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74 CJ5 fuel pump mystery

740 Views 17 Replies 6 Participants Last post by  Themightybluegill
I have a 72 CJ5 with a 74 AMC 232 in it. Ford motorcraft 2100 carburetor. Mechanical fuel pump.

Mechanical fuel pump developed a leak that seems to be coming from the seam between the top and bottom of the pump.

Picked up a new one at AutoZone and installed it. Jeep fired right up, but suddenly I had a lot of fuel overflowing out of the top of the carburetor. This has never happened.

Shut the Jeep off. Waited 5 minutes. Started back up and revved it up to use up that extra gas. Rubbing pretty good for a couple minutes...

No more gas pouring out the top. But now the new fuel pump has developed the same leak as the old one. !?

Less than 5 minutes later, the new fuel pump is no longer pumping.

I put the old fuel pump back on and it is not pumping either. (I took the output line off of the pump and cranked the engine expecting gas to come out of the top of the fuel pump.)

Then, like an idiot, I put my mouth on the fuel line to see if there might be a leak in the line and there was gas right there and I got a mouthful. It came very easily. I want to say that if my pump had even the smallest amount of suction it would have easily gotten some of that gas.

When I installed the fuel pumps I started off leaning back, so that the flat part of the lobe was resting against the cam. I put grease on it. I slowly tightened it up going back and forth on the sides so that it would Mount up evenly.

I wonder if this is enough information for any of you to give me a confident diagnosis of what I have going on here.

I am perplexed.

Thanks in advance,

Matt
Chattanooga, TN
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Seems quite a few folks are having fuel pump issues lately.

Your original pump may be "tired" and finally failed--they all do eventually.

Where did you get your new pump from?

There might be some kind of diaphragm issue from cheaper or foreign made pumps.

In other recent threads, other folks have gone to a different store to try a different brand.

I'm pretty sure a lot of them have had good luck with NAPA auto parts fuel pumps.

Standby, you'll get the scoop soon from another!

I've had mine a long time and bought a spare that I keep in my Jeep.(Both were purchased at

Advance Auto Parts with a lifetime warranty). This being before the recent problems happened.

Even though mine are the "inexpensive" types, they have lasted for years.

Maybe the issue will finally get fixed and even the cheaper pumps will work right.

Try a different store at minimum.

As far as the volcano carburetor, your issue sounds like the float was stuck down, not letting the

needle and seat to close when the fuel in the bowl was at it's proper height.

Really high fuel pressure can also "over power" the float, I can't see a mechanical pump doing this,

I could be wrong!

-----JEEPFELLER
 

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Discussion Starter · #3 ·
Thanks so much! I got the pump in AutoZone and the brand was deli something as in New Delhi India. I just bought the pump a few days ago and so I'd imagine AutoZone would let me take it back. Unless I hear otherwise I'll definitely try another brand. Thanks so much for that!
 

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I'm in the middle of a frame up rebuild on a friends 73. I (we) have found just about every replacement part, gasket, and seal to be crap out of the box. Sloppy timing chains, stuck oil pump gears, intake seals, the list goes on and on.

The point of my rant is replacement parts, even "name brand" ones seem to be reboxed chinese junk, so for you to install multiple malfunctioning fuel pumps seems to be more the norm than the exception......
 

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Discussion Starter · #6 ·
Take a vacuum gauge to the parts store and bench test the pump before you leave. It should hold vacuum.

It won't guarantee that the pump will last, but at least you'll know it will work for a bit out of the box.

The alternative is a low pressure electric pump.

Matt
Great idea. Can I put vacuum on either side of it and it will hold?

Thanks Matt!
 

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Attach the vacuum gauge/pump to the inlet side of the fuel pump. If it doesn't hold vacuum, give it back to the clerk and ask to try another one.

Here's the vacuum gauge/pump that I use.


Matt
 

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Discussion Starter · #8 ·
Attach the vacuum gauge/pump to the inlet side of the fuel pump. If it doesn't hold vacuum, give it back to the clerk and ask to try another one.

Here's the vacuum gauge/pump that I use.


Matt
So I put a vacuum gauge on the old pump which is currently in a box and the new pump which is currently mounted to the block. The old pump does not hold back in but the new pump does.

It's worth noting that the old fuel pump worked before, but it was leaking.

The new fuel pump worked at first, but worked so well that gas was flowing out of the top of the carburetor.

After turning off the car and restarting, it no longer flooded the carburetor but it was leaking in the same way the old one was.

On the 3rd startup it wasn't even pumping gas.

Is there any chance I've been installing this incorrectly and I am the problem? I feel like I'm doing it the right way where it goes in leaning back with the flat end of the arm resting on the cam and the engine and then I slowly tighten each side so that it lines up well.

Stumped...
 

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The 1st time I put one on, I was worried that I might have stabbed

it into the hole wrong.

To make the arm "EZer" in the "down position" as I inserted

the arm into the hole.

And have less "stress" while tightening the bolts.

I used a hand mirror that I bought from a dollar store (originally used when giving fresh

Ranger haircuts in the barracks for every Monday morning formations)

I had my buddy bump the engine until I could see the Cam's Fuel Pump Lobe was "heavy" on the bottom side,

Then I installed the fuel pump.

That was a long time ago, I've since got the "feel" for doing it blindfolded!

------JEEPFELLER
 

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Discussion Starter · #10 ·
I was reading today that some Jeeps have a fuel filter with a secondary outlet in order to let extra fuel recirculate back to the tank. Mine does not have that. Is there any chance that it should and that maybe the reason that the last two fuel pumps have been leaking is that there's too much pressure building up? Perhaps this would also explain why my carburetor was overflowing with the new fuel pump?

I picked up another fuel pump at Napa today. I will let you all know how it goes when I install it.
 

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Yours should not have a return to the tank, your filter is not like 1976 on up.

This will get you real familiar with how things should be.


This will be the best "written work" you will ever find for your Jeep.

----JEEPFELLER
 

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I have a 72 CJ5 with a 74 AMC 232 in it. Ford motorcraft 2100 carburetor. Mechanical fuel pump.

Mechanical fuel pump developed a leak that seems to be coming from the seam between the top and bottom of the pump.

Picked up a new one at AutoZone and installed it. Jeep fired right up, but suddenly I had a lot of fuel overflowing out of the top of the carburetor. This has never happened.

Shut the Jeep off. Waited 5 minutes. Started back up and revved it up to use up that extra gas. Rubbing pretty good for a couple minutes...

No more gas pouring out the top. But now the new fuel pump has developed the same leak as the old one. !?

Less than 5 minutes later, the new fuel pump is no longer pumping.

I put the old fuel pump back on and it is not pumping either. (I took the output line off of the pump and cranked the engine expecting gas to come out of the top of the fuel pump.)

Then, like an idiot, I put my mouth on the fuel line to see if there might be a leak in the line and there was gas right there and I got a mouthful. It came very easily. I want to say that if my pump had even the smallest amount of suction it would have easily gotten some of that gas.

When I installed the fuel pumps I started off leaning back, so that the flat part of the lobe was resting against the cam. I put grease on it. I slowly tightened it up going back and forth on the sides so that it would Mount up evenly.

I wonder if this is enough information for any of you to give me a confident diagnosis of what I have going on here.

I am perplexed.

Thanks in advance,

Matt
Chattanooga, TN
Do you have a auxiliary gas tank under your drivers seat? If not maybe you need a return line to the gas tank. The pump may be building up so much pressure that it is rupturing the pump. I had to put a fuel pressure regulator on my carb to lower the pressure there to prevent it from overflowing.
 

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I was reading today that some Jeeps have a fuel filter with a secondary outlet in order to let extra fuel recirculate back to the tank.
Buick V6 application. Later Jeeps used a fuel filter with a return line.
The pump may be building up so much pressure that it is rupturing the pump.
Fuel pumps are designed to stop pumping in the 5 to 7PSI range. All pumps do this. A pump would have to be defective in order for it to rupture due to pressure.
 

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Buick V6 application. Later Jeeps used a fuel filter with a return line.

Fuel pumps are designed to stop pumping in the 5 to 7PSI range. All pumps do this. A pump would have to be defective in order for it to rupture due to pressure.
Since his fuel pump quit we will never know. The way they make aftermarket parts today it wouldn't surprise me if his pump wasn't putting out so much pressure that it burst the diaphragm. He might also check to see if he has gotten any gas in his oil.
 
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