Question on LTF numbers

[DiverBob57]

Today I was driving back from Arkansas on US67 through the Ozark mountains. On our ScanGauge I started to watch Long Term Fuel trims closely.

Do these numbers seem “normal”?

At idle: +1 to +3
At 65mph on level ground: +6 to +7
At 65mph climbing a 3% grade: +12 to +14
At 65mph going downhill: +3 to +4

I never observed a 0 or negative reading.

Thanks for any input.

[CaptainJerry]

Seems a little low. I can only restate what I have taken note of from earlier posts from the experts - maybe UltraRV:

LTFT normal is:
at idle - 6 - 10 grams per second
at 2,500 rpm at wide open throttle at shift from first to second - 15 - 26 grams per second

[AKIQPilot]

Originally Posted by CaptainJerry

Seems a little low. I can only restate what I have taken note of from earlier posts from the experts - maybe UltraRV:



LTFT normal is:

at idle - 6 - 10 grams per second

at 2,500 rpm at wide open throttle at shift from first to second - 15 - 26 grams per second

You might be thinking of MAF numbers not fuel trim. MAF reads in grams/second. Fuel trim is measured in percentage.

[AKIQPilot]

Originally Posted by DiverBob57

Today I was driving back from Arkansas on US67 through the Ozark mountains. On our ScanGauge I started to watch Long Term Fuel trims closely.

Do these numbers seem “normal”?

At idle: +1 to +3
At 65mph on level ground: +6 to +7
At 65mph climbing a 3% grade: +12 to +14
At 65mph going downhill: +3 to +4

I never observed a 0 or negative reading.

Thanks for any input.

Your idle and 65mph numbers are within reason. Once you put some load on the motor the trim numbers climb toward the limit. My Itasca with the URVP tune does the same thing. Ive cleaned the MAF several times with no improvement in the numbers. Ive had the tune for several years. My LTFT numbers were not always this high.

My Adventurer with a stock tune has low LTFT numbers. Always below 8-10.

Keep an eye on it. If you havent cleaned the MAF recently you should to see if the numbers change.

[jim58]

Originally Posted by DiverBob57

Today I was driving back from Arkansas on US67 through the Ozark mountains. On our ScanGauge I started to watch Long Term Fuel trims closely.

Do these numbers seem “normal”?

At idle: +1 to +3
At 65mph on level ground: +6 to +7
At 65mph climbing a 3% grade: +12 to +14
At 65mph going downhill: +3 to +4

I never observed a 0 or negative reading.

Thanks for any input.

Idle - wouldnt be too concerned.

65 level - seems high
65 climbing a 3% - that's high. A 3%er is nothing that should cause 12 to 14+'

65 downhill - should zero out for most of the time



The big thing you posted that would concern me is never seeing 0 or a negative number. That's telling you that your computer sees a reason to ALWAYS be adding fuel. That tells me that something is forcing the computer to always see a lean condition.



What do the STFT look like? They represent what happening at the moment moreso than the long terms that chnge slower and over time.


I think you should be seeing 0's and negative numbers. Not ALL positives.



I may be way off base but all positive numbers would indicate a lean situation, the way I understand it.


Jim58

[Isaac-1]

My first thought is there is nothing to panic about here, though you probably have some issues that may need attention. Now let me ask a few questions, does LF1 and LF2 both track close to each other? How are your spark plugs, how many miles on them, what about the spark plug wires, and when was the MAF last cleaned or replaced? Have you ever checked your fuel pressure at the test port?

[CaptainJerry]

I must apologize for my incorrect post #2. It was the parameters for MAF sensor readings, not long term fuel trim.

[DiverBob57]

Originally Posted by Isaac-1

My first thought is there is nothing to panic about here, though you probably have some issues that may need attention. Now let me ask a few questions, does LF1 and LF2 both track close to each other? How are your spark plugs, how many miles on them, what about the spark plug wires, and when was the MAF last cleaned or replaced? Have you ever checked your fuel pressure at the test port?

Thanks for suggestions.

- MAF wire is going to get cleaned next week when I replace the air filter.

- Plugs and wires are brand new from URVP. They made a difference in mpg and better pickup.

- both LF1 and LF2 track close to each other... within 1-2%

[jim58]

Seeing as your numbers are close on both sides the air filter and maf cleaning are a good place to start. Something hokey going on there and it will affect both sides.



Have a look at your short term numbers, not long term, before and after, and see if they change.



Jim58

[Isaac-1]

You may want to also check the fuel pressure it should be 60 psi +/- 2 psi, I don't know how it is regulated on your coach as the fuel system was redesigned in 2004, with pre-04 models like mine having an adjustable fuel pressure regulator with a return fuel system and post 04 models having a mostly returnless fuel setup.

[jim58]

Originally Posted by Isaac-1

You may want to also check the fuel pressure it should be 60 psi +/- 2 psi, I don't know how it is regulated on your coach as the fuel system was redesigned in 2004, with pre-04 models like mine having an adjustable fuel pressure regulator with a return fuel system and post 04 models having a mostly returnless fuel setup.

I would agree with you on that next step. Weak pressure could explain why his trims go high trying to maintain 65mph climbing a hill.


Still interested why he never sees the trims going negative to positive to negative, or zero, even on flat land. It's always going to be determined by temp, load, wind, etc. But I would think that under a steady low load, flat ground, no wind, he would be seeing negatives and positives. That's assuming no issues of course.



Hope he finds the issue and posts what he finds.


Jim58

[DiverBob57]

Update: After replacing Air filter with an OEM Workhorse brand from Ultra RV products and cleaning the MAF wire, both LTFT gauges are at 0% or +/-1% Also the MAF reading improved for idle.

Readings BEFORE Cleaning MAF and filter change



Not sure if that is a Fram Air filter with a glued piece of foam rubber for pre filter. Definitely needed replacing.



MAF was dirty. Had stuff come off on the paper towels I used. Be in well ventilated area when using MAF wire cleaner.



Readings AFTER cleaning MAF and changing filter



Thanks all for input! Taking it on road trip in two weeks through Smokey mountains. Will report back if anything odd pops up.