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Unread 07-23-2014, 07:21 PM   #1
zsquared1
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1977 CJ7 
 
Join Date: Jul 2014
Location: Wichita Falls, Texas
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New jeep and new to wrenching HELP

So this is kind of an intro and a question rolled into rolled into one post so bear with me here. My background is that I grew up in a jeep family and helped my dad convert a junk cj2a into an MB when i was a kid so I know a bit about jeeps. Im pretty mechanically inclined and I'm learning how to be a crew chief in the Air Force. So I just got out of Basic and of course, I had to buy a jeep, a used 1977 cj7 in pretty good shape. It runs great and I'm in love with it. here is my question. The jeep runs great and starts fine but randomly the fuel pump stops pulling fuel from the tank. It has two fuel pumps for whatever reason the mechanical one and an electronic one. I disconnected the fuel line into to electronic pump and it has suction but no fuel is being pulled into it. Any insight, advice is welcome as is any other random facts about wrenching on jeeps ext.
Thanks in advance

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Unread 07-23-2014, 07:55 PM   #2
RenoF250
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1985 CJ7 
 
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Location: Foresthill, CA
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Sounds like you may have some junk floating around in the tank that is occasionally blocking the pickup.
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Unread 07-23-2014, 08:05 PM   #3
zsquared1
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Location: Wichita Falls, Texas
Posts: 4
How would I go about getting the junk out of the tank...drop the tank and then...?
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Unread 07-23-2014, 11:03 PM   #4
BagusJeep
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1981 CJ7 
 
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Location: Bali, Indonesia
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A common issue on the CJ is leaking or cracked fuel hose above teh tank. They suck in air and the first time you may notice this is going uphill.

If the bolts are not rusted solid it takes about 20 minutes to drop the tank. It is strapped down to the tank skid plate and the whole asembly offerred up to the underside and bolted front and back.

Whislt you have it out is a good time to rinse it out with clean petrol, paint the tank and skid plate and replace all rubber hoses. If your fuel gauge does not work it is a good time to investgate the sender unit but in any event it is easy to remove to check the sock filter on the end is clean (make sure you keep the O ring).

Any larger debris should come out of the sender hole, it is about 2 1/2" in diameter.
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Unread 07-24-2014, 03:38 PM   #5
zsquared1
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Location: Wichita Falls, Texas
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Thanks for the info. I will have to check that out. I am giving my self a crash course in electrical this weekend as my windshield wipers, temp gauge, and gas gauge are not working and there are so many electrical issues with my jeep. I'll be sure to report back next week
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Unread Yesterday, 09:21 PM   #6
zsquared1
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Well I found out what was causing the fuel issue. The supply line coming out of the tank is dry rotted and sucking air in to the pump. The next step is to fix the gas and engine temp gauge. It looks like the engine temp sensor isn't hooked up to the engine, would that cause the fuel gauge to not work either? thanks for the patience and the help I'm having a blast working on this thing!
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Unread Yesterday, 11:22 PM   #7
Marshal
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Fuel guage could be a bad sending unit (in tank), float that isn't floating (also in tank), bad ground, or bad wire(s) between sending unit and fuel gauge, and of course bad fuel gauge. The temp sensor shouldn't have anything to do with the fuel gauge.

Typically there's a 2 or 3 wire setup. One sends a power signal to the sending unit. This should be either 5 or 12 volts, but someone here may know the specific number you want. The float is attached to a resistor that modifies this signal and sends it back to the fuel gauge on a second wire. If there's a third wire, it will be a ground. I would do a continuity test on all wires to the unit to verify they are unbroken, check voltage in, then verify ground (if applicable.)

You can test the float by putting it in liquid (I recommend gas in a clear container to avoid cross contamination issues) and seeing if it floats. If t doesn't you may be able to replace the float, but if I already had it out and any part of the unit was suspect, I would replace the whole assembly. You can test the resistor by attaching an ohm meter between the input wire and output wire and actuating the float arm manually. You should see the resistance rise and fall smoothly. If it's open at any point you have a dead spot and the unit is bad - you may be able to get just the resistor, but see recommendation above.

If you suspect you have a grounding issue you'll probably find it was a body ground. DO NOT just clean this area up and reattach it to the body. It will rust out again, and you'll be pulling the tank again to re diagnose it and fix the same problem. Run a dedicated ground from the battery to the unit. In fact, if you're going to have the tank down, do this anyway just to prevent it going wrong in the future. Oh, don't thank me for the dedicated ground advice, thank JeepHammer and the OP of this thread:

http://www.jeepforum.com/forum/f8/be...hammer-833631/

Until I read that, my dumb @$$ would have just cleaned up the ground and reattached it. Now I know better.

Now, if you've checked all of that, run your dedicated ground if applicable, and done the same for your fuel gauge because Jeep loved their body grounds, and your fuel gauge still isn't working it's the gauge itself or you're just out of gas. Don't laugh, I've seen customers do it. It's usually the most expensive 2 gallons of gas they'll ever buy, because it comes with a dealership markup and at least a half hour diagnostic fee. But they learn to read their fuel gauge real quick.
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Unread Today, 04:38 AM   #8
Mike Romain
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Quote:
Originally Posted by zsquared1 View Post
Well I found out what was causing the fuel issue. The supply line coming out of the tank is dry rotted and sucking air in to the pump. The next step is to fix the gas and engine temp gauge. It looks like the engine temp sensor isn't hooked up to the engine, would that cause the fuel gauge to not work either? thanks for the patience and the help I'm having a blast working on this thing!
Look up posts by John Strenk for links to testing the gauges. Just a heads up, if you have the dash off and turn on the power, you will fry those gauges. The dash needs a good ground to test things. I use a battery booster cable from the dash to the battery neg for this.
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