Fuel Pump Test - file this under "don't tell OSHA"

Post date: Feb 19, 2012 12:27:35 AM

The big worry with my hair-brained fuel pump plan is that it wouldn't be stable at the low pressure required for a carb (~7psi). EFI fuel pumps really aren't any different than carb fuel pumps - an engine pulls the same amount of fuel regardless of how it's delivered. EFI pumps are capable of running at 50+ PSI line pressure, while carb pumps would just cavitate and puke before that pressure. The actual delivery volume is about the same (ignoring hi-po pumps).

So that's great. But the key with keeping electric pumps alive, quiet and happy is to use a bypass regulator. Since the pumps are good at pressure, if your bypass can't keep up with supply then you over-pressurize. The in-tank pump I'm using (from an F350!) has a 3/8" supply and 5/16" return, which is a little concerning. It's best if the return is as large, or larger, than the supply. Given a sub-optimal configuration, I just needed to test to make sure it would be OK.

Testing a fuel pump is obviously dangerous. Pumping around gas and playing with supply voltages, varying pressures, and temporary electrical connections sounds like a really bad idea. I couldn't find any fuel system test fluid locally, ie VISCOR 16, so I used another tip: isopropl alcohol and distilled water. Get about a 50/50 mix in a bucket, drop in the pump, play without going boom. I do smell like alcohol now, though.

Here's the setup:

It's a contraption! I used plastic pipe to barb fittings, clear plastic tubing and an air shutoff valve. The American Autowire kit came in handy - the included ignition switch is a great high-current switch that's easy to wire up.

The setup is obviously not 100% accurate to the final install, but close. I had 1/2" supply and return lines, with the return necking down to 3/8" close to the return fitting. This is about as close as I could get without spending lots of money on temporary tubes and fittings.

Threw all that together, and the findings were really positive. The minimum pressure was about 4psi with the outlet closed and the regulator turned out all the way. The adjustment up to 7psi was pretty smooth. The pump did get into some kind of bad phase at one point and had really jerky output - the pressure wobbled about 1psi and it was obviously shaking. I messed around with it, couldn't see what was causing it. Turning it off and on a couple of times got it back to good. Cross fingers that doesn't happen again.

The surge tank works really well. I pulled it up out of the water while the outlet was closed, and it just happily recirculated.

I then got paranoid about the parts rusting out, so I tore it all down. The fitting going from the top of the pump to the bottom of the tank was glued into the tank (oops) and the filter on the bottom of the pump had a plastic-welded retainer (oops). Both easily fixed. A quick blow out with air then a quick run with gas and it should be fine.

The pump inlet filter has black something inside of it. I didn't note if it did before I started, which has me worried that the alcohol broke down the black tubes from the lid to the tank. After some more inspection, I don't think that's the case. Maybe some sort of carbon element?

Fun fact: the pump is actually a Walbro, with the assembly sold by Spectra. It's easy enough to get higher-spec Walbro universal pumps. I also removed the fuel level indicator as I'll be using the one that comes with the gauges.

Really fun fact: since the bypass worked perfectly, and this pump isn't super high-spec, the fuel pump controller is really unnecessary. Oh well. It's an investment for the future. Yeah.