mechanical fuel pump issue? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 01-12-2014
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mechanical fuel pump issue?

Not sure exactly where to post this question as it relates of an '84 Ranger with a 2.8L V6. Have also posted the same question in the 2.9L subforum to cover my bases.

My son's Ranger has sat for about 6 months and we are just getting it on the road for him now that it has hit the magic 30 year old mark and can be permanently registered as a 'classic' vehicle. After we parked it for the rest of last year, we have gone through and done some needed maintenance on items that though functioning, were starting to show signs of wear or needed refreshing. New starter, new starter relay (ran into some problems here that are documented on the General Technical and Electrical sub forum, now solved), fresh belts/hoses/vacuum lines, cleaned up electrical connectors and straightened out the wiring looms, fresh plugs/wires/distributor components, and a cleaned and rebuilt carburetor. Each component refreshed followed up with confirmation that the truck ran when completed whenever needed.

Now that I've listed the things we have done I will pose my question:
Just before parking it for the latter part of the summer/fall, my son put in a new (mechanical) fuel pump. Worked fine, he drove it for almost a month with no issues. Now that it has passed the magic age of 30, he is ready to re-license it. It turns over great but we are not getting any fuel to the carb from the fuel pump. New filter installed on front of carb during rebuild and works properly. Trickle gas into carb from bottle and truck runs fine. Removed line from fuel pump and ran a hose into a bottle to measure fuel flow and nothing comes from the pump. Removed fuel line from output side of pump and there is not any pressure coming from the pump.

Is it possible the diaphragm inside the pump has dried up and is no longer forming a sufficient vacuum to pull gas from the tank? Any other thoughts or words of advise are appreciated. He REALLY wants to get this thing on the road again and I'm anxious to have my 'spare' rig back home. ---rick
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Old 01-12-2014
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Not too savvy on mechanical fuel pumps, but is there a way to prime it? May just need primed before flow gets going
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Old 01-12-2014
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Yes, unhook fuel line at the carb and pour some fuel down the line to the fuel pump, give it time to get past the air in the line, i.e. fill it slowly until is stops bubbling.
Tap on line with screwdriver handle to get air out faster.
I have had to prime some pumps twice.

Mechanical pumps can't pump air so they rely on the fluid(gasoline) they push out to create the suction on the line to the fuel tank to pull more fluid in.
Once the flow starts any residual air in the line should be purged in the float bowl.


If fuel tank is filled to the top for storage usually that pressure keeps fuel in the pump, if tank is not full then fuel can siphon back to tank over time, fuel in the carb evaporates and float opens check valve, this allows air in and because of carbs height relative to fuel tank the fuel in the line gets the siphon to start.

Last edited by RonD; 01-12-2014 at 03:57 PM.
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Old 01-12-2014
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RonD, I've seen you post on a few subjects, and each post is a block of solid info... Thanks for sharing the knowledge, and keep up the good work!
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Old 01-12-2014
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Quote:
Originally Posted by 03edge View Post
RonD, I've seen you post on a few subjects, and each post is a block of solid info... Thanks for sharing the knowledge, and keep up the good work!
Nice of you to say that, thank you


And I forgot another method to prime the old systems.
Remove fuel line at carb.
Get a shop towel and short hose.
Remove gas cap
Wrap towel around hose and stick it in the tank opening
Blow in the hose, your lungs can generate about 2psi, that is enough to get gas pushed up and over the top of the tank and it will flow to the fuel pump, assuming at least a 1/2 tank of gas, via siphoning action.

Open end at carb allows air to be pushed out easily
reconnect fuel line and start engine, might take a few cranks if carb was dry.

Do NOT use an air compressor for this, you will blow off fittings if you do, this is a 5-9psi system

Last edited by RonD; 01-12-2014 at 04:12 PM.
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Old 01-12-2014
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Will prime pump next

I agree, 03Edge. RonD has provided some solid info and advice to me and to others and definitely deserves some kudos and sincere appreciation.

I've a few errands I have to do this afternoon and will stop and pick up some more gas in my can while out. I am also filling a 5-gallon can to try and top off his tank to make sure there are no issues there. When he parked it we put some StaBil in the tank to help keep things fresh, as well the fact that the gas he uses is not 10% ethanol but pure gasoline. Should have helped some. (BTW, the prevalence of 10% ethanol fuel everywhere is one of the reasons we replaced all of the rubber parts of his fuel system with higher grade fuel lines.)

I'll go out tomorrow morning, after doing some work to pay some bills, and re-install the pump. I'll work at priming the pump as RonD has suggested and keep working at it. Hopefully, with a full tank of gas, a primed pump, and some luck this thing will be visiting the DMV tomorrow to get licensed. ---rick
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Old 01-15-2014
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mech fuel pump update

Wanted to provide an update to let everyone know what is going on with the truck. Yesterday proved to be a bit more of a business day and not as much a truck repair day due to more time spent in the morning on work and then rain in the afternoon.

We did go out today to try to prime the fuel pump in the fashion described by RonD. We tried to fill the rigid fuel line running from the fuel pump to the carb four different times. Even fashioned an new funnel to have a small enough tip to go into the flared fuel line. Filled it each time with fresh gas, filling slowly and tapping the line with a heavy screwdriver to make sure all of the air was purged out of the line. Each time, following the line being filled with gas, I attached a piece of flexible fuel line to the rigid line and ran it into the bottle partially filled with gas to observe if gas was being pumped from the tank toward the carb. BTW, we have completely filled the gas tank at this point to rule out any issues there. All to no avail.

After reading RonD's most recent post we will go out tomorrow after lunch to try to pressurize the tank to make sure gas is flowing TO the pump via gravity and slight amount of pressure from blowing into tank opening with hose/towel method. I will disconnect the hose fitting on the inlet side of the pump to make sure we are getting fuel to the pump. If there is gas at the inlet side, we will connect the line to the pump and try RonD's suggested alternative method.

Will report back tomorrow evening. ---rick
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Old 01-15-2014
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An alternative approach?

As a bit of an aside, is anyone aware of any reasonably priced retrofit kits that would provide for a bypass of the mechanical fuel pump (installing a plate over the attachment location) and installing a low pressure electronic fuel pump? NAPA has some low pressure/low volume pumps listed that run 5-9 psi and about the same gallons per hour as the mechanical pump. Would there be a need for a fuel pressure regulator for something like this? Could just wire it all to the ignition switch circuit. Would I need an in-tank pump as well? ---rick
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Old 01-15-2014
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Google: ford mechanical fuel pump block off plate

Usually run under $10

I think the stock mechanical fuel pumps only generated 3 or 4 psi, "super mechanical pumps" were used when engines were upgraded to bigger carbs, they were 5-9psi.

Adjustable 5-9psi would probably be ok, you just have to remember that too much PSI will cause fuel to push past the float check valve in the carb.


Yes, new fused 12v line of correct gauge would be needed, I would probably use a 12v relay that was activated with key in RUN position, as fuel pump can draw 10-20amps, so tapping into any existing circuit would most likely blow a fuse or fusible link.
Relay draws less than an amp so won't effect any circuit you tie it into.
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Old 01-15-2014
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My next update

My son and I went out this afternoon to try again to get the truck running. We tried filling the fuel outlet line (pump ---> carb) and combined that with blowing into the tank using the hose/rag combo. Still no luck.

We tried to feed the pump from a small gas can held in place on the fender, above the pump, to see if the pump would draw any gas from the can. No luck. We were able to confirm, later in the afternoon, that by putting positive pressure on the tank fill side we are getting gas out of the (disconnected) gas inlet hose that goes to the inlet side.

Ordered a new fuel pump from the local NAPA and picked it up this evening after we were finished for the day. Will install the new pump tomorrow and report back.

RonD, thanks for the info on the electric pump retrofit. When I went to NAPA today I had them look up the specs on the OEM pump. 23 gallons per hour, 4.5 - 7 psi. They have an electric pump that feeds 4-7 psi but also puts out 34 gph. I don't believe that the gph is as important as the psi, am I correct? If this pump does not work we are going to a bypass method and installing an electric pump along the frame rail, accompanied by a much larger fuel filter upstream of the pump. The block off plate will of course follow. The relayed connection to the RUN position on the ignition sounds appropriate. But I am getting ahead of myself...
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Old 01-18-2014
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One other thing to consider when using an electric fuel pump is, heaven forbid, an accident, an electric fuel pump just keeps pumping fuel out a ruptured fuel line even with engine off.

EFI engines all use electric fuel pumps and they addressed this issue with an inertia switch.
It just has 12v IN and 12v OUT connections for fuel pump power, inside there is a weight that will pop out if there is a sudden stop or rollover, cutting the 12v connection.
They also have a reset button if they pop accidentally, which they don't unless they are broken.
$30-$80 new, or
$5-$10 at a wrecking yard, they don't really wear out but can be broken if accident(why vehicle was at wrecking yard) tripped it hard enough

Last edited by RonD; 01-18-2014 at 01:42 PM.
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Old 01-18-2014
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latest (and last) update on fuel pump issue

Hi everyone. Just want to provide the latest, and last, update on the mechanical fuel pump issue my son and I have been working to resolve the past week or so. As I wrote in my last update, we purchased a new mechanical fuel pump from the local NAPA dealer. I was tied up with work so my son, and my oldest son who lives 6 hrs north of us, installed the new pump yesterday morning. I went out to see how they were progressing and they were finished. They had not primed the pump in advance, so I recommended to them to just try letting the new pump get it's own prime going first (in lieu of taking the hard line off). After about 30 seconds the motor chugged to life.

Truck is back on the road and is sporting brand new "classic" plates. Have a few minor carb adjustments to make tomorrow but other than that all issues have been resolved. Thanks so much for all of the help and advise.
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Old 01-18-2014
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Nice work
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