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Mark, I'm trying to keep the stock ECU's in the system, but firing into dummy loads for the injectors & coils. I need to keep them in order to pass an annual OBD2 scan to get a state inspection, and renew the registration on the car.

An aftermarket box will be running in parallel with the stockers and will actually be running the engine.

To keep the stock ECU's happy, they need MAF signals, which in this case is just a 1.0 to 4.5v analog signal, proportional to the airflow. No PWM'ing required.

My other strategy (besides installing mini-MAF's) is to try & synthesize a MAF signal from the MAP+IAT+RPM+TPS, but I'm a real dummy when it comes to embedded processors and other fancy electronics. Apparently other Real Smart Guys have already tried this, and have had very mixed results. Hence my reticence, and interest in looking for other alternatives.

Author:	cribbj [ Sun Aug 07, 2016 8:18 pm ]
Post subject:	Smallest MAF?
Am thinking of alternate strategies for measuring air flow with ITB's, and still keeping the stock ECU's happy. One idea is to put small MAF's on 2 cylinders and let the Motronic ECU's think they're getting total airflow. As long as the MAF reads somewhere above 1.0v at idle, and 4.5v or so at WOT, the Motronics "should" be happy, right? So where to find a small MAF that gives that kind of output from measuring airflow for a single 500cc cylinder? I used to have a Bosch PDF that showed the range of all the MAF's they make, but I must have lost it in a computer crash. FWIW, my individual intakes are about 43mm in diameter.

Author:	mk e [ Mon Aug 08, 2016 9:11 am ]
Post subject:	Re: Smallest MAF?
No help on your actual question. hmmmm...if it were me and I was trying to keep the stock ECU I'd be looking for a cheap/easy processor to convert MAP&TPS into an output to match what the stock ECU is looking for. An Arduino setup could do it I'm pretty sure. or are you planning to control the engine with a new ECU and just leave the stock ECU thinking it's working? In the case most ECUs have a PWM output you can tie to LOAD and use an external circuit (maybe from pololu or again look to the Arduino. EngineLab can give you a freqency tied to load directly, but would need an external DAC to convert to voltage....I'm not sure what the bosch MAF is?

Author:	cribbj [ Mon Aug 08, 2016 9:19 pm ]
Post subject:	Re: Smallest MAF?
Mark, I'm trying to keep the stock ECU's in the system, but firing into dummy loads for the injectors & coils. I need to keep them in order to pass an annual OBD2 scan to get a state inspection, and renew the registration on the car. An aftermarket box will be running in parallel with the stockers and will actually be running the engine. To keep the stock ECU's happy, they need MAF signals, which in this case is just a 1.0 to 4.5v analog signal, proportional to the airflow. No PWM'ing required. My other strategy (besides installing mini-MAF's) is to try & synthesize a MAF signal from the MAP+IAT+RPM+TPS, but I'm a real dummy when it comes to embedded processors and other fancy electronics. Apparently other Real Smart Guys have already tried this, and have had very mixed results. Hence my reticence, and interest in looking for other alternatives.

Author:	mk e [ Tue Aug 09, 2016 8:28 am ]
Post subject:	Re: Smallest MAF?
cribbj wrote: Mark, I'm trying to keep the stock ECU's in the system, but firing into dummy loads for the injectors & coils. I need to keep them in order to pass an annual OBD2 scan to get a state inspection, and renew the registration on the car. An aftermarket box will be running in parallel with the stockers and will actually be running the engine. To keep the stock ECU's happy, they need MAF signals, which in this case is just a 1.0 to 4.5v analog signal, proportional to the airflow. No PWM'ing required. My other strategy (besides installing mini-MAF's) is to try & synthesize a MAF signal from the MAP+IAT+RPM+TPS, but I'm a real dummy when it comes to embedded processors and other fancy electronics. Apparently other Real Smart Guys have already tried this, and have had very mixed results. Hence my reticence, and interest in looking for other alternatives. Ok. 1.0V to 4.5V should be pretty easy to fake from nearly any ECU you buy. They all have a PWM out signal that you can tie to somehting that should be useful, englab lets you tie to anything you please. I know you don't want PWM but nobody I know of has a true analog output but it's VERY easy to convert the PWM to analog, it's just a resistor and a capacitor: http://www.instructables.com/id/Analog- ... o-Voltage/ You can buy something pre-made or solder it up and heat shring it in-line. Very easy either way. then you just enter the correct PWM dutycyle in the control table for the voltage you want. 1V = 7.2% (of 13.7V) and 4.5V=32.8%. Once you know what ECU you're using we just need to figure out the best option for setting up the PWM output. Thinking about it you could probably just use the injector drive signal is worse comes to worse....it is a PWM tied to load, RPM,etc so filter it, add a voltage divider to get it in the right range and you've got synthetic MAF. This is real parts not programing so there will be a little trial and error type tuning which is why it wouldn't be my first choice but it will produce the signal you need without needing to program anything.

Author:	cribbj [ Wed Aug 10, 2016 9:15 am ]
Post subject:	Re: Smallest MAF?
That's a good idea using a (smoothed) spare injector output signal from the aftermarket box to simulate a MAF input signal to the OEM boxes. I don't know how closely the OBD2 error checking algorithms in the Motronics 5.2 boxes watch the MAF signal before throwing codes, but it's certainly worth a try. The 5.2 boxes were the first generation attempt at OBD2, and were apparently cobbled together pretty badly, and I've already confirmed their misfire detection does not work, so perhaps their error checking on airflow isn't that precise either.

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Author:	mk e [ Wed Aug 10, 2016 1:18 pm ]
Post subject:	Re: Smallest MAF?
Misfire detection is pretty easy on a 4cyl but pretty hard on a 12 cylinder so I guess I'm not surprised to hear it doesn't really work To smooth an injector output you'll need a decent size capacitor ...at a 1000rpm idle it's like a 500hz PWM. And you'll need a voltage divider to get it into the right range....but it should work. Using a spare optional output should give you more control though depending what options your ECU has.

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