LTFT help
 

The only mods I have done to the car are an agency power midpipe and coolant throttle body by-pass. The car has 41k miles on it and if it helps I changed the plugs around 20-25k(due for those soon) and coils + wires at 30k.

I am having trouble with my long term fuel trim(ltft) being high. Until today I could only measure it when I got a cel with freeze frame data but I purchased a much better obd2 scanner and can now see live data.

First let me just say I have tried to locate a vacuum leak with carb cleaner and failed so I bought a little tank of propane and that also failed to find anything. I went through the whole engine bay with the propane and never got any change in idle at all. I have also cleaned my MAF a few times with no success.

A month ago my ltft was as high as +16.4% so I reset the ecu but now the highest I have seen is +12.5%. It changes pretty frequently by large amounts, and no I am not confusing the stft with the ltft. When I get on the highway and accelerate fast it goes as low as about +5% and then once on the highway and cruising it changes to +8-12%. When idling or just driving around the city normally it is usually +10.9-11.7% but every now and then drops down to around +8%. It is almost always in closed loop the only time it hits open loop is when I accelerate fast like getting on the highway or when I take my foot off the gas and coast. Otherwise I have not really seen it go open loop.

Is this an issue or am I just worrying about something that is normal? Everyone seems to have a different answer, some say up to +12% is fine and others say it shouldn't stray far from +/- 4%. Why does it change so frequently and by such big amounts when it is supposed to be long term?

bump

Nobody checks this section, I'm sure paimon or ash will say something eventually. I almost posted it in series 1 but this section needs more love.

A vac leak would show up as a FT at idle...but much less as the rpm and load increased...because the % of the leak to airflow would get a lot smaller

I would hazard a guess that your fuel pressure has dropped...or you have an injector that isn't outputting what it should. Either that or your WBO2 sensor is reading wrong

The Maf has different set points for LTFT

Meaning you may very well have a different LTFT at idle than you do at cruise (30-50 g/s or so)

I've been fighting a -3% LTFT at cruise while my idle is 0% LTFT

It does look like a vac like and I hate vacuum leak hunts.

Hard to do much more without any data logging

Yup +1

The LTFT does not vary quickly. It's a running average of STFT under varying conditions. (Unless SII is somehow different). The only variations you should see quickly will be to a change in gm/sec airflow which selects a different stored % based on the MAF reading. That's my understanding anyway.

With cruise on at 70 mph, my LTFT would read +6% or +7% for hours on end. After a simple scaling of the MAF calibration table, it now reads 0 or +1% for hours on end. The remaining nonzero values in my LTFT are at idle (+4%) and very low airflows.

Perhaps you're getting bad or unstable readings from the MAF or another sensor that's getting flakey. If it were a vacuum leak, at first thought, one would think the LTFT correction would be highest at low speed and lowest at high speed.

Might be time for a compression check. Especially if your fuel economy is bad. Not enough compression=> slower burn =>more o2 goes by Wideband O2=> pushes up LTFT. Or could be your wideband is on the way out.

I checked my MAF readings today and WOT in 2nd gear maxed at 19 lbs/min near 9k rpm and then in third I got 21 lbs/min max. I know these numbers are low so maybe there is a problem with my MAF from what I have read I should be seeing 220 gs/sec or 29 lbs/min. I think I also read that this could be an indication of a motor going bad if the MAF is fine?

I hope its not compression, it was good 10k miles ago. Easy_e1 helped me do a check but I only checked my rear rotor at the time and he said it was like new. I have no issues with starting cold or hot, it actually seems to start slightly better when warm. If anything phils8 will hopefully let me come over sometime and do another test just to be sure but I really don't want to pay for one.

Series 1 info isn't applicable to Series 2 cars, and the oldest Series 2 cars are less than a year out of warranty so far. It's gonna take a while before the knowledgebase builds up.

There is a ton of info that is applicable to series 2, the cars did not change 100% there were only some engine changes and whatever else is listed in the thread that explains it. I understand that some things changed but things like what the MAF should read or how to figure out why my LTFT is high should be able to be handled by both sub forums.

I wish I could post some type of log for you guys but my obd2 scanner just does not have that capability. I am going to try and swap MAFs with someone local because I really don't want to spend $100 to find out that is not the problem. I tried cleaning it last night and it didn't do anything.

Swapped MAFs with someone tonight. We checked the readings in his car first and he was getting 25-27 lbs/min or around 200 grams/sec. Swapped it into my car and I got the same so there is definitely something wrong with my MAF.

On the way home I tested my MAF again and it read up to 25 lbs/min now. It seems to be working intermittently I guess but I am still going to replace it. LTFT was up to 14% tonight when cruising.

Bluetooth OBD2 dongle + Android device + Torque Pro app. If you already have the Android device, the total cost is less than $20.

I don't even have a cell phone let alone a smart phone lol. I know about that app though. I have no plans on buying a smart phone any time soon but maybe some day.

You do understand that the flow numbers can change quite a bit due to intake
air temp?

Cooler temp = higher readings (because air is more dense)
Higher temp = lower readings (air is less dense)

You have to take both air temp and MAF rate into account together

Most of the readings were between 50-65ish degrees outside at night so the iat should have been pretty similar. The iat was probably ~10 degrees higher than outside temps, at least according to the readings I saw the few times I checked them. I have got the 19-20 lbs/minute readings at those temps and also got the 25-26 lbs/minute around those temps.

How much of a temperature difference would it take to drop from 26 lbs/minute to 19-20?

if that's the case it could be any number of issues, the MAF itself could be completely accurate or not

only way to know for sure is a proper diagnosis

It seems to be accurate sometimes and other times it measures low. While I am driving the car can suddenly get a bit sluggish, nothing major but a difference I can definitely feel. Other times it drives fine. The maf seems to be working intermittently, I don't know if something else could affect it like that but the maf seems to be the problem. I will know in a few days anyway.

Have you looked for vacuum leaks, specifically on the accordion tube? My 6 had a split section, on the lower part of the tube, inside the crease. When the engine pulled, and shifted a bit, it would open the slit, let in air, run rough, and then magically heal when you let off the gas.

Vacuum leaks can be a PITA, that one was. Car ran great with a new one. You could try test while flexing lines and that hose.

Fuel pump idea is not a bad either.

Yes I have run propane and carb cleaner everywhere I possibly can in there and can find nothing. I hope it is not a vacuum leak that happens only when revving the engine like yours, that would be extremely annoying to find.

Squeeze the intake hose to flex it. That should reveal any hidden cracks in the hose.

Turns out what was causing the high fuel trim was an exhaust leak at the header -> cat flange. I was using the stock exhaust gasket there and my midpipe must have a slightly larger cutout to accommodate it than the stock pipe. It was not a huge leak but it was enough to screw with my trims.

I bought a nice carbon crush gasket from Brice at raceroots and I'm 120 miles in and so far still sitting at 0.0 LTFT. I don't have my good obd2 reader anymore so this is being read whenever I get a CEL by looking at freezeframe data. Before I fixed it it would have been easily 10+ by now.