How does "Fuel Trim" work in the ECU?
Oct 4, 2006, 10:02 AM
#46
Evolved Member
iTrader: (17)
Join Date: Aug 2004
Location: In da streetz
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by EVOtagger
great info in here
Oct 4, 2006, 02:56 PM
#47
Evolved Member
iTrader: (17)
Join Date: Aug 2004
Location: In da streetz
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
Eric, I let the car idle for a while, like 10-20 minutes and logged the ST & LTFT's. The STFT were bouncing around 0, but the actual A/F on my WB was in the 12s during that time. For some reason now the LTFT @ idle is 5% instead of -9-11% like I mentioned above.
since the LTFT is now adding 5% of fuel should I scale my injectors around 5% bigger?
since the LTFT is now adding 5% of fuel should I scale my injectors around 5% bigger?
Oct 4, 2006, 05:22 PM
#49
Originally Posted by AlwaysinBoost
Eric, I let the car idle for a while, like 10-20 minutes and logged the ST & LTFT's. The STFT were bouncing around 0, but the actual A/F on my WB was in the 12s during that time. For some reason now the LTFT @ idle is 5% instead of -9-11% like I mentioned above.
But, what seems very weird is that you said your wideband is reading in the 12s. Something is wrong. Either the wideband reading is wrong, the wideband sensor is messed up or your front O2 sensor is messed up, or something else I can't think of at the moment. You're not simulating your narrowband O2 with your wideband, are you? Also, you don't have a breather filter on your breather hose, do you? Is it still connected to the intake?
We have to figure out what's going on with this first before I can give the right advice. Your ECU thinks the mixture is at stoich, which is 14.7:1, and uses your trims to maintain that. So, I'm confused as to why your wideband is giving a reading of 12.x. So, at idle your wideband isn't bouncing around 14.7?
Originally Posted by AlwaysinBoost
since the LTFT is now adding 5% of fuel should I scale my injectors around 5% bigger?
If your LTFTs at idle and cruise do turn out to be drastically different, then we may have to use the injector latencies to fix that. What we really want are the LTFTs at idle and cruise to be around the same positive or negative number. Then the scaling will fix both of them.
Another question for you:
Is your battey voltage at idle a lot different than at cruise? Did you log that by any chance? If so, let's take a look at that and also at your latencies.
We may be able to use the latencies to fix up the idle and use your cruise LTFT as the target for scaling the injectors.
Eric
Oct 4, 2006, 06:07 PM
#50
Evolved Member
iTrader: (17)
Join Date: Aug 2004
Location: In da streetz
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by l2r99gst
You're not simulating your narrowband O2 with your wideband, are you? Also, you don't have a breather filter on your breather hose, do you? Is it still connected to the intake?
Originally Posted by l2r99gst
We have to figure out what's going on with this first before I can give the right advice. Your ECU thinks the mixture is at stoich, which is 14.7:1, and uses your trims to maintain that. So, I'm confused as to why your wideband is giving a reading of 12.x. So, at idle your wideband isn't bouncing around 14.7?
Originally Posted by l2r99gst
Another question for you:
Is your battey voltage at idle a lot different than at cruise? Did you log that by any chance? If so, let's take a look at that and also at your latencies.
We may be able to use the latencies to fix up the idle and use your cruise LTFT as the target for scaling the injectors.
Eric
Is your battey voltage at idle a lot different than at cruise? Did you log that by any chance? If so, let's take a look at that and also at your latencies.
We may be able to use the latencies to fix up the idle and use your cruise LTFT as the target for scaling the injectors.
Eric
I really don't believe that I have an exhaust leak and the front o2 sensor was just replaced <5k ago, plus I never ran leaded gas so it should be 100%. What other info can I give you?
Oct 4, 2006, 07:25 PM
#52
Originally Posted by AlwaysinBoost
I don't have the breather hose connected to the intake tube, its just hanging there. I'm talking about the breather hose thats located in the front of the engine and connects to the stock intake boot.
Originally Posted by AlwaysinBoost
the 12.x:1 reading was weird because it doesn't happen often. Normally when the A/F is bouncing around it will settle @ 14.7 eventually, I don't know what it was reading so rich this time.
This is what I would do if you really want to try to solve all of your problems with your trims and dialing in your injectors:
1. Connect your breather hose back to your intake pipe after the MAF. If you have a hard pipe that doesn't have this, you can easily tap it and buy a hose nipple at any hardware store. Over the years on the DSMLink board, the unconnected breather hose was problably the #1 biggest problem/headache when it came to messed up fuel trims and dialing in injectors/dead times.
2. Re-do what you already did with idling/cruising to see where your trims are at then. My guess will be that they will be much more negative than they are now. When we get those numbers, my guess would be that you will have to scale your injectors larger by a certain percentage to bring the trims down, follwed by that same percentage increase in your open-loop maps.
What size injectors do you have and what are they scaled to? Are they currently scaled much smaller than they actually are?
Eric
Last edited by l2r99gst; Oct 4, 2006 at 07:29 PM.
Oct 4, 2006, 07:46 PM
#53
Evolved Member
iTrader: (17)
Join Date: Aug 2004
Location: In da streetz
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by l2r99gst
Well, this can definitely mess up the trims a lot. A breather hose not connected to the intake pipe (MAF pipe) is letting in unmetered air. This may be why you were experiencing so many problems in the first place. That hose is normally connected to the intake pipe after the MAF, so the air is metered (counted). With the hose just hanging there, when there is vacuum in the intake manifold (like idle and cruise), the PCV valve is open. The air comes in through the breather hose, through the valve cover/crankcase, and out the PCV valve, into the intake manifold and then into the cylinders. The MAF never gets a chance to count this air, so you will be running leaner than the ECU expected, so your trims will be much more positive than on a stock setup to counteract the unmetered air.
This is what I would do if you really want to try to solve all of your problems with your trims and dialing in your injectors:
1. Connect your breather hose back to your intake pipe after the MAF. If you have a hard pipe that doesn't have this, you can easily tap it and buy a hose nipple at any hardware store. Over the years on the DSMLink board, the unconnected breather hose was problably the #1 biggest problem/headache when it came to messed up fuel trims and dialing in injectors/dead times.
2. Re-do what you already did with idling/cruising to see where your trims are at then. My guess will be that they will be much more negative than they are now. When we get those numbers, my guess would be that you will have to scale your injectors larger by a certain percentage to bring the trims down, follwed by that same percentage increase in your open-loop maps.
This is what I would do if you really want to try to solve all of your problems with your trims and dialing in your injectors:
1. Connect your breather hose back to your intake pipe after the MAF. If you have a hard pipe that doesn't have this, you can easily tap it and buy a hose nipple at any hardware store. Over the years on the DSMLink board, the unconnected breather hose was problably the #1 biggest problem/headache when it came to messed up fuel trims and dialing in injectors/dead times.
2. Re-do what you already did with idling/cruising to see where your trims are at then. My guess will be that they will be much more negative than they are now. When we get those numbers, my guess would be that you will have to scale your injectors larger by a certain percentage to bring the trims down, follwed by that same percentage increase in your open-loop maps.
Originally Posted by l2r99gst
What size injectors do you have and what are they scaled to? Are they currently scaled much smaller than they actually are?
Eric
Eric
Thank you for all the time you've taken to help diagnose my problem, I really appreicate it.
Oct 4, 2006, 07:47 PM
#54
Evolved Member
iTrader: (17)
Join Date: Aug 2004
Location: In da streetz
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by nothere
which wideband are you using? where is it located?
Oct 5, 2006, 06:22 AM
#55
Evolving Member
Thread Starter
iTrader: (8)
Join Date: Jul 2003
Location: Clarkston, MI
Posts: 449
Likes: 0
Received 0 Likes
on
0 Posts
I'm not sure I understand the explanation for how air is going in through the PCV breather hose. Can you elaborate? I mean, I always thought that the point of these was to hold a steady vacuum from the intake hookup, pulling a vacuum into the crankcase (to prevent the crankcase area from ever pressurizing and causing oil leaks).
The PCV valve itself is a check valve that prevents air from going IN to the crankcase, so how do you get unmetered air into the intake with the hose disconnected? Even if air somehow got into the crankcase through the PCV, how does it get into the cylinders? I mean, that's like saying that if you left your oil cap off your fuel mixture would get messed up.
I'm not criticizing here.. I just want to understand the logic. Thanks!
The PCV valve itself is a check valve that prevents air from going IN to the crankcase, so how do you get unmetered air into the intake with the hose disconnected? Even if air somehow got into the crankcase through the PCV, how does it get into the cylinders? I mean, that's like saying that if you left your oil cap off your fuel mixture would get messed up.
I'm not criticizing here.. I just want to understand the logic. Thanks!
Oct 5, 2006, 06:35 AM
#56
Originally Posted by Rob W.
I'm not sure I understand the explanation for how air is going in through the PCV breather hose. Can you elaborate? I mean, I always thought that the point of these was to hold a steady vacuum from the intake hookup, pulling a vacuum into the crankcase (to prevent the crankcase area from ever pressurizing and causing oil leaks).
The PCV valve itself is a check valve that prevents air from going IN to the crankcase, so how do you get unmetered air into the intake with the hose disconnected? Even if air somehow got into the crankcase through the PCV, how does it get into the cylinders? I mean, that's like saying that if you left your oil cap off your fuel mixture would get messed up.
I'm not criticizing here.. I just want to understand the logic. Thanks!
The PCV valve itself is a check valve that prevents air from going IN to the crankcase, so how do you get unmetered air into the intake with the hose disconnected? Even if air somehow got into the crankcase through the PCV, how does it get into the cylinders? I mean, that's like saying that if you left your oil cap off your fuel mixture would get messed up.
I'm not criticizing here.. I just want to understand the logic. Thanks!
OK, you have two holes in your valve cover. One is occupied by your PCV valve by the intake manifold and the other is the occupied by a straight through nipple and breather hose connected to the intake pipe, after the MAF.
The way the PCV valve works is as follows:
At idle, there is vacuum in the IM. This opens the PCV valve and begins to pull in air from under the valve cover. This is to pull any blow-by gases from the crankcase into the IM to be burnt. The breather hose is there so the vacuum in the IM will pull in fresh clean air to combine with any blow-by gases. Basically, the path of the air is as follows. Air filter, though the maf, into the intake pipe, into the breather hose, into the valve cover, combines with any blow by gases, out through the PCV valve, into the intake manifold, into the cylinders.
The exact wording in the manual is this (perhaps it explains better than I can right now):
The positive crankcase ventilation system is a sys-
tem for preventing the escape of blow-by gases from
inside the crankcase into the atmosphere.
Fresh air is sent from the air cleaner into the crank-
case through the breather hose to be mixed with the
blow-by gas inside the crankcase.
The blow-by gas inside the crankcase is drawn into
the intake manifold through the positive crankcase
ventilation (PCV) valve.
Eric
Last edited by l2r99gst; Oct 5, 2006 at 06:37 AM.
Oct 9, 2006, 06:37 PM
#58
Evolved Member
iTrader: (17)
Join Date: Aug 2004
Location: In da streetz
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
ok I haven't responded to this thread in a while because I was out of town for a wedding.
I finally got a chance to re-route the PVC hose to the MAF pipe and go for a long cruise. My trims now are:
idle:
STFT: between 3 & -3
LTFT: 0 (yes thats right ZERO)
cruise
STFT: between 6 & -6
LTFT: -12
I got those numbers after a long 1-2hour drive on the highway.
I also think I narrowed down the strange rich-lean surge I was getting at idle, it was related to my coolant temps and the high speed fan kicking on. WHile I was ideling looking at the info from my logs I noticed my idle would surge at right around 190-192* and then once the temps dropped back down to 180 or so it would settle.
So I looked through my ECUFlash parimeters and noticed "Desired ISCV inital step position with AC off" setting. I increased the numbers in the two highest temp readings and it seemed to fix it.
So now that I have my LTFT's nailed down what would you suggest?
I finally got a chance to re-route the PVC hose to the MAF pipe and go for a long cruise. My trims now are:
idle:
STFT: between 3 & -3
LTFT: 0 (yes thats right ZERO)
cruise
STFT: between 6 & -6
LTFT: -12
I got those numbers after a long 1-2hour drive on the highway.
I also think I narrowed down the strange rich-lean surge I was getting at idle, it was related to my coolant temps and the high speed fan kicking on. WHile I was ideling looking at the info from my logs I noticed my idle would surge at right around 190-192* and then once the temps dropped back down to 180 or so it would settle.
So I looked through my ECUFlash parimeters and noticed "Desired ISCV inital step position with AC off" setting. I increased the numbers in the two highest temp readings and it seemed to fix it.
So now that I have my LTFT's nailed down what would you suggest?
Oct 9, 2006, 07:01 PM
#59
You may have to lower the injector voltage latency slightly and lower the injector size again to get your idle trims back to zero, once its balanced your cruise LTFT's should be closer to zero than -12.. Your actually right in the zone my car hovers now.. so your almost there.