new style electric fuel pump

[geezer]

I've been dealing with a lean condition in my barn find.  It's a '72 280se 2.8 engine (sorry but the help for this fuel system seems to be more helpful here). 

Before I go fiddling with the injection pump I wanted to be sure that the basics are within specs.  What the engine does backfire through the intake upon acceleration.  I replaced the burned points & condenser and set the timing.  Pulled the plugs and they are a white color.  Changed the suspicious cap & rotor. 

Did a fuel flow test for the electric pump an it flows about 3 quarts per minute. That is a bit low.  Ipulled the strainer from the bottom of the tank and it's clear.  Removed the electric pump.  The impeller looked OK, no dabris in the inlet screen.  The motor spins freely and there is battery voltage at the terminals.  Changed the fuel filter.

The WRD appears to be working.  Upon cold start up I get a high idle and air stops flowing through the air filter when the engine warms up slowing the engine to an expected 800rpm.

My question is; I know that the fuel flow is low from the electric fuel pump.  Could that be the root cause for my symptoms?  Or is there plenty of fuel flow so the engine should at least accelerate before the engine begins to suffer from low fuel flow?

[ja17]

Hello geezer,

How is the fuel pump pressure? Volume is not that far off. Did you block the fuel return line when you did the test?   11 to 15 psi is enough to work.  Also did you check and set up all the linkiages?

[geezer]

Hello geezer,

How is the fuel pump pressure? Volume is not that far off. Did you block the fuel return line when you did the test?   11 to 15 psi is enough to work.  Also did you check and set up all the linkiages?

ja17,

No I didn't check the pressure.  Couldn't find my fuel pressure gauge.  I did check the linkage and the rod from the inj pump to the crossover shaft was 9'' long.  I stretched that one out by about 3/16" and it ran a whole bunch better.  Just took the car out for a test drive and it started backfiring again. %$^()&*&%#.  I ended up walking home.  When I went back to get the car I took a couple of wrenches.  The pump motor runs but no fuel delivery.  I suspect that the pump doesn't deliver when warm.  Any suggestions?  I don't mind buying a new elect pump it's just that the cost is staggering.  Is there anything inside of the elect pump that would prevent the pump from delivering fuel when warm?

Charlie D

[Iconic]

Hey Geezer,
Where are you measuring fuel flow?
Have you measured it right at the point that it returns to the tank?

[geezer]

Hey Geezer,
Where are you measuring fuel flow?
Have you measured it right at the point that it returns to the tank?

After I cleaned up the electric pump I measured the fuel flow at both the discharge from the electric pump and at the return at the tank.  Both were nearly equal. 

When I checked for fuel delivery, after I walked home and the engine was warm, I checked at the fuel return port at the inj pump and the inlet at the fuel filter.  Both of those points were dry.

Could there be something in the gas tank causing the problem?  However, when I pull the fuel line off between the pump and the tank the gas flows freely.

[ja17]

The fuel pump must be mounted low. It is gravity fed fuel. So if the mounting has been altered make sure the pump is mounted at the original level.  You can temporarily correct some fuel delivery problems by making sure you have more than 1/2 tank of fuel.

[geezer]

ja17,

The fuel pump is mounted in the correct position and there are no droops in the hose from the tank to the pump.  The tank is at an "indicated 1/2" now.  The problem has become progressively worse as I have used fuel.  I'll top off the tank and see what happens.

I also looked at the fuel system in the tech manual.  I wonder if the "flower pot" is running out of gas due to a plugged hole under the fuel return.  Is it possible to get to that hole through the tank sender opening?

[ja17]

Hello,

Yes, your diagnosis would be my guess also.   You can view the condition of the inside of the tank and actually clear the intake hole in the flower pot with a wire from the sender opening.  Be careful to use a heat and spark free light source. Gas fumes will ignite !! 

[geezer]

Hello,

Yes, your diagnosis would be my guess also.   You can view the condition of the inside of the tank and actually clear the intake hole in the flower pot with a wire from the sender opening.  Be careful to use a heat and spark free light source. Gas fumes will ignite !! 

Thanks for the vote of confidence.  Looks like I have a project for Saturday AM.  I promise not to use a match for a light source.