Thread: LTFT pegged at 16.4

would a big exhaust leak cause this?

Vacuum leak.

so a exhaust leak would not cause this excessive of a difference?

If it's before the first o2 sensor it will. I was leaking right at the collectors on my front header, left me at 16.4 all the time. Fixed the leak, back down around +5

Originally Posted by Fivefingerdeathpunch

Vacuum leak.

x2! Check your gaskets on the Throttle body and all your vacuum lines. Spray brake cleaner around them and if the idle changes and your LTFT goes up you found the source.

well my cam makes it very hard to notice idle changes. VERY lopey

Ususally vacuum leak will cause + fuel trims, Exhaust leak will cause -. Replace the SC lately?

Evap opened , has a leak. Goes away when closed. Just a thought.
While its running, pull the line going to the solenoid and see if the solenoid is sucking air. If it is, it's open. Plug the line going back to the motor and see in real time the trims settle

Originally Posted by crazyguy03

Evap opened , has a leak. Goes away when closed. Just a thought.
While its running, pull the line going to the solenoid and see if the solenoid is sucking air. If it is, it's open. Plug the line going back to the motor and see in real time the trims settle

i recently deleted the evap system and plugged the tb vac nipple, i deleted it trying to fix my fuel trim. no dice..

replaced my vac lines to boost solenoids, they are all new, new t's and lines.

i had to take apart the top end for a rebuild, new gaskets everything.


also why would a exhaust leak give negative fuel trim?? anything under 0 is leaning out your afr. if you have a exhaust leak, it reads extra oxygen, at that point it would add fuel, not take it away.

lol unplug my o2 sensor? ur a animal...

Yes. He's suggesting u run off commanded AF/R

i dont have any tuning software at the moment, and having a hard time getting zzp to get back to me about what the commanded afr is and if i could run in open loop.

i asked my instructor about it as well, he said i could if i was tuned for it, but being its a canned tune, not a good idea.


i did a WOT 1 and 2nd gear pull and i got 6.6lbs of boost. is that a normal number for my flow mods with a 3.5 pulley? if its normal, then it cant be a vacuum leak. one large enough to peg my LTFT would drop my boost, yes?

dont have access to scanner at the moment, but did find something interesting, when i move my egr valve, you hear a sucking sound...

so now i have to source a new egr valve, i dont want to delete it and then start knocking bc of higher cylinder temps. i definitely smell heavy exhaust fumes around that area, but could be coming up from under the car where my large exhaust leak is.

Question. How does deleting hot exhaust fumes from entering your intake manifold RAISE cylinder temps?

Originally Posted by crazyguy03

Question. How does deleting hot exhaust fumes from entering your intake manifold RAISE cylinder temps?

It doesn't.

It REMOVES hot air from the intake side LOWERING intake temps and killing the carbon build-up that always is associated with EGR. People claim EGR hurts MPG's...I never saw a loss in MPG's, people just like to b1tch.

There's your problem and your vacuum leak. Just block it off with two pennies and some RTV so you don't have to worry about it again.