I know all cars equiped with a MAF go a bit rich upon throttle lift.
Mine seems to be excessive.
After acceleration, in the time between the instant I lift and injector shut-off at closed throttle (so what's that; maybe, half a second!), it goes off-the-charts pig rich.
My question really is: is this a problem? I guess I'm concerned about fuel washing the cylinders and flames going through the turbine (it's a light show at night!)
Is there anything one can do to minimize this? I already use the lightest possible spring in my aftermarket recirculation valve. That's all I can think of.

 

What chips are you running, what MAF etc...

I have an updated Scivision MAF, and am using MaxTune to custom tune, and have a little blip on throttle lift, but nothing below 11:1 or so...

Wash is definitely a concern, but not sure how rich your setup is going...

 

Do you have a recirculating diverter or a atmospheric BOV?

 

recirc... OP also states he is using a recirc (I'll make a guess and say forge, but I could be wrong...)

I do plan to upgrade to the SFR blow thru MAF and an atmospheric dump, but for now it is recirc...

 

Yup, it's a Forge recirculation valve.
I see as rich as in the 9s air/fuel on throttle lift!
The thing is that I'm seeing flames out the exhaust, so maybe the excess fuel is being burned as opposed to washing down the cylinders. Lots of turbulence going on in the cylinders at that instant, so maybe the fuel doesn't have a chance to pool down the walls. Is this just wishful thinking?
Vitesse MAF, by the way.

 

Thomas, Is this with the water/Methanol injection in place?
Have you tried this without the water injection?
What sort of AFRs are you running with and without the WI at WOT.
Is the throttle body shutting close 100% and TPS picking up the idle signal (best to check this at the DME Idle Input).

A bit rich AFR after lift off from WOT is normal. The only way to see if the injectors are shutting off is to log the TPS signal with the injectors line to see their relationship (a scope is needed for this).

 

Old problem – the recirc air is actually going in reverse flow – from the valve back out the air filter for a brief second – the MAF is metering this air and adds fuel accordingly.

Get the MAF as far away from the recirc valve ports as possible.

 

John,
this problem occurs with or without the WI being activated.
I could be accelerating at half throttle, with no WI taking place, air/fuel at about 13 to 1, and the instant I lift, pig rich.
I have a good wideband that shows "air only" the instant the throttle is closed. So, I'm pretty sure the injectors are turned off with the idle signal.
No, the issue is the very short time it takes the throttle spring to close the plate from the moment the operator lifts his foot. It's during this second that the problem occurs.
I don't know if there's anything I can do about it. So, I'm wondering if this will do any harm.

Chris White's above post states that the MAF could be re-measuring the air from reverse flow. MY MAF is pretty close to the diverter ports.
However, I always thought that it's the momentum of the air flowing over the MAF, but not getting to the engine, which is causing this temporary richness.
So one school of thought, I guess, would be to delay the operation of the diverter valve.
And I was thinking to get the diverter to be as sensitive as possible.

 

If the richness is from the time you lift to the time the TB shuts and the TPS send the Idle signal to the DME. Till the DME receives the signal it will not know to shut the injectors. Also, till the TB is closed, you will not build vacuum to open the BOV. Do you have a factory BOV you can try?

Chris brings a point about the MAF remeasuring the air (reversion). However this did take place with the old style MAF, not as much with the new style as Thomas is using. I wonder if something is amplifying this: Camshaft, BOV...

I'm using the same MAF on my car, I'll go and do a run to see if I notice the same behavior. I'm running 95# injectors, so if it's going to show it'll do it.

 

John, when you say CV, you mean the recirculation valve, right? aka diverter valve, or BOV (everybody calls it something different)
I did have the stock one in there, but switched to this Forge unit hoping to solve the problem somewhat; no change from the stock one.
The only other thing I can think of: where would be the best place to get a vacuum signal for this recirculation valve? I'm thinking, maybe, T'ing off the brake booster line.
Also, I wouldn't think that you would need full intake manifold vacuum to activate the recirculation valve. Wouldn't you just need the pressure differential between what's in the IC pipe in front of the TB, to what's in the intake manifold, and that to be greater than the spring in the recirculation valve?

 

All you realy need is some video of your car throwing bad **** tail pipe flames then you'll feel all manly and enjoy the over feuling

 

You are correct I was using CV for circulating valve, to be clear I changed it to BOV (Blow Off Valve or Recirculating valve). You will need enough vacuum to open the valve.

 

So much does the spring tension in the RV affect the performace overall, MAF, etc. ?

What is the best spring rate?

 

To most of us...OK, to some of us...well, Ok...to me, the CV is the cycling valve that contorls the boost in a stock system....

 

I am with you Chris on that! Also doesnt Porsche call it a recirculation valve? So wouldnt that make it a RV? lol BOV!

After reading about this post. My car is doing the exact same thing. Very rich even to pops and flames after letting off from full throttle. I did put a firmer spring in my forge BOV. I will try the original spring after I fix my oil leak. I hope this will fix it. I am running Johns Vitesse Stealth mode set up and hope that the MAF is not too close to the BOV to cause this condition.