Fuel pump function...or lack thereof

1945 - 196*, Willys CJ series, questions, discussions, regarding anything related to the post war jeep.®
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tcrozier
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Fuel pump function...or lack thereof

Post by tcrozier » Tue Jul 10, 2018 7:08 pm

Been having some issues with rough idle or running as of late but it came on really quick. One of the things I did was add a clear fuel filter between the fuel pump and carb so I could see the actual fuel flow. Well, there isn't much, like won't even fill the sight glass and occasionally is literally empty. I had assumed since my clear glass bowl top on the fuel pump was full then my line should be as well. As another suggestion I had tried to squirt a little carb cleaner around the carb base to see if it smoothed out, checking for leaks, but there was no change at all. I don't understand the mechanics of the fuel pump so my question is, even though the glass bowl is full and stays that way I could have an obstruction between it and the new filter/carb? I will add that during this recent discovery I have noticed what I believe to be new is that the gasket between the two metal halves of the lower part of the fuel pump are a little wet when I run my finger around it. Went and tightened the screws just a little, optimistically, but to no avail. This is a late CJ2A engine I'm working on

Thank you!
Thomas
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Re: Fuel pump function...or lack thereof

Post by Scoutpilot » Wed Jul 11, 2018 4:39 am

There appear to be a couple of issues here, but full information is lacking. You need to help us help you. Idle RPM? Clean, fresh gasoline? How about a vacuum reading? "Running rough" more often than not, means the ignition system has issues, such as loose connections, improper points, crossed and/or failing resistor-type plug wires. Wrong or poorly maintained or failing spark plugs. Aluminum contacts in the distributor cap. A cracked distributor cap. Are you using rubber fuel lines? If so, how old are they? Over time, cracks develop in the rubber. These cracks won't leak fuel, but they will suck in air. Okay. Your turn.
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Re: Fuel pump function...or lack thereof

Post by Wolfman » Wed Jul 11, 2018 7:42 am

Fuel pump has a diaphragm that has a rod attached to it that is connected to a lever that is activated by a lobe on the camshaft.
The diaphragm is sandwiched between the upper and lower pump body halves and a spring pushes up on the diaphragm.
When the cam lobe raises the lever it pulls down on the diaphragm. When the cam lobe lowers the lever, a spring pushes the diaphragm back up.
2 check valves. on top of the diaphragm. One inlet and one outlet. When the diaphragm moves down, the inlet check valve opens, allowing fuel to be pulled into the pump. When the spring pushes the diaphragm up, the inlet check valve closes and the fuel, in the pump is pushed out the outlet check valve to the carb.
That answers how it works.
Two things you are interested in. Is the pump volume sufficient to keep up with demand and what is the fuel pressure ?
Output volume can be checked by taking the fuel line off at the carb. and holding a container under the line while someone cranks the engine over. Is there good flow ?
Yes. on to the pressure test. No. could be the pump or a supply problem from the tank.
A gauge needs to be attached to the end of the line to check pressure. With gauge in place, crank the engine and read the max. pressure. On an old jeep, this would be 4 PSI give or take a little. The pump should hold the pressure for a bit but it will eventually drop down.
If the pressure comes up and then drops back rapidly, you have a problem with the outlet check valve.
If the pressure test checks out but no flow, you have a supply problem.
As for the leak. Yes it is. Since tightening the screws did not help, time for a rebuild or another pump.
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Re: Fuel pump function...or lack thereof

Post by Wolfman » Wed Jul 11, 2018 8:05 am

One more thought.
The clear fuel filters rarely fill with fuel.
They usually look like they are full of air.
The clear fuel pump bowls usually have an air bubble trapped at the top that won't go away either.
Mike Wolford
CJ-2A
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Comm./Inst. SEL
AOPA ( 44 yrs)
EAA ( 44 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

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Re: Fuel pump function...or lack thereof

Post by athawk11 » Wed Jul 11, 2018 8:05 am

I will add...

It is not common to see the glass bowl full of fuel on a functioning 2A style fuel pump. Generally, you just want to see enough fuel to cover the two circular check valves seen on the surface at the base of the glass bowl. If the bowl is full, I would suspect that something is blocking the fuel flow from the pump to the carburetor. Even if the lines are clear of debris, the float inlet needle might be stuck and not letting the fuel into the carburetor.


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Re: Fuel pump function...or lack thereof

Post by Ben Dover » Wed Jul 11, 2018 10:48 am

Do not remove the class bowl out of curiosity, the gasket does not usually survive intact. Lots of Jeep owners take a peek and do not see a thing after the bowl is off.
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Re: Fuel pump function...or lack thereof

Post by artificer » Wed Jul 11, 2018 11:13 am

Great description of fuel pump operation Mike.
Plus Scoutpilot 's listing of what to check for & taking on board 80-90% of thought to be fuel problems turn out to be ignition.
Ignition can be eliminated in minutes & should always be checked first.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Fuel pump function...or lack thereof

Post by tcrozier » Wed Jul 11, 2018 4:57 pm

Scoutpilot wrote:
Wed Jul 11, 2018 4:39 am
There appear to be a couple of issues here, but full information is lacking. You need to help us help you.

Idle RPM?
It runs rough from the get go, idle or trying to get it to increase the RPMs.

Clean, fresh gasoline?
For sure, I only burn the real unleaded stuff in it a few gallons at a time, no ethanol gas but I haven't added any stabilizer either.

How about a vacuum reading?
I do not have a vacuum system on this one, ports are all plugged and the carb is, as I understand it, a non-vacuum ported fuel pump.

"Running rough" more often than not, means the ignition system has issues, such as loose connections, improper points, crossed and/or failing resistor-type plug wires. Wrong or poorly maintained or failing spark plugs. Aluminum contacts in the distributor cap. A cracked distributor cap.
In the last 50 miles or so I have replaced the points and condenser and the spark plugs with Autolite 295's. I checked and yes the pickups in the cap are aluminum. Is that a bad thing? The rotor and cap are also new during this time. The plugs are labeled 7mm Hi-Temp Radio Suppression and when I checked them last week resistance was between 8k and 11k ohms. I have replaced a couple of the spaded terminals around the engine compartment but not yet done the wire from either the voltage regulator to the coil (which is also new) or the other side from coil to distributor, which I am guessing is a ground wire maybe? I don't remember the values now but the resistance on the coil was also within specs.

Are you using rubber fuel lines? If so, how old are they? Over time, cracks develop in the rubber. These cracks won't leak fuel, but they will suck in air.
I am but they are literally brand-new this week as is the in-line filter.

Okay. Your turn.

Thank you!!
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Re: Fuel pump function...or lack thereof

Post by tcrozier » Wed Jul 11, 2018 5:05 pm

Wolfman wrote:
Wed Jul 11, 2018 7:42 am
Fuel pump has a diaphragm that has a rod attached to it that is connected to a lever that is activated by a lobe on the camshaft.
The diaphragm is sandwiched between the upper and lower pump body halves and a spring pushes up on the diaphragm.
When the cam lobe raises the lever it pulls down on the diaphragm. When the cam lobe lowers the lever, a spring pushes the diaphragm back up.
2 check valves. on top of the diaphragm. One inlet and one outlet. When the diaphragm moves down, the inlet check valve opens, allowing fuel to be pulled into the pump. When the spring pushes the diaphragm up, the inlet check valve closes and the fuel, in the pump is pushed out the outlet check valve to the carb.
That answers how it works.
Two things you are interested in. Is the pump volume sufficient to keep up with demand and what is the fuel pressure ?
Output volume can be checked by taking the fuel line off at the carb. and holding a container under the line while someone cranks the engine over. Is there good flow ?
Yes. on to the pressure test. No. could be the pump or a supply problem from the tank.
A gauge needs to be attached to the end of the line to check pressure. With gauge in place, crank the engine and read the max. pressure. On an old jeep, this would be 4 PSI give or take a little. The pump should hold the pressure for a bit but it will eventually drop down.
If the pressure comes up and then drops back rapidly, you have a problem with the outlet check valve.
If the pressure test checks out but no flow, you have a supply problem.
As for the leak. Yes it is. Since tightening the screws did not help, time for a rebuild or another pump.
Thank you for all the above!! The operational functionality description was great! I had planned on getting, somewhat out of curiosity, a cylinder pressure gauge as I was told the engine was recently re-built and wanted to check the compression. I do not have a pressure gauge to test fuel pump pressure but maybe I can get one from the parts store when I 'rent/borrow' the other gauge.
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Re: Fuel pump function...or lack thereof

Post by tcrozier » Wed Jul 11, 2018 5:07 pm

Wolfman wrote:
Wed Jul 11, 2018 8:05 am
One more thought.
The clear fuel filters rarely fill with fuel.
They usually look like they are full of air.
The clear fuel pump bowls usually have an air bubble trapped at the top that won't go away either.
Roger that, I used my vacuum pump to charge the line and filter from the carb end and while it quickly filled up that way, I reconnected and started it but it quickly depleted the filter contents.
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Re: Fuel pump function...or lack thereof

Post by tcrozier » Wed Jul 11, 2018 5:09 pm

athawk11 wrote:
Wed Jul 11, 2018 8:05 am
I will add...

It is not common to see the glass bowl full of fuel on a functioning 2A style fuel pump. Generally, you just want to see enough fuel to cover the two circular check valves seen on the surface at the base of the glass bowl. If the bowl is full, I would suspect that something is blocking the fuel flow from the pump to the carburetor. Even if the lines are clear of debris, the float inlet needle might be stuck and not letting the fuel into the carburetor.
I wondered about the float as I had recently rebuilt the carb with an original Carter WO kit I did try meticulously set both the float level and metering rod, the latter of which I re-checked this past weekend.
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Re: Fuel pump function...or lack thereof

Post by tcrozier » Wed Jul 11, 2018 5:17 pm

artificer wrote:
Wed Jul 11, 2018 11:13 am
Great description of fuel pump operation Mike.
Plus Scoutpilot 's listing of what to check for & taking on board 80-90% of thought to be fuel problems turn out to be ignition.
Ignition can be eliminated in minutes & should always be checked first.
I tried everything I could think of, re-gapped the points, checked the plug wire resistance, checked coil resistance, looks for 'leaks' in my plug wires, replaced the spark plugs, I even tried pulling one wire at a time to see if the miss got worse while it was running. I haven't looked yet to see how, or if it's possible, to check my condenser. I'll be interested to see what the shortcomings are as I replied to someone above that my rotor cap had aluminum pickups in it. I had never heard that before but darn if I don't learn something new everyday, hope it never stops, means I'm still alive and kicking!!

Many thanks for the reply, you guys know some stuff!!
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Re: Fuel pump function...or lack thereof

Post by athawk11 » Wed Jul 11, 2018 7:59 pm

Well, it sounds like you're getting all the bases covered. One thing I learned the hard way is that it is important to polish the tongue/tang on the float...that contacts the fuel inlet needle. Any scratches, burrs, etc can cause the needle to get stuck. It's prone to scratches if one is a little aggressive whe setting the float level. Although, it's more common for it to get stuck in a way that causes the bowl to overflow.

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Re: Fuel pump function...or lack thereof

Post by artificer » Wed Jul 11, 2018 8:03 pm

Go to HF & spend $14 on a fuel pump vacuum pressure gauge....https://www.harborfreight.com/fuel-pump ... 62637.html
This inexpensive tool can be used for check fuel pumps, engine condition, tune & timing. Indispensable on these old vehicles in diagnostics & eliminating good stuff to find the bad.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Fuel pump function...or lack thereof

Post by Scoutpilot » Thu Jul 12, 2018 3:16 am

To add to Artificer's suggestion, locate and purchase a good Dwell/Tachometer.
Aluminum distributor contacts do not pass the amperage required for a decent, bright blue-white spark. Brass does. "Resistor"-type plug wires have a carbon core which will not pass the amperage required for a decent, bright blue-white spark. Copper core wire does. You don't want resistor wires unless you are an avid AM Radio listener. A spark plug emitting a less-than decent, bright blue-white spark is more susceptible to fouling which further degrades performance. If your timing is set dead nuts on 5º BTDC you may need to advance it to accommodate the modern fuel. 5º is perfect for 67 Octane fuel. You're likely running 87 Octane. In which case 5º is too late for a complete burn. The higher the octane rating, the slower the burn rate. Slightly retarded timing will lead to carbon fouling in the cylinder due to incomplete burning. If you wish, I can send you a link to a video that shows exactly how to perform an often overlooked final stage of a complete tuneup.
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5

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