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ksjeeper 03-02-2013 06:06 PM

Cj not running good
Ok so my jeep is not running good at all. It will idle just fine and will run alright until it gets to about 25mph. When it hits that it starts backfiring and cutting out. When I slow down to 20 it runs fine again. I have no idea what is wrong with it. Any ideas??

NHflannelman12JK76CJ5 03-03-2013 04:33 AM

others will know much better than I - but have you checked the distributor cap? I think that's the first place I'd look. Make sure the firing order is the way it should be.

bc3_Jeep 03-03-2013 06:30 AM

Does it also start this issue when it is sitting still but you crack the throttle open????

Sounds like it is starving for fuel to me.

Might also check to make sure yor vacuumn advance is working properly.

As always, check to make sure all of your ignition parts (plugs, wires, D cap, rotor) are in good working order with no carbon tracking. I am still leaning towards a fuel issue.

ksjeeper 03-03-2013 08:42 AM

No it doesn't do it at all when it's sitting. I can open the throttle up and it won't do it. Just when I'm driving down the road. I was thinking maybe a fuel pump?

bc3_Jeep 03-03-2013 09:17 AM

How long are you holding the throttle open???? If it is a fuel pump issue, it should probably show up moving or NOT moving....

Hold it open for a bit (as long as it takes you to get to 25MPH)....... running a safe RPM..... and see if it sputters......

Also..... check the fuel filter.......easy and cheap.....

luv2bmx22 03-03-2013 09:26 AM

If it runs fine while reving it up a little and holding it there while stopped, it shouldn't be the fuel pump, because the motor is pumping the same amount of fuel in as if you were driving. Try using different gears if its a manual and see if it still does that.

ksjeeper 03-03-2013 09:31 AM

Ya I hold it open for a little while and it never sputters or backfires. I will replace the fuel filter and see if that works. Thanks for the advice. I will let ya know what I find out

4Jeepn 03-03-2013 01:01 PM

My did that.. vacuume line issues as i recall.. amazing what one messed of line will do to that system. My would idle fine but at speed would want to cut out and die.

ksjeeper 03-03-2013 06:25 PM

Well I found the problem. Checked the filter and that didn't stop it ended up replacing the fuel pump and she runs like a top again.

cwyatt6 03-04-2013 08:33 AM


bc3_Jeep 03-04-2013 08:50 AM


Originally Posted by ksjeeper (Post 3449905)
Well I found the problem. Checked the filter and that didn't stop it ended up replacing the fuel pump and she runs like a top again.

Thank you for the feedback..... always good to get the answer at the bottom of a problem.

ksjeeper 03-04-2013 10:33 AM

Ya I was pretty happy about it. I think the pump has been going to awhile now cause its running better than it has for a long time.

NHflannelman12JK76CJ5 03-18-2013 11:41 AM


Originally Posted by ksjeeper (Post 3453373)
Ya I was pretty happy about it. I think the pump has been going to awhile now cause its running better than it has for a long time.

I may have run into the same issue with my 76 this past weekend. Previous owner said she's been sitting 5/6 months. It's the 304 with Mototcraft carb.

I got in and tried to start her up, she was free but not turning over. Cracked the hood (spark plugs were OKAY, but need to be replaced), new battery, air filter was fine/clean.

Sprayed some started fluid down the carb, got her to fire up briefly. Looked at the carb - a bit milky looking where the intake line is (my guess is there's some water in there and the carb needs a rebuild). However, when inspecting the line, it was dry - followed it back to the fuel filter and there wasn't much of anything in there.

Now, this is where I need help (more than usual) I followed it back to the fuel pump - cam mounted? but I can't find the fuel line that feeds the pump.

So I tried to follow it back from the tank - looks like it rides the frame-rail for awhile but then I lose it under the drivers side door (near the break-lines I believe). After that I proceeded to, literally, bash my head off an old plow mount and then hit the back of my head off the concrete. I know - you're jealous of my klutz-induced concussion.

I'm not 100% dumb but could use a diagram (do have the Haynes, but not finding much help there). Does anyone have one? Or could anyone guide me through it?

I know I can replace the fuel pump (not that expensive of a pump) but I'm worried that the fuel line is clogged somewhere so I'd like to clear the lines out.



Goofyjumper 03-18-2013 01:19 PM

A good trick I use to blow out fuel lines to use my air compressor (regulated to low pressure like 25 psi) and connect to the fuel line going from the pump to the tank. The pump (located on the timing chain cover) will have a line going up to the carb and another to the tank. Disconnect the line headed to the tank and attached the air compressor line to this. Warning: Do this outside and ground the airline to the vehicle to prevent sparks. Also open the fuel filler lid to allow pressure to be relieved from the tank.

If this doesn't work then your fuel pump may be gummed up by old fuel. Easy fix for this is to remove the fuel pump from the engine (two bolts) and spray carb cleaner in it. Then manually work the pump to loosen it up.

When you put the fuel system back together it will need to be primed to function correctly.

Good luck!

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