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please educate me on MPI vs throttle body

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  • 1 Post By billinstuart
  • 1 Post By Lawton73

please educate me on MPI vs throttle body

Old 06-19-2019, 04:24 PM
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Default please educate me on MPI vs throttle body

so I was made aware by THT'ers last year when I bought my boat, that I have Multi port injection and not throttle body injection on my 5.0GXI BF....I now know this to be the case,but I still have a flame arrestor, and under that flame arrestor sits an orifice, and in this orifice is a butterfly just like i'd expect to find in a carb or throttle body.......WTF is that for.
reason i ask is that the flame arrestor was FILTHY, and I expect robbing me of performance and fuel mileage by causing rich condition.the butterfly is also covered in carbon, or crud, whatever it is.
where does this butterfly lead to and do I need to ensure its also decarbed and clean, is it simply air that goes out the exhaust, burned in the cylinder?
if I've been running rich all last season do i now need to do a plug.wires rotor change ?
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Old 06-19-2019, 04:34 PM
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Throttle body injection is a digital carburetor..the air/fuel still goes thru a manifold. Multiport injects fuel at the cylinder itself..nothing goes thru the manifold but air.
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Old 06-19-2019, 04:41 PM
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FI - Injectors in the throttle body
MPI - injector in each cylinder intake
DFI - Injector in each cylinder like a spark plug.

FI can also cover all three ways as a generic term.
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Old 06-19-2019, 05:11 PM
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Originally Posted by billinstuart View Post
Throttle body injection is a digital carburetor..the air/fuel still goes thru a manifold. Multiport injects fuel at the cylinder itself..nothing goes thru the manifold but air.
Well, that is a stretch Bill.
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Old 06-19-2019, 05:14 PM
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Originally Posted by Lawton73 View Post
so I was made aware by THT'ers last year when I bought my boat, that I have Multi port injection and not throttle body injection on my 5.0GXI BF....I now know this to be the case,but I still have a flame arrestor, and under that flame arrestor sits an orifice, and in this orifice is a butterfly just like i'd expect to find in a carb or throttle body.......WTF is that for.
reason i ask is that the flame arrestor was FILTHY, and I expect robbing me of performance and fuel mileage by causing rich condition.the butterfly is also covered in carbon, or crud, whatever it is.
where does this butterfly lead to and do I need to ensure its also decarbed and clean, is it simply air that goes out the exhaust, burned in the cylinder?
if I've been running rich all last season do i now need to do a plug.wires rotor change ?
You are confusing the throttle body with the point of injection.

The throttle body (sometimes throttle bodies) are at the front of the intake manifold. They control the amount of air that is allowed into the intake manifold.

The injector(s) can be either at the throttle body, deep down within the intake manifold (usually just ahead of the intake valves) or they can on the cylinder head. Latter being direct injection.
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Old 06-19-2019, 05:21 PM
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Originally Posted by alloyboy View Post
Well, that is a stretch Bill.
Well, yea. But it does atomize fuel which then flows thru the intake manifold, and has a fuel line hooked to it...
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Old 06-19-2019, 05:50 PM
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Ok.thanks.
so if the throttle body only controls airflow the flame arrestor Is really just there to keep out debris right, theres actually no fuel or combustion going on there.( I do have mpi with injectors each cylinder.)
should i get down in the throttle body with some cleaner or is not going to make a difference.

Nevermind.i guess if fuel and air are mixing in the manifold there is still a blowback risk requiring the flame arrestor
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Old 06-19-2019, 06:26 PM
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The flame arrestor is there to control backfires the throttle body lets Air in and the MAF aka air flow sensor adjust the amount of fuel that is let in.
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Old 06-19-2019, 07:03 PM
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Originally Posted by Lawton73 View Post
theres actually no fuel or combustion going on there
Let's hope there is no combustion going on there. That would be very bad.
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