Megasquirt No Throttle - Lean (decel)

yarin · Post by **yarin** » Mon Jun 12, 2006 10:40 am

I have an issue on my Porsche 914 with MS II V.3.0 that may or may not be an issue. This is a general question:

From conversations with others I've gathered that most factory cars and aftermarket standalone fuel injection systems essentially shut off injectors on deceleration.

Is this true? From what I've seen megasquirt does not reduce fuel supply on deceleration (triggered by MAP, RPM, or TPS) with the exception of TPSDQ(Decel fuel amount %). It sounds like to duplicate this decel - lean condition we have to setup our tables to do so. Is there any reason to aside from fuel savings?

Reason I ask is that from idle when letting off the throttle my AFR increases, sometimes to full lean. I attached a data log and .msg file. (i've got other issues, unstable idle to deal with as well).

Thanks

maztah · Post by **maztah** » Tue Jun 13, 2006 12:14 am

it is natural for the ego to read too lean mixture during fast decel because of sudden vacuum when the butterfly flap closes fast. About the fuel delivery cut when the throttle is on idle position, maybe some systems cut the supply when decel and resumes supply when the engine reaches the idle rpm, the issue would probably be a well designed control system for a/f mixture.

coyoteboy · Post by **coyoteboy** » Tue Jun 13, 2006 3:11 am

I can confirm that Toyota's ecus from as early as 88 do this. Mine sets the idle control valve open and cuts fuel completely even between gear changes until throttle goes back above 0 OR it reaches a set RPM at which point it fuels again and the idle controller catches the stall.

I've been using the over-run fuel cut of MSnS-Extra to do exactly this. I set the settings so that anything almost 0 throttle and fairly low map cut the fuel after 0.1seconds. This was the only way i could stop it hanging at high idle when running as piggyback. Saves a fair amount of fuel too lol.

J