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fuel flow sensor location for 2 barrel TBI A1G2 SBC.

tuna_man

tuna_man

Regular Contributor
For a friend.
he just bought a navman fuel flow sensor. Looks like the same one common to many brands.
Were not sure if it will work on this engine.
Theres only one line coming from tank. Goes straight to filter/seperator.monted on engine.
Im thinking it will work on that line. (Except wont be filtered).
However there is a return line to the filter, from a diaphram switch attached to the fuel cooler?

So i understand on EFI donks there is usually a return line to the tank, this one does not, but does have a returrn to the filter sep , which actually may be a common area inside the filter to the inlet from the tank. Im strugglin to find the right words here, boy i wish i could a way to draw a picture on this android.

so where do we put a single flow sensor on a alpha 1 gen 2 SBC, with 2 barrell throttlebody injection?

(Only one fuel line at throttle body, which contradicts the diagram in his Clymer manual).
 
Me in blue text.


tuna_man said:
For a friend.
he just bought a navman fuel flow sensor. Looks like the same one common to many brands.
Were not sure if it will work on this engine.
If for gasoline, and if for the correct fuel demand, it should work.
I'd check with Navman.

Theres only one line coming from tank. Goes straight to filter/seperator monted on engine.
Im thinking it will work on that line. (Except wont be filtered).
That is correct!
You can install another Marine Fuel Filter cartridge prior to the OEM filter and prior to the fuel flow sensor.
DO NOT be tempted to use one of the small metal "in-line" filters. The filter media square area is far to small to serve as primary filtration.

BTW.... some of these fuel flow sensors must be mounted vertically.
(see the Navman instructions)


However there is a return line to the filter, from a diaphram switch attached to the fuel cooler?
The TBI may have a return, but will not return to the fuel tank.
If it returns to the OEM fuel filter, the sensor must be upstream from the filter inlet.


So i understand on EFI donks there is usually a return line to the tank, this one does not, but does have a returrn to the filter sep , which actually may be a common area inside the filter to the inlet from the tank. Im strugglin to find the right words here, boy i wish i could a way to draw a picture on this android.
If only one fuel line from the fuel tank to the OEM fuel filter, it is definitely a supply.
This supply will come from the fuel tank's "outlet", which is imediately followed by an "anti-siphon" valve.


so where do we put a single flow sensor on a alpha 1 gen 2 SBC, with 2 barrell throttlebody injection?
Upstream of the OEM fuel filter..... but with a second Marine fuel filter in the loop just ahead of the fuel flow sensor.
The quantity of fuel that does return to the OEM filter will have no bearing on actual engine fuel consumption.
Think of it as a "zero sum gain".

Again....... DO NOT be tempted to use one of the small metal "in-line" filters. The filter media square area is far to small to serve as primary filtration.

(Only one fuel line at throttle body, which contradicts the diagram in his Clymer manual).
Toss that Clymers in the recycle bin, and pick up an OEM manual.
Too many errors in the Clymers and Seloc manuals! :mad:
Click to expand...
 
Ok, thanks guys, so now were looking into installing another 10 micron filter separator (new primary), upstream of the sensor.

My only concern now is, will the electric fuel pump be able to suck thru two filters and a flow sensor?

Mark
 
tuna_man said:
1..... Ok, thanks guys, so now were looking into installing another 10 micron filter separator (new primary), upstream of the sensor.

2.... My only concern now is, will the electric fuel pump be able to suck thru two filters and a flow sensor?
Click to expand...
Mark,

1.... I agree. Lots of filtration square area and w/ little restriction.

2.... you have no choice but to install a filter prior to the flow sensor if you want to protect it. (Navman recommends pre-filtration)

Your fuel pump should be capable of pulling through the additional filter, and in particular if both of them are routinely replaced.
In theory, the new primary will catch any/all debris, leaving the OEM filter free to flow.
If overly concerned, replace the OEM filter at the same time that you do the installation.


Back to the sensor location:

If you were to install the flow sensor after the OEM primary, it will read the return flow rate as well as the engine consumption. That would be counter-intuitive.

If you were to install the flow sensor upstream of the OEM primary, it will only read the actual engine consumption (regardless of the return rate), of which is what you want to read.



.
 
Install Mercruiser part numbers:

QTY: 1) 864572 Fuel Filter

QTY: 2) 47841 Hose fittings

This is an inline strainer designed to protect the expensive electric fuel pumps and only restricts the line when it has done it;s job. Replace annually.



Merc.jpg
 
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