MAF same as MAP sensor??? - Page 2 - JeepForum.com
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post #16 of 22 Old 07-05-2010, 08:08 PM
Sundowner
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Originally Posted by bb-sd View Post
None taken... the MAP's just under $20, and I wasn't sure what a PIA it would be to find a leak somewhere else... I haven't done it before. I was just thinking systematically.
Systematically, you troubleshoot simple problems first. Logically, you are not likely to fix a problem without knowing what's broken. Throwing money at a problem rarely solves anything, save for lightening your pockets. Besides, if you troubleshoot thoroughly, you learn a lot more about how the engine works.

If you replace a sensor that's already working, you haven't fixed anything. You've just wasted money, and your problem is still present. That's why "I replaced everything!!! How can it still not work???" happens.


If it's worth doing, then it's worth overdoing.

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post #17 of 22 Old 07-05-2010, 08:22 PM Thread Starter
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Originally Posted by Sundowner View Post
Systematically, you troubleshoot simple problems first. Logically, you are not likely to fix a problem without knowing what's broken. Throwing money at a problem rarely solves anything, save for lightening your pockets. Besides, if you troubleshoot thoroughly, you learn a lot more about how the engine works.

If you replace a sensor that's already working, you haven't fixed anything. You've just wasted money, and your problem is still present. That's why "I replaced everything!!! How can it still not work???" happens.
By systematically I meant that if I rule out the MAP, I don't spend my time chasing a leak that doesn't exist, but I see your point and thanks for the advice.
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post #18 of 22 Old 07-05-2010, 08:41 PM
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Yes, I know what you meant. You can go that route if you want...but I never spend money that I don't have to spend just to "rule out" something unless it's the last option. Been there, done that...and I'm poorer for the efforts. If you spend three hours chasing a vacuum leak that doesn't exist and it does turn out to be your MAP sensor, then I look at that as first-rate education on how the vacuum system works.

Perhaps you can learn about testing MAP sensors to see if they're functioning or not...then you can rule it out without spending that $20, and educate yourself in the process.

If it's worth doing, then it's worth overdoing.

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post #19 of 22 Old 07-05-2010, 09:18 PM Thread Starter
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I don't see any picture, but I don't need to. You don't have one. Trust us.
You're right... what I saw in the pic was the Intake Air Temperature sensor
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post #20 of 22 Old 07-05-2010, 09:34 PM
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No, Mass Airflow Sensor is usually found in the air intake system and measures airflow to the engine.
Manifold Absolute Pressure sensor is usually found in the intake manifold and measures vacuum? (anyone fell free to jump in here and correct me).
Half marks.

As I recall, the Mass AirFlow sensor uses a "speed density" calculation to measure the amount of air flowing over a heated wire, by determining the amount of current needed to maintain the wire at a given temperature (or measuring the drop from a given temperature, which is derived from a steady current applied to the wire. I don't recall which offhand - MAF is a Ford thing, and I avoid Fords...)

The MAP is part of a "temperature/density" measurement setup. It accomplishes the same results by providing a "density" measurement (absolute pressure,) which is then correlated with an intake temperature reading (from the IAT,) to derive airflow into the engine. It doesn't directly measure the airflow proper, so it's a shade less accurate - but that's what the feedback/trim signal from the HEGO is for (in either case.) GM and ChryCo use the temperature/density setup.

Given a choice, I'd prefer to use the temperature/density system anyhow. You've got a feedback loop for fuel metering trim, so that's not a problem. The volumetric efficiency (how much air is actually moved vice theoretical displacement) should be known at all RPM ranges by the factory, so that's a workable correction. Between the temperature/density signal, the HEGO feedback loop, and the variation of practise with theory, you should be able to chart a workable map of fuel values and only require slight trim to correct.

Besides, the IAT and MAP together tend to cost less than the MAF unit; and are more reliable, and you can replace one or the other when it fails (for $30-50, vice dropping $200-300 on a MAF sensor...)

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post #21 of 22 Old 07-05-2010, 10:17 PM
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5-90, that's a much better description than I gave. Thanks for providing it.

I'd like to add that speed/density systems are basically more fine-tunable since they can be more easily set to the exact operating parameters at the time, but MAF systems are inherently more adaptable.

If it's worth doing, then it's worth overdoing.

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post #22 of 22 Old 07-05-2010, 10:41 PM
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OK,generally,a bad map sensor will cause a rich condition in the entire engine.
not just bank 1.
a lean code can be caused by anything that puts more o2 into the exhaust or by a weak o2 sensor.
ie;exhaust leak ahead of o2 sensor/ignition misfire/burnt valve etc. etc.
a grounded o2 sensor signal wire may also cause a lean code.

FWIW ford and gm use both speed density and mass air systems
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