Delphi Mechanical Fuel Pump stops pumping fuel

[Zed Head]

10 minutes ago, SteveJ said:

His car has stalled without restart except with starting fluid (knowledge of his problem from outside this forum). From how he has described it to me, I lean toward a fuel pick-up problem.

Could also be a weak spark problem.  The empty filter might be a red herring.  Time to fish...

[David Downs]

21 minutes ago, Zed Head said:

You didn't really say if you had a problem with the engine starting.  Sometimes people think things but don't actually write them down.

The drain back to the tank from your filter is not surprising.  It's higher than the tank.  The engine will start with what's in the float bowls and the filter will refill in a second.  I counted 9 clicks so that would be 18 revolutions of the engine.  Lets' say 20, for the math.  At 1200 RPM, that would be one second to refill the filter.

So, is this an actual operational problem or a "this bothers me" problem?

Sorry I wasn't clear. I will drop the tank and have it cleaned to make sure its not a tank pick up line issue. Has anyone installed a fuel check valve? This could help keep the fuel closer to the carbs with less cranking.

 

[David Downs]

3 minutes ago, Zed Head said:

Could also be a weak spark problem.  The empty filter might be a red herring.  Time to fish...

Interesting thought. Can you offer more details on what to look and test for? New coil? Would a weak spark cause fuel starvation?

[Zed Head]

I had a problem with a weak ignition module, the engine would only start with fluid.  Then it would run fine.  That was on an EFI car though.  I had done some work and left two spark plugs disconnected so I had a clue about what the problem might be.

Only you know how the engine behaves when it restarts, or how it behaves when it stalls, but the only good reason for a no-start that is fuel-related would be if the float bowls emptied.  Just offering ideas.  If it fires right up and runs well on the first shot of fluid you have to wonder why it didn't start on the fuel that was in the bowls.  

More details!.....  What type of ignition are you running?

[David Downs]

17 hours ago, Zed Head said:

I had a problem with a weak ignition module, the engine would only start with fluid.  Then it would run fine.  That was on an EFI car though.  I had done some work and left two spark plugs disconnected so I had a clue about what the problem might be.

Only you know how the engine behaves when it restarts, or how it behaves when it stalls, but the only good reason for a no-start that is fuel-related would be if the float bowls emptied.  Just offering ideas.  If it fires right up and runs well on the first shot of fluid you have to wonder why it didn't start on the fuel that was in the bowls.  

More details!.....  What type of ignition are you running?

Pertronix and everything looks stock.

[Zed Head]

There are other things you could check before dropping the tank.  The Pertronix is one of them.  You could also try an electric pump in the engine bay as a short test.  Another thought.  You might be able to keep the filter full by adding a length of hose in front of the filter that is higher than the filter.  It would depend on how strong the siphon effect is.  Or you could add a check valve in the engine bay.

Either way, don't be surprised if the problem is still there after the tank cleaning.  I don't think your symptoms really support a fuel supply problem.  Your "finger" pumping filled the filter in 9 stokes.  That's a pretty powerful pump action.

I would focus on the float bowls, not the filter.  See if they have fuel.  There's a thread about a float tuning tool that actually works like a sight glass.  You can see the fuel level in the bowls.  If you're planning to tune your carbs it might be worth doing first.  You could probably rig up a temporary "sight glass" also.

Just another view.

Edited April 25, 2020 by Zed Head

[Zed Head]

This is the bothersome part.  I'm not an SU guy.  But the float bowls should not be siphoning empty with the filter's emptying.

Edited April 25, 2020 by Zed Head

[siteunseen]

This is the cheapest and easiest way to get a close level of the float chambers.  $2 worth of clear hose from Lowes.  The red arrow in this pic.  The fuel in the hose should be even with the top of that rectangular boss on the side of the carb.

 

[siteunseen]

These are what Zed's talking about.

 

Edited April 25, 2020 by siteunseen

[David Downs]

3 hours ago, Zed Head said:

There are other things you could check before dropping the tank.  The Pertronix is one of them.  You could also try an electric pump in the engine bay as a short test.  Another thought.  You might be able to keep the filter full by adding a length of hose in front of the filter that is higher than the filter.  It would depend on how strong the siphon effect is.  Or you could add a check valve in the engine bay.

Either way, don't be surprised if the problem is still there after the tank cleaning.  I don't think your symptoms really support a fuel supply problem.  Your "finger" pumping filled the filter in 9 stokes.  That's a pretty powerful pump action.

I would focus on the float bowls, not the filter.  See if they have fuel.  There's a thread about a float tuning tool that actually works like a sight glass.  You can see the fuel level in the bowls.  If you're planning to tune your carbs it might be worth doing first.  You could probably rig up a temporary "sight glass" also.

Just another view.

Today I drove the car around and stopped at 2 locations. Once I left the second stop the pump stopped pumping. I confirmed this by opening up the float bowls and cranking the engine with the fuel line to carb off. I could not get any fuel to squirt from the carb hose. The carbs were rebuilt and floats adjusted per the instructions. I adjusted the floats again just in case they were set too low. Also, I removed the pump and manually pumped fuel back to the carbs to see if she would start. She fired up and ran out of fuel 200' from my last stop. I don't think I'm having an ignition problem because she always has great spark. My impression is the fuel pump is not getting enough motion. I believe the pump should pump on a 7mm lift. I think it needs more lift to get a full pumping stroke. Time to add an electric fuel pump.

Edited April 25, 2020 by David Downs
added more info

[David Downs]

1 hour ago, siteunseen said:

This is the cheapest and easiest way to get a close level of the float chambers.  $2 worth of clear hose from Lowes.  The red arrow in this pic.  The fuel in the hose should be even with the top of that rectangular boss on the side of the carb.

 

I will try this as well. Though I don't think this is my issue. At least I will have my floats at the correct level. Thank you!

[siteunseen]

My cruddy tank would let me drive about a mile before clogging up the fram g2 I had right out of the tank. Took the front hose off at input of that filter. Blew like crazy with my mouth until it was gurgling in the tank then I could get back home, barely.