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What is this for????

1K views 11 replies 6 participants last post by  Luckymac 
#1 ·
I found this unplugged and I do not what it is for. It is located on the passenger side at the rear of the motor. It is a 4.2.

Thanks in advance.
 

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#4 ·
I believe its the oil pressure switch. Different than the sending unit.
 
#5 ·
You can actually see the oil pressure sender in that pic too....

EDIT.... oops, I coulda sworn you said 4.0....
Luckymac got ya....
 
#6 ·
It's an electric choke switch. It closes with oil pressure (per the 1988 Factory Service Manual for carburetor circuits.

If your jeep starts and runs well, disregard it.

Good Luck, L.M.
 
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#9 ·
Find a post by Got it at last. In his signature there's a free link to several Factory Service manuals and a couple Factory Parts Manuals.
Open that link and click on the manual that you need.
In the 4.2 engine section of the FSM, you'll find the carburetor section and there will be instructions on how to set the choke.

Your fuel filter should be mounted with the smaller outlet to the fuel return line on top, at 12 o'clock.

If your Jeep starts up easily once it's been running, but has to crank for several seconds or more after it's sat for a couple days, you can add a one way valve as shown in the pics.
The pic shows a plastic one way valve, but the metal ones seem to last longer. Google "gasoline one way valve".

Pic 1- is the wrong way to mount the filter (overflow to 6 o'clock, and no one way valve.

pics 2&3 show the correct mounting position.

Good Luck, L.M.
 

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#11 ·
Seems to me that the check valve should be on the inlet side of the filter not the return line...
 
#12 ·
A couple or few years ago another poster discovered in the FSM that there's supposed to be a check valve in the fuel return line where the rubber hose connects to the metal line that runs back to the fuel tank.
Through the course of years, when the fuel filter gets changed, the tiny check valve gets discarded along with the old rubber hose.
The check valve is no longer available.

The other poster speculated that with the check valve missing, the fuel in the fuel bowl gets sucked back into the tank over the course of a couple days. With an empty fuel bowl,it takes a few seconds of cranking to fill the bowl and get fuel into the cylinders.

The aftermarket check valve (one way valve) is normally closed. It takes a certain amount of pressure from the feed side or vacuum from the tank side to open the valve.
I'm guessing that any vacuum caused by cooling gasoline or whatever reason isn't enough to overcome the normally closed valve.
When I first installed a plastic valve, it cured my "hard start after two days". The plastic check valve worked fine for a few months and then quit.
I bought a pack of metal check valves, but they don't appear to have a strong enough check valve spring to resist the vacuum generated in the tank.

When the other poster (I don't remember his name) discovered this, there were several threads with titles like "Hard start after two days".
With 4.2s becoming scarce there are fewer and fewer threads with questions about carbs and related problems.

Good Luck, L.M.
 
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