Electronic fuel injection was a big leap forward for engine control. However, early implementations often left something to be desired. This was the case for [Rob] and his Porsche 944, which had relied on an old-fashioned mechanical air flow meter (AFM). He decided to replace this with a modern mass air flow (MAF) sensor instead, and documented the process online.
AFMs are a replacement target on older cars. Sometimes they rely on a shutter that moves a potentiometer over a carbon track that wears out over the years. In some cases, they may also provide airflow restriction, which restricts performance. MAF sensors, on the other hand, measure the amount of air flowing using a hot wire. The amount of air required to maintain the temperature of the cable indicates the amount of air flowing through the sensor. They are less restrictive and easy to come by, as they are used in many cars today.
To run a MAF in the AFM position, you need a circuit that emulates the AFM output. [Rob] used STM32 Cortex-M0 to read the MAF, then fed the appropriate voltage to Porsche’s engine through PWM and a low-pass filter. To discover how to map the MAF exit to fit the AFM, [Rob] built a platform for blowing air through the two devices in series and measuring its exit in an oscilloscope. This knowledge was used to program the STM32 to produce the emulated voltage of the correct type for the given MAF signal.
It’s a great piece of work from [Rob] that has his Porsche running happily on new parts. We’ve seen similar hacks done to other cars before, as well! Video after the break.
I’m one to complain about long videos on HaD, but 7 seconds?
It could be a NGL gif.
Whatever many things, however, if it is my old engine, I would be involved on the algorithms of the ECU that compensate for the intake temperature. An AFM measures the volume and a MAF measures the dough. It will be verified to approximate the mass of the admission load as a volume and temperature service. This would possibly execute the threat of converting AfR depending on the temperature.
I had a BMW 325i from this vintage.
The compensation is the least of your issues.
The original flap has a contact potentiometer and a spring. The spring wears out and potentiometer wears. They are long out of stock. Mine would start oscillating at low engine speed and never got it fixed. The refurbished flap sensor was more than twice what I paid for the car.
I question the point of measuring the old worn out one to adapt the mass air sensor though.
If you still have it, there is an undeniable solution. The cause of the problem is that the short steel scraper slots in a relatively wide strip of resistive material. When repositioning the windshield wiper and bending it to contact an unlawful area, it will work again as new.
I moved the windshield wiper. Spring is tired and is about to return the right resistance.
There have been drop in MAF conversion kits for the 944 since at least 2009, though most also come with a new eeprom for the DME (Bosch speak for ECU) to take full advantage of the superior flow characteristics of the less restrictive intake. Still, there have been enough plug and play setups that if this were an issue someone would definitely have noticed by now.
The O2 sensor feedback will compensate for the Mixture difference because of the Volume VS Mass Issues..
However, the VE calculations will be incorrect, so the engine ignition plate will be bad. But how can you guess?
If you manage the “Fuel Trips” in the ECU and adjust your MAF output to keep the trims close to zero, then you are close enough.
It is trivial to burn a new EEPROM for the ECU on those cars. That’s why the maximum MAF kits come with a new chip.
The O2 sensor in those cars is narrowband and, of course, only used on a closed circuit. My understanding with other brands of the same antiques suggests that it is necessarily used only when sailing, at idle and at 50% in an AFM-based open flag with built-in temperature and RPM sensor.
I had a Jetta VW with a golf GTI engine in it and for one or two years they used the mechanical flow. This engine is still run in Rally and for collectors… There is just no replacement available. My Jetta was left to rot. I don’t even know how it ended.
I came to shout that I could not do this in California, but a year 1989 is over 25 years old, which means that it is free of Smog, so you can modify things of admission everything you want. Great trick.
Everything that is 1975 and more recent still requires Smog in California.
Will they even notice? If you do well, they don’t. They also use a 5GAS analyzer to verify the emissions of the exhaust pipe.
I put my VR6 and the saying 4Cyl.
True story. I was very pleased that my 1976 was registered in VA, a state with permanent vintage car registration and under the Servicemember’s Civil Relief Act (SCRA), it did not ask me to replace my registration until the existing one expired. . . which VA has never done. did.
My car is over 30 years old and still requires smog. Unless something changed recently California requires smog for all gas car made after 1975. If you could make it look stock enough you might get it passed CA smog. But judging from the wall sockets this hack was done in the UK (maybe?).
California requires all cars after 1967 to have all emissions controls installed, possibly even going back to 1964, not exactly sure since it’s been over 30 years since I moved to California. . . I don’t forget being there The 80 with my 1970 car that was not a California supplied car and then had genuine disorders recorded. I later had a 1972 of the same make and style that I was able to register, but only after having to remove it due to the prices of taking it beyond the strict needs at the time, there. At that time, a vehicle had to be able to improve 10% and maintain prices under a constant car restriction for an express age. As for the hassle of equipping an older vehicle with EFI, I don’t see why anyone would go through all this effort, as there are aftermarket corporations that create formulas to convert older cars to this. DIY Autotune is one of many. Now, I’m not sure about running them through an emissions test, however, if the vehicle can be configured with an EFI formula that has all or even some of the features that a later style formula would offer, the exhaust quality quality quality. From the quality of what the OEM fuel formulas have produced, it turns out that the state approves or deserves to approve. They are actually anal in any internal shipment with combustion. Some brands have been able to qualify their products in automobiles and in those cases, cert. The #s are Factord and if modifications are made to a car and they can submit this Cert # to the emissions testing facility, the DMV will have to factor a registration for the vehicle. That’s how it was back then. I read about how things progressed a few years APASS with the aftermarket device and it was that way for a long time.
There was a dude on the net putting the motor from a Chrysler LS series into a VW bus, thought it would be cake to get a pass going from nasty early 70s carbs to late 90s injection motor with all the emission equipment in place, ha ha, nope.
You take it to a referee who verifies all the smog equipment is indeed functional. Then you get a plaque in your engine bay stating it has been re-engined with the engine you have now. It is doable.
There is actually already an exemption for 80s VW vans with a specific Subaru motor. A company went through the process and got a C.A.R.B. (CA Air Resources Board) exemption anyone can use.
Technically, they require that all the devices against the smog be installed. In practice, once 25 in 1975 arrived, they stopped and do not review 75 onwards.
“They are concerned about any form of internal combustion transportation. »
Very clever and handy
To do this correctly, you also want temperature compensation. If the air temperature is adjusted from the temperature at which it was calibrated, the MAF reading would change, while the AFM reading would not.
AFM measures flow, MAF measures mass by measuring how much a hot wire cools down. Colder air at the same flow = more air mass.
If the colder air also cooled the hot bead.
All the AFMs I opened also had IAT sensors. As, I believe, the maximum of the MAF of, integrated.
Interesting project. I took another direction with my 944 ’87, also with the aim of replacing the AFM.
Replacement of the entire ECU by a Megasquirt. This has led to several adjustments to the sensors. The old O2 sensor could only provide a binary output, so I connected a new Bosch Lambda probe to a giant-band O2 controller. I can now set it to 14. 7 for the most productive emissions and the most productive energy efficiency.
The AFM was released here, while the Megasquirt supplied a rudder sensor tube. Take it to the vacuum, then weld a jump to a piece of pipe. A GM intake temperature sensor is screwed in and connected to the old harness. The lack of restriction of the restriction The ingestion of AFM led to the screw being placed in the socket as a slow movement too high. This replacement eliminated the low RPM lag, caused through the AFM barn door.
Finally, use Tuner Studio Pro to adjust the configuration of the air fuel ratio in all RPM and the inactive air valve at all motor temperatures so that the engine works gently. I could not be happier with the transformation.
Is there an option for a pre-built PCB like Ordiuno or anything else?
Is it imaginable to use pre-build PCBs like Arduino or another?
Be cool and respectful to make the comment segment great. (Comment Policy)
This uses Akismet to reduce spam. Learn how your feedback insights are processed.