89 YJ 4.2 fuel Pump - JeepForum.com
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Unread 11-20-2013, 05:31 PM   #1
89-jeep
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89 YJ 4.2 fuel Pump

Help. Jeep ran great, I did the head light mod and waited for dark to try them out. Got the dogs loaded up and jeep wouldn't start but turned over. I gave a shot of starter fluid and it ran for a few seconds. That eliminated an electrical issue, I have spark. The fuel pump is a mechanical off the cam. I disconnected fuel line from the carb and cranked and no fuel flow. I eliminated filter and pressure regulator and no fuel out of pump. I replaced fuel pump and still no fuel coming out. I connected a suction pump to line from the gas tank and got fuel. I thought bad fuel pump, got another from autozone and still no fuel. I also blew compressed air down fuel line to tank and did not appear to be blocked. Any suggestions? Just an FYI, I did the nutter by-pass years ago and have a Weber carb on it.

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Unread 11-20-2013, 06:23 PM   #2
Hotrodyj
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Pressurize the tank to prime the pump and hook everything back up and try it again. You can also keep it running by pouring gas in the carb with everything hooked up to help prime the pump
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Unread 11-21-2013, 05:53 AM   #3
89-jeep
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That makes sense, I'll try that. I replaced the pump about 3 years ago and it pumped fuel no problem without priming it? I know what you mean when you say pressurize the tank, but what would be the best way to do that?
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Unread 11-21-2013, 06:15 AM   #4
vadslram
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You never have to prime a mechanical pump, they are diaphram type pumps and will pull past 6 ft of difference.
If it didn't run with a shot of starter fluid it could have been a busted cam ir timing chain but since it did you can rule that out.
You already ruled out pre pump clogging.
Only two things left it could be.
Try taking the pump off but leave the fuel line attached and manually cycle the lever to see if it moves and if it pumps. If you can't get any fuel out that way then the new pump is bad too. If you do get fuel then look past the pump to be sure the lines to the carb and the needle valve are not plugged or stuck.
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Unread 11-21-2013, 07:16 AM   #5
Hotrodyj
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The motor usually won't spin fast enough with just the starter with no fuel in the pump to pull fuel all the way from the tank. I've had to do it many many times in the past 25 years of mechanic work. The easiest way is to use a blow gun and wrap a rag around it to seal the fuel fill opening. It won't take much air to pressurize it and push the fuel up to the engine
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Unread 11-21-2013, 01:04 PM   #6
89-jeep
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Thanks hotrodyj. I took my cheapo HF liquid transfer pump and put it on the line coming over the top of the engine and it took a while but I finally got fuel. I then connected all my lines back up (filter vent on top) and nothing. I poured a little gas in carb about ten times and pump primed and runs great. First time I ever had to prime a mechanical pump. ??? All I know is it worked!
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Unread 11-21-2013, 01:10 PM   #7
Hotrodyj
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Good deal. Glad it worked.
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Unread 11-21-2013, 01:27 PM   #8
zeus87gn
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Don't forget to check your oil to be sure there isn't any gas in it!
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Unread 11-21-2013, 08:35 PM   #9
89-jeep
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I checked the oil, still a quart low, no gas smell, so all is good. ( Rear main seal leaking after 3 attempts at fixing by me and twice by a mechanic and still leaking. I gave up, my wet spot is now driveway art until I rebuild )
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Unread 11-22-2013, 05:15 AM   #10
superj
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i have to prime the one on my sons cj5 every time we break the line.
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Unread 11-22-2013, 07:40 AM   #11
vadslram
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Just shows to go ya
I believe every story about having to prime mechanical fuel pumps yet In all the years and all the engines from a 1940 Allis Chalmers tractor to a 2000 rebuid on a chevy blocked boat I have never had to do it.
I must live under a guardian grease monkey.
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Unread 11-22-2013, 07:43 AM   #12
Hotrodyj
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Dang wish I was that lucky lol
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Unread 11-22-2013, 10:26 AM   #13
superj
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me too. sometimes i had to prime the pump on my karmann ghia. it was easy though, you could just put your hands around the filler on the tank and blow as hard as you could and it would push fuel out the back
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