Diagnosing high positive LTFT

[JB86'd]

Originally Posted by KoolBRZ

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.

That first paragraph is incorrect. Header to overpipe leaks affect LTFT greatly and should be fixed. End of story.

[cjd]

Originally Posted by FRSBRZGT86FAN

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

Plug one tip, put a vacuum to the other. You can now use a tube to the ear to listen for leaks. A lot less chance of burning yourself. be careful, you can overheat your vacuum running it like this but it definitely can find leaks.

[Tectoniic]

Had it up on the lift last night at my buddy's shop and we went over the entire intake and exhaust while the car was running with no signs of a leak anywhere. All welds looked good, No black dust out of any gaskets(Checked Header to OP like fifty times), Drop in filter is properly seated in the stock intake. All sensors are properly tightened.

When I was talking to the shop owner about the high flow cat in FT86 UEL he was mentioning that is probably the cause for the high LTFTs (AFRs are still normal in idle, low throttle, and WoT). I could find some stuff on the 4Runner forums that went along with High Flow Cats messing with the LTFT but wasn't sure if that was sort of his way of saying "everything I can see is fine so I'm not sure."

There were a few threads about people running the stage 2 OpenFlash tunes with a high flow cat instead of stage 1 with no problems so I'll try that and log for a few weeks and see how it looks.

[steve99]

Originally Posted by Tectoniic

Had it up on the lift last night at my buddy's shop and we went over the entire intake and exhaust while the car was running with no signs of a leak anywhere. All welds looked good, No black dust out of any gaskets(Checked Header to OP like fifty times), Drop in filter is properly seated in the stock intake. All sensors are properly tightened.

When I was talking to the shop owner about the high flow cat in FT86 UEL he was mentioning that is probably the cause for the high LTFTs (AFRs are still normal in idle, low throttle, and WoT). I could find some stuff on the 4Runner forums that went along with High Flow Cats messing with the LTFT but wasn't sure if that was sort of his way of saying "everything I can see is fine so I'm not sure."

There were a few threads about people running the stage 2 OpenFlash tunes with a high flow cat instead of stage 1 with no problems so I'll try that and log for a few weeks and see how it looks.

If you confident theirs no exhaust or intake problems, then just do some maf scaling and your ltft will be sorted.


Its not unusual to see ltft at idle and low rpm be "off" up to 8% or so especially with large variations in intake air temps, some cars are off more than others


Try to do the maf scaling around the average temps for your area, if you do multiple scaling runs try to do them at similar temps.


if its only "off" below 2000 rpm or so and its not bogging or hesitating don't worry too much

[GT86meMR2]

If there is a leak in midpipe resonator would IT have these issues to?

[cjd]

Originally Posted by steve99

If you confident theirs no exhaust or intake problems, then just do some maf scaling and your ltft will be sorted.


Its not unusual to see ltft at idle and low rpm be "off" up to 8% or so especially with large variations in intake air temps, some cars are off more than others


Try to do the maf scaling around the average temps for your area, if you do multiple scaling runs try to do them at similar temps.


if its only "off" below 2000 rpm or so and its not bogging or hesitating don't worry too much

I'm So glad you mention this - that suggests I did fix my exhaust leak and am in the clear on that now. I live in the city and a ton of the worst behavior is stop and go. Intakes temps push 140 when not moving much. A long highway trip head IAM back to 1 and low LTFT. I know the Grimmspeed is close but it could easily account for a little variance.

Trying different gas brands to work the FLCK first...

[Tectoniic]

Small update.

I have been on the Stage 2 UEL E85 Tune now for about 100 miles since it is warm enough.

Worst LTFT I have seen is -3.12 regardless of idle/low throttle/WoT. I know the fuel trims can vary quite a bit with e85 but for now I think the previous high LTFTs were a result of running a high flow cat on the catted tune. Come winter I'll try the stage 2 93 tune and see if that works better.

Thank you again to everyone for your suggestions

[ChesterV]

I'm literally having this problem on my 22 BRZ, so far I couldn't find any exhaust and vacuum leak. 😢

[tomm.brz]

Originally Posted by ChesterV

I'm literally having this problem on my 22 BRZ, so far I couldn't find any exhaust and vacuum leak. 😢

Log?