Intermittent fuel starvation problem, found something

[geezer]

I've been chasing an intermittent fuel starvation problem in my M130 engine for a few weeks now.  I found that there was quite a bit of sludge and goo in the gas tank, had that cleaned out, replaced the fuel filter, cleaned the screens in the electric pump & fuel tank.  Next I suspected that the gas flow out of the electric pump was weak.  The pump delivery is weak at 3 quarts per minute.  But the dang thing would just runout of gas.  I took one suggestion and topped up the tank.  I checked for proper voltage at the pump, OK.

Each time I thought that I had it fixed I'd have to walk home.  When I get the car home all is well again. %$*^)**%$@#&

I finally decided to just let the car run in the driveway until it dies and check it out the moment that if croaks.  After a bout 1/2 hour of running at 2000rpm it died and would not restart.  With the key on I could feel the pump running.  Cracked the fuel line at the cold start valve and gas squirted out.  Cracked the line at the return port on the injection pump and nothing.  I suspect that there is some sort of bugger either at the inlet fitting or something is floating around in the passage in the injection pump.

From what I see the fuel passage is straight through the inj pump from front to back.  Will it foul anything up if I blow air into the return port in the injection pump?  Hopefully that will blow any guck back out the inlet port of the inj pump.  

[geezer]

Well I dug into the problem last night.  Ultimately what I found was some guck in the return check valve, on the injection pump, which made the valve stick open and at another time it would stick closed.  Got the check valve cleaned up and now it operates freely. 

Unfortunately I have to finally condemn the electric fuel pump.  Though it free flows a bunch of gas through an open hose I can put my finger over the hose and stop the flow.  Clearly the pump still cannot consistently produce enough pressure to overcome the spring tension in the return check valve on the injection pump thus I am not getting any return fuel flow to the tank nor am I getting enough flow & pressure for the engine to operate properly.

[geezer]

FYI a new electric fuel pump did the trick.

[Peter van Es]

Congratulations. How is it running now?

Peter

[Iconic]

Excellent, I'm thrilled for you.
Now you can do what it was created to do,  ...DRIVE IT !
Enjoy.

[thelews]

Last summer, on a beautiful summer days drive, my car quit...early '67 250 SL.  Had it towed home and the fuel pump (tall version) was not running.  Not having anything to lose, I removed the pump and then started dismantling the motor on the bench.  What a mess of filth after 42 years.  I blew it out, cleaned it out with carb and electrical cleaner, in general, spiffed it all up inside.  The brushes were worn, but still making contact.  Reassembled, attached a 12V external source and I was in business again.

Last Saturday, 900 miles later, things were getting funny on the throttle while on the freeway.  I exited as soon as I could and the car died.  Pump out again.  Towed home, removed pump, took a quick look and decided the brushes were probably too worn.  Took it to a local electric motor shop.  He confirmed my brush theory, custom fit a set of new brushes and said all is well.  $78.  I reinstalled a nicely humming pump and went for a spin.  While my car has always been a pleasure to drive and is very smooth, it seemed to hit a new level of smoothness and responsiveness.  With the pump operating at full capacity, the injection pump is now most likely getting a consistent flow of fuel at full volume allowing it to operate even more efficiently, while before, without the new brushes, it may have been flowing at a slightly diminished capacity.

[geezer]

The car runs great now.  I am amazed at how much better it runs.  Heck I even did a burnout at a stop sign (there was a little gravel that helped).