WicketMike

iTrader: (13)

Ive been logging with A-Tap and while im driving and let off the gas and coast the Lterms go 20+ and even 25+.

What would make them go this lean but only when coasting?

thanks

NoGo

iTrader: (2)

A small vacuum leak will cause LTerms to spike up under low RPM and high vacuum conditions.

All your PCV hoses on?
Are you running a breather with your PCV system still hooked up (common problem).

WicketMike

iTrader: (13)

its only bank 1
i have an oil catch and if that was loose, would it only cause the lean on bank 1?

thanks

wrencher

iTrader: (2)

If it is high rpm's it is normal for pcm to lean it out on decel.
What kinda R's is this happening?
Watch your pulse width & o2's.
At real high R's on a full decel pcm will even go to a 0.0 pulse width.

WicketMike

iTrader: (13)

ill have to check my logs to see what rpms, but i think its happening almost at all rpms. and why would it only be on bank 1?

ChrisB

Any possibility of a small exhaust leak around the vicinity of the o2 sensor - unter decell you may have very low exhaust volume, and are more likely to have atmospheric air enter - causing a lean indication from the o2's.

If it's isolated to one bank this would be my first guess.

Ferocity02

iTrader: (60)

As far as I know it is supposed to do this. At least thats what I heard. On my car, coasting down a hill in 4th, using the engine as a brake, the car will go super lean like you said at 1900 rpms. This is a built in tool which shuts off or lowers the amount of fuel going into the engine. It helps the car slow down and save gas. Pretty neat huh

XLR8NSS

iTrader: (4)

Yep, my truck does this also after letting off the gas and coasting. It doesn't do it all the time so I'm assuming certain conditions have to be met in order for it to happen?

It's very strange to watch the wideband display go to 25:1 and then read error. It'll do that for a little bit and then if you just barely touch the gas it'll jump back to 14.5:1 VERY quickly. It shows up on EFILive as the O2's going down and staying in the .0X mv range and not switching like normal.

I'm fairly certain I have no exhaust or intake leaks.

red ws6 99

I would say its normal. You go from a ton of fuel,air, rpm and load. Too no air, no fuel, high rpm and hardly any load. I see 20:1 on the wideband (probably higher but thats how I have it scaled) You will get the exact same thing going down a steep hill. Throttle blade is shut, no fuel, but rpm is up pretty high (if your engine braking). Of course it could be exaust leak, but it fits perfectly the way pcm operates. I also get right back to 14.7:1 if I give it any throttle at all.

Gary

WicketMike

iTrader: (13)

my bank 1 is leaner then bank 2 by atleast 6% all the time, now when i let up and coast it jumps up even higher then bank 2
it wasnt like this a week ago

wrencher

iTrader: (2)

Switch those sensors with each other & see what happens.

WicketMike

iTrader: (13)

i changed both 02's because i thought it might be those, but even after changing them its still happening.

WicketMike

iTrader: (13)

would the MAP reading on Atap tell me if i for sure have a vacuum leak?

its reading around 45 at idle

Blackbird

interesting mine is the opposite.
coast in gear and a/f goes from 14.7 to 12:1 or richer.