1 hours worth if time with the dealer computer!

I understand they have to make money, but $400?!?