How's it going?

As usual, the iroc is giving some problems...
The car in question is a 1990 camaro iroc-z 350. Mods include Dart Iron Eagle 165 cc heads, comp 212/218 .488/.495 cam, and edelbrock headers. There is a transmissioncenter transmission there with a 2600 stall. The car is chip tuned fairly well and the car idles and accerlerates like it's a champ (fairly close to 128 blm counts). However, if I floor or give heavy throttle the car and the car gets to high speeds, and I let go of the throttle complete (at 0% throttle), I receive through the datalogger that a lean condition goes as high as 160. Also, there is a popping sound coming from the exhaust as this lean condition occurs and the throttle is at 0%. There were no knock counts, and I fattened up the low map and low rpm areas in the VE tables 3 times! Nearly 10% increases each time!? If anyone wants to take a look at the bin, please let me know your email address. I don't know what else to do....

Blake

 

Hey..long time so see...
As far as your question you are seeing the Decelleration Fuel Cut Off routine in action...it is normal. Depending on the editor you are using, you can edit those values. Do a search for DFCO on the board.

 

What you are seeing is a phenomenon known as "Decelleration Fuel Cutoff (DFCO). After a hard accelleration run, the ECM will totally turn off the injectors to save fuel and reduce emissions. There is a status flag that indicates when the ECM enters this mode that can be datalogged. As for the popping, I am going to assume you are experiencing backfiring (in the exhaust , it is more properly termed afterfire). The most likely cause is an overly rich mixture during WOT. When you let off and the ECM enters DFCO, the unburnt extra fuel is mixing with air and igniting from the heat in the exhaust. JMHO

*EDIT* Arrggghh!!! Slow89Iroc-Z, you beat me to it.

 

Yep its normal.

I eliminated the popping on overrun by adding more timing in the 20-40MAP areas.

 

Does anyone have suggestions for values? I see where they are and I have some understanding about the enabling and disabling. I understand that both map and mph conditions must be met. And I understand that the map conditions are reverse of the mph conditions. I see there is some need for DFCO, what's probably the surest values to work and still be economical. I ask this because I won't have a chance to change the chip until tomorrow, and it's better than going up and down the stairs, in and out five times trying. Any good estimates or rules to keep in mind while adjusting the values would be appreciated guys. thanks

PS Currently they are set for

1400 RPM enable
1100 RPM disable

20kpa enable
28 kpa disable

2.0 sec time between