Hyper-Technical: Exposing The 348/355/MondialT Bosch MAF

Bosch part # "0 280 213 012" is Ferrari 355 M2.7 part #154916
This is also found on the 1991-93 Saab 9000 B234 Turbo


Bosch part # "0 280 212 018" is Ferrari 348/Mondial t M2.7 & M2.5 part #136374
SAAB pn: 78 72 393
SAAB pn: 88 27 453
SAAB 9000 16v Turbo CD (1990?)


MAF rebuilders:
Python
Fuel Injection Corp
BBA-REMAN
Direct Auto: http://www.directautomotiveproducts.com/afmacv.html
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Our MAFs are expensive components. They are also important for precise engine operations at all temperatures and speeds.

MAFs are wear components (OK, Bosch claims otherwise, go figure). Eventually they will have to be replaced (expensive!) or rebuilt.

Shown below are the MAF locations for the 348 (Mondial t is similar) and 355 M2.7 versions...part #'s 9 & 6 respectively.
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To repair a Bosch MAF, first remove the silicon seal from around the top of the black plastic circuit cover.
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With the silicon seal removed, *gently* pry up the top cover:
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With the top covers removed, an older Bosch MAF circuit is shown next to, but facing the opposite direction from, a Ferrari 348 MAF:






*note: the older MAF has no MAF resistance adjustment screw, but sports the same microprocessor circuitry internally...and has the 3 internal connections (unused), for the variable resistance pot.
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Interchanging parts from cheaper Bosch MAFs to our more expensive MAFs may be possible for quick repairs, however, you have to mach the MAF signal curves.

I'm aware of 4 different MAF curves (shown below). If you have a working donor MAF with the correct signal curve, then you should be able to move it from your donor MAF over to your Ferrari 348/355/Mondial t MAF.
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The 348/Mondial t MAF screw turns the internal adjustment bezel on the blue resistance pot. 348 MAF's are factory set initially at 383 Ohms resistance each. You can adjust their resistance (this resistance can be measured with the engine off by connecting an Ohm-meter to the outermost metal pins, number 1 and number 6, on the data connection) to or from this value via the MAF screw beneath a disposable blue/silver cap on each MAF sensor. Adjusting the MAF resistance value will change your Air/Fuel mixture setting.

Turning this MAF screw clockwise with a flat-blade screwdriver increases resistance and leans your air to fuel mixture ratio.

Conversely, turning the MAF screw counter-clockwise enriches your fuel/air mixture and **DECREASES** the resistance value that is measured between the outermost pins (i.e. pins #1 and #6). The lower the resistance, the richer the mixture.

 

383 ohms is the Ferrari factory preset value for the 348 and Mondial t, but this is more ideal for fuel economy and emissions testing. I consider 383 ohms to be on the lean side.

If your mixture is too rich or too lean, then your ECU's will set off one or more trouble codes. As a general rule of thumb, both MAF's should also have identical resistance values, regardless of your preferred resistance value setting (typically close to the factory pre-set 383 Ohms).

 

It's close enough, but bear in mind that 383 ohms is already running a bit on the lean side for better emissions.

So it wouldn't hurt to have a slightly smaller number.

 

Mine popped out (OK, I sort of helped them with some long nose pliers), but some need to be drilled, then insert a screw, turn, and yank.

 

From personal experience, 375 ohms to 380 ohms is absolutely safe for a stock 348. 370 may be a little rich for some, however.

 

No.

 

Here's Marco's cool 348 MAF repair thread: http://www.ferrarichat.com/forum/showthread.php?p=137812643