STFT and LTFT reading? [Archive] - GrandAmGT.com Forum

PDA

View Full Version : STFT and LTFT reading?


G.I.Ceo
09-18-2011, 06:06 PM
Well I started tuning my GA the other day just to get a feel of what I need to work on. I am extremely new to this so I know it will take me some time to get used to it. I am using a DHP Powrtuner for the tune. My question is what is a good STFT and LTFT reading at idle so I can know if my fuel trim is in line and I can move onto scanning? Right now mine read 24-25 at STFT and 20-21 at LTFT while idling? Anyone know what a good reading is?

Malaclypse
09-18-2011, 07:41 PM
A good reading should be 0 or as close to zero as possible. Usually + or - 5 is acceptable.

+24 in short term means you're running VERY lean. To the point that the pcm is unable to compensate for it.

AleroB888
09-18-2011, 08:20 PM
Well I started tuning my GA the other day just to get a feel of what I need to work on. I am extremely new to this so I know it will take me some time to get used to it. I am using a DHP Powrtuner for the tune. My question is what is a good STFT and LTFT reading at idle so I can know if my fuel trim is in line and I can move onto scanning? Right now mine read 24-25 at STFT and 20-21 at LTFT while idling? Anyone know what a good reading is?

Bad vacuum leak could contribute to that, or wrong setting of FPR, or wrong IFR setting in PCM.....

G.I.Ceo
09-18-2011, 08:57 PM
Bad vacuum leak could contribute to that, or wrong setting of FPR, or wrong IFR setting in PCM..... I'm wondering for the vacuum leak if my valve cover air filters could cause that. I will put the oil cap back on and see if that makes a difference. My FPR is adjusted to 50 psi with the car running and vacuum hose pulled off. I do not know what IFR means so I can't tell you what my setting is.

unchained_01
09-19-2011, 06:43 AM
IFR. Is injector fuel rate. And is your fpr stock ? What size injectors do you have ? 28's 36 or 42. Also do you have the tuning notebook ? If not let me know and someone here will send you the PDF too. Make small changes and take your time !! And don't forget to reset trims after changes.

G.I.Ceo
09-19-2011, 02:17 PM
IFR. Is injector fuel rate. And is your fpr stock ? What size injectors do you have ? 28's 36 or 42. Also do you have the tuning notebook ? If not let me know and someone here will send you the PDF too. Make small changes and take your time !! And don't forget to reset trims after changes.

No I have a Casper AFPR. My injectors are stock. I do have the tuning manual and I think what I should do is start with a absolutely stock .bin and work my way from there. I also do a reset of my fuel trims whenever I load a new .bin or make adjustments.

AaronGTR
09-19-2011, 02:56 PM
I'm wondering for the vacuum leak if my valve cover air filters could cause that. I will put the oil cap back on and see if that makes a difference. My FPR is adjusted to 50 psi with the car running and vacuum hose pulled off. I do not know what IFR means so I can't tell you what my setting is.


It depends. How do you have them set up? Are there filters on both the front and rear covers, and did you plug the holes they go to? I wouldn't remove them to begin with, but the PCV is supposed to be a closed system. If you put a breather filter on one valve cover, but leave the other hooked to the intake or manifold, then yes you will have a vacuum leak. And that will definitely affect your fuel trims.


quick note on fuel trims: As Malaclypse said you want them as close to zero as possible. I try and keep mine within +/-4 on the LTFT. The LTFT is an average of the STFT's, so if you reset your fuel trims (either manually with the tuner or by unplugging the battery for 30 min.), when you restart the car your LTFT should be at 0 but your STFT's will immediately start making larger changes. Once it's gotten enough STFT numbers it will start changing the LTFT. Usually within 15-20 min. of driving around the LTFT should pretty much settle on a number. The LTFT will change though based on engine load (also known as the fuel trim cells) which you can usually keep track of by throttle % or MAP. It can take a bit more driving to get enough readings for the LTFT to settle down in those cells since it's dependent on how much time you spend at that load. Professional tuners (and obsessed people :D) will do that tuning on an eddy current dyno like a Mustang dyno because they can change the load on the car and hold it at any speed/rpm/throttle % they want, which makes it easy to fine tune those load cells.

Just a little info to digest for the future. :)

Malaclypse
09-19-2011, 06:04 PM
A filter in place of the oil cap or rear breather tube will cause a lean condition. Its allowing unmetered air to be drawn through those filters and into the engine.

Its best to have the factory PCV valve and breather hoses hooked up.

G.I.Ceo
09-19-2011, 07:06 PM
It depends. How do you have them set up? Are there filters on both the front and rear covers, and did you plug the holes they go to? I wouldn't remove them to begin with, but the PCV is supposed to be a closed system. If you put a breather filter on one valve cover, but leave the other hooked to the intake or manifold, then yes you will have a vacuum leak. And that will definitely affect your fuel trims.


quick note on fuel trims: As Malaclypse said you want them as close to zero as possible. I try and keep mine within +/-4 on the LTFT. The LTFT is an average of the STFT's, so if you reset your fuel trims (either manually with the tuner or by unplugging the battery for 30 min.), when you restart the car your LTFT should be at 0 but your STFT's will immediately start making larger changes. Once it's gotten enough STFT numbers it will start changing the LTFT. Usually within 15-20 min. of driving around the LTFT should pretty much settle on a number. The LTFT will change though based on engine load (also known as the fuel trim cells) which you can usually keep track of by throttle % or MAP. It can take a bit more driving to get enough readings for the LTFT to settle down in those cells since it's dependent on how much time you spend at that load. Professional tuners (and obsessed people :D) will do that tuning on an eddy current dyno like a Mustang dyno because they can change the load on the car and hold it at any speed/rpm/throttle % they want, which makes it easy to fine tune those load cells.

Just a little info to digest for the future. :)
Yeah I do have have a filter for my oil cap and the PCV system still hooked up. Tomorrow I will take it off and do another scan on the readings. When I do reset my fuel trims I am doing it by using my DHP to do it. Last time I did it I reset them and then went driving around for a hour just like Eddy's handbook says to do.

When I do start the car and do the reads both the LTFT and STFT read zero at the same time and then they slowly climb up to 20 for the LTFT and 24 for the STFT is that normal for them to be that high? I know by the sounds of it it's saying it is running lean? So should they be around 14 or so since optimal A/F mixture is 14.6? Like I said I am new to this and I know it will take time to learn but I am not scared to try and I love to learn new things. I wish I had access to a dyno but right now the cost out ways things for me.

I really do appreciate all your guys help because I don't know anywhere to turn to and the DHP site is pretty much dead.

AleroB888
09-19-2011, 07:27 PM
What are you reading for fuel pressure with the engine warmed up, and all vacuum lines in place?

Malaclypse
09-19-2011, 08:43 PM
No its not normal for your fuel trims to be that high. Before you go editing anything, fix the lean condition. Put your oil cap back on and reset your fuel trims. See where they are after that.

Here's an explanation of fuel trims:

The computer is always trying to keep the car stoich (14.7 :1 Air/fuel ratio) while idling, cruising and under light acceleration. If your fuel trims are at 0 that means the car's air/fuel ratio is close to 14.7:1. While you can't be 100% accurate without a wideband O2 sensor, its damn close enough.

If your fuel trims go positive it means your AFR Is running higher than 14.7:1 and the computer is adding fuel to try and compensate. Typical causes = vacuum leak, plugged injector, plugged fuel filter etc.

If your fuel trims are in the negative range it means the engine is running too rich and the computer is removing fuel from its injector maps to compensate. Typical causes = stuck open injector, misfires, clogged air filter, leaking fuel pressure regulator.

So to re-iterate, fix the vacuum leak and see where your fuel trims are. Also, consider that you may not have enough knowledge to properly tune your vehicle without an increased risk for serious damage. Not saying you're stupid, just saying you don't seem to have the knowledge to tune on your own.

I don't know how to do it either so don't feel alone.

G.I.Ceo
09-19-2011, 09:31 PM
What are you reading for fuel pressure with the engine warmed up, and all vacuum lines in place? I'm not sure. The last time I adjusted it was with the vacuum hose off and running and it was adjusted at 50psi. I will try and get a reading with the line connected for you.

No its not normal for your fuel trims to be that high. Before you go editing anything, fix the lean condition. Put your oil cap back on and reset your fuel trims. See where they are after that.

Here's an explanation of fuel trims:

The computer is always trying to keep the car stoich (14.7 :1 Air/fuel ratio) while idling, cruising and under light acceleration. If your fuel trims are at 0 that means the car's air/fuel ratio is close to 14.7:1. While you can't be 100% accurate without a wideband O2 sensor, its damn close enough.

If your fuel trims go positive it means your AFR Is running higher than 14.7:1 and the computer is adding fuel to try and compensate. Typical causes = vacuum leak, plugged injector, plugged fuel filter etc.

If your fuel trims are in the negative range it means the engine is running too rich and the computer is removing fuel from its injector maps to compensate. Typical causes = stuck open injector, misfires, clogged air filter, leaking fuel pressure regulator.

So to re-iterate, fix the vacuum leak and see where your fuel trims are. Also, consider that you may not have enough knowledge to properly tune your vehicle without an increased risk for serious damage. Not saying you're stupid, just saying you don't seem to have the knowledge to tune on your own.

I don't know how to do it either so don't feel alone.
Got it. I understand it now. I know I sound like a noob at this which I am and I admit it that's what the questions are for. I will do research and study that tuning manual as much as I can. I know I ask a lot of questions but I am trying to learn and I have to basically do this on my own. I know it will take time and I am not trying to do it over night.

I will make a a stock file, reset the trims, put the oil cap back on, and check my fuel pressure with the car warmed up and vacuum line on and go from there.

AaronGTR
09-19-2011, 09:35 PM
^This. The fuel trim is a percentage (plus or minus) of correction the PCM is making to your base fuel table to achieve close to 14.6:1 AFR using corrections from the O2 sensor. IE if your fuel trim is -5 that means the PCM is pulling %5 fuel from the injector pulse, and if it is 20 that means it is adding 20% fuel to the injector pulse. Negative means you are running rich. Positive is running lean. You are running way lean as Scott said, and need to get rid of that filter and put your oil cap back on because you have a huge vacuum leak.

G.I.Ceo
09-21-2011, 01:43 PM
What are you reading for fuel pressure with the engine warmed up, and all vacuum lines in place?I will know the answer to this tomorrow. I ordered a gauge so I can have one attached to my fuel rail at all times and I can keep a eye on it. What would be a good setting to keep the FPR adjusted to? Like I said right now I have it set at 50psi with the vacuum hose pulled off.

^This. The fuel trim is a percentage (plus or minus) of correction the PCM is making to your base fuel table to achieve close to 14.6:1 AFR using corrections from the O2 sensor. IE if your fuel trim is -5 that means the PCM is pulling %5 fuel from the injector pulse, and if it is 20 that means it is adding 20% fuel to the injector pulse. Negative means you are running rich. Positive is running lean. You are running way lean as Scott said, and need to get rid of that filter and put your oil cap back on because you have a huge vacuum leak.
I pulled the filter and put the cap back on today and reset trims. I got better reading on one but same on the other. I think I am going to redo a stock bin file and start over from scratch. I'm thinking that will be my best choice right now. I also checked for leaks and none seam to be found.

AleroB888
09-21-2011, 04:21 PM
I will know the answer to this tomorrow. I ordered a gauge so I can have one attached to my fuel rail at all times and I can keep a eye on it. What would be a good setting to keep the FPR adjusted to? Like I said right now I have it set at 50psi with the vacuum hose pulled off.
.

44-48 with lines in place should be about right. My stock '99 regulator ran about 35 at idle, and stock 2003 was about 45.

G.I.Ceo
09-29-2011, 02:07 PM
Well I finally checked it and my fuel pressure was way to high. With the vacuum line off I was reading almost 65psi. I adjusted it back down to 46psi with the car idling and lines all hooked up.

Now I have noticed that after a couple of hours of the car being shut off my fuel pressure gauge slowly drops down to 0 for a reading. Is this normal or should I be looking for a leak? My fuel pressure gauge is mounted right on my schrader valve.

AaronGTR
09-29-2011, 03:12 PM
That is normal. Fuel pump only kicks on for about 3 seconds when you turn the key to on, then it shuts off until you crank the engine. There is a check valve built into the fuel pump assembly to hold the pressure after it turns off, but it isn't a tight sealing valve and will only hold pressure for a couple hours.

AleroB888
09-29-2011, 10:56 PM
When I filled up my tank today after it was almost empty, My LTFTs went way negative. After about 20 minutes of driving, they returned to normal. I wonder if that was from the colder fresh pumped gas hitting the system??

AaronGTR
09-30-2011, 07:44 AM
I wouldn't think that would make any difference. It should be pretty warmed up by the time it hits the engine, and even so a tiny difference in fuel density wouldn't make that much difference in AFR that it would require much adjustment in the fuel trim. I'd think something else is responsible.

Malaclypse
09-30-2011, 11:11 AM
When I filled up my tank today after it was almost empty, My LTFTs went way negative. After about 20 minutes of driving, they returned to normal. I wonder if that was from the colder fresh pumped gas hitting the system??

That's probably related to the EVAP system. And I'd say its normal operation.

When you fill your car up with gas, the fumes which are displaced in the tank by fuel are captured in the charcoal canister. As you're driving the PCM has the engine draw these vapors into the intake to be burned. It does richen up the car a bit and the fuel trims would show some compensation for that. It won't be a huge amount off and since the trims returned to normal after driving, I'd say the system is doing its job.

I think you're good to go man.

G.I.Ceo
10-22-2011, 03:59 PM
Well my Lean DTC code set again today but this time it's a 171 code. It's saying I either have a bad injector or a fuel pump going bad.

How can I troubleshoot this to know which one I will need to replace?

My fuel pressure gauge seems to be holding pressure where it needs to be but I cant tell under driving conditions because its under my hood.