right!, what conditions put the ECU into openloop ? TPS over a certain amount? anything else?

cheers
dave

 

What does your Coolant temp sensor read when your switching to open loop ?
I think anything under 70 degrees coolant temp is still Open loop.

 

I have encountered a similar problem right after putting my test pipe on and now my car reads high 13's AFR at idle and 8 AFR while at WOT, when previously i tuned for an 11.0-11.2 AFR range at WOT.....could this be because of the rear o2 sensor thinking it is supposed to read something and reading something else and trying to compensate for the difference?

 

To my knowledge, the rear O2 is simply there to measure cat efficiency and nothing else.

Eric

 

^ He's right.
Rear 02's doesn't affect performance or AF ratios regardless what it is reading.
The front one however does.

 

When the ECU goes to open loop mode the feedback is 100. Check an area of your logs when your TPS is 100 and your feedback will be 100 also. However I dont disagree that it could be a front o2 sensor. Something to check anyhow.

 

I think I recall I had richened my fuel map a little excessively into the lower load columns and besides getting bad gas mileage I noticed that my afr's were acting weird during part throttle driving. It was only holding 14.7 on super light pedal and any pedal at all it would go very rich - up and down excessively. I dont think the car can really try to hit a target of 13 or 12 because it's o2 sensor cant read that rich so it just thinks it should be in open loop mode. I dont have any additional fuel added below load column 100 in the 2500-3500 columns.

 

Do any of you guys have specific info on what range the primary O2S has(i'm assuming it's a semi-wideband)? Also, have you guys found a way to datalog voltage from the primary O2S? If you knew the range, you could scale the voltage(.0-.5v) to double check the sensors accuracy with a WBO2S. I have heard the primary O2S is just a narrowband, but this would not make any sense to me, as at least a semi-wideband is needed for proper control.

I'm just now getting into the EVO's ECU, as i'm used to tuning Honda's(speed density). And i must admit, i'm not really familiar with this ECU(slowly learning the advanced inner workings this ECU). But it seems like it has some obvious drawbacks in the way it was engineered by Mitsubishi. I have a very deep knowledge of speed/density and have worked as a tuner and R&D for a prevelent aftermarket ECU company that specializes in Honda OEM ECU reverse engineering on several projects for the k-series engine development. So i'm slowly learning how this particular MAF system works.

What are you doing to force open loop? We do this with speed/density to allow for proper tuning in part throttle and idle, to get fuel trims as close to "0%" as possible(obviously this holds true with this ECU as well), but i'm not sure with all the open loop maps in ECUflash how to force open loop or even what all the open loop tables do.

CJ

 

The primary O2 sensor is just a narrow band sensor. The resolution anywhere but stoich is useless. It is used just to maintain a stoich mixture during closed loop fueling.

You can use the table for min coolant temp for closed loop. If you want to always run in open loop, just set that value to a high enough coolant temp that you'll never reach.


Eric

 

The narrowband senso is useless for anything but maintaining Stoich, as its the only value that is fairly consistent.. And even at that it can vary by a half point either way...

However its designed to swing back and forth until it hits the stoich voltage thats programmed and thats how it determines the fuel trims..

The problem is fuel trims only have a range of operation, anyting that causes it to be outside that range will throw off the trims enough to not be able to compensate.

This is manifested by wild swings of AFR, and Idle speed, then it goes into open loop, then the trims reset, and it tries again..

If there is a problem with the sensor, it reads a flat signal, the coolant temp is low and the car isn't warp, or whatnot, the car will run in open loop mode. You can force this by raising the coolant temp for closed loop higher than you can ever hit.. If you do that, you can alter your injector scale, latency, and fuel maps until you get an AFR in open loop where you want.. Once its done, letting it run in closed loop again will place the Fuel trims real close to its target 14.7 and not have to adjust as much..

There is also some enrichment based on air temp and atmospheric pressure, this also comes into play when the car is cold (especially on cold days) as the air temps when the car is cold are much lower than when its runningw arm.. Atmospheric pressure is also slightly higher when the air temps are cooler..

 

^^ I will have to try this out

I am actually getting this problem so frequently at idle that I am getting bank 1 rich CELs

 

I am at a loss then.....below are are some screen shots of one data log session on the highway....the first two screens things check out for me fuel wise....then wham...straight to the 8-7 range it is and they gradually get lower and lower....can someone help me figure this out?

 

Anyone???

 

Maybe your wideband is faulty? thats seriously rich and would expect lots of black smoke like that

 

my first thought is the wideband instillation, location? although I don't know the failure signs of a bad WB.

because it doesn't "look" like you are using more fuel than you were in the better graphs.