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

[smslyguy]

can your L.T.F.T. closer to 0 give you better fuel econonmy? I mean if you L.T.F.T. are at say 20% and you get them closer to 0 would you see improved fuel econonmy?

[mr.prick]

Are your LTFTs 20%, or is this a hypothetical question?
High LTFTs cause AFR to be whacked.
The easiest way to find out is to log WBO2 and see how BENs are in CL.
For me, BENs are between .99 to 1.02 with LTFTs averaging -2%,
being a little lean from idle to 1200 RPM.

LTFTs that high could be an intake or exhaust leak.

[smslyguy]

Are your LTFTs 20%, or is this a hypothetical question?
High LTFTs cause AFR to be whacked.
The easiest way to find out is to log WBO2 and see how BENs are in CL.
For me, BENs are between .99 to 1.02 with LTFTs averaging -2%,
being a little lean from idle to 1200 RPM.

LTFTs that high could be an intake or exhaust leak.

yes my 2000 gmc the ltft are that high. I wil have to check and see if i do have an intake leak, although if i had it should be ideling higher than normal, which it's not. and no to the exhuast leak.

[smslyguy]

just check for an intake leak and it turned out negative, there is not a intake leak. The truck runs fine no hesatation or stalling just the ltft are around 20% here is a scan i ran

[mr.prick]

Any mods to the truck?
I don't know if it is normal for a truck to have high LTFTs but
it would go against common lore of having LTFTs 0% or slightly negative.

[98 tigershark]

I had just worked on a 2000 Camaro that had those type of LTFT's and it was an exhaust leak that looked very small but caused the trims to be out of wack. An exhaust leak is not as easy to find sometimes.
98 tigershark

[smslyguy]

Any mods to the truck?
I don't know if it is normal for a truck to have high LTFTs but
it would go against common lore of having LTFTs 0% or slightly negative.

no mods at all it is a stock 5.3 truck

[smslyguy]

I had just worked on a 2000 Camaro that had those type of LTFT's and it was an exhaust leak that looked very small but caused the trims to be out of wack. An exhaust leak is not as easy to find sometimes.
98 tigershark

no exhuast leak either. I do however, have a code po452 (fuel tank pressure sensor condition. don't know if this is related to the ltft or not??

[98 tigershark]

That could affect the LTFT and STFT as they are both OBDII issues.
I have heard of that before. Do you know what to do to fix the problem. It could be a bad sensor or even a bad fuel cap. It is hard to tell but again I have heard of this effecting the fuel trims but have not seen this personally.
Regards,
98 tigerhark

[smslyguy]

That could affect the LTFT and STFT as they are both OBDII issues.
I have heard of that before. Do you know what to do to fix the problem. It could be a bad sensor or even a bad fuel cap. It is hard to tell but again I have heard of this effecting the fuel trims but have not seen this personally.
Regards,
98 tigerhark

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.

[mr.prick]

Did you put acetone in your fuel tank?
acetone improve fuel econonmy? (http://forum.efilive.com/showthread.php?t=11578)

[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? (http://forum.efilive.com/showthread.php?t=11578)

[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 tigersharklol... 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...:hihi:

[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.php?p=59107#post59107

[ssvolvo]

Most 5.3 trucks I've seen with fuel trims out this much are caused by failing intake manifold gasket/o-rings.

Could be a dirty MAF also.

I wouldn't TUNE it out if it's stock.

At the shop...we use a smoke machine to "smoke" the intake and look for the smoke leaking out.

Keep looking, you'll find it.

John

[smslyguy]

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


here is a scan with my l.t.f.t. around 20% take a look let me know what you think.

[joecar]

Can you re-log, but this time include MAF...

(if you have the LS1 PCM you can get 10 Samples/sec instead of 5 S/s if you reduce the pid channel count to 24 or less... remove some of the pids).

If there are no airleaks, then my estimate is either:
- PCM is calculating insufficient airmass (this leads to the next point...);
- insufficient fuel is being delivered;

maybe:
- MAF is dirty or low MAF reading.
- fuel pressure is dropping.
- fuel filter is dirty.
- injectors are dirty.

[98 tigershark]

Hey SSpdDmon,

Thank you for the link. That adds it up pretty well. When I tuned my car with the new motor, I crunched allot of numbers and spent allot of time asking questions and except for a few minor changes it is almost the same now as what I put on it then. The other day I took off the air filter to clean them. It is easier to take the maff off while doing so on my car. I was driving the car on the weekend and the maf and filter completely fell off away from the plenum (I forgot to tighten the Maf clamp). If a trouble light did not come on I would not have noticed as I was logging at the time. The maf is hooked up and does work. I also did the final tune on a dyno w my WBO2. I am not telling anyone to tune that way but I do crunch allot of numbers and I am surprised at how close you can get if you take the time and in my case allot of it. Converting the VE from % to G/S and watching (logging) the maf up to 4,000 rpms and reworking the VE in the G/S with the Maps from the scan and then using the IBPW formula for peak power for over 4,000 and make the maf and PE adjustments to match the IBPWs I want seems to get me very close with the fuel trims until they zero as well as the AFR. A WBO2 sensor is certainly the way to go but I was surprised at how little adjustments where needed on the dyno when doing the homework correctly.
I know you know how to build a base tune better than I but I do like the math involved. Did I explain what I do correctly (building a base tune with no WBO2 before the car is started))? and if so or not how would you go about building a base tune as your posts in the link was so clear I was hoping you might improve on the above. Thanks again.
98 tigershark

[smslyguy]

Most 5.3 trucks I've seen with fuel trims out this much are caused by failing intake manifold gasket/o-rings.

Could be a dirty MAF also.

I wouldn't TUNE it out if it's stock.

At the shop...we use a smoke machine to "smoke" the intake and look for the smoke leaking out.

Keep looking, you'll find it.

John

i cleaned the m.a.f sensor and also checked for leaks around the intake manifold, which came up negative.

[smslyguy]

Can you re-log, but this time include MAF...

(if you have the LS1 PCM you can get 10 Samples/sec instead of 5 S/s if you reduce the pid channel count to 24 or less... remove some of the pids).

If there are no airleaks, then my estimate is either:
- PCM is calculating insufficient airmass (this leads to the next point...);
- insufficient fuel is being delivered;

maybe:
- MAF is dirty or low MAF reading.
- fuel pressure is dropping.
- fuel filter is dirty.
- injectors are dirty.

how can you get low m.a.f reading from a stock tune?
fuel filter has been replaced
used fuel injector cleaner as well
did not check fuel pressure. Would you think it could possibly a fuel pressure regulator issue? But wouldn't that make a mil light come on?

[SSpdDmon]

Hey SSpdDmon,

Thank you for the link. That adds it up pretty well. When I tuned my car with the new motor, I crunched allot of numbers and spent allot of time asking questions and except for a few minor changes it is almost the same now as what I put on it then. The other day I took off the air filter to clean them. It is easier to take the maff off while doing so on my car. I was driving the car on the weekend and the maf and filter completely fell off away from the plenum (I forgot to tighten the Maf clamp). If a trouble light did not come on I would not have noticed as I was logging at the time. The maf is hooked up and does work. I also did the final tune on a dyno w my WBO2. I am not telling anyone to tune that way but I do crunch allot of numbers and I am surprised at how close you can get if you take the time and in my case allot of it. Converting the VE from % to G/S and watching (logging) the maf up to 4,000 rpms and reworking the VE in the G/S with the Maps from the scan and then using the IBPW formula for peak power for over 4,000 and make the maf and PE adjustments to match the IBPWs I want seems to get me very close with the fuel trims until they zero as well as the AFR. A WBO2 sensor is certainly the way to go but I was surprised at how little adjustments where needed on the dyno when doing the homework correctly.
I know you know how to build a base tune better than I but I do like the math involved. Did I explain what I do correctly (building a base tune with no WBO2 before the car is started))? and if so or not how would you go about building a base tune as your posts in the link was so clear I was hoping you might improve on the above. Thanks again.
98 tigershark
My math on base tunes is very simple. Find a car that had a similar setup and start from there. LOL "Free time" hasn't been a friend lately. So, trying to back into something like you describe isn't much of an option. Outside of fueling, it just comes with experience, talking to other tuners, etc. Wish I could offer more than that...but, it is what it is.

[98 tigershark]

The fuel pressure regulator has no electrical supply. If you have one fuel line to the rail your regulator/filter is close to your left rear wheel. If you have 2 lines a feeder line and return as mine (suburban) does, than the regulator is in the fuel rail and the filter is back by the driver side rear wheel. There are no wires to the regulator or filter and if the regulator is a single line system it has the filter built into it. A new stock regulator/filter is around 50 to 60 bucks at an auto part store. The filter for the dual line system is around $20.00. It is not a bad idea to change the filter and or regulator/filter once in a while. The dual line with the regulator in the rail can also be replaced, but I have not heard of that regulator going bad before.
98 tigershark

[98 tigershark]

I fully understand. I cannot tell anyone how much time I spent as there were no cars or tunes close to what I put into my car at that time. It was a fun but a very time consuming task. You are very wise to say get a base tune from a similar car. The math and experience involved is most likely not going to happen in a post like this. IBPWs are important to me and that is a time eating monster to get right math wise all by itself.
I worked very hard and put in long hours and could not even expect a tuner to put in that amount of time. Joe and Bruce gave me some very good comparison tunes but the geometry of my motor was very different and thus the time factor and money of course. So as the newer LS setups come out a begged, borrowed or stolen base tun is the way to go.
Thanx



My math on base tunes is very simple. Find a car that had a similar setup and start from there. LOL "Free time" hasn't been a friend lately. So, trying to back into something like you describe isn't much of an option. Outside of fueling, it just comes with experience, talking to other tuners, etc. Wish I could offer more than that...but, it is what it is.

[joecar]

how can you get low m.a.f reading from a stock tune?
fuel filter has been replaced
used fuel injector cleaner as well
did not check fuel pressure. Would you think it could possibly a fuel pressure regulator issue? But wouldn't that make a mil light come on?If MAF is dirty it can read low... leading to smaller airmass and advanced timing.

Fuel injector cleaner may or may not do the job... how many miles on your injectors...?

If the spring in the FPR has weakened, then the regulated pressure will be less... the only way to know is to test the pressure with a gauge.

We first want to rule out any physical problems first.

I take it you're sure about no leaks in the exhaust (anywhere between heads and 18" past front O2 sensors).

[smslyguy]

If MAF is dirty it can read low... leading to smaller airmass and advanced timing.

Fuel injector cleaner may or may not do the job... how many miles on your injectors...?

If the spring in the FPR has weakened, then the regulated pressure will be less... the only way to know is to test the pressure with a gauge.

We first want to rule out any physical problems first.

I take it you're sure about no leaks in the exhaust (anywhere between heads and 18" past front O2 sensors).

there is 120,000 on the truck. Have you heard of transmission fluid working as injector cleaner?

[smslyguy]

If MAF is dirty it can read low... leading to smaller airmass and advanced timing.

Fuel injector cleaner may or may not do the job... how many miles on your injectors...?

If the spring in the FPR has weakened, then the regulated pressure will be less... the only way to know is to test the pressure with a gauge.

We first want to rule out any physical problems first.

I take it you're sure about no leaks in the exhaust (anywhere between heads and 18" past front O2 sensors).

there is 120,000 on the truck. Have you heard of transmission fluid working as injector cleaner?

and yes i do not have any exhaust leaks check the exhaust and the egr as well

[98 tigershark]

I have not had a chance to check out the scan but I thought you said you cleaned the MAF. 1.) Did the maf read low before cleaning and how dirty were the elements? 2.) WHat did you clean the maf with. Those small wires you see in the maf measure the change in air temp to come up with a correct air volume reading for volume based on the change and they are very fragile and sensitive. Many dealerships tell you not to clean the MAF because of a film that is left behind on the MAF with most cleaners that are used. I have also seen dirty MAFs that seem to have had the LTFT and STFT make adjustments for this over a long time. If you successfully cleaned the maf with out a film left behind the fuel trims may be adjusting for that in a big way as the MAF may now be again measuring correctly but the computer needs to relearn for a while. I will still take a look and get back to you. Like Joe said, You do have to eliminate the physical problems. Thats allot of milage and was one of my next questions. The blowby that is returned prior to the maf can make the maf filaments very dirty.
98 tigershark

[smslyguy]

I have not had a chance to check out the scan but I thought you said you cleaned the MAF. 1.) Did the maf read low before cleaning and how dirty were the elements? 2.) WHat did you clean the maf with. Those small wires you see in the maf measure the change in air temp to come up with a correct air volume reading for volume based on the change and they are very fragile and sensitive. Many dealerships tell you not to clean the MAF because of a film that is left behind on the MAF with most cleaners that are used. I have also seen dirty MAFs that seem to have had the LTFT and STFT make adjustments for this over a long time. If you successfully cleaned the maf with out a film left behind the fuel trims may be adjusting for that in a big way as the MAF may now be again measuring correctly but the computer needs to relearn for a while. I will still take a look and get back to you. Like Joe said, You do have to eliminate the physical problems. Thats allot of milage and was one of my next questions. The blowby that is returned prior to the maf can make the maf filaments very dirty.
98 tigershark

the m.a.f. sensor did not look dirty and i cleaned it with maf sensor cleaner spray. there was no changed from before to after.