Fuel Flow problem with new Electronic SU Pump

[mwagon]

Replaced original none working square body pump in Tri Carb with a new double polarity SU AZX1307 pump, but pumps not able to create fuel flow on its own effort. Checked both fuel tank to pump & fuel pump to carb lines for obstructions. Pump is installed with the outlet at top & the top side marked on pump in top position. Pump makes normal clicking sound, making you think its trying to pump. Tryed without gas cap installed. Tryed giving pump a priming boost by applying ~ 10 psi thru fuel fill. This gets the fuel flowing to carbs, but after releasing pressure boost, pump doesn't seem to be able to create enough flow on its own, once again.
My only thought now is to setup a low pressure gauge on the pumps outlet to verify its lack of ability to create sufficient fuel pressure. Past posts on internet, make it sound like there itsn't any special priming effort needed for a electronic SU pump, but maybe someone else has had similar problems & has a possible idea to try next

 

[RAC68]

My initial thought was that the diaphragm is not adjusted correctly and the pump is not creating sufficient throw to provide pump-specific vacuum and pressure. My second thought is that the pump valve may be leaking and, again, will not allow the pump to create sufficient vacuum and pressure.

Although both issues are potential, an improperly adjusted diaphragm may be more commonly experienced. In this case, the rod (and magnet sensed by the hall-effect sensor) would be retarded from rising sufficiently to triggering the solenoid. Once sufficient fuel resistance is developed, the pump would stop ticking.

Since you noted that the pump was clicking regularly, the second cause came to mind. In this case the pump is ineffective due to a leaking valve. The pump would tick at a regular or faster rate but no pressure would develop. This condition is rectified by replacing the valve and cleaning the seat. You can detect this fault by placing a vacuum gauge on the input side and knotting a gauge spike at each pump click followed by an immediate fall off.

Although either of these conditions may be the cause of your problem, since your pump is new, I would first expect a leak in the input line that would not allow the pump to develop sufficient vacuum to pull fuel from the tank. Although you have indicated pressurizing the tank and gaining fuel flow to the pump (and past), can I assume that you saw no leaks to the input side of the pump?

Being the most common problem, it is worth rechecking the lines and especially the seal at the pump input. I would also blow are through the input line for good measure.. It took almost 20 years before a piece of silicon seal, previously used on my fuel gauge sending unit, showed up in my line to create a partial blockage.

I hope this helped a little as I appreciate your frustration…especially after purchasing a new pump to solve your problem.

Good luck,
Ray (64BJ8P1)

 

[Bob_Spidell]

I was a fan of the SU electronic when I had one operate trouble-free for over 40K miles. But, that pump finally gave up the ghost this summer; early symptom before intermittent action and eventual failure was what I called 'fibrillation.' The pump literally acted like a heart fibrillating; i.e. it pumped rapidly but shallowly and never completely pumped-up. Finally had to install my points-driven backup to get home.

I bought a new SU electronic, thinking I'd get another 8-10 years out of this one, but it was erratic almost from the start (can't return it because I tapped it for SAE-threaded studs). I tried adjusting it--you have to set the magnet depth with a special spacer and adjusting the shield. It seemed to work so I reinstalled it and all seemed good, but it went south after less than 100 miles. Back to the points-driven backup.

IMO, the SU electronic pumps are hit-or-miss, and may have a recent quality issue. There is little you can do to adjust them besides setting the diaphragm/magnet length and adjusting the shield. If that doesn't work--or if it appears to but the pump isn't reliable--you're basically SOL. Sounds like you've ruled out the usual air/vacuum leak problems; you may just have to return the pump and try another.