I don't quite know whats going on here. Speed is 55 mph going downhill and I let off the throttle. MAP is 20, TPS is zero, AFR shoots up to 18:1. While still coasting, I LIGHTLY set my foot on the pedal and bring the TPS up to about 5%. MAP remains at 20 but the AFR drops rapidly down to about 11:1.

Initial throttle lift happens at 6:17 and you can see the problem in the following 30 seconds or so. As the road levels out the problem disappears.

I have a datalog but it's too big to attach here, stingy 1MB limit! I can email it to whoever..

 

DFCO?

RBob.

 

DFCO Enable Temperature is set at max 151* C, so it should not be cutting off fuel right?

 

What does the data log say? Without that it's just a SWAG. . .

RBob.

 

According to datalog DFCO never comes into play. Also, asynch has always been disabled on my car. The only other thing different between the 0-TPS/18-AFR area and the 5-TPS/11-AFR is the TCC (unlocks closed throttle, locks with cracked throttle) and the NB 02 voltage which goes almost to zero. PW is 1.1 and I've never had a problem at that PW before, the injectors usually don't stop flowing till the PW is down about .8ms.

The problem here is with my VE learn. Coasting down the hill with no throttle and an 11 AFR makes the VE learn subtract like 12 like points from that area. Rest my foot on the gas (5%TPS) and the AFR shoots up and the VE learn quickly goes from -12 to 0 all the way up to 12. The MAP is bottomed out so the RPM/MAP location is the same.

Off Topic - Would a slightly larger cam be easier to tune? Its a stock L05 right now. I'm stuck with these 90# BCC injectors unless I can get a killer deal on some 68s or 65s.

 

Interesting dilemma. At that low engine load being rich or lean won't hurt the engine. Although on the lean side you could run into mis-fire. Which can be hard on a cat (the real reason for DFCO).

For now I wouldn' worry about the VE Learn in that area. Get the rest of the VE table squared away first. Then edit the 20 KPa column for the best driveability. The reported AFR can help when changing the VE.

Another item to check is the IAC throttle follower. When you touch the go-pedal the TF may be kicking in. When the IAC opens there is fuel pulses added.

RBob.