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The fuel pump is running but...

The fuel pump is running but...

Boxcarburt

Jeeper
Posts
19
Thanks
0
Location
DFW, Texas
Vehicle(s)
1979 CJ, 304 V8, 3 Speed Transmission. Stock
Hello everyone. This is my first actual post.

I am asking about a 1979 CJ7 AMC 304 .

Several times now, the jeep has started to run very rough after several minutes of driving. Occasionally she will die. When she dies, sometimes she will start right back up and sometimes she will pout for several days.

The first time this happened was 2 hours after buying her. I assumed she was out of gas so I put 5 gallons in from a new 5 gallon red tank. Started right up! I drove to the gas station that's 1/2 mile away to fill her all the way up, and put in $2...

I'm a harley guy. I traded my motorcycle for this because it's much more family friendly. So... I have the inner dialog with myself: "Does it only hold 6 gallons? I guess it could... maybe people mod Jeeps to have small tanks because it mean's less weight so it climbs better..." Then I think: "This AMC 304 should really be able to torque it's way up a wall with a few sumo's sitting in it! The tank weight shouldn't play a part!"

I drive her to work the next day to show her off, with no problems. At lunch, she acts like I am out of gas again. The previous owner put an electronic fuel pump towards the back. This guy to be exact: https://www.amazon.com/Mr-Gasket-12...5289-239-3---143-3-0&sr=1-2&ymm=1979:jeep:cj7

As you can see, 50% of folks say it's a hunk of junk. But mine is running... Now, sometimes if I pull the fuel hose off from the filter up in the engine compartment, gas flows out no problem. Other times, no dice. Dry as a bone.

So, after all of that, here is where I am at and my questions that I have. I will be replacing all the fuel lines, filter, and all vacuum lines. My CJ7 is missing the charcoal canister, the thingy that kills the jeep if you flip over (cant think of the name) and anything else that normally sits between the tank and the carb. (Besides pump and fuel filter.) The tank has some dirt at the bottom, the fuel sending unit has some white corrosion stuff on it, so they are being replaced as well.

Fuel pumps... I'm going to replace it. Do you guys recommend the stock mechanical, an electric, or a combination of both? If you recommend electric, how do you incorporate a kill switch?

All the missing fuel system pieces... which ones are important to replace? I can't find charcoal canisters anywhere.

While I am replacing everything listed above (also a new air cleaner & spark plugs) what else would you recommend while I am doing all this work?

I know this is ridiculously long, but I wanted to make sure I gave y'all as much info as possible!

Thanks in advance for you time and attention.

-Boxcarburt; DFW, Texas
 
If the AMC 304 is stock, I would use an OEM fuel pump, I am
running mine with such without any issues.
If you replace the fuel lines & filter and the vacuum hoses, I would
rebuild the carb and replace the EGR and crankcase ventilation valve.
I found that after replacing all lines and filters that the carb needs rebuild.
If you rebuild the carb, note, that all(!) rebuild sets do not contain the
choke pull off valve...
CARQUEST Carburetor Parts Choke Pull-Off 779-070: Advance Auto Parts
 
Welcome :chug: Replacing all the fuel lines isnt a bad idea, especially if old and cracked. I had a similar issue with my 8 years ago, ended up being a pinhole in a section of the hard steel line before the electric fuel pump. Electric pumps like to push fuel but not too fond of sucking it, it doesn't take much to air lock it. The roll over valves are obsolete but when I replaced mine I took it down to Napa and we found a close enough match from a Nissan (sorry, I dont remember which model)
 
I too have an electric fuel pump, not that one, but one nonetheless. I don't have the original rollover check valve, or charcoal canister plumbed in either. Yours is a 4-7psi pump, which should be fine without a fuel pressure regulator - although the 7psi end is really pushing against the needle valve which can cause a flood condition. Are you using the original one-in-two-out fuel filter? Where are you checking for fuel when you say it's fine sometimes then dry others? Dry is obviously not good, but we need to find some correlating issues to it being dry.
 
AMC 304 does just fine with an OEM mechanical pump. Have you changed the fuel filter?
LG
 
There are a few things that can make your CJ run as it does. not having a vented fuel tank is a possibility. When you drive for a while and it starts to run bad you should try and remove the gas cap. If you hear air rush in that would indicate poor fuel tank venting and since you have no charcoal canister, the vent line could be plugged off. A standard cp3045 will work for a replacement canister or a cross reference from that number. Here is a link to help you set it up:My Tech How-To for the Carbon Vapor Canister - International Full Size Jeep Association
Looking a repair manual or better yet the factory service manual will help also. Installing a roll over valve will prevent fuel from entering the canister from the vent hose.
 
If the AMC 304 is stock, I would use an OEM fuel pump, I am
running mine with such without any issues.
If you replace the fuel lines & filter and the vacuum hoses, I would
rebuild the carb and replace the EGR and crankcase ventilation valve.
I found that after replacing all lines and filters that the carb needs rebuild.
If you rebuild the carb, note, that all(!) rebuild sets do not contain the
choke pull off valve...
CARQUEST Carburetor Parts Choke Pull-Off 779-070: Advance Auto Parts

I appreciate the info. Naturally, you tell me that All rebuild kits need the extra pull off valve, and the first thing I'm going to do is question that :D! Mine has an Eddlebrock with an automatic choke. It looks fairly new, but I have no problem rebuilding it as the whole idea behind this repair is to know that then entire fuel system has been corrected. That being said, will I need the choke pull off for an automatic choke carb?

I will add the EGR and the CVV to my list!
 
Welcome :chug: Replacing all the fuel lines isnt a bad idea, especially if old and cracked. I had a similar issue with my 8 years ago, ended up being a pinhole in a section of the hard steel line before the electric fuel pump. Electric pumps like to push fuel but not too fond of sucking it, it doesn't take much to air lock it. The roll over valves are obsolete but when I replaced mine I took it down to Napa and we found a close enough match from a Nissan (sorry, I dont remember which model)

Awesome! Good to know I can find something that will work. I appreciate the info!:chug:
 
I appreciate the info. Naturally, you tell me that All rebuild kits need the extra pull off valve, and the first thing I'm going to do is question that :D! Mine has an Eddlebrock with an automatic choke. It looks fairly new, but I have no problem rebuilding it as the whole idea behind this repair is to know that then entire fuel system has been corrected. That being said, will I need the choke pull off for an automatic choke carb?

I will add the EGR and the CVV to my list!

Your questioning is correct, I only can talk about the original Motorcraft carbs... :D
I do not know about Edelbrock carbs, but it was not specified here.
My experience was that the carb was far off with the new fuel equipment,
so due to ist 38 year age, I decided to rebuild instead of readjust...

Concerning the EGR, if you are not under time pressure, take your time to
look, because I bought two new ones as spares some months ago at 20$ each at Rockauto at a gross seller close out...
 
I too have an electric fuel pump, not that one, but one nonetheless. I don't have the original rollover check valve, or charcoal canister plumbed in either. Yours is a 4-7psi pump, which should be fine without a fuel pressure regulator - although the 7psi end is really pushing against the needle valve which can cause a flood condition. Are you using the original one-in-two-out fuel filter? Where are you checking for fuel when you say it's fine sometimes then dry others? Dry is obviously not good, but we need to find some correlating issues to it being dry.

Thanks for the info! She does have the original one in two out fuel filter, which will be replaced with a new one (Same type).

I originally checked the fuel at the carb, no fuel. Then I checked the fuel before the fuel filter, no fuel. (My fuel system is Tank to Pump to Filter to Carb.) Then I check the line after the pump, nothing. Wait 30 minutes. (Any 30 minutes will do, regardless if the Jeep was run before or not). Check the fuel after the pump, there's fuel! Check it after the filter, there's fuel! Check it at the carb, there's fuel! Drive for a few minutes to a few days without issue!

I will say, when I dropped the fuel tank, there were two hoses on the right-hand side of the jeep... one for the filler hose and one for the vent hose. The vent hose was crimped in two places. Would this crimp be enough to lock up the system?:confused:
 
There are a few things that can make your CJ run as it does. not having a vented fuel tank is a possibility. When you drive for a while and it starts to run bad you should try and remove the gas cap. If you hear air rush in that would indicate poor fuel tank venting and since you have no charcoal canister, the vent line could be plugged off. A standard cp3045 will work for a replacement canister or a cross reference from that number. Here is a link to help you set it up:My Tech How-To for the Carbon Vapor Canister - International Full Size Jeep Association
Looking a repair manual or better yet the factory service manual will help also. Installing a roll over valve will prevent fuel from entering the canister from the vent hose.

Actucally, the vent line on the right hand side of the fuel tank was crimped in two places. I do have a technical manual and a Chilton's (the Chilton's kinda stinks... in several places it's all "You set-up may be different" which really does no-one any good.

I'm going to look up the canister you mentioned!
:notworthy:
 
Your questioning is correct, I only can talk about the original Motorcraft carbs... :D
I do not know about Edelbrock carbs, but it was not specified here.
My experience was that the carb was far off with the new fuel equipment,
so due to ist 38 year age, I decided to rebuild instead of readjust...

Concerning the EGR, if you are not under time pressure, take your time to
look, because I bought two new ones as spares some months ago at 20$ each at Rockauto at a gross seller close out...

I am/ am not under time pressure. I want to get her going again as soon as possible so we can enjoy her, but I can also wait a few weeks if it would save me $$$!

Thanks much for your input!
 

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