1999Porsche911

Since you are still working on your degree, you should be in a "learning" mode rather than trying to "teach" things you do not understand. I built by first boosted engine long before you were even born.

With Mother's setup, you MUST calibrate the MAF to reflect the actual air getting to the engine, whether you use a resister or some other method such as allowing unmetered air to pass into the system. To suggest that simply reprogramming the computer will somehow eliminate the problem, is also wrong as the range of the MAF is too narrow and you WILL burn it out. An inline resister is no different than buying a MAF that has the correct calibration to begin with. The only difference between hot wire MAF's is the rating of the resisters it is made with. You could get the same results by replaing the resister INSIDE the MAF, but I suspect that that is a task that few people are capable of doing.

The fact that airflow is cirrculated while off boost does not eliminate continued and excess airflow past the MAF. Review your Physic books for further details.

Finally, I have no idea what you are saying about the engine not seeing WOT until the tuning is done. This, also is not true.


If your intention is to take such a simply concept and make it complex, you seem to be succeeding. This is a simple and long standing calibration that has been done since resister based sensors began measuring intake flow.

Mother

2000 996, The wire I have is WHT/BLk as signal wire and the R/Violet as 5 Voltage.?

Tippy

Hey, I am not claiming to know more than you, but I have been around some impressive boosted FI'd cars.

Mother is not going to run WOT with just his injectors changed and no comp upgrade. So how is the computer going to "burnout" the wire? Simply wont be enough airflow. At idle, I can see what you are talking about because you will be tricking the computer into thinking there is not much airflow reducing the fuel, I gotcha' on that.

My degree is in Business by the way, my mechanics degree is from the school of hard knocks.

By the way, I was boosting blow through carbs (above 20 PSI) back in '96 before the aftermarket world caught on, I was only 16. If you want to talk about it, PM.

Tippy

I am bowing out of this thread, good luck Mother on the S/C!!! Keep us posted and relay the info from FVD. I would love to turbo my car someday, got to get the FI side panned out. The turbo fabrication side is the easy part.

1999Porsche911

It would be the white/black. This wire should have no voltage with key on and engine not running. The oither 2 NON ground wires will have 5 volts and 12 - 14 volts. Wire #5.

BTW: You may get a smoother idle right off the bat by starting the car without the MAF connected as the computer will default to the maps.

Mother

Sounds like fun project Tippy good luck. I will post progress so check back.

Mother

Makes sense I'll give it a try later. I have not tried diconnecting the MAF since I had my injectors reflowed. I should know soon after startup on results as you said then get back to FVD on maps and take it from there.

JasonAndreas

I'll be the first to admit that I have zero experience with supercharged engines but how on earth can a resistor modded MAF account for the effects from a blowoff or diverter valve? The compressor is pulling air through the MAF so the MAF is aware of it. The only questions are will the measured airflow value get clipped by the sensor & ECU and what happens when the throttle closes and air is recirculated? The 996 egas MAF has a measurement range of 47.3 kg/h to 1285.0 kg/h. So you might throw a CEL if the diagnostic plausibility checks are left untouched.



If air is diverted around the throttle-body isn't the usual (i.e Bosch) method that corrects for this involve adding a pressure sensor? How can reducing the MAF value (installing a resistor) account for this?

1999Porsche911

All the resister is doing is reducing the voltage that is reported to the computer to reflect the fact that not all the air is goiing to the engine during off boost operation. Therefore, idle and most off boost operation, the S/C engine will run pretty close to normal on the stock program. At WOT, all the air passing by the MAF is getting to the engine and the resister is now under reporting the voltage to the computer and the fact that you are no longer running a 3.4 engine but one that is much bigger because of compression. This is where the remapping comes in. The tuner now changes the paramters of the maps to reflect for the fact that the MAF signal is lower and cylinders are bigger.

As I explained before, it does not matter what the absolute MAF reading is as long as it changes predictably with airflow. The new program will be completed to reflect what fuelng is required based on throtte position and MAF signal and other parameters.

i.e. the stock program may have assumed that there was 200 g/s of air getting to the engine at WOT when the MAF signal was 4.8 volts. Because of the supercharger, the program would be changed to think that their was 200 g/s of air when the voltages was only 4.7 and fueling would be adjusted accordingly.

Don't let the reported "airflow" range of a MAF confuse you. The difference between a MAF for a 996 and a TT is NOT the amount of airflow it reads or the range of voltage that is generates. The amount of airflow is a calculation done by the computer based on voltage only.

Mother

In a closed loop system regarding the BOV or recirculating valve once the metered air passes through the MAF (with resistor or not) and calculated by the ECU and any excess air is dumped during vaccum via BOV back "after" the MAF sees no change since it has already been measured everything remains moot. I think I confused myself.

Tippy

I put some thought into this and take it how you want, how about this?

First things first, put an EGT gauge on it!!!

Put the resistor on the MAF, now the motor thinks it is taking in less air leaning the idle mixture.

Now, put a FMU (fuel management unit) after the fuel regulator.

Adjust idle mixture until engine runs clean and lean until EGT barely raises over rich condition.

Last bring up RPM and make sure EGT doesnt pass say a few hundred degrees past idle @ rich. I dont know what the proper EGT temp should be? Temps can vary depending from point of exhaust flow.

FMU's can be adjusted to reflect boost increase , example 1:1, 1:2, and up. Now for every pound of boost, you can get a ratio of fuel pressure. This is how we did it, no maps needed changing, used the stock timing and fuel maps, just tricked it with a lot of fuel pressure under boost.

Tippy

Of course, once the FVD programming comes in, take off the FMU. I would have an EGT on any S/C'd car, it is a must.

Tippy

I had to get back into this thread.

I snapped when '99 said to use a resistor, this will take care of the MAF.

I was amazed that an engine would even run with the "wrong" injector size, now I know it will.

Since it does, and the reisistor will work, I thought why not control the fuel by a FMU and adjustable fuel pressure regulator using an EGT? We done this with Mustangs many a times in the early days except we had a MAF that matched the injectors and CFM capabilities of the S/C.

JasonAndreas

The problem with inserting a resistor (fixed function) is that it will modify the reported flow at all times and not just during off-boost. You're trading one problem for another that requires more work to fix properly. And even then, if you're not measuring airflow you'll be screwed eventually as things age or if problems arise and something else can't compensate. There is no reason to hack the system up in this way if you have complete access to the ECU sensor calibration, which is something FVD does.

Actually with the torque based ME7 it does matter, the MAF is the primary load sensor.

The difference between the MAF & housing for 996 and 996TT is that the different measurement ranges produce different voltage levels corresponding to different flow levels. The chart that I posted was created from the actual calibration data from 996 and 996TT ECUs that I disassembled. The sensor does actually measure airflow.

1999Porsche911

So, installing a resister in the TT MAF is the right solution, yet, somehow installing it "outside" the MAF housing is not? The MAF does absolutley nothing to control fuel, load, or anything else. The computer determines what to do with the signal.

Example:

The MAF has a limit of 5 volts. By not calibrating it, you reach the 5 volts at 90% throttle and 6000 rpm after you install an S/C. At this point the program (stock or modified) is responding to the 5 volts by dumping fuel, etc. What tells it to add more fuel when the throttle hits 100% and rpms hit redline? Can the MAF's voltage increase from 5 volts or is it some miracle that automatically allows the computer to "guess" what the fuel trim should be for the top 10% range?

It's not a complex issuue. There is no way to substantially increase airflow to an engine and provide the correct fuel mixture using a stock MAF without somehow modifying the signal of the MAF. If you modified the housing of the MAF, you have modified the MAF reading.