Could somebody define "fuel trim" and how adjusting fuel trim is accomplished. Thanks guys... Bob

 

Bob, here is a good place to start: https://www.jaguarforums.com/forum/g...ed-quiz-49317/

 

Fuel trims can be a little tricky to understand. Why do you ask?

 

My 2000 XK8 hasn't been up on the back of a ramp truck in a few months, so I thought it might be time to start worrying about things... Actually, my highway fuel mileage ain't that great...maybe 22mpg@ 70, I'm easy on the throttle and brakes. Maybe my fuel consumption is where it should be? I'll study the fuel trim primer and see if I can better understand the system. Thanks to all who contributed... Bob

 

A generic intro to modern engines is on several sites such as OnBoardDiagnostics.com - Engine Basics

The very brief answer is that the critical sensors let the PCM estimate the fuel based on air and then adjust based on O2 sensors. It's why ALL the critical things must work.

This stuff is essentially forced on all car makers by law. (USA, Europe & just about everywhere.)

 

I would not be concerned until the car starts acting up. However, if you want to see what is going on you could perform a MAFS test to see if the air and fuel are within a suitable range. It will not tell you what is wrong but could ease your mind.

Link JagRepair.com - Jaguar Repair Information Resource

 

Not sure if the 2000 is much different than my 97 on fuel mileage. The best I've ever seen on my 97 is 25 and that's at the speed limit on the freeway and literally from gas pump to gas pump with no side trips and warmed up to begin with. I used to routinely put 600 miles per week on it between Portland and Seattle so I had the mileage pretty much dialed in. I've also got taller/narrower tires than stock (235/55-17) for better ride and less drag. Push it to 70 or 75, it knocks it down a notch or two. Around town normal is 17 for me if I take it easy, 15 if I'm getting ambitious. Now, the 03 and later models with the 4.2 and 6-speed is a different story. They'll get upwards of 30 on the freeway as I understand it.

Mike