injectors not closing on deceleration
 

Just wondering if anyone has noticed that the injectors don't fully shut down on deceleration. Since I have installed my Wb, I notice that sometimes when I let off the throttle the injectors will shut off like all my other vehicles and sometimes the injectors will keep functioning and keep the afr's a little on the rich side.

are you seeing this at high load? when the engine temps are high and the load is high, I think this happens as a cooling precaution. unburnt fuel removes heat. I know some DSM's used to actually fire the injection during the intake AND exhaust cycles under high load/heat conditions. Horrible for fuel efficiency, but great for not melting and having a minimal impact on performance :D Can anyone confirm that the evos also do or don't behave like this?

If they do, this should also only happen during open-loop operation, where there is no feedback from the o2 sensors. So the ridiculously rich AFRs don't matter so much since they are not totally the byproduct of combustion, even though the exhaust stream will see rich afr pocket spikes.

blk_majik, which DSM's did this?

And I gree with the OP, it seems the injectors do not close when you're off the throttle. Sometimes it does it, sometimes it won't at all, and sometimes there is a delay and then you feel them close.

This is exactly what I am noticing. I have not gotten any kind of repeatability with it.

I know that my dsm does not act like that. My dsm is a 90 and as soon as you let off the throttle the injectors close.

yes injector overrun shutoff is MUCH less predictable now.

luckily you can see the fuel usage gauge on the dash to determine when they are OFF :)

i have notice such behavier when the car is fitted with VTA BOV. is this your case?

many cars i tuned with aftermarket BOV are recording rich AFR in the overrun period (off throttle.

I am having the same issue with a forge bpv

Its because you are running the car on a MAF and during light throttle decel (prior to decel fuel cut) the BOV is bypassing counted air, the air reaching the cylinders is much smaller in volume than what the MAF says, so it runs rich, regardless of recirc or open BOV venting. The further you get away from the factory parts/calibration, the worse it can be.

Its very possible this is one of the functions of the MDP sensor, as there are illogical areas between intake manifold pressure and MAF airflow where you can apply a negative fuel trim and eliminate this phenomenon entirely if you have an ECU that will allow it.

Couple it to the fact we have to deal with DBW and it gets even more fun. I havent seen any of the local Xs do it Daniel, but I have seen it once or twice in 8's and 9's.

I am actually experiencing the same. I am running the stock bov.

I see this once in a while too but it's hard to duplicate. I'm using a Works BOV which is a slightly stiffer spring than stock but still recircs. If I can catch the behaviour on a datalog and compare it to normal decel where the injectors shut off we might be able to tweak the tune to make it more consistant.

I see it on stock car in low speed and/or low RPM. sometimes they close after a few secs, sometimes it does not at all.

Wow had not seen this thread in a while.

For those that asked, I am on a stock everything.

With the injectors closing it is very and I mean Very unpredictable. I can actually feel them close when coasting to a stop.

Aaron email me your number and the next time I am in town I will give you a call and see if you have any free time.

This past weekend I actually kept a close eye on my afr and around 3500rpm to 3000rpm my afr goes to around 11-12 afr and then goes back to normal. When I was stock I never noticed this. Im Cobb stage 2 now.

That's not the case for droppinbottom's Evo. When I was with him, the injectors would go from dumping a fair amount of fuel to shutting off entirely. It wasn't a gradual event. It almost felt a bit as if the ISCV valve was operating too. I'm thinking now that it might be good to log ISCV stepper position to see what its doing as well.