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Burning Lean on decel

91_740Turbo

91_740Turbo

New member
Joined
Aug 25, 2011
Location
Tampa FL
Hey guys,

So I've noticed when driving on the highway, when I let go of the gas after accelerating it will sometimes burn lean, not a little bit and for a second, it goes to the limit (my Analog wideband goes to 20) and it stays there until I accelerate or start giving it gas to maintain speed. Today I was paying more attention to it and I noticed it only did it around the 2500 RPM range, if I accelerated the car and I let go of the gas and it lands on 3000+ rpm it doesn't lean out that high, it will lean a little bit like you would expect but it will correct itself, but if I let go of the gas and its around 2500 RPM it leans out to 20. Anyways I've been thinking what can be causing this? at first I thought maybe its time to change the fuel filter but then I thought thats probably not it because under acceleration it richens up between 12-10 (10 is a bit extreme) so now I'm thinking maybe its the MAF. The drivetrain is stock and the 13c turbo is putting out 5PSI.

Thanks for the input!
 
My MS system does the same thing. Though, when going down long steep hill, it can go full lean for too long and make me nervous...putting it in neutral brings it back to idle and solves that.
 
Dakar09 said:
My MS system does the same thing. Though, when going down long steep hill, it can go full lean for too long and make me nervous...putting it in neutral brings it back to idle and solves that.
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I wouldn't worry about it. On my s70 the wideband did the same thing, and that was on factory management.
 
Standard issue fuel cut on decel, Bosch was a bit ahead of the masses for doing it. Nothing to worry about at all. It should hit fuel cut any time the throttle is closed and the rpm is over 1500.
 
For coasting in gear, a later-model vehicle with a fuel-injected engine will realize more gains from the burn and coast technique than older carbureted engines because the engine control units in most fuel-injected engines will cut fuel to the engine when the car is in gear, the throttle is closed and the engine is running faster than idle speed. This is sometimes referred to as "deceleration fuel cut off". This will often engage while a car is coasting down a hill and is common in both automatic and manual transmission vehicles, although the particular engine speeds at which it will engage vary
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unplug your idle switch / TPS and you'll see it'll behave "normally"
 
240Psycho said:
if it didn't it would sound like an SRT dodge. Lots of rumbling and back firing.
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Heh, our K-jet and carbed 240s do that.

It sounds kind of neat through less restrictive than factory mufflers.

Who needs them fancy electronics anyway?

On the other hand, lack of decel fuel cut is just one of many reasons our fuel economy is so bad.
 
sim said:
On the other hand, lack of decel fuel cut is just one of many reasons our fuel economy is so bad.
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My dollar in a bet says that your driving style has more effect on fuel economy then the dab that decel fuel cut may save.

Soooo much more to life then good gas mileage.

Smile as you stand on it!
 
JohnLane said:
My dollar in a bet says that your driving style has more effect on fuel economy then the dab that decel fuel cut may save.

Soooo much more to life then good gas mileage.

Smile as you stand on it!
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Like I said... One of many reasons.

Gasoline is cheap entertainment.

The worn out old SU carb is another big reason, she runs on
the rich side. I refuse to sink any time into the carb though,
it's going EFI soon.
 
sim said:
The worn out old SU carb is another big reason, she runs on
the rich side. I refuse to sink any time into the carb though,
it's going EFI soon.
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Raise the seat for the needle or lower float level just a dab... Either will lean it out. Both are under half hour operations.
 
When in decel, the transmission is spinning the engine, so you don't need to inject fuel to keep the pistons moving. Nothing to worry about. The only time you really want fuel on decel is if you're racing and want some added cooling effects.
 
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