Hey all,

I am tuning a local time attack car, the class rules state he must run a catalytic converter.

Since reduction catalysts work only at 14.7:1 AFR, closed loop operation is a must. I do not want him to sacrafice power by having a loaded catalytic converter, I would like to run closed loop operation for when he is at idle/part throttle/cruising to maintain stoichiometric fueling.

Have any of you tried closed-loop operation using CROME? What is the load threshold for open-loop?

If this is not an option, I might have him step up to a DTA S60 for a real target-lambda table and closed loop functionality.

Thanks.
Marshall

 

I have not had any experience with Crome, although Hondata, AEM, and obviously more expensive systems do this very well. AEM has a user definable lambda table, that is very well implemented.

 

Exactly, both the DTA and AEM systems I've used all have well implimented target lambda maps.

I usually tune open loop to 14.5:1 - 15.5:1, but this is not precise enough to keep the reduction catalyst at operating temperature. The concern here is that the catalyst will load up and cause a restriction to exhaust flow if stoichiometric ratio isn't maintained.

I did some reading over at PGMFI.org and found a plugin for CROME that allows you to define TPS enable/disable criteria for closed loop operation at 6 different engine speed ranges.

I tested this on my car last night, and the primary oxygen sensor targets 14.7:1 nicely at part throttle and cruising when closed loop is activated. Since I am running Skunk2 Pro-3 Camshafts, I decided to lower the TPS disable for closed loop because moderate tip-in (~50 TPS) will reach 600-800 mbar, that is right about the region where I like to lower the fueling to ~13.5:1 or so.

Seems like the closed loop operation in CROME works well for targeting stoich, but since you cannot define a target lambda map, you have to be careful to define your TPS enable/disable so that you do not run lean at moderate loads.