I have a growing annoyance with my Osiris tune but have been living with it when compared to my first tuning experience.

The issue is that my AF spikes off the gauge for a few seconds every time I lift my foot off the gas. The Z has never died or stalled but it seems strange that I can go from ~12 - 13 under normal throttle, lift the throttle as I approach a red light, and see the AF go off the gauge "lean" for a second only to bounce right back to 12 - 13 as I finish braking to the light (no throttle).

• Is it normal for the fuel to be completely cutoff like that when you lift the throttle?

• The lean AF spike is annoying but is there any danger of causing damage to the engine?

• Should a pro -tuner be able to get rid of the spike or at least smooth it out?

Thanks!

 

Mine does the same thing. I was cipher logging my air/fuel ratio and at no throttle or at WOT it would stay around the safe area but the moment I would let off the throttle it would spike up to 30 (highest the widebands can read) for a few seconds. This still concerns me and im glad you made this thread. Hopefully someone can chime in and give some insight.

 

It ties in with the fact that you use way less fuel when decelerating in gear than in neutral. If I'm not mistaken, the ECU transitions into a sort of deceleration map in which it mainly utilizes the inertia of the car/transmission/etc to keep the engine moving. As opposed to in neutral, where it needs to inject more fuel to keep the engine rolling, so to speak.

I'm sure I'm screwing up all kinds of language and terms here, but I hope what I'm trying to say is still getting through.

At any rate, the reason the AFR spikes is because the engine just doesn't need the fuel to keep it running, so the ECU tells it not to feed it. There's absolutely no damage occurring, to my knowledge, and it's really just a sign of you using less fuel as your car is rolling. It was annoying for me, because I would sit there and try to see how high my AFR got, and the max reading would be 30, which is useless to me.

But just so you know, it's nothing bad. It's completely normal, and I hope my explanation helped shed some light on what's going on. The moral of the story is that you use much less gas while decelerating in-gear than in neutral. I go to neutral anyway, because I have the feeling that it's easier on the engine (less wear/tear at lower rpms).

To answer more succinctly:
1. I'm not sure it's completely cut off, but what you're experiencing is normal.
2. Should be no danger whatsoever.
3. I don't think so. It's normal, and probably something you want to keep, actually.

Hope I helped. (Anyone: Please correct me if what I said was wrong in any way.)

 

Ah thanks. That makes PERFECT sense. Good reply

This ties into the whole thing about how they say "you use less gas when your decelerating while your in gear (no throttle) rather than putting it in neutral. Putting it in neutral while slowing down (no throttle) a/f is spot on around 14.9 because the ECU is feeding it fuel to stay alive. It all makes sense.

 

Good thread. I'm still learnning about Rich Vs Lean, still confused..lol
I'm running vortech also.
Normal drive, A/F gauge shows around 14~15
When i go WOT, A/F shows 10~12.
When i let my gas, it shows 19~20.

I asked to many people, they said it is pretty good and running rich. What A/F gauge are you running? i'm running haltech.

Also, anyone can explain about crystal(?) inside the muffler tip?

 

I think the lean condition is misleading. What is actually happening is the engine is getting fed no fuel. The wideband sensor represent no fuel as super lean. But yeah whatever we all got the same issues, nothing to cry about.

 

Correct. Deceleration in newer cars as far as the ECU is concerned is a full fuel and ignition cut. Your motor is just pumping air. The reason for the A/F gauge ramping the number to 30 and then turning off is in the gauge electronics itself. It actually goes to zero fuel for emissions purposes as soon as the car goes into decel. So it's just air moving through the motor and it reduces emissions and cools the motor at the same time.

On big build vehicles with large injectors where the injector doesn't fully shut off it may still have some fuel left in it, but it really shouldn't be enough to allow combustion. On big injector cars you may have backfires etc because of the small trickle of fuel and lack of spark. Once that small amount of fuel hits the cats or something hot in the exhaust it may ignite. But that only happens are large injector cars.

 

I have the DW 600cc injectors and do get some burble coming thru my headers and straight exhaust

It's difficult to describe exactly what the Z is doing but under decel it's like I turn the key off immediately after lifting the throttle (AF gauge max's out) but then the AF goes right back to ~12 - 13 as I continue to decel. It's kind of herky jerky except you can't really feel it.....just hear it and see it on the gauge.

Air pumping thru the motor during decel would not be registering on my AF gauge after the initial cutout unless there's fuel too.

Sounds like this is normal and that I can't get it smoothed out?