Greetings All,

Several unsuspecting forum members have asked me to post details about how I converted from the stock mechanical fuel pump to an electric pump on my '84 F250 (351W). I previously had heat-related fuel issues on my truck. After being stranded a couple of times, I went into FullOverkillMode™, made several changes (including the electric pump) and the problem has never returned.

If you've got a few days to spare, you can read about my travails here, specifically post #6, before the conversation devolved into the Great Fuel Quality Debate of 2016, complete with name calling, fisticuffs, and threats of nuclear war and/or a Justin Bieber concert:

https://www.ford-trucks.com/forums/1...e-vs-heat.html

Now, if you're also thinking of converting to an electric pump, I absolutely, positively insist you include some sort of automatic shut-off feature for the pump. This is so important, I'll repeat myself, using all caps, italics, AND underlining. If only I could figure out the logistics, I'd even type standing up with both hands on my hips and tapping my foot. Yeah, it's that important:

YOU MUST INCLUDE SOME SORT OF AUTOMATIC SHUT-OFF FEATURE WITH AN ELECTRIC PUMP

If a fuel line were to leak (in a crash or otherwise), the electric pump would not know and would keep running and potentially feed a fire. For an automatic shut-off, I've added an oil pressure safety switch. This is similar to the switch for an oil pressure idiot light, but works in reverse. The oil pressure safety switch only makes contact when oil pressure is present. I used a NAPA #OP6616.

Adding the oil pressure safety switch mimics the general safety standard of a mechanical pump, i.e. if the engine is turning, it is already receiving fuel, which hopefully means the fuel lines are intact so it should be safe to continue feeding it fuel. If the engine stops turning for any reason, the oil pressure drops to zero and the electric fuel pump also stops. You can't use an ordinary on/off toggle switch and assume you'll be able to manually shut it off in an accident. The risk of creating a Car-B-Q is just too great to not have an auto shutoff feature.

If you're still not convinced, please click that little X at the upper corner of your screen. Thanks.

Here's a basic wiring diagram:




My truck does NOT have power windows, so I tapped that blank spot in the fuse panel to power the fuel pump. If you have electric windows, you will need to figure out another power source that shuts off with the ignition. Make sure the fuel pump is the only component on your new circuit, because if something else overloaded the fuse, the fuel pump would also stop. I used a 20A fuse.

Note the momentary-on toggle switch on the wiring diagram. This switch is mounted on a small bracket under the bottom edge of the dash. Since my truck often sits for days at a time, the fuel typically evaporates from the carb bowl. I can turn the key to the ACCY position and hold this spring-loaded toggle switch to run the pump before engaging the starter. This replenishes the carb bowl and lets the engine start almost instantly. I don't have to crank and crank to refill the carb bowl like with the original mechanical pump. Also please note fuse #14 is only hot in ACCY and RUN, but not START. This hasn't been a problem for me because I always run the electric pump first if the engine hasn't run for a few days, but if you'd rather just hit the starter and crank and crank, this fuse location won't work for you.

As an added bonus with this switch on the dash, should the oil pressure safety switch ever fail in the open position, I can manually hold this toggle switch and still limp home. Shifting gears won't be fun, but it's better than being stranded.

Getting ready to dive under the hood, here's the NAPA #OP6616 oil pressure safety switch before installation:





There's not a lot of room to install this switch on a 351W. Just inboard of the power steering pump is a hollow hex-shaped standoff with a threaded hole for the sender to the oil pressure gauge. I removed the standoff, drilled and tapped a second hole for the oil pressure safety switch, and then reinstalled the standoff with both components. Alternatively, you could add a tee fitting at the sender for the oil pressure sender. This picture makes access look horrible, but it's not that bad:



Edit: Five years later, here’s a picture of the same area, but with the engine partially stripped down and on a stand.





While you're under the hood, you'll need to remove the stock mechanical pump and add a block-off plate. I used a short length of rubber fuel line and a pair of clamps to bypass the pump location.

Here's the moment we've all been waiting for, the installation of the pump itself. This view is looking inside the driver's side frame rail, just forward of the fuel tank selector valve. Since the pump set me back about $100, I wanted to protect it with a fuel filter on the inlet. I used the same NAPA #3081 as at the carb inlet for simplicity. The new filter at the pump inlet is now the primary filter. If the pump ever starts disintegrating, the second filter at the carb inlet (stock location) should hopefully protect the carb.




The pump is suspended on small rubber isolators beneath an L-shaped bracket. This bracket is further insulated from the frame by another set of isolators, although this second set is optional. The pump is fairly quiet, and makes just enough noise so I can tell it's running before I start the engine. Once the engine is running, you can't hear the pump.

I've also added a fuel pressure regulator. When I first installed the pump, I noticed the output ranging up to about 12 psi on occasion, although it's only supposed to put out 6-8 psi. I wasn't sure if this was just a normal variation of the pump or if it was defective, but the engine ran fine regardless. Just to be safe, I added a fuel pressure regulator and now the output range is very tight. The regulator hangs off the side of the pump by the very short length of pipe connecting the two components. I didn't see any need to mount the regulator on its own bracket. If I were to do it all again, I'd probably pick another regulator, as this one's plumbing arrangement is tee-shaped and has two output for dual carbs. You plug the second outlet if not needed. A regulator with only one outlet would have made more sense for my application.

Here's a little more detail on the new fuel filter installation at the pump inlet. I used a short length of steel line (with a reverse flare fitting) to connect to the inlet side of the filter. That way, when it's time to replace the filter, I just unthread the flare fitting from the filter. I don't have to break the junction between the rubber hose and the steel line:




I formed a bubble on the end of the steel line where it inserts into the rubber fuel line. This helps make a good seal. This was easy to fabricate, using a double flare set. Forming a double flare is a two-step process. The first step is to make a bubble using a special die, so just stop there. Voila, you've got a bubble almost as good as any factory application for joining a steel line to a rubber hose:




Parts sources:

Carter P4600HP Electric Fuel Pump:



Edit: Delphi FE0539 looks to be identical to the Carter P4600HP:



Carter 18-14U Fuel Pump Mounting Kit (optional):



NAPA #OP6616 Oil Pressure Safety Switch:

https://www.napaonline.com/napa/en/p...6616/ECHOP6616


NAPA #3081 Fuel Filter (same as stock filter at carb inlet):

https://www.napaonline.com/napa/en/p/FIL3081/FIL3081


There is one disadvantage I should point out. This electric pump isn't stocked at most parts stores, unlike the original mechanical one. Should you ever need a pump replacement while away from home, it might take a while to get a new one. During the summer, I often load up the camper on the back and travel to some pretty remote locations. Not wishing to tempt fate, I carry a spare pump (and oil pressure safety switch) as a precaution. Overkill, probably, but better safe than Catholic...

 

Nice write up.


Only thing I would do different if I was going to do this is run a relay so the pump gets a full 12 volts.


I use an electric pump (Holley blue) on my drag car and a relay made a big difference on the pump keeping steady PSI thru out the run. I know this because I have a PSI gauge mounted outside the passenger area where I can see it.
Dave ----

 

Nice write up Karl. What are your thoughts on using a electric fuel pump just for priming? Is it doable or will it just mess up the mechanical pump? Over the summer here (100 + F) all the fuel boils out of the carb and I think also the fuel line as far as the pump. If the high temp is 95 or less it doesn't happen.

 

You run the danger of the mechanical fuel pump diaphragm failing and then then the electric pump puts fuel into the crankcase of the engine.

 

That's what I was afraid of

 

Thanks. I thought long and hard about using a relay, but decided to omit it for simplicity and then see what happens. As the African big game hunter said, "Safari so goodie." I have a fuel pressure gauge and haven't seen low pressure at all with the direct wiring I used.

 

I'm not sure this is a problem with the OEM mechanical pump. (I've had that problem on other vehicles, though.) I'm pretty sure the OEM pump has a seal between the diaphragm and the crankcase. In addition, there's a weep hole in the casting beneath the diaphragm. In theory, if the diaphragm were to leak, the fuel would be blocked from reaching the crankcase and would be vented overboard via the weep hole.

All bets are off with an aftermarket mechanical pump. No guarantee it has the seal, but I'd hope so. Does anybody have a spare fuel pump sitting around to confirm if there's a seal?

 

I ran a hybrid setup like that for about 12 years. I kept the stock mechanical pump and added an electric boost pump just forward of the tank selector valve. The electric pump was a Carter P74022:

https://www.amazon.com/Carter-P74022.../dp/B000CSXSTA

This pump is designed as a boost pump and can be installed in series with another pump downstream. When the boost pump was switched off, the other pump could still easily draw fuel through it.

The electric boost pump worked great to prime the carb before start. It would push fuel through the inlet and outlet check valves of the mechanical pump. I'd also run it during hot weather, climbing hills, etc. It pretty much took care of vapor lock. Don't forget this type also needs an automatic shutoff feature for safety.

I ran the fuel system with two pumps in series for about 12 years and thought I had the best of both worlds. However, I suddenly had some new heat-related fuel problems a couple of years ago. I'm pretty sure most of that was caused by excessive heat in the intake manifold due to the exhaust crossover passage.

I blocked off the crossover passage but also wanted to reduce any other possible sources of heat affecting the fuel in the carb bowl. I looked at the mechanical pump sitting near the exhaust and decided that may have been adding a small amount of heat as the fuel passed through.

Was it much heat being added? Probably not, but after being stranded twice in the boonies, I hated the thought of putting this faithful old truck out to pasture. I decided to keep the fuel reaching the carb as cool as possible so ditching the mechanical pump was part of that strategy. I've had zero fuel issues since then, even under identical circumstances, so I'm happy.

So yes, you could add an electric boost pump like I previously had and you'd probably be just fine.

 

I noticed in the LMC catalog that they sell a harness with relay and switch that uses the tach signal to send power to an electric in-line pump. At start-up,the system will power for 3 seconds and stop until it gets a tach signal. If the engine shuts down, no signal no pumpee. Looked like a clever set-up for about $70

 

Cool beans! Any idea if you could cycle the key to repeat the 3 second run? If the fuel has evaporated from the carb bowl, it takes longer than that to replenish it.

 

I don't think that detail was covered in the catalog, but I don't see why not.

 

I would second that. Then you can do away with the oil pressure switch and the momentary push button and for fuel cut out install an inertia switch robbed off just about any vehicle in the wrecking yard. All vehicles manufactured with an electric fuel pumps have to have a inertia switch installed in the relay control circuit that disables the relay and in turn the fuel pump in the event of an accident.
Just cause you have an accident does not guarantee the engine will shut off or stop running.

I'm not a big fan of putting fine filters in front of elec fuel pumps, as these filters plug up and restrict flow they put stress on the pump and it's seals.
The sock on the pick up is fine enough to filter our any big chunks that would damage the pump. The pumps are built to digest certain amount of garbage with no ill affects. The installation of a fine pre-filter has a bigger chance of damaging the pump than any crud that gets past the filter sock in the tank.

 

That's how the fuel injected Fords work. The computer looks for a signal from the dist module or the crank sensor, and then grounds the fuel pump relay to make the pump run. It can lead you down a rabbit trail sometimes if you figure out you don't have power to the fuel pump, but in reality the original problem is in the ignition system and the computer is not turning on the fuel pump relay because of it.

 

Or you could wire an inertia switch in series with the oil pressure safety switch and have the best of both worlds.

I'm not very familiar with inertia switches. Do they only work on impact, such as in a collision? Would they also trip if the vehicle were to roll over slowly, without any sudden jarring? That's where I like the oil pressure safety switch, because even if the carb still managed to work on its side or inverted, it wouldn't matter. The oil pump pickup would no longer be submerged, oil pressure would drop, and the fuel pump would quickly shut off.

As far as the possibility of the engine continuing to run after an accident (not necessarily a rollover), the level of safety with an oil pressure switch is still equivalent to the stock mechanical pump. If the engine is still turning, the mechanical pump will continue to operate. If fuel doesn't reach the carb (a broken fuel line for example), both types of pumps will stop once the fuel in the carb bowl is consumed. If fuel does reach the carb and the engine stays running, the fuel will be safely consumed. I realize it's not perfect to have the engine still running, but it's not raw fuel being dumped in that scenario.

Re: the momentary on switch, you don't want to eliminate that. That's the best part! It's great to be able to refill an empty carb. I don't drive my truck every day, so the carb bowl is often empty when I next try to start the engine. Holding the switch for a few seconds sure beats cranking and cranking and cranking the engine like with a mechanical pump. Also, the fuse I picked is not powered during start, so it is necessary to prefill the carb before cranking if the truck hasn't run in a few days. It's almost like an antitheft system. If you'd rather have the pump powered during start, you'd have to pick another power source.

 

Yes an inertia switch cuts current with an impact or a roll over. It was great gag on the Crown Vics give the passenger side rear quarter just behind the c pillar a quick smack with the palm of your hand as it pulled away and you would trip the Inertia switch and the car would shut off leaving the driver scratching his head.


Unfortunately you can not put the inertia switch inline as it is low amp device, it would never be able to handle the amps of the fuel pump. It is meant to used in the control circuit (at least in the Fords). I'n not even sure the Oil pressure switch can handle amps for the fuel pump as they are generally just used to illuminate a small light bulb, you may end up burning it up in short order.

With the inertia switch as soon as you key on the ignition the fuel pump is on just like a modern EFI vehicle and the carb fills. No need for the push button at all. If you want an anti theft device just put a hidden switch in line in the control circuit.

Also the Mech fuel pump is on the engine leaving only the fuel line from the pump to the carb under pressure.

The Elec pump is under frame if the line between the pump and carb is compromised you will be spraying fuel all over. The line may not be severed enough to stop all fuel flow. Elec pumps deliver way more volume then a Mech ever pump will, and to a carb all you have to do is get fuel to it ,even 0.2 psi is enough to feed a carb at idle.

The Oil switch is a good idea to protect an engine against oil loss related damage and is used on stationary engines (IE gen sets) but as the first line of defense no, especially since you really have no idea if the contacts have welded shut as it is a normally open switch (N/O) and given that these switches are not meant to carry less than an amp in most cases I would not bet on it's longevity.

I did I real quick and dirty schematic in MS paint to give you an idea how it would be wired.