What does this do?and why would I want to do it?Do you reset it at Idle? driving down the road my L Terms are in the Neg like 5.0 to 6.0%,Will it mess with wot?I am low on power from mid to High end....Thanks guys...Scott

 

It just speeds the LTFT re-learn process. If they are way off +15 from a bad tune and you put a good tune in the PCM, it will still use the LTFT Correction for fueling and make you think your tune is off until it re-learns your new tune and brings them back to 0 (as this may take many miles of driving). So you want to start it off from 0 to see if your tune is making it negative or positive.

 

Basically what he said... LTRIMS are the average amount of fuel that the PCM has to add or remove based on O2 input to maintain 14.7 AFR ...

You want your LTRIMs to be 0 or as close as possible to 0 on the negative side in order to get a good tune... if the LTRIMS are > 0 then when you go WOT they lock in and the PCM adds fuel...

 

My L Terms are -4.7 to -6.1 at idle in park,but they go up -10 when I am driving down the rd.Is this aceptable?
Thank you

 

Yes, a few stock cars that I have checked were like that so I'm guessing GM knows what they are doing!

 

Great to see you Bill,The VE table rocks and car is starting good,I dont know if you seen my post ?but I IAC was bad,put another one in and I was able to tune it right in Thanks! I was thinking about resetting them I just reflashed pcm,When resetting do you do it in park at idle or driving?

 

From what I have been reading the LT's are just an average of the ST's. The ST's are always moving because they are real time. With that in mind I am starting to think that one should be more concerned with the real time data than the average of it. That's why the LT's do not move up or down as fast because of the constant averaging. Now how would one go about tuning using the ST data?

 

Using the VE table. ST tuning is slightly more advanced and involved than LT tuning. It's best to get the LT's looking right so WOT fueling will be consistent and then tune the ST's.

 

That's what I was thinking but what are the ST's suppose to look like? I know the LT's are negative and go to 0 at WOT but nothing on the ST's. Would it be the same and what would the max values want to be?

 

Horist jump in at any time. I believe he is/was tuning for ST's and was shooting for +/-5. As far as I know, there aren't any real guidelines for tuning ST's, but I highly doubt you'll get them all negative without having some seriously negative LT's.

 

Thanks Magic. I think I will go do some scanning to get familar with how the ST's read compared to the LT's in order to get an idea of whats really going on.

 

Yeah, that was what I am curious about. Me, seeing anywhere inbetween -5/+5 and 0 at wot. If I tried getting all below 0 I'd probably see some real high negatives. No?

 

Okay I did a quick scan. Car was cold so this would probably change as the car gets warmer but at idle the LT's were -1.6 and ST's stayed at 0. I know at temp the ST's jump around but it was interesting to note that when cold even when I rev'd it a little they stayed right at 0. I will see what they do next time its warm.

 

that's because you're running open loop when cold... when you first start the car you have to wait for it to switch to closed loop before you really care about the LTs and STs... car could be 100% warmed up... shut it off and turn it on and it'll do the same thing

 

Thats what I thought.