Long term fuel adaptions need to be near zero. But it's not about being at zero all the time. It's about being able to make adjustments to whatever is going on right now,going up a hill, pulling a jeep out of a puddle, or pulling a trailer down the interstate. I had a really good instructor tell me that he liked his fuel trim to be adding a little fuel(so positive #'s) because that meant to him that his vehicle was running cleaner and getting better fuel economy.
I personally would like to see it moving back and forth thru zero. Taking a screen shot of a # that should be moving is really not useful info.
But that being said, you had a very nice truck and I'm glad you got that kind of money for it. It's good for all of us.
The STFTs definitely fluctuate between positive and negative numbers when it's running, compensating for load, driving conditions, etc. And in Open Loop (pedal to the floor), STFT stop calculating and return to 0 per specification. My understanding is that positive and negative fluctuation of the STFT numbers should occur in a manner that keeps the LTFT numbers at the perfect mix rate of 14.7:1 or 0.0%
STFTs on both banks add up over time to the more static LTFT numbers on both banks. LTFT shouldn't fluctuate that much but when they do should still end up around 0 plus or minus a little bit. A higher LTFT shows that the system has been adding fuel over time to compensate for lean, and lower (negative) LTFT shows the system has been metering less fuel due to a rich condition.
At one point when I first started messing with this thing my LTFT numbers were obscenely high - 20% or so. I was told that was an air leak and compensation. Didn't find air leaks and discovered it could be something in the fuel system, so replaced the canister, pump, pressure regulator, filter and injectors (all of that stuff was 20+ years old anyway). Brought numbers down to acceptable level back in August.
I was getting a random cyl misfire code with no rhyme nor reason as to when it would show up, so replaced the original coil pack with a gently used one from Will. That, and new plugs that I added in prep for sale, appears to have ditched that code for good. Since I had the wires off and on off an on off an on for 2 years while I did all this stuff I have a new set of wires I ordered for the new owner in case any misfire code pops up.
The only thing it could possibly be at this point if it pops back could be a leaking exhaust gasket, so I sent a new set of those with the new owner since I didn't get to replacing them. (a leaking gasket could be sucking air before the 02 sensor causing it to think it's lean at the cylinder and dump fuel which could trigger a misfire code).
But in a number of drive cycles since the coil pack the misfire hasn't popped back up anyway.
I think we're agreeing, LTFT numbers don't calculate or change constantly - maybe every 20 seconds or so? STFT numbers fluctuate constantly, less than every second.
And I agree. I'm glad mine was recognized by more than one bidder to be worth good positive numbers - mine, combined with the well done 97 that sold for $11k, and the G4 on BAT now which will hit 20-25K (already at above 15k with days left to go), plus the 22k TreK should bring Disco prices up overall. I mean mine sold more than the RRC, which surprised me.
https://bringatrailer.com/listing/1994-land-rover-range-rover-county-lwb-2/
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