LTFT question
Thread Starter
Junior Member
Joined: Mar 2021
Posts: 44
Likes: 3
2003 E55 AMG
LTFT question
Hey guys, I wanted to get some input on an issue I have been experiencing, not even sure if it’s in issue or if I’m thinking too deep into it since there are no drive-ability issues or codes.
Summary:
LTFT reset to zero if the car is not started in 5 days. What would cause the LTFT to reset?
LTFT bank 1 quickly goes to +9.1 and stays there, bank 2 fluctuates between +2.3 & +3.1. Highest I’ve ever seen it is +4.7. What can cause the bank 1 LTFT to be that much higher ?
Can I smoke test from the metal purge valve line coming from back of the supercharger, on driver side?
Things i have done recently:
Questions:
It only gets driven 30-40 miles a weekend haven’t taken it on a longer drive to see what happens to LTFTs. Swapping O2 between banks makes no difference either, and no exhaust leaks.
I have the MAP sensor, which I’ll replace along with other hoses and gaskets when I pull the supercharger, but I don’t think the MAP sensor would cause an issue with one bank being leaner then the other. What could cause the LTFT resetting and being higher, or am I just chasing a ghost.
Summary:
LTFT reset to zero if the car is not started in 5 days. What would cause the LTFT to reset?
LTFT bank 1 quickly goes to +9.1 and stays there, bank 2 fluctuates between +2.3 & +3.1. Highest I’ve ever seen it is +4.7. What can cause the bank 1 LTFT to be that much higher ?
Can I smoke test from the metal purge valve line coming from back of the supercharger, on driver side?
Things i have done recently:
- valve cover gasket and re sealed breather cover
- NGK spark plugs
- Bosch wires and coil packs
- gaskets for the surge tanks
- Y pipe & gasket for intake
- throttle body gasket
- camshaft & crank sensor
- IAT sensor
- crank case breather hoses
- grommet and hose for purge line from back of super charger
- air intake filters
- fuel pumps & fuel filter
- fuel injectors
- fuel pressure regulator
- belts, tensioners & pulleys
- exhaust manifold gaskets and had the manifold welded at the connector for the cats.
Questions:
- I drive the car on weekends only so it’s pretty much parked 5 days a week. Every time i start it after the 5 days it resets the LTFTs to 0. This won’t happen if I start it after 3-4 days, 5 days always resets them to 0. I have checked the battery and it tested good (less then 2 years old) & all monitors are always complete.
- Once running My LTFT for bank 1 goes up quickly to +9.1 and pretty much stays there, bank 2 fluctuates between +2.3 & +3.1 mostly, the highest I’ve seen is +4.7. I know the LTFT are supposed to be within +-5 %, anyone have any idea why they are going higher?
- To smoke test the car, can I do it from the purge valve line that comes from the back of the supercharger and is held on the valve cover.
It only gets driven 30-40 miles a weekend haven’t taken it on a longer drive to see what happens to LTFTs. Swapping O2 between banks makes no difference either, and no exhaust leaks.
I have the MAP sensor, which I’ll replace along with other hoses and gaskets when I pull the supercharger, but I don’t think the MAP sensor would cause an issue with one bank being leaner then the other. What could cause the LTFT resetting and being higher, or am I just chasing a ghost.
Last edited by fruitsalt; Apr 10, 2022 at 12:38 AM.
Super Member
Joined: Aug 2018
Posts: 697
Likes: 172
From: Seattle, WA
2019 M5 Comp, 2005 Ariel Atom 2
Yeah I would look at leaks first, good idea as a next step, and yes you can use that line just make sure you're blocking off the throttle body properly before smoke testing.
MAP would likely not cause a single bank issue.
For what it's worth, I use my iCarsoft scanner to watch fuel trims, it's just easier than getting into STAR whenever I want to monitor something, however I have observed some oddities through OBDII when comparing to STAR. My LTFT readings can be jumpy sometimes, probably the transition between open and closed loop, and sometimes they stick at one value for a while. I wouldn't be surprised if internal programming reset the LTFT monitor after a certain period of time, so I wouldn't worry so much about that.
See what the smoke test reveals, and if you're pulling the SC do all the gaskets, bypass valve seal etc.
9% also shouldn't grenade the motor either so I wouldn't fret too much driving it in the meantime.
Good luck!
MAP would likely not cause a single bank issue.
For what it's worth, I use my iCarsoft scanner to watch fuel trims, it's just easier than getting into STAR whenever I want to monitor something, however I have observed some oddities through OBDII when comparing to STAR. My LTFT readings can be jumpy sometimes, probably the transition between open and closed loop, and sometimes they stick at one value for a while. I wouldn't be surprised if internal programming reset the LTFT monitor after a certain period of time, so I wouldn't worry so much about that.
See what the smoke test reveals, and if you're pulling the SC do all the gaskets, bypass valve seal etc.
9% also shouldn't grenade the motor either so I wouldn't fret too much driving it in the meantime.
Good luck!
Thread Starter
Junior Member
Joined: Mar 2021
Posts: 44
Likes: 3
2003 E55 AMG
Yeah I would look at leaks first, good idea as a next step, and yes you can use that line just make sure you're blocking off the throttle body properly before smoke testing.
MAP would likely not cause a single bank issue.
For what it's worth, I use my iCarsoft scanner to watch fuel trims, it's just easier than getting into STAR whenever I want to monitor something, however I have observed some oddities through OBDII when comparing to STAR. My LTFT readings can be jumpy sometimes, probably the transition between open and closed loop, and sometimes they stick at one value for a while. I wouldn't be surprised if internal programming reset the LTFT monitor after a certain period of time, so I wouldn't worry so much about that.
See what the smoke test reveals, and if you're pulling the SC do all the gaskets, bypass valve seal etc.
9% also shouldn't grenade the motor either so I wouldn't fret too much driving it in the meantime.
Good luck!
MAP would likely not cause a single bank issue.
For what it's worth, I use my iCarsoft scanner to watch fuel trims, it's just easier than getting into STAR whenever I want to monitor something, however I have observed some oddities through OBDII when comparing to STAR. My LTFT readings can be jumpy sometimes, probably the transition between open and closed loop, and sometimes they stick at one value for a while. I wouldn't be surprised if internal programming reset the LTFT monitor after a certain period of time, so I wouldn't worry so much about that.
See what the smoke test reveals, and if you're pulling the SC do all the gaskets, bypass valve seal etc.
9% also shouldn't grenade the motor either so I wouldn't fret too much driving it in the meantime.
Good luck!
I always have a basic obd connected whenever I'm driving the vehicle.
Do you by any chance know what the MAP sensor should read warmed up at idle ?
Also Do you know if there is a write up on what needs to be done with the supercharger, I was planning on replacing the MAP sensor, the oil in the supercharger and the gaskets between the super charger and head. what other items should I be replacing ?
Super Member
Joined: Aug 2018
Posts: 697
Likes: 172
From: Seattle, WA
2019 M5 Comp, 2005 Ariel Atom 2
I can't remember on the MAP at idle, I think upper 30s inHg? Someone can chime in if they know but I think that's where mine usually sit.
On the supercharger - plan on doing the rubber hose/seal that the bypass valve uses to attach to the bottom of the supercharger, those seals collapse over time and have been known to leak. It looks like you've done most of the other items already. I don't know if there is a DIY on removal, but here are a few tips:
-Be careful with the supercharger magnet wire harness, it can break easily where it's attached to a tab on the supercharger. Not the end of the world if it does but you'd need to glue or zip tie it in place later and there isn't a lot of room to work.
-Don't use a gasket where the intercooler seals, use 3bond/rtv. I think they used to sell a thin gasket but they can leak. Don't overtighten those bolts either or the gasket might not cure and seal as well as it should.
-If you have one, using an engine hoist to remove and reinstall the SC makes life 1000% easier, its heavy and needs to come basically straight up out of the car which is awkward with how far back it is.
-When reinstalling, use guide rods of some sort in the bolt holes, the intake gaskets want to move around and you need it aligned before putting the bolts back in. I used some plastic rods from my kids bicycle trailer flag and some marshmallow skewers haha. Worked great!
On the supercharger - plan on doing the rubber hose/seal that the bypass valve uses to attach to the bottom of the supercharger, those seals collapse over time and have been known to leak. It looks like you've done most of the other items already. I don't know if there is a DIY on removal, but here are a few tips:
-Be careful with the supercharger magnet wire harness, it can break easily where it's attached to a tab on the supercharger. Not the end of the world if it does but you'd need to glue or zip tie it in place later and there isn't a lot of room to work.
-Don't use a gasket where the intercooler seals, use 3bond/rtv. I think they used to sell a thin gasket but they can leak. Don't overtighten those bolts either or the gasket might not cure and seal as well as it should.
-If you have one, using an engine hoist to remove and reinstall the SC makes life 1000% easier, its heavy and needs to come basically straight up out of the car which is awkward with how far back it is.
-When reinstalling, use guide rods of some sort in the bolt holes, the intake gaskets want to move around and you need it aligned before putting the bolts back in. I used some plastic rods from my kids bicycle trailer flag and some marshmallow skewers haha. Worked great!
