Trying to diagnose fuel supply issue after running out of gas

[MaxGlide]

1977 Mercruiser 140, four cylinder engine, serial #3847982. Using a mechanical fuel pump.
Ran boat completely out of gas (faulty gas gauge showing more than we had).
Put gas back in, new fuel filter, filled up fuel filter with gas.
Fuel line from tank to filter unit is clean and clear.
Not self priming, or priming using bulb going to small motor. (Used to be able to pump until bulb got hard)
Won’t start while turning over.
Few tablespoons in carb, fires right up and runs until fuel level drops below intake spout in fuel separator unit.
When you take the filter off, it is always down about 1”.
All connections checked.
Fuel filter on top of fuel pump is collapsed as in photo. Could this be the problem?
Could I bypass fuel filter and connect hose from tank directly to fuel pump to see if something around the fuel filter assembly is the problem? (Of course not run it like that permanently)
Could the fuel pump have failed when we ran out of gas?
Any insight is very much appreciated!

 

[crazy charlie]

That does not look like a marine gas filter for a mercruiser carb?????

 

[MaxGlide]

It’s the filter in the fuel pump, the bell part

 

[Scott06]

1977 Mercruiser 140, four cylinder engine, serial #3847982. Using a mechanical fuel pump.
Ran boat completely out of gas (faulty gas gauge showing more than we had).
Put gas back in, new fuel filter, filled up fuel filter with gas.
Fuel line from tank to filter unit is clean and clear.
Not self priming, or priming using bulb going to small motor. (Used to be able to pump until bulb got hard)
Won’t start while turning over.
Few tablespoons in carb, fires right up and runs until fuel level drops below intake spout in fuel separator unit.
When you take the filter off, it is always down about 1”.
All connections checked.
Fuel filter on top of fuel pump is collapsed as in photo. Could this be the problem?
Could I bypass fuel filter and connect hose from tank directly to fuel pump to see if something around the fuel filter assembly is the problem? (Of course not run it like that permanently)
Could the fuel pump have failed when we ran out of gas?
Any insight is very much appreciated!

Yeah filter should not be collapsed. Leave it out put bowl back on and see what happens.
my 3.0 originally had a sintered ceramic filter with a spring holding it in place. Spring rusted out from water in bowl. No idea how many years i ran just fine without the filter in place and essentially bypassed

also may want to pull drawoff tube from tank they may have a screen in yours that picked up sediment

 

[bbook83]

My 1974 Mercruiser 140 had a problem with a fuel restriction in the pickup tube. While that was happening, the fuel filter, which is identical to the one you have shown, would collapse, also as shown. My theory was that the fuel pump kept pumping while there was no fuel being delivered to it, causing the filter collapse. Your empty fuel tank would create the same condition. For me, the fuel filter collapse was a symptom, not a cause, although I agree with Scott that you should be able to run without the filter short term. Your 140 was not made with a fuel/water separator, so I am not sure how that is plumbed, but you should confirm that running to the point of emptying the tank did not cause debris to clog the pickup tube. I am a broken record on this, but running on a remote tank would confirm or eliminate the pickup tube clog, which may not be evident when you pull the tube and look at it. The debris that clogged my pickup tube, which did not have a screen at the bottom, would drop away from the tube when it was pulled. I discovered the debris by running a cheap endoscopic camera through the fuel gauge sending unit hole of the empty tank.

 

[racerone]

Perhaps there was a failure.----Perhaps you did not run out of fuel.

 

[Scott Danforth]

check the anti-siphon valve and if the tank has a pickup filter. you could have sucked all the crud in the tank and plugged the anti-siphon valve.

 

[tank1949]

check the anti-siphon valve and if the tank has a pickup filter. you could have sucked all the crud in the tank and plugged the anti-siphon valve.

I don't know why builders put these small screens into pickup tubes. They are headaches. I suspect fuel pumps suction collapsed filter.

 

[Scott06]

I don't know why builders put these small screens into pickup tubes. They are headaches. I suspect fuel pumps suction collapsed filter.

Probably to keep debris from manufacturing out of the fuel system long enough to get it through warranty.

 

[MaxGlide]

Yeah filter should not be collapsed. Leave it out put bowl back on and see what happens.
my 3.0 originally had a sintered ceramic filter with a spring holding it in place. Spring rusted out from water in bowl. No idea how many years i ran just fine without the filter in place and essentially bypassed

also may want to pull drawoff tube from tank they may have a screen in yours that picked up sediment

I suspect it did collapse due to suction after emptying tank. I will replace.

 

[MaxGlide]

My 1974 Mercruiser 140 had a problem with a fuel restriction in the pickup tube. While that was happening, the fuel filter, which is identical to the one you have shown, would collapse, also as shown. My theory was that the fuel pump kept pumping while there was no fuel being delivered to it, causing the filter collapse. Your empty fuel tank would create the same condition. For me, the fuel filter collapse was a symptom, not a cause, although I agree with Scott that you should be able to run without the filter short term. Your 140 was not made with a fuel/water separator, so I am not sure how that is plumbed, but you should confirm that running to the point of emptying the tank did not cause debris to clog the pickup tube. I am a broken record on this, but running on a remote tank would confirm or eliminate the pickup tube clog, which may not be evident when you pull the tube and look at it. The debris that clogged my pickup tube, which did not have a screen at the bottom, would drop away from the tube when it was pulled. I discovered the debris by running a cheap endoscopic camera through the fuel gauge sending unit hole of the empty tank.

I removed the hose from the filter to tank, so straight line to tank. Blew into it, heard bubbling in tank. Light siphon and gas filled my mouth in about a second. So clear from tank to filter.

 

[MaxGlide]

My 1974 Mercruiser 140 had a problem with a fuel restriction in the pickup tube. While that was happening, the fuel filter, which is identical to the one you have shown, would collapse, also as shown. My theory was that the fuel pump kept pumping while there was no fuel being delivered to it, causing the filter collapse. Your empty fuel tank would create the same condition. For me, the fuel filter collapse was a symptom, not a cause, although I agree with Scott that you should be able to run without the filter short term. Your 140 was not made with a fuel/water separator, so I am not sure how that is plumbed, but you should confirm that running to the point of emptying the tank did not cause debris to clog the pickup tube. I am a broken record on this, but running on a remote tank would confirm or eliminate the pickup tube clog, which may not be evident when you pull the tube and look at it. The debris that clogged my pickup tube, which did not have a screen at the bottom, would drop away from the tube when it was pulled. I discovered the debris by running a cheap endoscopic camera through the fuel gauge sending unit hole of the empty tank.

I removed the hose from the filter to tank, so straight line to tank. Blew into it, heard bubbling in tank. Light siphon and gas filled my mouth in about a second. So clear from tank to filter.

 

[MaxGlide]

Perhaps there was a failure.----Perhaps you did not run out of fuel.

100% out of gas. We took the fuel sending unit off to service it, and the tank was bone dry.

 

[MaxGlide]

check the anti-siphon valve and if the tank has a pickup filter. you could have sucked all the crud in the tank and plugged the anti-siphon valve.

Where would I find this valve? Is that at the intake of the line going from tank to filter/pump?

 

[MaxGlide]

MORE INFO.
Boat ran perfectly fine with current set up of filter/separator. I’m just trying to figure out was could have failed due to completely running out of gas.

1. Fuel line not clogged
2. New fuel filter installed
3. Lotsa gas
4. Filter primed
5. Starts when gas put in carb
6. All line tight.

My next trouble shooting steps.

1. Check lines from filter to pump and pump to carb for air tightness and crud. (Though filter in pump was totally clean.)
2. Take fuel line off carb, turn over and see if it pumps fuel.
3. Bypass filter and go directly from tank to pump. See if problem is around fuel filter assembly. Also should tell me if pump is working.

Anyway, thanks again for all tour inputs. I really appreciate it all.

 

[Scott06]

MORE INFO.
Boat ran perfectly fine with current set up of filter/separator. I’m just trying to figure out was could have failed due to completely running out of gas.

1. Fuel line not clogged
2. New fuel filter installed
3. Lotsa gas
4. Filter primed
5. Starts when gas put in carb
6. All line tight.

My next trouble shooting steps.

1. Check lines from filter to pump and pump to carb for air tightness and crud. (Though filter in pump was totally clean.)
2. Take fuel line off carb, turn over and see if it pumps fuel.
3. Bypass filter and go directly from tank to pump. See if problem is around fuel filter assembly. Also should tell me if pump is working.

Anyway, thanks again for all tour inputs. I really appreciate it all.

So you did nothing and it eventually primed- with collapsed filter? Could have been some debris in pump check valves that kept it from priming.

 

[MaxGlide]

So you did nothing and it eventually primed- with collapsed filter? Could have been some debris in pump check valves that kept it from priming.

It has not primed yet. I think i found the location of the anti siphon valve. I believe it’s at the intake of the fuel filter. As mentioned, sucking it dry maybe pulled ALL debris towards filter and buggered the anti siphon

 

[MaxGlide]

Is it possible by sucking everything out of tank, junk included, this (red) part of the fuel filter is clogged?
I see that this type of anti siphon valve is screwed into this part of the assembly? (Green area)

 

[flashback]

I would disconnect the fuel line feeding the carb and stuff it into a jug. Hit start and you will get gas if all is good..if you do, then the problem is in the carb.

 

[Scott06]

Is it possible by sucking everything out of tank, junk included, this (red) part of the fuel filter is clogged?
I see that this type of anti siphon valve is screwed into this part of the assembly? (Green area)

Antiphon valve will be on tope of tank. Someone added this screw on filter As they are not standard on 2.5/3.0 s that have the filter in the bowl of pump. You are pulling enough suction in the pump to collapse the pump filter. So something uo stream is closed off.