Fuel feed problems and solutions


Symptoms:- loss of power at 40mph +
  1. It may be a faulty fuel pump (but if it is new, it should be ok). It is possible that the cam in the engine (which operates the arm on the fuel pump) is worn and is not lifting the arm fully. This is not very likely but is possible.
  2. It could be the rubber fuel pipes. When they are old, the rubber swells inside and makes the pipe narrower. This restricts the amount of fuel going to the carb. Possible.
  3. The metal fuel pipes could be crushed or bent or dented. This restricts the amount of fuel going to the carb. Possible.
  4. The filter in the fuel tank, on the end of the pickup tube (the pipe inside the tank) is blocked with dirt and grit. This restricts the amount of fuel going to the carb. Possible.
  5. You are using the wrong fuel cap for the type of fuel tank. Maybe you have a non-vented cap on a tank that needs the “Vented” cap. Or maybe if you have a vented cap, it is blocked at the valve…..or the valve is in the “closed” position, or maybe the valve is just faulty. *Very possible*
  6. It may be the float level is set wrongly in the carb. *Very possible**

There are some straightforward things to check. Here's how:-

.

Test No.1 (Tank-to-Pump)


(You need two people for this task)
  1. Disconnect the fuel pipe (tank-to-fuel pump) at the fuel pump.
  2. Connect a rubber or plastic tube to the free end of the pipe. Remove the fuel tank cap.
  3. Blow down the pipe.
  4. Your other colleague should be stood with his/her ear to the tank filler tube.
  5. Can they hear air bubbling in the tank? (from your blowing)
  6. No? - line is blocked or crushed somewhere between pump and tank.
  7. Check the line for dents, crushes and flattening. Check rubber hoses for interior swelling.
  8. Remove fuel pickup pipe from tank. Check condition of filter on end of pickup pipe.

Test No.2 (Fuel Pump)


(You need two people for this task)
  1. Romove fuel pipes from both sides of fuel pump.
  2. Connect a temporary pipe to the “inlet” side of fuel pump. Pipe should be long enough reach into a jerry can / fuel can).
  3. Place the open end of pipe into jerry can (Take care with fuel…. usual rules and safety procedures apply here).
  4. Get colleague to ensure that the free-end of the pipe stays immersed in fuel.
  5. Crank engine (with ignition switch “off”).
  6. Does fuel spray out of pipe at carb end?
  7. No? - fuel pump blocked or faulty.

Test No.3 (Fuel Pump to Carb)


  1. If fuel pump is working ok, reconnect both fuel pipes.
  2. Remove fuel pipe at carb (or at in-line fuel filter if fitted).
  3. Crank engine with ignition “OFF”.
  4. Does fuel spray out from end of feed pipe?
  5. If “No”, line is blocked or crushed somewhere between pump and carb.
  6. Check the line for dents, crushes and flattening. Check rubber hoses for interior swelling.
  7. If “Yes”, remove in-line filter (if fitted) and blow through the “carb” end. Clear?
  8. If “No”..replace filter. If yes, problem lies in carb (probably float level incorrect).

Test No.4 (Fuel Tank Cap)


  1. Is the cap correct for the tank you are using?

M151 and M151A1 tanks, also Ford A2 and pre-emission early AMG tanks use a VENTED cap. Emission controlled AMG tanks use a NON-VENTED cap. Do not interchange between versions.

  1. If you have a vented cap, is the valve in the “OPEN” postion? Is it working correctly?

That's all there is to it. Ken

 
fuel_feed_problems.txt · Last modified: 2013/10/26 12:33 (external edit)
 
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