4.2 fuel in oil - JeepForum.com
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post #1 of 3 Old 04-02-2014, 11:01 PM Thread Starter
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1980 CJ5 
Join Date: Mar 2014
Location: San Diego
Posts: 4
4.2 fuel in oil

My issue is my engine wont start up anymore during my build. Everything was fine during the build up and suddenly wont start, in cranks over. Checked all electrical and everything seems to be hooked up like it was before the last start up about 3 days ago. Checked the dip stick and theres definetly fuel. I can smell it and the oil is very thin, just slides of the dip stick. I have not replaced the mechanical fuel pump yet. How hard is it? and any tips are appreciated. There is fuel going to the carb but no ignition. Rotor is good and plugs on spark plugs are hooked up. Any help is appreciated.

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post #2 of 3 Old 04-02-2014, 11:51 PM
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1981 CJ7 
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Location: Bali
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The mechanical pump diaphragm has a pressured fuel side and an air side, with a small hole at the bottom of the pump housing. When it leaks you can see a small stream of fuel out of the hole, most of it however goes in the block.

It is also possible that a stuck inlet valve on the carb or float issues can have fuel streaming into the manifold, washing down the bores into the oil.

Either way it is not healthy.

Alternatvely it could just be bec ause you have started it many times on full choke and you are smelling left over fuel in the cylinders. In any case that oil will be toast.

Changing the mechanical pump is 5 minutes work with a spanner. When you put the new one you either force it in or insert the bolts a little and then tighten it down. the spring in the pump will fight you on the way in.

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post #3 of 3 Old 04-02-2014, 11:53 PM
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1986 CJ7 
Join Date: Jun 2001
Location: Mobile
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Pump diaphragm may be bad and allowing fuel into crankcase. If your sure there is fuel in the oil, replace the pump and change oil. The pump is easy, a threaded hard line on top and two side bolts.
Confirm fuel IN carb, not just going to carb. Look down in as you pump gas and see if accel pump squirts fuel. Also see if plugs are wet. Check for sparks at a plug by grounding the threaded part and watch the end (and your fingers)

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