Modifying code to switch to open loop based on MAP

[CSXRT4]

I dont really like the way the SMEC is setup to switch fuel and spark tables based on TPS. Most systems I have tuned with switch to open loop based on engine load or in the case of speed density "MAP". I was thinking that it might be easy to modify the code where it determines if it is at full throttle and change it to set the full throttle bit if it is over a certain MAP value.

I was thinking the functions to be modified would be
CheckThrottle_GotTpsValue:
CheckThrottle_AtFullThrottle:

If the function called the current MAP value instead of TPS value and then you could just rescale/rename WOTDLT to be a MAP value like 5psi or something. Then just rename all the Full throttle and Part throttle tables to Open Loop and Closed loop or High load and Low load.

Any adverse affects of doing it this way? What would be the best way to re-write the code?

[ShelGame]

I think the problem would be transient fuel. If you use a set MAP point to switch to Open-Loop (instead of TPS), then what happens when you go WOT, but MAP is only 1psi? You run on the P/T fuel and timing table, which would likely be dangerous.

I think a better solution would be to ADD a condition to go open-loop. So, leave the current TPS condition, but add the condition you proposed.

Currently, the ECU already goes open-loop if boost is above a set level (BOOSTP), but it still chooses the appropriate spark/fuel table based only on TPS. So, we could simply swap the condition for the spark/fuel tables from the WOT flag, to the open-loop flag.


So, you could change the code at L1578 from 'BitFlags_4f, #b4f_FullThrottle' to 'BitFlags_50, #b50_OpenLoop' and do the same for the spark lookup 2 lines down from 'DetermineHotAdvanceFromMap'. Then, you'd just have to set BOOSTP to be your MAP for switching to open loop. In the stock code, this is set to 0xFF (basically disabled so that the ECU stays in closed loop even in boost - ouch!). These changes would basically do what you want.

[CSXRT4]

Ok that sounds like it would work a lot better. So those code changes would switch to the WOT fuel/spark maps and turn off O2 feedback when MAP is higher than BOOSTP. But the condition used to make the switch is the #b50_OpenLoop flag, is there anywhere in the code that will set the #b50_OpenLoop bit based on if you are at WOT? If so I would need to remove that.

Actually, what determines Open loop in the stock code?? I thought it was mostly TPS based but I cant find where it would do that in the code.

[turbovanman²]

Interesting,

[ShelGame]

Why would you remove that? That's the primary way it determines if you should be in open loop or closed loop. Otherwise, the only determination of closed/open loop would be BOOSTP. I guess you could do it, but you'll want to tune the adaptives for that MAP range so that the computer isn't trying to get 14.7:1 A/F...

[CSXRT4]

Why would you remove that? That's the primary way it determines if you should be in open loop or closed loop. Otherwise, the only determination of closed/open loop would be BOOSTP. I guess you could do it, but you'll want to tune the adaptives for that MAP range so that the computer isn't trying to get 14.7:1 A/F...

All the systems I have ever tuned determine open loop and closed loop based on engine load. I would like my ignition timing, Fuel, and O2 status to be consistent with my MAP conditions rather than with the TPS. If im at 10psi of boost, I dont want different timing/fuel based on the throttle position. If I set the BOOSTP to 2-5psi then it would be 14.7:1(Closed loop) up to that point and then I could taper it rich as I want it to and I dont have to worry about what position the throttle is at. Ill give it a shot this way and see if it works well, if not I can always revert back to the stock configuration.

Where in the code does it switch to open loop based on if its at WOT? I tried finding it but I cant seem to dig it up

[ShelGame]

L1201 in T-SMEC is the check for WOT. If it's WOT (and the O2 signal is valid), it forces it to open loop...

[CSXRT4]

Ok thats why I couldnt find it, I should have been searching for instances of "b4f_FullThrottle"

Thank you for the help though. Im going to give this a shot and see how everything reacts. Not sure if you are interested at all but I could probably upload some datalogs after I get some tuning done. Hopefully cold weather will hold out a little longer since this engine is in a dune buggy haha

[ShelGame]

Definitely interested in the results...

[zin]

Where's that popcorn emoticon..... Also very interested.

I was thinking about doing something like this for mileage, running an optimum A/F for mileage while cruising. The factory couldn't really do that as the CAT wouldn't work as well, and the exhaust would likely be a much higher temp, but since the turbo heads have Inconel valves it should deal...

Mike