Lowrance Fuel Flow Sensors

Mike

Mike

New Member
May 29, 2007
62
Middle River, MD
I am getting ready to install the Lowrance LMF 400 Fuel Flow Sensor in my 1992 370 Espress. I have twin 454 mercs / carburated. The installation guidelines state 3 suggested guidelines; 1. Install in a vertical direction 2. have fuel flowing through the sensor in an upwards direction and 3. above the tank fill level.

Due to how my fuel lines are run it won't allow me to have these sensors meet all three suggestions, particulary the fuel flowing upwards. Fuel is feed from rear of boat; out of tanks to can filters, down to bottom floor of ER, horizontal to front of EB, to fuel water seperator at engine block and then on to pump and carb.

Has anyone had any experience with this sensors and or install any other types of sensors?
 
Yup...there is one spot that will work on your boat. You have to place the sensor between the Fram canister filter for each tank and the fuel tank selector manifold. As you will notice, there is a loop of hose between the Fram canister filter and the fuel tank selector manifold.

You will need to replace the hose with a slightly longer one so that you can insert the fuel sensor just below where the fuel flows up into the fuel tank selector manifold. The original fuel hose is cut a 1-1/2" below the fuel tank selector manifold, the sensor is inserted into the stub (fuel flow up) and a new hose with a slightly longer loop is connected to the sensor and the Fram canister filter. The longer hose allows the sensor to be in a near vertical positon, above the tank and fuel flowing up.

-John
 
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I am looking to put the Lowrance system in my 370 SD as well. I will assume that the location described would be the best place to go for my install as well? I did not know if the sensors had to be as close to the engine as possible or just in the loop somewhere after a filter. Any pictures of an install out there?
 
Thanks for the info, i'm going to go look at that layout today. I will try and get some photos. Still waiting for the sensor to come, Lowrance only distributes "X" amount of the sensors and every distributor I checked was out till the 16th, so hopefully anyday know. I need something to do on the weekends!
 
Scott,

I believe that location will work on your boat as well. The Lowrance/Northstar/Navman installation is different from the Floscan installation since the sensors are fundamentally different. The Lowrance/Northstar/Navman employ a small turbine contained in a fuel resistant plastic housing that needs a vertical orientation (fuel being drawn up) in order to spin properly. It will not spin properly in any other orientation and as a result will in produce inconsistent readings.

Floscan uses an optical sensor contained in a pot metal housing. It must be located at the fuel line's low point and in a horizontal position.

For both systems, the sensors must not be mounted on the engines, or after the fuel pump. They are also designed for carburetor based engines.

The fuel tank selector manifold is the only location I know will work for the Lowrance/Northstar/Navman. That manifold is the only point on the boat which is higher than the fuel tanks and the sensor can be installed with the proper orientation.

I wish I had a photo for you. I just changed a boat from a Navman to a Floscan system. I need to do a better job of shooting pictures of such things! In that case, the head Navman F3100 display began to fail (Navman was sold to Northstar...Northstar did not offer the F3100) and the owner wanted a working fuel management system.

I had originally installed the Navman system five years ago. You guys will be very happy with the Lowrance systems. Having a working fuel computer will save you its cost in one season.

Let me know if you need step by step directions for the sensor installation. I'm off to Atlanta today so I might not get to them until the weekend.

-John
 
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Hope this is close enough on topic of fuel sensors not to be considered a hyjack.:smt001

I am going to install the Northstar sensors on my 5.7 EFI twins before the main engine fuel filters with a separate inline auto canister filter prior to the fuel entering the sensor.

I figure since the fuel pump pressure high side is after the sensor. The sensor will not be damaged. It is before the engine main filter that has a return line fitting. Any unused fuel is returned to the main engine filter and not the tank. Since it does go back to the tank it does not flow through the sensor twice causing an erroneous reading.

I figure since the tank is vented and the sensor is on the suction side of the pump and filter this should work.

Anybody think this will not work? It was only after I got the sensors from Jim that I found that they mentioned the “carb engines only” Northstar did not say why.:huh:
 
Mike,
I haven't installed Northstar or Floscan sensors on an EFI motor so I would be guessing. Your approach seems right but I would definitely get it verified with Northstar or someone who has done it on your boat.

-John
 
For you Carburetor junkies.....

Installing Northstar/Navman/Lowrance fuel sensors on 34-37' Express or Sundancers.

What you will need:

6' of 1A fuel line (you may need less)
6 -1" stainless steel hose clamps
2 -3/8" 90 degree hose barbs
1 tube fuel resistant sealer (NO teflon tape)
1 -fuel catch can
adustable wrench
clean rags
fire extinguisher
a new razorknife or hose cutter
wireties
a small friend (especially if you are over 200lbs)

Let me start with a couple of comments. First you should be comfortable working with gas and all the engine hatches (as well as the canvas) should be open. Second, I like flare fitting fuel hoses for a lot of reasons. Unfortunately, this installation calls for barb fittings and hose clamps. The good news is that we are on the suction side of the pump so there is no pressure to be concerned about.


Step 1: Mark the end of each sensor wire with either a green or red piece of electrical tape.

Step 2: Switch the fuel settings for each tank to off. Move all battery switches to OFF. Switch shore power to OFF.

Step 3: Disconnect the "out" hose fitting from the port filter canister. This is the hose that connects the canister to the tank selector manifold. When you unscrew it from the canister, fuel WILL leak so be prepared with a rag and a catch can. Once the catch can is in position, lower the hose and the can to the floor of the bilge so that all the fuel drains from the line. Put the catch can back on deck away from anything that can knock it over.

Step 4: (Why am I cutting a perfectly good fuel hose?????) With the sharpest blade you have, cut the hose 1-1/2" down from where the hose screws into the tank selector manifold. Make sure it is a clean, straight cut. Put the piece you cut back on deck with the fuel catch can.

Step 5: Place a clamp over the freshly cut stub of the fuel hose and insert the Port sensor with the flow arrow pointing up and tighten.

Step 6: With the wrench, unscrew the hose fitting on the cansiter and install the 90 degree hose barb fitting facing down. Be sure to use a gas resistant sealer on the threads of the fitting.

Step 7: Place a clamp on the end of your new 1A fuel hose and slide it over the 90 degree barb and clamp in place. At this point you need to eyeball enough hose to create a smooth loop to the bottom of the sensor that will permit the sensor to have a vertical orientation when secured with plastic wireties. Once you have done that, cut the hose and clamp it down on the sensor.

Repeat steps 3-7 for the starboard side making sure that you don't confuse the generator fuel line (which bypasses the tank selector manifold).

Step 8: Why you need a smalll friend......to run the sensor wires to the helm. I like to run them along the wire conduit path, securing them with wire ties along the way every 12" or so. The hardest part is finding a path up through the deck and to the helm. On ECs this path is over the batteries and up the main wiring harness. I usually find it easier to push a guide wire down to the bilge from the deck and pull the sensor wires up and connect them.

Step 9: Battery switches on. Blower on for 5 minutes. Tank selectors to port and starboard. Shore power on. Start engines and check for leaks. Pay extra attention to the 90 degree elbow and the clamped hoses.

Step 10: Close the hatches and grab a beer. Some units have calibration and setup steps to follow.

This is a great upgrade for carbureted Sea Rays. It gives you a sense of the condition of each engine and can really help with diagnostics. Both engines should consume the same amount of fuel at the same rpm. For example, if you see eratic fuel readings, either air is getting in the line (tighten clamps on the suction side) or a fuel pump is failing. If the readings are stable but one engine is consuming more fuel, then it might be working harder due to a prop/shaft/alignment problem. You will also see the benefits of a clean boat bottom and its relation to fuel consumption.


-John
 
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