MAF vs MAP sensor?

You can't just substitute one for the other. Both can be (and are) used in injection control systems, but each is a whole system with other gizmos and the right kind of ECU -- not just a single component. Wikipedia has a good description of the two:

http://en.wikipedia.org/wiki/MAP_sensor

http://en.wikipedia.org/wiki/MAF_sensor

 

Have you tried driving your 348 with your MAF's disconnected? Motronic 2.7 is supposed to switch over to throttle position if there is no MAF signal (perhaps it throws a trouble code when so doing). You've already got a throttle position sensor or two, so you should be good to go with no MAF's (just won't be as precise fuel control at partial throttle - but for idle when cold and full-power anytime, the MAF signals are already ignored by M2.7).

 

If you pull the MAF on just about any EFI computer, it's going to go into pig-rich mode to keep the engine from going boom. It's a very unwise thing to do. Throttle position is just one metric in calculating fuel maps, certainly not enough to keep an EFI system happy. It'll run, yes, but you'll be down on power, kill your cats (if you have them), and basically make the car run like crap.

You can convert a MAF car to speed/density (MAP), though at the very least you need a conversion box similar to the HKS VPC that was once popular in the import world. There are a few people who make similar units, though I've yet to see one adapted to a Ferrari.

If you really want MAP, the only safe way to do it is with a standalone computer (Motec, et al) that supports a MAP signal and can do speed/density fuel calculations.

 

Reading through the motec manual, they actually recomend thottle position for NA engines, but do want a MAP open to atmosphere for barametric changes.
That said I can't imagine that just unplugging the MAF is a good idea...although it is possible that ferrari did map the engine both ways for some reason. I guess you could get an A/F meter hooked up, unplug the MAF and see what you see....but I wouldn't plan on it working.

 

There is a big difference between a Motec and a Motronic.

Aaron

 

I think that the clever thing to do for a budget racer would be:
1. backprobe the TPS and MAF sensors, then track their values side-by-side on a dyno so that you can see if there is a somewhat linear relationship (e.g. TPS shows 1 ohm when MAF shows .5 volts, TPS shows 5 ohms when MAF shows 1 volt, TPS shows 25 ohms when MAF shows 2 volts, etc.).

2. simply disconnect the MAF and make a series of runs from ultra cautious to mildly aggressive.


These two steps should give a budget racer enough information to decide to either forgo the MAFs or else have a circuit built that delivers better TPS values for a given RPM/load (good college EE students should be able to knock one out in a weekend - read an ohm, deliver a different ohm to the ECU, perhaps even taking into account a newly installed additional MAP sensor value).



Keep in mind that for street driving the MAFs can be reconnected. Out on the track, the partial throttle and idle functions that the MAF influences have less value, so disconnecting them there is of less concern, I'd say.

 

Partial throttle is all important on a race car. The throttle is not a toggle switch. The guy with lousy throttle response and progressivity will finish last provided he does not just put it in a wall because he cannot balance the car mid turn.

 

Good point, at least for races with turns.

 

Well, step 2 above is pretty cheap to try!

 

Just put the car on a dyno and do a baseline run. Then unplug the MAF and try again. You'll have your answer in about 3 seconds.

 

At the end of the day, there are two ways to do it.

1) The right way, which is expensive and at the very least requires buying a computer and either tuning it yourself or having someone do it for you if you lack the experience. The upshot is that you'll be able to squeeze considerably more power out of the engine, know exactly what it's doing at any given time, have awesome throttle response, and not always be wondering if you're about to break something.

2) The half ass way, which means you yank parts out and/or jerry-rig stuff and hope it's going to work, at the risk of losing performance (or your engine if things go very wrong), all for some eye candy.

Cost is relative, I suppose. I'd just leave it alone, were I you, unless you're ready to roll your own FI system to look and work the way you want it to. Pulling apart the system and using half measures all for cosmetic reasons is pretty silly in my opinion.

If you want a bare bones, bottom dollar solution to do what you're after, buy a megasquirt, find an EE student, and order up a bunch of beer.

 

there are a lot of options for EFI conputers. I you keep you eye on ebay, decent stuff turns up for under $1000. I've got one on there right now that would do it, but they turn up pretty regularly. I think that's the way you're going to need to go.

 

Bruce, Motronic 2.7 stock is *fine* for what you want to do. The Landshark Ferrari 348 Competizione LM used stock M2.7 with 8 throttle bodies to race Le Mans: http://www.landshark.com/348Lemans.html

Going to 8 throttle bodies was the major source of power for taking 320hp Ferrari 348's to the 430hp (at the rear wheels!) Michelotto LM 348's (well, that and raising the M2.7 redline to 9,000 rpms as well as using the F-40's half-shafts for the rear wheels). Same Motronic 2.7.
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That all sounds right....but you need to be able to re-map it to do any of that. The factory can, most others can not. The ability to easily re-map is really all you get going to an aftermarket ECU.

 

Actually not.

Any modern EFI computer will have "limp-home" modes where the ECU will
replace the (deemed faulty) MAF value with a table lookup based upon
TPS and RPM (called Alpha-n).

The better ones (E46 BMW M3 for example) will then compensate this
value with barometric pressure and manifold air temperature.

This provides a very close approximation of the actual MAF value under all
normal operating conditions from sealevel to high altitude.

 

You need some kind of sensor to tell the ECU how much load the engine is under. TPS is not enough info for an engine to run at its best. MAP is good, but MAF is much more accurate. Intake air temperature is also a very important perammeter the ECU need to see.

 

This is all true and important, but not "All Important." Keep in mind that Motronic systems have feedback from the O2 sensors and data from the RPM sensor.

The O2 sensors tell Motronic if you are running too rich or too lean. Motronic then adjusts the fuel mixture (and spark timing per rpms) reactively, as appropriate to your current rpms.

In contrast, the MAF (or MAP for some systems) sensors permit Motronic to anticipate the right air-fuel mixture and adjust (spark timing and mixture) proactively in anticipation of what your rpms will demand. This is superior to reactive adjustments, but when you are talking about computers that are processing a million readings per second, not as entirely all powerful as one might think.

With the MAF sensor and TPS, Motronic can be rather precise. With just the TPS, Motronic is less precise up front, and then adjusts based on feedback from the O2 measurements (which lag behind by some amount of time to factor in the speed of the exhaust out of the cylinders going the distance to the O2 sensor, etc.).

Motronic has built-in air-fuel maps for the initial fuel metering, modifies the fuel metering based upon the O2 sensor feedback, and builds new run-time air-fuel maps while you drive as the system tunes your car.

Which is to say that even without a MAF, Motronic is eventually going to build fuel metering maps that get the air mixture reasonably close to desired values...because the system adjusts to the feedback from the O2 sensors and remembers what worked.

Of course at wide-open-throttle, Motronic *always* ignores the O2's and also always ignores the MAF's. WOT fuel metering and spark advance is/are only driven by the on-board air-fuel maps per rpms.

 

Bruce,

I say do it the right way but cheap. Megasquirt!

Better yet in case you guys do not know is Jim C aka landshark is "the man". If Jim is not too busy tweeking BMW's perhaps you can convince him to help you with your project. Could you imagine what a plus it could be to 348 owners with 355 TBS and a remapped comforti chip in the stock 2.7 motronic ECU's?

 

http://www.megasquirt.info/

You buy it I'll build it. I can solder a circuit board. I understand all the parts. I just have not had actual experience tuning on a dyno and laptop. My understanding is the older MS1 is better than the 2 for our application and allows more options like sequential vs wasted spark. It is a cool little system that some very smart people are using in racecars vs the motec that are big bucks

 

Uh, yes, and those alternate tables are generally very rich, with very little timing, which is what I said to begin with. It's hardly a solution for frequent use.

It'll work, but it won't work as well as leaving the MAF there, or properly replacing it, either with a MAP translator or an aftermarket computer.