MAFload Weirdness

[winstonusmc]

I switched over to MAF a while ago and I will never go back. I just installed a BOV today and was adjusting it to minimize surge and I notice something odd about MAF load. I am not using MAF load in any load calculations, but I was looking at it in the log to observe compressor surge, as it would show up in MAF load and not MAP. I see the MAF load drop out indipendently of MAP or even MAF volts or Mass Air Flow. If the air was fluctuating through the MAF, then the MAF Volts should at least show this trend. Not sure what is going on. It happened in the older firmware as well as the current 1.3.

For those who are observant, no I havent gotten rid of the surge yet.

mafload.msq

mafload.msl

[winstonusmc]

OK, here is what I just figured out. It seems that it is tied to MAT sensor somehow. I didnt reinstall my temp sensor when switching to MAF because I didnt think I would need it. It seems the floating ground fluctuations that happen normally are affecting MAF load. Is there any way to disable the Air Temp sensor or is it tied into more than just fuel calculations in speed density mode?

[elutionsdesign]

Did you notice MAT fluctuating between -39 and +176 to the same moves as MAF load?

Whoops, just after you did.

[winstonusmc]

I assume that it uses MAT to calculate the load in the same way speed density calculates airflow, just in reverse. I just wonder what else this affects. I may just reinstall the MAT sensor, just dont have a spot for it at the current.

[Matt Cramer]

Is there any MAT input connected at this point?

[winstonusmc]

No, the plug is vacant.

[kaeman]

the MAT sensor is pretty important in the calculations, you need to reinstall it. Or you wont be able to get anything to stabilize.

[shauer]

the MAT sensor is pretty important in the calculations, you need to reinstall it. Or you wont be able to get anything to stabilize.

Not really true with MAF. The MAF sensor takes intake air temp into consideration already. Technically speaking, I do not think the MAT sensor should be needed at all for MAF operation but as already mentioned, I think MAT is included in the synthetic MAF load value calculations.

Easiest thing is to just reconnect the MAT sensor. Mine is still installed in my car as well even though it really isn't doing much anymore. I like having it still installed as I can revert back to ITB mode tuning for limp mode if the MAF sensor ever dies on me.

[winstonusmc]

Problem is that I don't have a spot for it with the new manifold. I used that spot for my throttle cable bracket on my cable conversion. I think I can make it work though. It kinda sucks with MAF and the lack of info and knowledge that is available.

[Matt Cramer]

I would put it upstream of the throttle body instead of in the manifold.

[winstonusmc]

I had it in the aux injector spot directly behind the Throttle. I really hate paying for welding here in SD, seems I get charged $100 for every job. I don't know though.

[shauer]

Since the MAT sensor really does not appear to play a significant role in operation when using MAF, I would just place the sensor in the most convenient location. Mine is located in the intake air stream in between the MAF sensor and the throttles. You could simply thread it into the intake tubing somewhere.

Once the 1.3 source code is released I want to go through it and understand exactly where MAT is still being used in MAF related features such as MAFload. I may be wrong, but my current opinion is that MAT should not be used anywhere in the system if you are configured for MAF.

[winstonusmc]

I wish there was a way to disable the sensor. I guess I could put a resistor there to keep a steady value so I could at least use it for load.

[whittlebeast]

If you create a new field on MLV named MAPxRPM and plot that new field against the MAF, you will quickly spot where the MAF is getting the wrong answer. This concept has lots to do with the blended tables concept. The trick is to know when one of the ways of estimating air flow is going the wrong answer.

The more data you look at, the more you will start to trust MAPxRPM more than a MAF

Note that the "extra" air flow going thru the MAF is true flow but that "extra air" is not making it to the motor as shown by the MAPxRPM. It is simply being blown off to atmosphere.

Andy