Diagnosing high positive LTFT
 

I've been using OFT's OTS Stage 1 93 tune since November and have noticed my LTFTs slowly creeping up over time for the 15-22% throttle range.


I have the OFT mounted in my car so I have it on for almost every drive and have slowly tracked it go from +2 under low throttle to +10.15 where it is now. Values at idle and very low throttle are usually within +/- 1 and anything above the 15-22% throttle range is usually within +/- 3. Both of these values have been consistent since flashing the tune back in November so I am not worried about these ranges.


I've been using the following article ( http://www.aa1car.com/library/what_is_fuel_trim.htm ) to try and understand this better and I'm thinking the likely possibilities are:


1. Leak in the intake or throttle body.

I'm leaning towards this as the leak may not be big enough that at idle the engine is not pulling enough air to be affected and at WoT there is enough air bypassing the leak anyway :iono: My K&N Drop in never fit the box as snugly as the OEM filter so I'm really hoping it is not something as stupid as this....


2. Dirty injectors

Really doubting this is it as the car just hit 10K miles and I was also running E85 in the summer which should have helped clean them if anything? Is it worth running a bottle of injector cleaner through the system to see if that does anything?


3. Misfires

My car definitely shudders on startup and when logging misfires in the past I had occasional misfires show up but never enough to trigger a CEL code. I remember reading that coil pack failure was common on these cars so I'm not sure if it could be that or a bad spark plug?
EDIT: Have been doing logging for misfires and not having any with the warmer weather now even on startup. Definitely leaning toward intake or exhaust leak


What values should I be logging in OFT to try and narrow this down?
Only 14 slots and at the moment I'm going to have:

RPM
Throttle %
Engine Load

STFT
LTFT

Cyl 1 mis
Cyl 2 mis
Cyl 3 mis
Cyl 4 mis

AFR
Cmd AFR

Any help/input is appreciated.


TL ; DR

High LTFTs and I am trying to find what values to log in OFT to help narrow down the cause between a possible Intake leak, Dirty Injectors, or Misfires.

You may have an exhaust leak.

I thought about that and about a month ago we tightened up all the exhaust components and it didn't really change anything.

Did you check the welds on the header as well?

Visually rechecked intake and exhaust from headers all the way to cat back and everything looks good.

Could it be something with the tune being based on the gas that was available in the early winter when I flashed and now that their summer blend has come in it is a bit out of whack? Would the ECU compensate for that on it's own? I've been using the same Shell 93 at the same station for almost every fill up.

Might need to rescale your MAF. Its a canned tune it will be better for some than others.

Are you super sure that you installed the new filter correctly?:
http://www.ft86club.com/forums/showthread.php?t=7975

Also as for winter vs summer blend, I have to deal with that as well and no problems with my LTFTs or IAMs.

I don't think maf scaling is at all necessary for a drop in @steve99 can correct me if I'm wrong


I really think theres still an exhaust leak

For a stock intake that shouldn't be an issue

I think you might be overlooking the obvious. If you change the tune to shut off Port Injection, that could tell you where the difference lies. If the problem goes away it is a PI scaling problem. I had to change my injector scaling to cure a persistent LTFT problem. If LTFT goes positive then negative this isn't the cure. Bear in mind this could throw off your entire MAF scale however.

Not all leaks can be found through a visual inspection. I used the vacuum trick last weekend to look for exhaust leaks, hope I got it... Haven't taken the car out yet to check. If I didn't, I need another trick.

I'm thinking I'm on a wild goose chase. LTFTs were only getting up to +7.03 this morning and at lunch. I'll see if if starts to go back down over the next few days.

It'll be up on the lift this weekend so I'll do a better inspection on the exhaust. Thank you to everyone for the suggestions.

I made a post awhile back regarding the LTFT and how mine was always high in the positives

I had a shop take a look at my exhaust leaks and it solved the problem I think.
I was having a leak and the Header to overpipe flange and also the Overpipe to midpipe flange.
They put a bunch of high temp sealant to shut it and it's been okay for a couple months now

Plug the tips hard with shops towels start the car at idle, and feel everywhere for rushing air

How was your car supposed to sense leaks that occurred downstream from the oxygen sensors? Your car has no sensors past the header. I'm betting they sealed up the Header-to-Head gaskets as well. The only leaks that need to fixed are those upstream of the sensors. That includes intake, both before and after the throttle body, and the intake resonator assembly.

LTFT negative, or positive can be brought back in line with MAF scaling, or if it is widespread, injector scaling. Now since these cars have both Port and Direct Injection, it's best to turn off Port Injection by zeroing out the tables and then check for LTFT errors. Scale the MAF first, or if the errors are widespread, change the Direct Injector Scaling. Once that is brought in line, then add back in the Port Injection. Any further errors are brought back in line with by adjusting the Port scaling alone.

AVCS timing changes can also cause LTFT errors. These should be brought back in line with MAF scaling changes alone.