L.t.f.t closer to 0 affect gas milage?

[mr.prick]

Did you put acetone in your fuel tank?
acetone improve fuel econonmy?

[smslyguy]

lol, no i actually just heard of this today and after researching it on u-tube it does not sound like a good idea at all to use it. I still have no reason as to why my ltft are out of wack.

[98 tigershark]

It is really hard to say and I have done allot of research into evap systems etc. Did you do any improvements recently? Not performance things but fuel injector cleaner into your tank or octaine booster change gas stations or anything like that but if your fuel trims are off that will and does effect fuel milage. Replace your fuel cap and see as that is as inexpensive as you can get. Drive about 20 miles and clear the DTC and see what happens. Use the right oil, Gas and no additives. I have heard warmer temps can also mess with the evap in the tank as the fuel temp and tank pressure can cause a questionable sensor or gas cap issue to come to your attention. Replace the fuel cap. Let us know as mr.prick know way more than I do.
98 tigershark

have you ever heard of this decreasing your fuel economy? Or does this not affect fuel economy? I beleive it is for fuel vapars, but i really can't see you loosing any m.p.g from your evap system?? No i don't really know the problem yet, but i am trying to figure it out.

[98 tigershark]

What is a lifetime member? Does that mean you are so old your lifetime is shorter than the life of your membership? really what is that?
98 tigershark

Did you put acetone in your fuel tank?
acetone improve fuel econonmy?

[joecar]

What is a lifetime member? Does that mean you are so old your lifetime is shorter than the life of your membership? really what is that?
98 tigershark

lol... I think it means you have 100 posts (I don't remember the actual number)...

As a mod I can change mine to say something silly...

[smslyguy]

It is really hard to say and I have done allot of research into evap systems etc. Did you do any improvements recently? Not performance things but fuel injector cleaner into your tank or octaine booster change gas stations or anything like that but if your fuel trims are off that will and does effect fuel milage. Replace your fuel cap and see as that is as inexpensive as you can get. Drive about 20 miles and clear the DTC and see what happens. Use the right oil, Gas and no additives. I have heard warmer temps can also mess with the evap in the tank as the fuel temp and tank pressure can cause a questionable sensor or gas cap issue to come to your attention. Replace the fuel cap. Let us know as mr.prick know way more than I do.
98 tigershark

i have replaced the gas cap and still the ltft are out of wack.

[98 tigershark]

The Gas cap is always a good thing to change.
Can you send me your stock tune and your new tune?
I would be happy to take a look. Also when you scan is all of your OBDII and system readiness check OK? And have you changed gas stations or have they changed their gas?
When I first tuned my vette for the first time (around 6 years ago) I had the same 13-20%+ LTFT bank 1 and 2. I have a 2001 Suburban with a 502 (I wish it had the 327) and also had fuel trim issues with the custom tune that someone put on it with a hand held programer (I wont mention) a while back. Then it also had Charging and battery issues with no trouble codes. Now it runs great but fowling a sensor is not all that uncommon according to SDPC and GM performance.
Send me the both tunes and a short log and we shall see, OK. It cant be that difficult to figure out(I hope). Do you use a WBO2?
Take care.
98 tigershark
rea.ltd@me.com

i have replaced the gas cap and still the ltft are out of wack.

[SSpdDmon]

FYI - assuming you were always in closed loop (i.e. you don't get into the throttle), your gas mileage will not suffer if your fuel trims are -20% or +20%. The PCM is trying to maintain a stoich AFR based on O2 feedback. If the initial fueling calculation is off, the PCM determines a trim is needed to bring AFR to 14.6:1. Either way, it's closed loop and it's still 14.6:1 - regardless of the positive or negative nature of the trim.

In open loop, it can be a different story because the PCM doesn't really know what's going on. It's basically assuming it knows. So if your trims are -20% during cruise, chances are you're borderline flooding the engine during open loop (assuming the fueling delta is consistent across the board). On the other hand...if your trims are +20%, you're likely lean up top too. But regardless of the positive trims being added in open loop, you could be anywhere AFR wise in open loop (rich/lean/spot on). It's a crap shoot really...

At the end of the day, fuel economy primarily comes from two things: 1) aerodynamics and 2) your right foot. If you keep your foot out of it and don't go cruising around with the windows down/t-tops off...that's how you'll get the best MPG's.

[98 tigershark]

The foot is the economaster!
The trims being discussed is a potential problem as it would certainly seem to be in closed loop for that vehicle I would think. Mine was. Dont you think 20+ or - LTFT's are a little more than searching for 14.6. Something has to be off I would think. What say you SSpdDmon?
98 tigershark

[SSpdDmon]

The foot is the economaster!
The trims being discussed is a potential problem as it would certainly seem to be in closed loop for that vehicle I would think. Mine was. Dont you think 20+ or - LTFT's are a little more than searching for 14.6. Something has to be off I would think. What say you SSpdDmon?
98 tigershark

My statement was also made on the assumption that the car is mechanically sound. If you have an exhaust leak, then a 20% increase from the fuel trims is obviously wasting fuel. On the other hand, an intake leak would generate higher fuel trims, but they wouldn't be a waste (unmetered air entering cylinders).

My point was, if you took a bone stock car off the factory floor and flashed in a tune that cut the MAF by 15%, you wouldn't help or hurt the fuel economy of the car at cruise. The O2's will call for fuel trims and bring the AFR back in line to hold 14.6:1. That's just a correction...because you were off by 15% from the start. It doesn't affect fuel economy.

Review this thread...
http://forum.efilive.com/showthread....9107#post59107