Ha! Nailed it ~~~~ I think

[BlueDragon]

I have been running some scans because it was running kind of rich. The LTFTs are too high, everything looks good, even the STFTs look ok. I did some compares to some past runs and on the O2 MV table I see the O2s giving me a higher mv reading by as much as 100mvs in some cells almost half. A while back I had LG headers installed and we put the rear O2s in the front location as suggested by LG and eliminated the rear O2s. I think the reasoning was that the rears worked better in that location with the headers. I guess I am going have to dial in the VE table to reflect the higher voltage. has any one experienced anything like this, or approached it from a different perspective? The O2s are switching just fine, just a much larger range. Should I go back and put the stock front O2s in or just dial in what I have. It is a bit of work to change O2s as I don't think I can get them out without dropping the headers as I have one of those thick tunnel plates on. I know I can dial in what I have.

[tblu92]

The inherent problem with LT headers is that they will make your closed loop fueling (part throttle) richer---I see an average of about a 14.0 in closed loop with a wideband--The LTFT correction won't fix this-
Because the LT 02 bung locations are now further back then they were with stock manifolds-you get erroneous 02 readings-The LTFT trims are trying to adjust for a 14.68 fuel ratio but even though the ECM is asking for it--It doesn't neccesarily mean that's what you end up with-beacuse of the Lt's---The LT's generally won't make your LTFT's go too haywire--
To correct a now rich 14.0 for example--you would have to trick the ECM by asking it for something leaner like a 15.2 in order to end up with the stoich. 14.68--This is where it gets tough---No one really knows how to do this correctly--some change the 02 switching points -in theory if you subtract from that table it should make it leaner--Also some try to ask for a Stoich of something leaner as well--i haven't had much success either way--But i did get some improvemnt--I also played with the VE table by leaning it down in the lower RPM's--

When going into PE or WOT the 02's aren't being used to deliver your fuel--they are now being used only as a tool to measure the PE fuel ratio-It's not the ideal way to do it-best would be to use a wideband to check your PE fuel--But you can get it close with the stock 02's by trying to get the voltage around .900 millivolts--using the rear 02's in the front is a common practice-and they do work better as they heat up quicker and are more sensitive

depending on your mods i would leave the VE table alone unless you have a hds/cam engine---the best way to lean the PE fueling down is with the PE table based on RPM's--You may again have to trick the ECM here by asking for something leaner--For example if you are rich and you have a 12.5 commanded--you would ask for something like 12.8 (in order to get 12.5) make any sense ??
make sure your fuel trims are 0 or slightly negative just before going to PE--you can check this with the data logger---remember that a positive fuel trim will add that % to your PE fuel making it richer yet--a negative fuel trim however will lock on "0" during PE
i will always make small LTFT corrections with the MAF table--The changes happen immediately--whereas tweaking the VE table takes learning time to change---

[BlueDragon]

Tblu92,

Thank you, Finally! Your write up is excellent. I had my suspicions, but just could not confirm. This is exactly what is happening here.

The car is running great, just on the rich side. The tables and scans prove that to be true.

As much as I was trying to deny the fact that I needed to purchase a wide band set up to dial it in to where I wanted it, there is now no doubt in my mind that is exactly what I need to do!

Guess I will put things on hold until I get my wide band installed. The car is running well right now and to go in and trial and error with O2s that we know are in error without a true~accurate AFR measurement, would be a waste of time.

Any one have a good suggestion of which wide band to buy? I want to keep the price to the mid range.

[knyght4]

Originally Posted by BlueDragon

I have been running some scans because it was running kind of rich. The LTFTs are too high, everything looks good, even the STFTs look ok. I did some compares to some past runs and on the O2 MV table I see the O2s giving me a higher mv reading by as much as 100mvs in some cells almost half.

A while back I had LG headers installed and we put the rear O2s in the front location as suggested by LG and eliminated the rear O2s. I think the reasoning was that the rears worked better in that location with the headers.

I guess I am going have to dial in the VE table to reflect the higher voltage.

has any one experienced anything like this, or approached it from a different perspective?

The O2s are switching just fine, just a much larger range. Should I go back and put the stock front O2s in or just dial in what I have. It is a bit of work to change O2s as I don't think I can get them out without dropping the headers as I have one of those thick tunnel plates on.

I know I can dial in what I have.

I had this issue also. I have ARH 1 7/8in headers, 3x3. I had ordered the HPTuners and finally got the time to take a look at my tune. My car is mostly stock with the exception of an intake, headers and suspension goodies... My LTFT were as high as 15.6 all the time. On a dyno run, A/F was in the high 9.x. I didn't think that was good at all. This past weekend, I got the car tuned and the LTFT are now down to 0 and running a little positive (~3) right now. During my last log, it was still a little here and I've been doing some reading lately, and I'll look to get it closer to 0.

Originally Posted by tblu92

The inherent problem with LT headers is that they will make your closed loop fueling (part throttle) richer---I see an average of about a 14.0 in closed loop with a wideband--The LTFT correction won't fix this-
Because the LT 02 bung locations are now further back then they were with stock manifolds-you get erroneous 02 readings-The LTFT trims are trying to adjust for a 14.68 fuel ratio but even though the ECM is asking for it--It doesn't neccesarily mean that's what you end up with-beacuse of the Lt's---The LT's generally won't make your LTFT's go too haywire--
To correct a now rich 14.0 for example--you would have to trick the ECM by asking it for something leaner like a 15.2 in order to end up with the stoich. 14.68--This is where it gets tough---No one really knows how to do this correctly--some change the 02 switching points -in theory if you subtract from that table it should make it leaner--Also some try to ask for a Stoich of something leaner as well--i haven't had much success either way--But i did get some improvemnt--I also played with the VE table by leaning it down in the lower RPM's--

When going into PE or WOT the 02's aren't being used to deliver your fuel--they are now being used only as a tool to measure the PE fuel ratio-It's not the ideal way to do it-best would be to use a wideband to check your PE fuel--But you can get it close with the stock 02's by trying to get the voltage around .900 millivolts--using the rear 02's in the front is a common practice-and they do work better as they heat up quicker and are more sensitive

depending on your mods i would leave the VE table alone unless you have a hds/cam engine---the best way to lean the PE fueling down is with the PE table based on RPM's--You may again have to trick the ECM here by asking for something leaner--For example if you are rich and you have a 12.5 commanded--you would ask for something like 12.8 (in order to get 12.5) make any sense ??
make sure your fuel trims are 0 or slightly negative just before going to PE--you can check this with the data logger---remember that a positive fuel trim will add that % to your PE fuel making it richer yet--a negative fuel trim however will lock on "0" during PE
i will always make small LTFT corrections with the MAF table--The changes happen immediately--whereas tweaking the VE table takes learning time to change---

I wish I found this thread sooner.