LTFT always adding fuel (Page 1/1)
TurboGN JUN 04, 12:13 PM
I have a 88 Fiero GT with the 3800SC. My logs in HP Tuners showed the LTFT adding 14% more fuel, so I adjusted the MAF table in those areas by 14%. It then showed it was adding 5% more fuel, so I changed those areas again to add 5% more fuel. It just never stops, it keeps trying to add more fuel, 11%, then 14.5% and now 12.8%. I have changed the values over and over again, and even lowered the AFR in the 175-185 degree ECT area where it always seems to need more fuel. Now that I've added about 50% more fuel, it's still showing up that the LTFT is adding 14.8%. I don't believe that this is still a fueling issue. At WOT my AFR is showing up as 9 - 10 on the wideband. Does anyone have any idea why it's always looking for more fuel?
There is 0 KR
Fuel pressure is rising with boost.
Injector duty cycle is under 50% most of the time.
fieroguru JUN 04, 10:42 PM
Probably an exhaust leak upstream of the O2 sensor.
It only measures air, so if the leak is pulling in more air (making it read lean, which would make the ecm add more fuel), it won't matter how much fuel you throw at is because the same amount of extra air is still coming in.
Frenchrafe JUN 05, 05:32 AM
Yeah, sometimes you just don't take into account the O2 sensor if everything else is OK.
Try old school techniques by looking at the deposits on your sparkplugs?
They can give you a much better idea of the engine's health and running.

------------------
"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

TurboGN JUN 05, 06:48 AM
Thank you both for your help. This thing is driving me insane, lol.
Frenchrafe JUN 05, 08:01 AM
You have a narrow band 02 sensor linked to the 3800 ecm?
And a wideband as well for monitoring?
Quite probably, as Fieroguru said, there's a crack in the exhaust.
I've had to weld up my manifolds a couple of times and the worse was to straighten/file flat the flange on one side. Leak between the head and the manifold.

I have the opposite "problem" to you, as I purposely run rich by fooling the MAF sensor by multiplying it's signal.
My ecu and NB O2 are always correcting down when cruising, both on short term and long term corrections.
However, I get exactly the power I want on WOT!

And as said before, I look at the colour of my plugs to really check if the engine is running fine.

P.S. If your exhaust is too short or little to no back pressure (because no muffler / straight through pipes), you can get false O2 readings as well.
------------------
"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

[This message has been edited by Frenchrafe (edited 06-05-2024).]

TurboGN JUN 05, 08:38 AM

quote
Originally posted by Frenchrafe:

You have a narrow band 02 sensor linked to the 3800 ecm?
And a wideband as well for monitoring?
Quite probably, as Fieroguru said, there's a crack in the exhaust.
I've had to weld up my manifolds a couple of times and the worse was to straighten/file flat the flange on one side. Leak between the head and the manifold.

I have the opposite "problem" to you as purposely run rich by fooling the MAF sensor by multiplying it's signal.
My ecu and NB O2 are always correcting down when cruising, both on short term and long term corrections.
However, I get exactly the power I want on WOT!

And as said before, I look at the colour of my plugs to really check if the engine is running fine.

P.S. If your exhaust is too short or little to no back pressure (because no muffler / straight through pipes), you can get false O2 readings as well.



Yes, I have both the stock NB, and a WB.
I'll have to pull some plugs and check them out.

[This message has been edited by TurboGN (edited 06-05-2024).]

TurboGN JUN 05, 11:42 AM
I checked the plugs and they look good, just a little orange discoloration from the octane boost.
I checked the exhaust, and there are no obvious leaks that I can see.