LTFT going to positive 25 and above

[corn_bread]

I added about 15% to PE and all has been good started adding a degree or 2 of timing (currently 4 up from stock across the whole graph) and all the sudden when coming out of open loop the ltft is going way high. When you give is gas it drops soon as it goes back to idle right back up then after a bit it comes back down. I thought this was a lean issue but the exhaust gases tells me it is still running rich. New to tuning been reading all kinds of threads just cannot find one on this certain issue.


any help appreciated

1999 Silverado TUNE 6 about right.hpttune 6 first.hpl

[5FDP]

Did you just add 15% on a shot in the dark or where you actually trying to make the commanded AFR 15% richer for some weird reason?

They already ask for a rich AFR from the factory, whether it's actually that rich requires a wideband o2 sensor to verify. Never just slap the PE with 15% more fuel without knowing the real air fuel ratio. Commanded needs to match actual, any addition or reduced amount of fuel needs to be added/taken from the VE table and MAF curve so it makes the real AFR match the commanded.

As for the really positive LTFT's, what is done to the engine?

Did you check for vacuum leaks or verify fuel pressure yet?

[corn_bread]

just headers and clutch fan delete for now.

Haven't checked for leaks or fuel pressure.

added the 15% due to not having wideband DID NOT want to go LEAN at full throttle. would rather be to rich at WOT.


I appreciate your knowledge and advice.

[5FDP]

I wouldn't do that, you won't have enough fuel flow.

Keep in mind your truck has the smallest fuel injectors ever offered in the LS based trucks. They are only 21lb/hr and you really need to think about the change you made.

Look at how fat you are requesting. You are asking the computer to command and air fuel ratio of 10.67 all the way down 9.55. That is super duper mega rich and likely not even possible with those injectors, they are probably running static (aka wide open, over 100% duty cycle). Add the injector pulse width avg to your logs and you can watch the duty cycle.

Go back to the stock PE table before you end up causing more harm than good.

Get a wideband, command a safe AFR of like 12.0-12.5 and tune the MAF curve and VE tables to make the commanded AFR match the actual AFR.

[corn_bread]

Thanks. I have some 42lb injectors/ .560 lift cam/ roller rockers this isn’t installed yet. I will definitely get the wife band and go back to stock table for now.

Thanks for all your knowledge!!