Fuel pump on 390 engine - Ford Forum - Enthusiast Forums for Ford Owners

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Old 04-15-2012, 12:52 AM
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Default Fuel pump on 390 engine

This is on a '72 F250 Last week when it would not start, I disconnected the fuel line where it enters the carburetor and found that the (mechanical) fuel pump was not delivering gasoline to the carburetor. Knowing that the fuel pump has been in there since at least 1978 when I bought it, and possibly since new in 1972, I was suspicious that it had failed. I bought a new (Carter) at Pep Boys and removed the old one (which involved disconnecting the power steering assembly and moving it aside). I then installed the new fuel pump and was disappointed to find that it did not move the fuel either. I then attached a fuel line to a container of gas and turned over the engine with the starter. The new fuel pump would not suck up the gas.

I then removed the new pump and tested it by running the fuel line into the container and moving the lever by hand. It sucked up the fuel readily.

Then I hooked up the old pump to the fuel line and tested it by hand. Lo and behold, it also sucked up the fuel just fine. This told me that my old pump was still working. I reinstalled the old pump and hooked it up to the container. It would not suck it up.

So, to review, both new and old (40 years old!) fuel pumps work fine when hand operated, and neither works when installed on the car.

Enters now the possibility that I did not install the new pump correctly. However, if that is the case, why was the old pump not working before I removed it?

By process of elimination, I am left with the unhappy prospect that the lever on each pump is not being moved up and down by the cam lobe. So I tried to peek inside that hole and noticed that there is what appears to be a chain inside, and it appears to be kinda loose, and I can move it by poking it with a screwdriver. When I crank the engine, the chain seems to move. I cannot see straight inside, but by putting in a screwdriver, I can feel what may be the eccentric disc, though I can't be sure. Looks like a huge job to remove the cover plate over this area to see what is going on. Hence my appeal to someone familiar with this area of this engine.

Could that eccentric cam not be moving? If so, if I run the engine, will I do more damage?
By the way, last time I ran the engine, it was just fine. Can't understand why, with the vehicle just sitting there, the cam would stop moving.

I plan to bypass the mechanical fuel pump and install an electric pump, but I worry that something is wrong inside the engine. What do you think?
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Old 04-15-2012, 04:19 AM
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When you crank the engine, can you see if the cam is moving ? If not, some engines had a fiber cam gear and it could have worn down to the point where the chain will not rotate the camshaft. If that is the case then an electric pump won't be much help.
It does appear that you may need to replace the timing chain and gear. I don't remember if those engines had a cam bolted on to the cam gear.
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Old 04-15-2012, 11:12 AM
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Welcome to FordForum..

As a quick timing component test, you could give it a short shot of ether, a fuel prime into the carb/intake, or 'carefully' fill the float bowl through the vent tube near the choke plate if you need a longer run time to check timing, move the truck ect.. If you fill the bowl the truck will idle for a few minutes on the contained fuel. Ether or a fuel prime and it should start and run for a few seconds until the prime is burned off. That way you'll know if it cam/timing related. If it does run, then it could be the the pump drive, or possibly a restricted sock inside the tank (if the fuel pump is still installed)

Does the lever on the old pump look ok? No excessive wear.

The original pump drive was a two piece roller type unit that was updated to a solid piece drive. There is a single bolt that holds the drive and cam gear in place. Rare that the bolt breaks, but have seen it happen.

If it were just the drive the failed and the truck runs fine primed, you could always install an electric pump as long as there is no tank restriction.

If the truck was running when last parked?, it 'should' have started and run on the fuel contained within the fuel bowl (unless the carbs power valve bleeds off) then stalled out if it were a pump, drive, or gear failure.

Sometimes if the cam gear is ready to let go, it will be running when parked, and then on the crank to start it will slip the teeth and fail timing on a weakened gear.

If it starts on a fuel prime assist, then you can rule of the cam gear..

Last edited by Hayapower; 04-15-2012 at 11:39 AM.
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Old 04-15-2012, 06:33 PM
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The fuel pump on these was driven off the front of the cam gear, which looks like a big circle (and is) which pumps the arm once a revolution. It's perfectly possible that the gears have worn to the point (if it's the O.E. phenolic gear) that the chain slips, which would also usually cause a timing problem (which might not be totally apparent when cranking).
If all is good there, then I'd look to the fuel line and specificaly the tank for a clogged fuel sock, which would indicate a rusty tank. Easy to imagine on something this old. Please let us know!
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Old 04-15-2012, 06:53 PM
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I've had a few of those trucks and damn do I miss them, the cam has the single bolt running through the cam gear and the disc that drives the fuel pump. so when you install the pump do this as you put the pump in the hole turn it up a little to make sure that the arm on the pump slides under the cam disc you will find that it takes some pressure to align the bolt holes for the pump but make sure that your arm for the pump is under that disc. because if it ain't then your pump new or old won't work. then you can check for blockage in your fuel line by removing the cap and blowing in the filler tube that little bit of pressure in the tank will push the fuel out of the tank and into the line. just have a catch can under the fuel line where the gas will flow into it if no gas then you have a blocked or clogged fuel line most of the time it's filled with rust. or you can just use an air hose on the tank side of the pump and it should pump the gas out of the tank through that line.
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Old 04-16-2012, 11:44 PM
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Default Fuel Pump on 390 Engine


I am the originator of this thread.
Thanks to HANKY, HAYAPOWER, GREASEWORK, and GRINDMAN for taking the time to respond to my inquiry. Your suggestions were
helpful. Here is some additional information:

This is a 72 ford F250.
My concerns now are with the eccentric on the camshaft that activates the
pump by means of the fuel pump rocker arm. I suspect the eccentric is not moving the lever up and down.
I need to decide if I am going to start the engine, or
indeed even turn it by hand or with the starter motor. My concern is that if
something is loose, broken, or fallen off, I could do severe damage by
turning the engine. Further, I could cause a problem if the cam sprocket is
not turning.
I realize I can get all my answers by opening up the timing case, but I want to
diagnose as much as I can without taking things apart.

Here are my questions
:1. How do I determine if this is an interference engine?
2. What is the easiest, safe method of determining if the camshaft is
turning when I turn the harmonic balancer/front pulley?
3. The distributor turns when I turn the crank pulley by hand. Does that mean the camshaft is turning?
4. Is there a method for determining if the eccentric is turning? Could I
insert a wood dowel in the hole to see if it moves?
5. Is there a way to determine if the bolt holding the eccentric to the cam
sprocket is loose? Could it come out? Could it come out far enough to cause
damage if the engine is running?
6. If the locating pin came out of position ( rather than
going in) could it be loose in the timing chain vault and cause damage in a
running engine?
7. How common is it for a cam/locating pin (referred to in the shop manual as a "dowel") to go in or out and not hold the eccentric cam in place?
8. Is it possible to insert a wrench into the hole and to check to see if
the bolt is on tight?
7. Does the bolt that fastens the eccentric cam also fasten the cam sprocket to the camshaft?
6. I have hooked up a temporary electric fuel pump to bypass the mechanical
one. I am now getting fuel to the carb. Is there a way to determine if it
would be safe to start the engine?
7. From your experience, is it posssible to put this fuel pump in
incorrectly. I don't see how.
8. The chain I see inside the hole appears to be loose. Is this a concern?
9. Taking the pumps off and putting them back on has been a pain. I have already removed the power steering unit and set it aside. There is a sending unit (?) just to the left of the oil filter. Is this removeable? It would make this job considerably easier.

I am guessing that the rebuilder of this engine may have not been meticulous
in putting on the eccentric. It has about 15,000 miles on the rebuild, and
it was many years ago. By the way, the fuel pump is the original from 40
years ago, and it still pumps, at least by hand when off the engine..


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Old 04-17-2012, 02:03 AM
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I'll take a shot at your questions

1. The engine isn't an interference fit, the pistons are valve relieved.

2. Either using the front crank/balancer bolt, or 'bumping' the starter to varify a rotation then checking distibutor timing/rotor pointing position @ TDC#1. TDC on the balancer, shoulod have the distributor rotor pointing at cap wire poistion 1. (if your not checking it 180 out) Also when/while engine cranking,, oil pressure will build. (doesn't mean the chain hasn't slipped) Compression test will varify cam rotation, and sometimes a slipped chain if the comp ranges are 'now' irregular.

3.If the distibutor turns the cam is turning, BUT, it could have slipped time on the cam gear/chain. Some looseness in the chain is normal wear.

4. Sometimes leaving the pump bolts loose you can feel the lever push against the spring tension of the pump. Suction/pressure In/out of the pump too. The lever is angled to reach the drive, you might be able to fab a tool to check.

5. If the bolt came loose, the pump drive 'could' come off of the pin but would still rotate. The pin holds the cam gear 'centered' along with the bolt. The pin presses into the cam (bottoms out in the bore), the cam gear is fit onto the nose of the cam and the pin locks it from spinning as does the bolt. The pin extends out beyond the cam gear once installed and catches the pump drive. Bolt holds the parts in place. If the bolt were to break or come loose, you should be able to pry against the cam gear (side to side) within the timing cover and see excessive movement of the gear. May 'possibly' see some suspended metals/debris in the oil.


7.Never seen a pin break or come out. Possible I guess if the bolt broke. The large thick washer on the cam bolt keeps the pin in place. Can't fall out.


9. The pump lever could be install 'on top' of the drive. Not sure if all pumps could since some pumps/levers were different.

10. If the gear appears tight, give'r a go If there's broken parts the only way to correct them is to pull the timing cover off, some pieces may make their way into the pan, and easily retrieved with the T cover off. An oil sample may show signs of trouble either with teeth from the cam gear included with the lube, or may show signs of suspended metals, or trash at the plug

11. The sender you see is the oil pressure sender. Easy to remove. Oil pressure gauge? or light?
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Old 04-17-2012, 07:22 PM
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Hayapower covered it just great !

I kinda remember something about those fuel pumps and that was if you moved the arm more than the cam does it seems to work just fine. Yet if there was enough wear on the arm and link to the diaphram the darn pump didn't pump.
It would be rare if the new pump didn't work, but as we know new pumps are never bad , ,,,,,,,,,,,,,are they?

Remember how you had to stretch the diaphram before tightening the housing screws or the diaphram couldn't move to pump.

Last edited by hanky; 04-17-2012 at 07:28 PM.
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Old 04-17-2012, 08:53 PM
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Default Fuel Pump on 390 Engine

Special thanks to HAYAPOWER for his detailed answers to my questions about the eccentric cam inside the timing cover.

When I get a chance in the next week or so, I will dig in to the pump and that area to see what I can determine about the condition of the eccentric.

HANKY, this raises the issue of whether or not I have a defective new fuel pump. It seems unlikely but possible. After I determine the condition of the eccentric, I'll have to make a judgment on this.

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Old 04-18-2012, 04:47 AM
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Thanks for your reply. Will watch to see what you find.
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