Was looking at something with the autotap tonight and I noticed that my long term fuel trims are both maxed at +25%. My short term trims are fine, hovering right around 0% like they should. I'm wondering why my long terms are so outta whack (maybe this is why my gas mileage sucks right now, like 10mpg).

I've been dyno tuned and all, so my a/f is good, but this problem concerns me. I wonder if it's related to my other problem (fuel pressure surges erradically unless my fan switch is on, see thread here).

Can't say for sure if it is related to your fuel pressure fluctuation problem BUT as far as the LTFTs being 25% Rich (by the way 5% more STFT and you'll be throwing the "Bank X Too Lean" codes), this is an easy one. The answer is in your signature...........C&L 80mm MAF. Here's what I posted in another thread here on the Corral:

"Exactly BadBud! Just to recap, here's what happens:

1. OEM Meter is calibrated to take into account the ratio of the sampling tube cross-sectional area to main bore cross-sectional area (among other things).

2. C&L effectively alters the ratio between the sampling tube and bore area. The desired effect is that this new ratio (which isn't very accurate) makes the PCM think that it's getting less air so the PCM leans out the mixture at WOT. However, during adaptive operation, the PCM notices that the reported airflow always causes the mixture to be lean so it has to up the fuel trims (enrichen) in order to maintain stoichiometric (14.7:1 air-fuel ratio).

3. The real problem occurs after the PCM has fully adapted to the C&L meter after some miles of driving. When you finally go to test the car on a dyno you run RICH! How is this possible? Open-loop works like this more or less: the PCM looks at the mass-air meter to read air-flow, it then goes to a table and picks the correct injector pulse-width to use to yield some predetermined air-fuel ratio (also in a table). Now, it also has this thing called the Open Loop Fuel Modifier which is essentially a history of how far off the mass-air meter has been when running adaptive. Different model years do different things here BUT they are all based off of the Long-term fuel trims (LTFTs). In general, if the meter is always causing you to be lean by 8% when in closed-loop, your LTFTs will be close to +8% (RICH). Then when you go WOT and your PCM goes open-loop, 8% fuel will be added to the computed injector pulsewidth in order to get the right air-fuel ration. The BIG PROBLEM is that this +8% actually causes you to be RICH by 8% because the LTFTs have adapted to a modified and inaccurate signal!"

So, you should check your LTFTs and STFTs across the rpm/load range by logging them with an OBD-II scanner during different driving conditions. The LTFTs are not just two data values but an array of data with RPM/load as indexes.

You say you were dynotuned. What is the time relation between installation of the C&L meter and the dyno tune? IOW, was the C&L already on your car before you went to get tuned OR did you install the meter after the tune? Did you or the shop tune kill the battery power anytime right before tuning your car (clear the KAM)? If you answer yes to either of these questions, there is a chance that you are running really rich at WOT now. If not, then you are probably OK at WOT. However, when the LTFTs get pegged (25% is maximum) the system tends to behave funny when running in closed loop. Check for posts here on the Corral by "onerichrunner" where he talks about how he used the MAFterburner to correct his out of whack LTFT problems caused by his new cams. Once he started getting the fuel trims down, the PCM started doing the right thing. Until then, the PCM was doing all funky stuff with fuel and timing to get the car to idle (unsuccessfully).

Anyway, a short-term fix is to ditch the C&L and go with another meter like an 80mm or 90mm LMAF. However, this will require a retune. You could also purchase a MAFterburner (my product) and use it to correct your LTFT issue caused by the C&L meter and further optimize your WOT air-fuel curve if necessary. You can also do a search here on the Corral for "MAFterburner". There are a lot of people who have successfully used it here.

For more tech information, see: www.seanhylandmotorsport.com/mafterburner

Or, you can join our tech forum at: www.seanhylandmotorsport.com/forum

Finally, if you have any other questions, you can email me at: info@mafterburner.com

In summary, the LTFT problem you have is caused by the C&L meter. I'd bet lunch on it! It happened to me and I've seen it many other times!

Mark Chiappetta

 

One more quick test that you can do is the following:

1. change back over to your stock meter

2. disconnect battery (+) for at least 30minutes to kill the Keep-Alive Memory.

3. Reconnect the battery (+) and do the idle relearn procedure(idle 5min with accesories off and 5min with AC on, I think)

4. Hook up the OBD-II scanner and recheck your idle trims and your fuel pressure.

5. Do the test that you do with flipping on the FAN and see if the fuel pressure continues to fluctuate wildly.

Mark

 

mjchip is almost right. A MAF reports X voltage. The EEC tansfer function translates this to an airflow value. The transfer function matches the stock MAF (unless changed with a chip, etc.). You swapped MAF's, and now the transfer function doesn't match. I'm not sure if you mean the long term trim is adding 25% fuel, or pulling that much. Either way, the MAF is not reporting the correct airflow to the EEC. Because the long term trim is correcting for the problem, the short term trims appear normal. You can fix this with a chip, a maf adjuster, a MAFterBurner, etc. If you are OK at WOT you could also drop fuel pressure a few psi to get the LTFT's back within the acceptable range. THIS COULD CAUSE A LEAN CONDITION A WOT!!!!

The cross section really isn't important. It's the MAF electronics that determine what voltage to report based on the temp differential of the control wire and the hot wire.

David

 

mjchip is almost right. A MAF reports X voltage. The EEC tansfer function translates this to an airflow value. The transfer function matches the stock MAF (unless changed with a chip, etc.). You swapped MAF's, and now the transfer function doesn't match. I'm not sure if you mean the long term trim is adding 25% fuel, or pulling that much. Either way, the MAF is not reporting the correct airflow to the EEC. Because the long term trim is correcting for the problem, the short term trims appear normal. You can fix this with a chip, a maf adjuster, a MAFterBurner, etc. If you are OK at WOT you could also drop fuel pressure a few psi to get the LTFT's back within the acceptable range. THIS COULD CAUSE A LEAN CONDITION A WOT!!!!

The cross section really isn't important. It's the MAF electronics that determine what voltage to report based on the temp differential of the control wire and the hot wire.

David

David is almost right also, right up until the point where he says, "The cross section really isn't important....."

Actually, the *ratio* of the sampling tube cross-sectional area to the overall meter cross-sectional area DOES MATTER. Yes, the MAF electronics is what determines how to convert air-flow to voltage, however, the MAF electronics converts the air-flow in the sampling tube only to voltage. The transfer function in the PCM actually takes into account the ratio of both areas to determine how much mass-air flow there is through the entire meter. This is how C&L alters the MAF signal, by changing the ratio of the two cross-sectional areas.

I stand by everything that I said earlier.

Cheers,

Mark

 

will be running that rich on a blower car be good or bad.i have been getting codes p0171 and p0174 for a while now.i'm waiting for my scanner to get here so i can look at my fuel trims.i have a prom77 calib for 36 lb inj.i know pro m calibrate the blower aplications on the rich side,so i'm lost as to why i get system lean bank 1 and 2.i only get the codes when i turn on the ac and it happens only in close loop.i have a jms chip,but it threw codes with and without the chip.i replace the o2 sensors,but i never disconected the battery.the car is running so strong i dont want to mess with it until i get the scanner.i've my prom77 for 4 years now and it just started throwing codes the last couple months.

 

Mark, I thought if the OBD2 device reads +25% that was a lean condition, and -25% was a rich condition?

 

will be running that rich on a blower car be good or bad.i have been getting codes p0171 and p0174 for a while now.i'm waiting for my scanner to get here so i can look at my fuel trims.i have a prom77 calib for 36 lb inj.i know pro m calibrate the blower aplications on the rich side,so i'm lost as to why i get system lean bank 1 and 2.i only get the codes when i turn on the ac and it happens only in close loop.i have a jms chip,but it threw codes with and without the chip.i replace the o2 sensors,but i never disconected the battery.the car is running so strong i dont want to mess with it until i get the scanner.i've my prom77 for 4 years now and it just started throwing codes the last couple months.

Well, on a supercharged car, rich is better than lean from a safety standpoint.

If you are getting "Bank 1 Too Lean" and "Bank 2 Too Lean" 4 years after making any other changes to your setup, the first thing I would suspect is graceful degradation of the EGO sensors. However, since you already replaced the O2 sensors (I would've disconnected the battery because the fuel trims are no longer completely accurate with new O2s) that rules out my first instinct.

There is a good chance that the Pro-M meter was calibrated lean causing your fuel trims to be very positive but not so positive that a DTC was thrown. Then, as your system normally aged, the limits were reached (+25% LTFT and +5% STFT on some model years) and the codes were thrown.

You need to get your hands on that OBD-II scanner.

Mark

 

Mark you have have been typing same time as me. See my question above yours.

 

Mark, I thought if the OBD2 device reads +25% that was a lean condition, and -25% was a rich condition?

You are correct. If the STFTs/LTFTs are positive, that means that the PCM needs to add fuel in order to compensate for a mass-air signal that results in a lean air-fuel ratio when monitored with the O2 sensors.

Likewise, if the STFTs/TFTs are negative, the PCM is pulling fuel out to compensate for a maf signal that causes the air-fuel ratio to be rich when monitored with the O2 sensors.

Mark

 

OK, just wanted to check. I follow all these A/F posts so I need to keep myself straight. So his LTFT is running super lean, not super rich.

 

Well, what you see in my sig is how I was dyno tuned. I was tuned by the Onerichrunner you mention in your post, and I even bought the C&L from him, hehe.

Hrm... what to do what to do. I don't have any money right now to buy a new meter or the MAFterburner (which I've followed closely, looks like a great product). I guess this is why a lot of people don't like C&L meters and go with ProM, since the ProM calibrated electronics report to the PCM corrently.

I'll can't swap my stock meter back in because I have 30lb injectors. The old superchip that came from vortech compensated for the stock meter w/larger injectors, however, my current chip is set-up for matched injectors and maf. I guess I can reset the pcm and see if that does anything...

Any other idea? Tell me a little about how the MAFterburner fixes LTFTs. Shawns post was regarding STFTs. I guess once you get your STFTs stable (like I said, I've only checked mine at idle, not under load), your LTFTs 0 out as well.

 

Let me try to understand something else: the PCM only uses the LTFTs to adjust fuel at WOT? Is this correct? I rarely, if ever, drive WOT. 95% of my driving is below 3000 rpms.

The +25% LTFT on my car tells me it needs to add +25% fuel, which would explain my god-awful gas mileage.

 

Well, what you see in my sig is how I was dyno tuned. I was tuned by the Onerichrunner you mention in your post, and I even bought the C&L from him, hehe.

Hrm... what to do what to do. I don't have any money right now to buy a new meter or the MAFterburner (which I've followed closely, looks like a great product). I guess this is why a lot of people don't like C&L meters and go with ProM, since the ProM calibrated electronics report to the PCM corrently.

I'll can't swap my stock meter back in because I have 30lb injectors. The old superchip that came from vortech compensated for the stock meter w/larger injectors, however, my current chip is set-up for matched injectors and maf. I guess I can reset the pcm and see if that does anything...

Any other idea? Tell me a little about how the MAFterburner fixes LTFTs. Shawns post was regarding STFTs. I guess once you get your STFTs stable (like I said, I've only checked mine at idle, not under load), your LTFTs 0 out as well.

Wow, small world. Shawn is a good guy and he is very familiar with the MAFterburner. The best thing to do is give him a call or email him about your situation and see if he thinks that a MAFterburner will help. Tell him about the fuel pressure fluctuation and every detail. Remind him about the C&L meter too.

In your case, you would use the MAFterburner to "recalibrate" the meter to match the current MAF transfer function that is in the chip. It's similar procedure to what Shawn did with his car to get the thing to idle with the new cams. Call him.

Mark

 

Let me try to understand something else: the PCM only uses the LTFTs to adjust fuel at WOT? Is this correct? I rarely, if ever, drive WOT. 95% of my driving is below 3000 rpms.

The +25% LTFT on my car tells me it needs to add +25% fuel, which would explain my god-awful gas mileage.

1. The LTFTs/STFTs are used in closed-loop adaptive strategies only, NOT WOT. However, history from the LTFTs is used in the form of the Open Loop Fuel Modifier variable during WOT. Basically, if the PCM knows from evaluating the LTFTs that your MAF signal always results in an air-fuel ratio that is 10% too lean during closed-loop, it will set the OLFM = +10% so when you go WOT, you get the calculated injector pulse-width + the OLFM. In some model years the PCM takes the LTFT at 3000rpm and uses that as the OLFM. In other years, I believe, it uses an average of LTFTs between a certain rpm range as the OLFM. Either way, the system has some non-ideal characteristics that can be inadvertently be exacerbated by otherwise well-intentioned mods.

If the MAF transfer function is off 10% lean at low to mid flow rates but is accurate at high flow rates, then your air-fuel ratio may end up being 10% too rich when you at at high rpms in open-loop.

2. The +25% LTFT means that the PCM is adding 25% fuel to the calculated injector pulsewidth. Like I said earlier, if the MAF is incorrectly reporting the mass-air flow which results in this erroneous 25% rich correction, your car will run extremely rich when the PCM goes open-loop.

Mark

 

So with a EEC tuner you could limit these closed loop offsets by decreasing the adaptive strategy to 5 or 10%?????

Thanks,

Shannon

 

Great thread!

My question: Do *all* EEC V's allow the reading of long/short term trim values? I didn't think any EEC IV's had that capability.

My comments:
1) About the gas mileage: As it is now, your misadjusted MAF does *not* affect your gas mileage *when the car is warn*. Once in closed loop, it seems like your EEC is able to run at stoic.

2) At least for the EEC IV's, RPM is used along with the MAF for calculating injector pulse width at WOT. I also thought that for the EEC IV's, the RPM is the major factor in determining the injector pulse width at WOT. That seems to contradict what I read on the MAFterburner forums.

 

Great thread!

My question: Do *all* EEC V's allow the reading of long/short term trim values? I didn't think any EEC IV's had that capability.

My comments:
1) About the gas mileage: As it is now, your misadjusted MAF does *not* affect your gas mileage *when the car is warn*. Once in closed loop, it seems like your EEC is able to run at stoic.

2) At least for the EEC IV's, RPM is used along with the MAF for calculating injector pulse width at WOT. I also thought that for the EEC IV's, the RPM is the major factor in determining the injector pulse width at WOT. That seems to contradict what I read on the MAFterburner forums.

1. You are correct about mileage as the PCM should still be able to maintain stoich in closed-loop adaptive mode.

2. Here is a quote from EEC-IV notes: "The EEC does 4 point interpolation on all tables. There is a minimal number of
cells in the fuel lookup tables. The EEC doesn't look up 'injector on time', it calculates the injector pulse width by looking at the desired Lambda and then, using the mass of air entering the engine and the injector size, it calculates the duty cycle needed to get the desired A/F ratio. (Lambda is an engineering term where stoich is 1, anything smaller than 1 is rich, anything larger than 1 is lean. To get A/F numbers from Lambda, multiply lambda value by 14.64. For example, an A/F ratio of 14.05:1 is a lambda of .85 lambda.)"

Hope this helps,

Mark

 

1) About the gas mileage: As it is now, your misadjusted MAF does *not* affect your gas mileage

My maf isn't misadjusted, it's just not accurate apparently.

Hrm, where to get $300 really quick...

Come to think of it, my first dyno pull (last month) we were lean, so we added fuel. Maybe these LTFTs are left over from my previous lean condition... how often do LTFTs get updated?

 

Sorry to hit the thread so late Mike. You still have that inconsistent surging fuel pressure deal?? We need to get a handle on that PITA FIRST. Remember, cure any known problems first or we can just chase our tails.

Sorry to get to the thread so late Mike. Give me a call sometime and lets try to get a handle on that fueling issue. I have 2 dynos tomorrow morning and trying to finish up the T56 in the late afternoon.

Shawn

 

 

Sorry to hit the thread so late Mike. You still have that inconsistent surging fuel pressure deal?? We need to get a handle on that PITA FIRST. Remember, cure any known problems first or we can just chase our tails.

Sorry to get to the thread so late Mike. Give me a call sometime and lets try to get a handle on that fueling issue. I have 2 dynos tomorrow morning and trying to finish up the T56 in the late afternoon.

Shawn

Mike, you' re in good hands now! I'm outta here!

Mark

 

You still have that inconsistent surging fuel pressure deal??

I'm narrowing in on it, check out the thread in EEC tech "HDEF/EDF Relays"...

 

Today when I was checking out Rev2 of the Autotap software , I noticed that my LT trims were +24% at idle. Using a gauge in the Windows software I noticed that it quickly went to 2% if I brought the revs up slowly. Now I know that the LT trims used to show around 2-5% at idle for the ProM75 silver bullet the last time I checked 6 months ago.
Hunted around for an air leak and found one. The hose for the PCV oil catch can was off as I bumped it loose when I emptied the PCV oil catch can last week. The air leak was into the passenger's side valve cover , through the engine, and back out the driver's side valve cover to the air intake tube. Pushed the hose back on and the idle trim numbers slowly drifted back down to 2-3%.
You may want to check for an air leak.
Winston.

 

I'm going to chime in here.

I have a 96GT with a DOHC motor. I am using the GT wiring harness on the engine and the GT PCM. I also have a twEECer and run a C&L 80mm MAF. Recently the car began running really horrible. I pulled the chip and it immediatlly ran better. Took the car to a Ford tech buddy of mine. I had a bad hego. With the chip in, the LTFT was 25%+. w/o the chip the LTFT began to drop. We replaced the bad hego and the LTFT with and w/o the chip came back into range.

So C&L MAF's can't be all that bad!

 

Winston,

You need to delete the KAM when looking at the STFTs. Disconnect the battery, turn the key to the run position and tap the brakes a few times. Unless you do that the STFTs will be based upon the tweaks from the LTFTs.

Chris Yates
96 Cobra