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  #1  
Old 11-09-2009, 02:29 AM
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Question I gotta know: CIS MAF sensor plate

When you push down on the MAF sensor plate on a CIS engine, it floods and stalls.

Hypothetical situation:

a CIS engine set up with a filtered cold air induction nozzle below, If driving along and you get a big gust of wind, and it pressureizes the intake tube, will it push the plate down and flood the engine?

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Old 11-09-2009, 09:26 AM
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Quote:
Originally Posted by PanzerSD View Post
When you push down on the MAF sensor plate on a CIS engine, it floods and stalls.

Hypothetical situation:

a CIS engine set up with a filtered cold air induction nozzle below, If driving along and you get a big gust of wind, and it pressureizes the intake tube, will it push the plate down and flood the engine?

It stalls because it's metering enough gas for about 1500 liters of air at idle. When you push the plate wide open, it meters gas for about 13,500 liters, thus "flooding" the engine.

I assume you mean a scoop or pick-up, not a "nozzle" - like a road-height "cold air" induction system? Don't waste your money. The difference in temperature between your grille and 8" above the road is about 1-3 degrees. With a naturally aspirated 4.5L engine, that's not enough to make any difference in performance.

Anyway, to answer your question, MB's aren't the only vehicles with pressure plate type MAF's (though most of them are located elsewhere), and none of them have ever flooded due to gusts of wind. Besides, it couldn't really pressurize the tube - with all the bends in it, it would simply create turbulence.

Oh, and road-height air pick-ups are also a great way to soak (clog) your air filter when you hit a puddle at speed.
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Last edited by dhjenkins; 11-09-2009 at 09:35 AM.
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Old 11-09-2009, 09:35 AM
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If you forced more air into the engine that could cause the plate to move giving more fuel... but you would also have more air in the engine to burn the fuel

Nitpick: CIS does not have a mass airflow sensor. It has an airflow meter. It has no way to know the actual mass of the air... that's what a hot wire or hot film MAF is able to figure out. Similarly my SDL has an airflow meter... a plate that is spring loaded and is forced open by air moving past it.

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Old 11-09-2009, 09:59 AM
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Originally Posted by compu_85 View Post
If you forced more air into the engine that could cause the plate to move giving more fuel... but you would also have more air in the engine to burn the fuel

Nitpick: CIS does not have a mass airflow sensor. It has an airflow meter. It has no way to know the actual mass of the air... that's what a hot wire or hot film MAF is able to figure out. Similarly my SDL has an airflow meter... a plate that is spring loaded and is forced open by air moving past it.

-Jason

Of course, you'd also have to have the engine spinning fast enough to do something with that extra air. If the throttle isn't pretty wide open, there's really nowhere for that extra air to go...

You should do an experiment with your existing pick-up tube to see how fast you need to go for any "forced induction" to take place. Get a vacuum gauge that also has a + side (usually called combo gauges for testing older domestic fuel pressure); 15 psi is more than enough. Put a small fitting in near the halfway point between engine & entry in your existing tube, and run some vacuum tubing under the back of your hood and duct tape the gauge to the windshield.

Let us know how fast you're going when/if it hits +2 psi (speed will be lower in cooler weather).

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Last edited by dhjenkins; 11-09-2009 at 11:13 AM.
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