I have been trying to figure out a lean condition I have. I have my tune pretty well set under all conditions except one. When I am going down hills, especially long down grades, the ECM (in Lean Cruise mode) leans out the AFR to anywhere between 17 and 19.6. This only happens under these conditions, under all other driving the AFR never gets leaner than 16.5. If I accelerate down the hill or I close the throttle blades and cruise until I get the the bottom it helps keep me out of the condition, but when I load the engine again to maintain speed the AFR goes really lean until I get passed what ever threash hold it needs to in order to get the AFR back to normal. I have tried richening the base fuel map, subtracting timing and other various parameters (each time I make one of these changes and it doesnt work I reset it back to what it was before). The richening and timing changes seemed to help, but hasnt fixed my problem. I am running a 350ci SBC, mild cam, TBI with an EBL Flash ECM, wide band O2 sensor and I am using Tuner Pro software. I am at a loss for what I should change, any help is appreciated. Thanks.

 

Sounds like DFCO, which is where the ECM turns off the injectors on purpose. This is done on decel to prevent damaging the cat-con.

A data log of the event always helps.

RBob.

 

Re-reading your post, is it possible that the fuel pickup in the tank is being uncovered?

Tapping the space bar with the WUD data logging, and being the top most window, will place markers in it. This makes finding this area in the data log much easier.

RBob.

 

Ok, I know earlier when I posted on this problem we checked DFCO and it isnt going into it as far as I can tell. I will try that trick with the data logs. The part that makes me think it is still getting fuel is the fact that if I continue to open the throttle blades, it keeps the AFR in a safe zone. Could it be an issue dealing the with my Vacuum Reference Fuel Pressure Regulator? I made sure to check box in the EBL utility when I was setting the tune up. Also, I am going to lower my fuel pressure some more, the DC is only at 40 during WOT. I will post back with the Data Log file. How do I upload it? Oh, I forgot to mention that the engine miss fires during this issue as well. Wouldnt DFCO cut off the spark?

 

Zip the .dat file and go to the Advanced dialog and up load it.

DFCO doesn't cut the spark, no need to.

RBob.

 

Thanks Bob. I will try to get it uploaded tomorrow.

 

Sorry for the later than expected message. I have been busier than expected the past couple days. For the time being, I disabled LC. I was surprised to find that it didnt really affect my fuel mileage that much. I did not have any problems after I disabled LC. I am thinking I may just try to make a separate tune, play with it and just not worry about LC.

 

i'm in for the answer ...