These readings were taken using the Innova OBD2 3040E unit attached to my 2003 Jaguar Stype 4.2L non turbo sedan as the car was running at idle. Where can I find the readings that should be considered as baseline/normal so that I can make a comparison with mine? For example, SBFT B2 says 1.6%, what would be the "normal" reading for that test?
Thanks for reading this,
Bob of Arizona
(I just finished reinstallingl the intake manifold after the throttle body coolant return line ruptured under the manifold. A delightful experience to replace a $17 part!)

 

A normal car will be running with STFTs near zero once it's been run enough because any largish STFTs move the LTFTs and in doing so the STFTs head nearer zero. (Thus the S & L in STFT & LTFT.)

So, in a steady state like idle, near-zero STFTs are what you'd hope to have.

Now, LTFTs at idle ought really to be near zero as well because they exist to compensate for small engine tolerances and minor wear.

Exactly zero is unrealistic but a rule of thumb would be within 5 of zero.

When they're larger it suggests all is not OK and yours look very much not OK.

(All this needs a hot engine so the cats are working - and they only work when hot due to the chemistry involved.)

There are multiple causes of raised LTFTs.

A common cause would be an air leak and a way to test is to rev (say to 2500) and see what happens to the LTFTs. If they drop near to zero you have an air leak.

Why? Because such a leak is allowing air in that the MAF doesn't see. The fuelling is done using the MAF (mainly). That means the PCM only finds out it's put the wrong fuel in from the O2 sensors. It adjusts and that shows up in the trims.

Then at high revs a leak is adding roughly the same amount of air but there's much more passing the MAF and so the adjustment is minor in comparison.

Oh, I should mention that trims are in effect a percentage change.

BTW a sort of typical V engine OBD car is along the following lines in terms of what the PCM is looking at (sensors) and controlling (actuators).
Diagnosticians.com - Engine Basics

(Don't get hung up on the exact details - e.g. many cars no longer need the idle air control valve because the throttle body is so high precision.)

 

JagV8, are you feeling okay? Normally a man of very few words, you’ve written an extended reply full of extremely well-presented details, explaining a subject that can be very difficult for anybody to grasp, self included.

Or is this an elaborate ruse? Has JagV8 been kidnapped and forced to hand over his password? Whatever your motives, you won’t get away with it! We’re on to you, and plan to notify the authorities. JagV8, stay strong! Help is on the way!

 

Thanks for that information and I will try that today. Also, thanks for taking the time to reply!
Bob

clay bar and mothers CMX ceramic spray after the manifold work

celebrating the removal of the manifold to replace the throttle body coolant return hose

after removal

after cleaning up

all reassembled and running again.

 

I was less busy than usual but normal service will be resumed have no fear.

 

I did the 2500 rpm test and the readings did drop to zero. The hunt is on for the vacuum leak! Thanks for your insight.
Bob

 

Way to go Bob....excellent work...how many miles since repair....

 

So far, about 40. No check engine lights, leaks or fires! Runs better than ever. I do have a vacuum leak to track down and I am working on that.
Thanks for the reply,
Bob

 

Keep checking trims...sometimes it takes varied driving and miles for them to settle....check the plasic connectors at the throttle body....they are a pain to see, but they can crack easily and create a minor vac leak at first... probably getting hot in your area ....mine too...sometimes that is a diy deterrent

 

I haven't driven it enough after all of the recent work including installing a new radiator. Great point.
Bob