Difference in fuel pumps?

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DARTLARRY

DARTLARRY

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I have a 1986 360 that I am working on, everything is fine except the mechanical fuel pump will not pump fuel. I thought I had a bad fuel pump, but I bench tested it, and it worked fine. I used a flashlight and a mirror to check to see if the pump arm offset washer was in place as I turned the motor over, and it was. I still cannot manage to get the pump to work.
I am using an early 70s model la engine fuel pump, did the pumps change on the later models la engines? I am also using a late model 1986 timing chain cover, is there a difference between the early and late model covers that would cause the pump not to engage the mechanism? Any help would be appreciated.
 
You also need to make sure the fuel pump eccentric is not rotating independently and loose of the camshaft gear. Sounds like you really should remove the timing cover and investigate.
 
Agreed! I recently got two bad pumps from AutoZone, two different brands.
Got one from O'reillys that worked. But if you bench tested it you've got some other problem.
I put a screwdriver in the hole and turned the engine over with a remote switch, I could tell the eccentric was moving up and down like it should. Suggest you try this.
Cam bolts have been known to loosen, why I always use lock-tight on 'em.
I'm sure you'll find it, before I knew the pump(s) were bad I put more gas in the tank, and blew compressed air through the lines, realized I should have tested the pump first!
Let us know what you find.
 
Is the return spring in good shape and correctly installed. The pump arm has to remain in contact with the eccentric,lol. The spring sets the pump pressure.
Any cover is ok. As is any pump with a similar arm.

I suppose you have proved the hard lines are clear and all the neoprene jumpers are intact and properly clamped and that the sender is not compromised, that the tank is vented and that there is actually fuel in the tank,lol.

If you fill the float bowl manually, the engine should run for a minute or two; enough time to do a pump volume test. Which should free-flow output 1 qt, in 1 minute or less, at 500rpm.And it should pull a 10 inch vacuum, and make 5 to 7 psi; on factory SBMs.
 
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I was trying to avoid pulling the cover, looks like I am going to be pulling it this weekend.
 
DARTLARRY said:
I was trying to avoid pulling the cover, looks like I am going to be pulling it this weekend.
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IMO, knowing what little we do at this point, you're getting ahead of yourself. The output test is cheap and easy, and
I've never seen an eccentric failure on a streeter,but
I have seen an occasional spring gone AWOL,
as well as debris stuck in one of the check-valves.
So if the pump does not freeflow the minimum, then you have to check the delivery to the pump. And if that is satisfactory, then on a rebuildable pump it would be time for an internal inspection. But on a sealed unit, now it's time to inspect the eccentric. And if that is working, now it's time to cut the pump open and have a look.
So if you pull the cover off first, IMO, you are getting ahead of yourself. Of course if the eccentric is bad, well then goodonya,lol. Time to buy some lottery tickets cuz Lucky is your middle name.
 
If you did not bench test with a flow restriction in place to build output pressure to around 5 lbs, you have not proven anything with a bench test with the outlet open. There are check valves at inlet and outlet, and if either one fails, it won't pump into a pressure build up on the output side.

I'd put on a new pump before pulling the cover if I thought the eccentric was on right.
 
When I bench tested it, it pumps fuel, when installed on the car and turning the motor over and fuel line disengaged and placed into a bucket it does not pump fuel.
Witw it still installed on the car, and using an electric pump and gas can to run the engine, it still does not pump fuel.
 
DARTLARRY said:
When I bench tested it, it pumps fuel, when installed on the car and turning the motor over and fuel line disengaged and placed into a bucket it does not pump fuel.
Witw it still installed on the car, and using an electric pump and gas can to run the engine, it still does not pump fuel.
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10 inches vacuum, 5 to 7 psi. Hook up a gauge. Maybe it is pumping........... pumping air that is.

Jack the back of the car up; Open the gas cap. The gas should find it's way to the front by gravity, and run out of the hard line by the pump.
 
I primed the line to the mechanical pump with an electric pump before starting the engine.
 
And then took the electric pump out? Or is it the kind that the mechanical pump can suck thru?
If there is fuel at the pump inlet we are waaaay ahead of the game. With the engine idling, just put a finger lightly on the outlet port. Your finger will be the checkvalve. Can you feel suction on the outlet side? If yes, the pump is likely defective. Keep your finger there for a few seconds, and the fuel should come. If it does not, then either the eccentric is not stroking the arm, or the return spring is not working, or the pump is defective. Do this with a short length of EFI hose, over a catch basin, and be prepared to shut the engine off. nm9 talked about this in post #8, but you mightof missed it.
 
How old is your fuel line? Any length of rubber section? Ethanol blend fuels these days really deteriorate flex hose and can easily collapse a fuel line or send chunks up the pipe and clog it

I'm not a fan of mechanical fuel pumps since they have a fatal flaw of potentially leaking fuel into the engine oil. Electric is the way to go, IMO
 
DARTLARRY said:
When I bench tested it, it pumps fuel, when installed on the car and turning the motor over and fuel line disengaged and placed into a bucket it does not pump fuel.
Witw it still installed on the car, and using an electric pump and gas can to run the engine, it still does not pump fuel.
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OK, that is good testing. Sure sounds like a lever problem on the pump, or the eccentric. Any chance this is an odd pump lever that is not right for this engine?

BTW, I re-read your last post and you still have not eliminated the chance that there is a crack in the rubber line from tank to steel line that is just pulling air. See the list in post #5.

Also, if you turn the engine so that the eccentric is down and to the right (about 7 oclock when looking from the front), when you install the pump, you will have to push the pump up hard up into place to push the pump arm against the eccentric. If the pump lines up on the bolt hols easy-peasy with the eccentric in that position, something is wrong.
 
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T56MaxTorq said:
How old is your fuel line? Any length of rubber section? Ethanol blend fuels these days really deteriorate flex hose and can easily collapse a fuel line or send chunks up the pipe and clog it

I'm not a fan of mechanical fuel pumps since they have a fatal flaw of potentially leaking fuel into the engine oil. Electric is the way to go, IMO
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This afternoon after much debate, I pulled the timing cover to check that by chance the eccentric was not in place. It was there, and looked fine. I have run the engine from the tank with an electric pump for at least 15 minutes, so the lines from the tank are fine. I am going to put it back together, and try a new pump, I am out of options at this point, this is not that complex a system.
 
T56MaxTorq said:
I'm not a fan of mechanical fuel pumps since they have a fatal flaw of potentially leaking fuel into the engine oil. Electric is the way to go, IMO
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Wait what? I have to call it the lessor of two evils.
I heard your opinion, and I raise you;
First; since 1969, I personally have never had a diaphragm rupture. And I have been driving carbed cars for all of those years.
Second; since 1969,the only instance I have ever heard of was one guy here on FABO. Now I'm not saying it doesn't happen, just that I only ever heard of one instance.And I haven't been wrenching on cars for all of those years, perhaps only 35 of them.
Third, and most importantly when the diaphragm ruptures, the engine more or less quits running. Then you fix it and change the oil. Yeah, I suppose a grandma might drive hundreds of miles with a small leak, and never notice it. I'll give you that.
Fourth; IMO the electric has a the worse fatal flaw, cuz if a situation develops, that pump can push all the gas from your tank,into your engine, at the rate of perhaps over 100 gallons per hour; say 1.8 gallons in a minute, or about 1 ounce per second.(Ok maybe not that fast on a QJ,lol) And the gas may not,will not, end up just in the oilpan, like a mechanical pump failure.Most of it will end up flooding the cylinders, the pipes, and the mufflers. Perhaps you bend a rod on the next restart;you know those SBM chambers at TDC, only hold about 75 to 85cc or so,or about 5 cubic inches.
And I have heard of several instances where this has happened, since 1969.

It is also my opinion that in either case, it can be dangerous,catastrophic,or even deadly.
No E-pump for this cowboy.
 
You have to buy 4 or 5 mech pumps before you find one that works. Then if it lasts over a year, you got lucky. Even the Carter replacement pumps are garbage now. On my 3rd one this year, one of them was junk right out of the box. In the process of saying screw it and buying a "good" electric pump, if there is such a thing and a decent regulator. Just my preference
 
I have had good luck with carders muscle car series pumps, stock psi, they are reasonable.
Parts store pump, might as well grab a fishing pole.
 
Like so many other things these days. I have had the same experience with two "new" master cylinders that failed within 6 weeks and two rebuilt alternators that didnt work right out of the box.....one of which didnt have insulating washers on one brush. Caused it to charge wide open. 17 volts..... good thing I caught it.
 
I dunno A/J...I suppose it comes down to what's more reliable with ethanol blend fuel, the fuel pump diaphragm that sits in hot fuel all the time or the carbs float, valve, and seat? Ethanol makes it more complicated today than the good ol' days.
 
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