Ubermensch

What conditions was this data collected under? I'm assuming this is just ideling, or are you blipping the throttle?

Your data is all over the place as you pointed out. If this is just at idle, I'd want to know why your throttle position is varying so much. For some perspective, when plot my MAF vs. rpm (100% throttle) I get nearly a perfect line.

Is your rpm hunting like this at idle?

Mother

Not sure what you mean but they do represent a hunting conditon. For instance at RPM 1,448 (line 4) MAFlow increases as the MAF voltage decreases?
Have a look.

Mother

My goal is to get it to idle, at present I have to (gently apply) the throttle to keep it running and when it kinda stabilizes above 1000 RPM it starts to hunt. I cannot check for vaccum leaks being I am the only one here so I cannot do both.

1999Porsche911

I am asking whether the MAF numbers are grams per second or pounds per hour, or what other scale they represent. And what is the difference between the F7 and F30 MAF numbers. I'm assuming F30 is in volts?

Mother

F30 is in Volts not sure of the F7 I will try to find out. I am using Durametric software.

1999Porsche911

I'm guessing kg/hr.

Put a resister inline as I suggested earlier. Cut the MAF cable white wire (pin #5) and splice back together with the resister inline. This will immediately reduce reported air flow and drop the amount of fuel to the engine. Disconnect battery cable for a few minutes and start her up. You will need this resister regardless of what the cause of the rough idle is, anyway.

In closed loop, your engine will balance the F/A ratio with no problem. However, until you get your remapping done, WOT operation will be running lean.

Mother

Thanks, I give it a try tomorow.

Durametric reply for the MAF reading is this

Reply: Durametric

The parameters that are available are not defined by us. They are defined by Porsche and match the factory service manual and Porsche training manuals. We can only represent the values that the cars computer is capable of displaying.

JasonAndreas

Mother,
It would be trivial for FVD to copy the HFM5 MAF characteristic curve and the OBD2 plausibility checks over from a 996TT to the 996 ECU. The 996TT MAF linearization curve has a measurement range from 126.2 kg/h upto 1598.7 kg/h which will cover your supercharger installation. Then all you will need to buy is a tube and MAF sensor from a TT. The MAF is the primary load sensor so trying to do this any other way (i.e. tricking the ECU) should be avoided if at all possible, which in this case it is!

1999Porsche911

Sorry Jason, that will not work. His problem is not with the accuracy of the MAF but with the fact that the amount of actual air running past it (which is being measured properly now) is not matching the amount of air entering the engine while off boost. Remember, his sensor is before the compressor.

The fix I suggested is standard practice and costs less than $1.00 to complete.

1999Porsche911

Your goal is to get your MAF reading to about 22 kg/hr at idle. This should keep the fuel/air ratio well within managable range for the O2 sesnors.

BTW: What year is your car? I can't remember.

Ubermensch

Just so I can understand what you're suggesting, are you saying that his MAF is reading accurately and that the supercharger has roughly tripled his airflow at idle? Since the idle characteristics of the ECU are looking for lower airflows it's hunting to find a good idle?

S.

1999Porsche911

Since the airflow and temperature is measured BEFORE the compressor and the majority of this air does NOT enter the intake while off boost, the MAF is over reporting airflow to the engine, even tho it it accurately reporting airflow it sees.

Therefore, if nothing is done to properly calibrate the MAF to equal the air to the engine, you will ALWAYS run rich while off boost.

redridge

thats how I see it.... but whats weird is its not under boost, and the maf should be able to read the current flow

1999Porsche911

Remember that the intake system (before throttlebody) is a living, breathing system which both inhales and exhales. If it was an true intake system only at the point of air measurement, measurment would be more accurate, but the recirrculating compressed air would very quickly reach unmanageble heat levels.

Tippy

I can vouch for the centrifugal S/C's, they put out a huge amount of air at idle, just like '99 said. You have to dump it to atmsophere or reroute it through the inlet of the S/C. This is what he is talking about.

My 0.02. Putting a resistor on at this current time is a not needed. Although it would work once properly tuned to the new "resistance". But currently, it is at stock settings.

WOT:

The engine will not see WOT until FVD tunes it. MAF "burnout" will not be an issue since the engine will not take it the full WOT air.

Idle:

If the air is recirculated through the inlet from the BOV, there will not be any excessive air above the requirement of idle drawn through the MAF since it is simply reintroduced to the inlet of the S/C. I have a hard time explaining this but this is how it works on Mustangs for sure.