why ltft's changing?

[killerrf]

why do the ltft's change sometimes? like yesterday... i was watching them on our travel and the outside temps were around 20-22C and the ltft's were around that -1.5 to -0.78.. that was in the late morning. then on the way home it was around 26-27C late afternoon and the trims were all the way up to 3.125-3.950 for each bank.

so last night it was down to 17C around 10pm and i logged the ltft's again and both were are still at 2.345 on each bank. so i dont know why its not in the - range.

there was only one other time this happened. it was a few weeks ago. ltfts were fine one moment then up to like 4-5 positive range. then on the way home it ran down to -0.78 to 0 range. so i dont know why the numbers would jump around like that. all travel speeds were same.

[Morgoth]

Different fuel can do that,if you have the stock intake,it can heatsoak.

[killerrf]

Different fuel can do that,if you have the stock intake,it can heatsoak.

not sure on the intake. i was running the same 26C temps before and never had ltft go out of the - range. but i did fill different fuel. i always use CO-OP gas and filled up at a station that gets its gas from shell. so maybe something there. ill have to experiment some more and see.
dont know if that is good its showing leaner or richer without changing anything in the programming.
dont know what would make the coop gas richer and shell leaner? must be some additives maybe that shell uses?

[06MonteSS]

fuel trims will not always be the same... that's their function afterall, to adjust the fueling "on the fly" so that the AFR remains at the stoich value of 14.7....

when outside temps change, the ltft's will change/fluctuate....

you can't be checking/changing your slope adjustment every day, you'll be chasing your tail....

pic a nice warm/hot day... do a stead driving/cruising data log... get your ltft's in the 0 to -2 range for that day, and that's it... leave 'em... set it and forget it!!

yes, they will still change, yes they will get out of that range sometimes... no worries...

you're killin' yourself man....

[killerrf]

ok well i leave it then. just didnt think it would fluctuate that much.

[06MonteSS]

air temp, humid or not humid, density altitude, etc etc all play a role in the fuel trims... a change in any one of those will change the fuel trims...

[killerrf]

i fiqured its probably normal because both banks were doing it but dont hurt to ask a question. thanks for your time.

[06MonteSS]

cool man..... no problem...

[jess]

What if you have a sometimes large spread between bank 1 and bank 2?

[rmck490]

What if you have a sometimes large spread between bank 1 and bank 2?

How large of a spread between banks are you talking about?

The long-term fuel trims adjust in increments of 0.78. It's common for the banks to be off from each other to some extent but should be reasonably close like two to three increments. A number of problems could cause a large spread above this such as:

Leaking intake manifold gasket (on the lean bank)
Exhaust leaks near an O2 sensor (pre Cat sensor on the lean bank)
A malfunctioning O2 sensor (pre Cat sensor on either bank)
Leaky fuel injectors (on the rich bank)

There may be other possibilities so I'll let others add to the list. One of the banks is either getting too much fuel or getting too much unmetered air. Or, a bad sensor is giving the PCM bad data.

[jess]

I did not know about the increments of .78. My 04 seems to be always with in one or two but my 2000 will sometimes be as much as 4 increments apart and always the same bank. most of the time just 1 or 2. the 2000 also has 200k on it.
Which bank is which?

[06MonteSS]

bank 1 is driver side... bank 2 is passenger side...

[jess]

any thing to worry about? with that spread?