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Old 03-17-2014, 02:51 PM   #61 (permalink)
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That can be one way that it is done--but it is usually not a very accurate way.

Most of the Hondas (up into the early 90s at least!) that ran fuel injection used Manifold Air Pressure (MAP) as the primary determinant of load--how much air is going into the motor. The throttle position sensor is used more to determine if the throttle is currently being opened more, or currently closing, or is already closed, or already wide open. That will add or subtract some from the basic metering, which is based on MAP.

More modern systems directly sense air flow (with an Air Flow Meter of some kind) to determine engine load and the primary calculation of how much fuel they add. Again, the throttle position is used to fine-tune that.

A few old systems, and also the Mechanical Fuel Injection used on older Diesels and some rather old gasoline cars (e.g., BMW 2002 tii, 69-72 Porsche 911s, etc.) did use throttle position as the primary measurement of engine load. It worked, but was not very clean or efficient.

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Old 03-17-2014, 03:21 PM   #62 (permalink)
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Quote:
Originally Posted by some_other_dave View Post
A few old systems, and also the Mechanical Fuel Injection used on older Diesels and some rather old gasoline cars (e.g., BMW 2002 tii, 69-72 Porsche 911s, etc.) did use throttle position as the primary measurement of engine load. It worked, but was not very clean or efficient.

-soD
Thanks for the explanation, I guess the above old systems will suffer more from dirty air filter as when you push the gas pedal down you are demanding more fuel but the air flow is restricted.
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Old 03-17-2014, 09:16 PM   #63 (permalink)
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Old 03-17-2014, 09:21 PM   #64 (permalink)
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What is the purpose of TP sensor on manual transmission vehicle? I thought the wider the plate opens the wider the pulse width of the injectors based on the voltage received from the TP sensor.
I could be wrong, but I was under the impression that the engine management system took into account several inputs other than throttle position to set the amount of fuel injected.

I'll admit to not know a whole bunch about this but I'm going to start learning.

Seems like the O2 sensor has some say, as well as engine temperature & such to regulate the fuel. So I was figuring the O2 sensor input would take into account a clogged filter situation and reduce the amount of fuel at a given throttle position to maintain the ~15:1 air to fuel ratio keeping the engine operating at close to peak efficiency.

Thems engines is smart I thought....am I giving the ECM too much credit? Or is it even more complicated than I think already?

Thanks for the good question, lets all learn something together here.
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Old 03-17-2014, 09:43 PM   #65 (permalink)
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If I am not mistaken the O2 sensor tells the computer the end result of the combustion so it will make better decision on how much fuel to put on the next cycle, on most cars 0 volt signal is lean and 1 volt means rich mixture.
IMO if the air filter is clogged the O2 sensor will send rich signal most of the time, therefore the computer will try to reduce the fuel amount that will cause performance issues along with FE reduction. again this just my opinion and I am still lurking and learning here.
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Old 03-18-2014, 10:42 AM   #66 (permalink)
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With modern fuel injection no air filter vs dirty air filter at the same partial load makes no difference other than the throttle plate will be opened a little farther with a dirty air filter. Air flow, fuel flow, and power output will all be the same.

Only at wide open throttle the clogged air filter might have a chance of becoming the controlling factor.
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Old 03-18-2014, 01:06 PM   #67 (permalink)
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With modern fuel injection no air filter vs dirty air filter at the same partial load makes no difference other than the throttle plate will be opened a little farther with a dirty air filter. Air flow, fuel flow, and power output will all be the same.
Only at wide open throttle the clogged air filter might have a chance of becoming the controlling factor.
I disagree, the main entrance (air filter) is still restricted, you are sucking PCV pressure and possibly some engine oil as well with dirty air filter which leads to carbon build up in the intake manifold causing even more restrictions. I understand that the computer in todays cars are programmed to compensate for our laziness on maintenance and will gather information from various sensors to come up with the best air/fuel ratio. The computer will try but there is no guaranty since air (O2) is limited and requires additional energy to get it.
let's assume we have 4 cylinder engine with 1-3-4-2 firing order, if #4 cylinder is on power stroke it only needs to move 4000lbs metal with clean air filter, while with dirty air filter it also needs to push #2 cylinder harder to suck air. Take a syringe and try to pull it down with the end clogged, you will need more power to do so compared to if the end is not restricted.
I think this can apply also to blower motors. you go to the repair shop because the heater doesn't work, the mechanic found that the resistor is burned, if he is good enough he will recommend to replace the blower motor and the cabin air filter even if the motor is running, why? the resistor burned because the blower motor demanding more amps to run. it turned out clogged Mr cabin filter was behind all this mess.
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Old 03-18-2014, 01:10 PM   #68 (permalink)
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Old 03-18-2014, 01:17 PM   #69 (permalink)
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All an air filter is, as it gets more restrictive, is a governor. That assumes you will surpass its flow capacity which most who drive for mileage will never do. I seldom see anything over 3500 RPM, if I keep the filter even fairly clean and stay away from following someone on a dirt road, it could last aslong as 100k miles, if I wanted to push it. The downside is as it gets more restrictive my WOT acceleration will gradually fall off.

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Old 03-18-2014, 02:25 PM   #70 (permalink)
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Quote:
Originally Posted by Honda View Post
I disagree, the main entrance (air filter) is still restricted, you are sucking PCV pressure and possibly some engine oil as well with dirty air filter which leads to carbon build up in the intake manifold causing even more restrictions. I understand that the computer in todays cars are programmed to compensate for our laziness on maintenance and will gather information from various sensors to come up with the best air/fuel ratio. The computer will try but there is no guaranty since air (O2) is limited and requires additional energy to get it.
let's assume we have 4 cylinder engine with 1-3-4-2 firing order, if #4 cylinder is on power stroke it only needs to move 4000lbs metal with clean air filter, while with dirty air filter it also needs to push #2 cylinder harder to suck air. Take a syringe and try to pull it down with the end clogged, you will need more power to do so compared to if the end is not restricted.
I think this can apply also to blower motors. you go to the repair shop because the heater doesn't work, the mechanic found that the resistor is burned, if he is good enough he will recommend to replace the blower motor and the cabin air filter even if the motor is running, why? the resistor burned because the blower motor demanding more amps to run. it turned out clogged Mr cabin filter was behind all this mess.
You are absoluty correct with the srynge anolgy. The only problem is you fail to include the biggest intake restriction of them all, the throttle plate. The srynge tests doesnt factor in
isobaric losses found on the intake process.
Your biggest restriction on a gas engine by far is the throttle. Throttling losses (isobaric expansion) acounts for up to 2 horsepower loss on a small 4 cylinder engine cruising down the road at high way speed. The 2 horses woth of isobaric loss you get while cruising down the road added to the tiny restriction offered by the air filter is immeasurable.

Now in a diesel, a restricted air filter tracts directly with fuel economy. Diesels dont have a pesky isobaric process to argue with, on a diesel its all about craming as much air mass into the cylinder as possible.
With that said the diesel world largely dislikes K&N air filters, they let more dirt in.

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