Testing a mechanical fuel pump

[JasonB]

I am tracking down a high throttle cut-out issue on my 302 Ford and I want to test and make sure the fuel pump is putting out enough pressure. I know I can make a rubber fuel line and T into it, but could I think my pump also has a second outlet port that is capped. If I put a barb on it and connect my pressure gauge, would I essentially get the same reading as teeing into the line to the carb?

 

[Apollo75]

Re: Testing a mechanical fuel pump

I am tracking down a high throttle cut-out issue on my 302 Ford and I want to test and make sure the fuel pump is putting out enough pressure. I know I can make a rubber fuel line and T into it, but could I think my pump also has a second outlet port that is capped. If I put a barb on it and connect my pressure gauge, would I essentially get the same reading as teeing into the line to the carb?

If it is a second outlet port you can test the volume and pressure from there.

If the boat is not surging at high throttle setting I would examine the ignition system.

OFM

 

[a70eliminator]

Re: Testing a mechanical fuel pump

Being a ford I'm guessing it's an OMC, the extra fitting on your fuel pump should have a tube that routes back up to the carb, if the fuel pump diaphragm goes rather than have raw fuel fuel leaking into the bilge it is diverted back to the carb via the clear hose attached to that nipple, so no you can't test the output from there but you can tee into the output with a guage.

 

[JasonB]

Re: Testing a mechanical fuel pump

Actually its a Mercruiser set-up, '76 vintage with a 2bbl rochester. At anything over about 3800, it stumbles bad and then picks back up at random 2-5 second intervals.

It could be ignition related, but since I have a pertronix, I want to check everything else first.

 

[Bondo]

Re: Testing a mechanical fuel pump

Actually its a Mercruiser set-up, '76 vintage with a 2bbl rochester. At anything over about 3800, it stumbles bad and then picks back up at random 2-5 second intervals.

Ayuh,... That sure Sounds like a fuel issue,...
I've only junked out a couple of those Fords,...
But I don't Ever remember seeing an Extra port on a fuelpump on Any Mercruiser, nor Any other boat motor for that matter...

 

[Bifflefan]

Re: Testing a mechanical fuel pump

if the fuel pump diaphragm goes rather than have raw fuel fuel leaking into the bilge it is diverted back to the carb via the clear hose attached to that nipple,

That makes no sence at all...
If the pump fails it stops running, it doesnt just pump fuel into the bilge.

 

[Apollo75]

Re: Testing a mechanical fuel pump

What is referred to here is a Marine fuel pump ----> if the pump diaphragm cracks or leaks ---> the fuel is diverted to the carburetor so no fuel leaks into the bilge.

OFM

 

[Bondo]

Re: Testing a mechanical fuel pump

That makes no sence at all...
If the pump fails it stops running, it doesnt just pump fuel into the bilge.

Ayuh,... But there are Degrees of Failure.....

It could easily suppy the carb some fuel to keep runnin',+ still put enough in the bilge to Blow Sky High....
Or fill the base....

 

[a70eliminator]

Re: Testing a mechanical fuel pump

Thank you Apollo, seems lately I've been a target and have to be very carefull with use of words.

 

[a70eliminator]

Re: Testing a mechanical fuel pump

Ayuh,... That sure Sounds like a fuel issue,...
I've only junked out a couple of those Fords,...
But I don't Ever remember seeing an Extra port on a fuelpump on Any Mercruiser, nor Any other boat motor for that matter...

Ayyyywhat! c-mon you've never seen a marine fuelpump with an overflow hose?

 

[Apollo75]

Re: Testing a mechanical fuel pump

Thank you Apollo, seems lately I've been a target and have to be very carefull with use of words.

Your welcome

The boat is 33-years old, I do not know what fuel pump is on it, hopefully a marine fuel pump.

OFM

 

[Bifflefan]

Re: Testing a mechanical fuel pump

In 45 years i have never seen or heard of a pump leaking fuel on the ground or in the bilge. I have seen plenty of them fill the engine with fuel, thats not good. (one that is still intact and attached to a running engine)

Trying to wrap my head around this.
But still, i dont see a second line going to the carb doing anything for this problem if it did happen. If there was a bypass type pump used the there would be to lines, one pressure one return. But i dont think ive seen this eather, without an evap can on a automoblie only.

I not calling anyone wrong, just trying to understand and may even learn something.

 

[Bondo]

Re: Testing a mechanical fuel pump

Ayyyywhat! c-mon you've never seen a marine fuelpump with an overflow hose?

Ayuh,... That's Not at all what I said,...
An over-flow hose goes to that port,.... It's Not an Extra port at All...

Fuel Filters may be multi-ported,... But not Fuelpumps....

In 45 years i have never seen or heard of a pump leaking fuel on the ground or in the bilge. I have seen plenty of them fill the engine with fuel, thats not good. (one that is still intact and attached to a running engine)

Trying to wrap my head around this.
But still, i dont see a second line going to the carb doing anything for this problem if it did happen.

I not calling anyone wrong, just trying to understand and may even learn something.

On the Atmosphere side of the automotive fuelpump your familiar with,...
There's a Hole in the casting Venting it....
If there's a failure,... Gas drips on the ground...

They thread that Hole on Marine fuelpumps,+ Vent it into the in-coming air flow of the carb....
It's Safer,+ Hopefully you'll Notice the Problem....

 

[Apollo75]

Re: Testing a mechanical fuel pump

True, but the key word here is "Marine"

Nobody wants the engine filling up with fuel either --- they are make totally different.

Costs a bit more too --- as expected.


OFM

 

[a70eliminator]

Re: Testing a mechanical fuel pump

Marine or not doesn't matter, even a car pump has the weep hole and they will weep fuel just like a waterpump does when the seal goes bad, only a car pump will leak fuel right onto the ground and the pump will still pump fuel, a marine pump just takes it one step above and leaks it right back to the carb causing the motor to flood out and run crappy or not at all.

 

[a70eliminator]

Re: Testing a mechanical fuel pump

Here's a typical automotive Carter pump for a Ford v8 429SCJ notice the weep hole. Also the fuel will leak out here before it has a chance to enter the engine unless some catasrophic failure happens, but usually it's brittle and dryrotted to the point you get little cracks in the diaphragm and the leaking fuel oozes out the vent while the pump continues to do the job.

 

[a70eliminator]

Re: Testing a mechanical fuel pump

Ayuh,... That sure Sounds like a fuel issue,...
I've only junked out a couple of those Fords,...
But I don't Ever remember seeing an Extra port on a fuelpump on Any Mercruiser, nor Any other boat motor for that matter...

I was thinking the (extra fitting) he spoke of is the overflow and somebody plugged it because there may indeed be an issue with a ruptured diaphragm.

 

[Apollo75]

Re: Testing a mechanical fuel pump

That could be the case or the caburetor could have been replaced --- who knows

I have seen fuel pumps with rails built in ---- three porters ---- seen many two porters --- saves the pretty chrome fuel rail on the firewall.

Marine fuel pumps do not have a weep hole to leak out --- they should not leak into the engine either ---> any leaks go to the carburetor and you are correct they usually run bad or flood out when the fuel is excessive. Think of it as a sign to check things.

I use the term different animals.

OFM

 

[Bifflefan]

Re: Testing a mechanical fuel pump

On the Atmosphere side of the automotive fuelpump your familiar with,...
There's a Hole in the casting Venting it....
If there's a failure,... Gas drips on the ground...

This I know. As i said, I have never seen on leak on the ground. I'm not saying it cant happen, I've just never seen one do it.

Here's a typical automotive Carter pump for a Ford v8 429SCJ notice the weep hole. Also the fuel will leak out here before it has a chance to enter the engine unless some catasrophic failure happens, but usually it's brittle and dryrotted to the point you get little cracks in the diaphragm and the leaking fuel oozes out the vent while the pump continues to do the job.

As for the weep hole in this pic, plz circle it. as I only see 2 possible holes, the top one is for the pivit pin and the lower one goes now where. These are simmular but smaller versions of the ones we use in racing.

 

[Bifflefan]

Re: Testing a mechanical fuel pump

Never mind,,
I agree that if there is a weep hole it needs to be vented to the carb.

But as to the leaking on the ground or bilge, I doubt that anyone will ever convince me of this leaking on the ground before it leaks into the engine. As i have changed many, many pumps that have filled the engine with gas and none for leaking on the ground out of these holes.