Testing Fuel pressure regulator 1993 YJ - JeepForum.com
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post #1 of 10 Old 06-30-2019, 01:21 PM Thread Starter
tdagner
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Testing Fuel pressure regulator 1993 YJ

Is there a way to test the pressure regulator on a 1993 4.0 engine? I have a brand new fuel pump and am pumping plenty of fuel up to the rail, but am not getting any past the pressure regulator into the rail. I pulled the pressure regulator and tried blowing air through it but couldnt even blow air through it.

The engine was pulled from a wrecked jeep and put into my cj5. Would really like to bench test the regulator before I spend $40 on a new one if possible. Jeep was running before it was wrecked.

Any help is appreciated.

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post #2 of 10 Old 06-30-2019, 01:32 PM
Luuca
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So on a MPFI engine, the FPR is on the return side and opens or closes based upon the pressure in the rail not coming from the pump. If you are trying to flow fuel from the pump throught he FPR on a MPFI engine, the lines are backwards. If you are not getting any return fuel - important in a return system for cooling the pump in the tank a little - simply go to pick and pull and find any number of them on wrecked chrysler minivans. Same part number and you can get 4 in 15 minutes for less than $10.
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post #3 of 10 Old 06-30-2019, 01:36 PM Thread Starter
tdagner
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Quote:
Originally Posted by Luuca View Post
So on a MPFI engine, the FPR is on the return side and opens or closes based upon the pressure in the rail not coming from the pump. If you are trying to flow fuel from the pump throught he FPR on a MPFI engine, the lines are backwards. If you are not getting any return fuel - important in a return system for cooling the pump in the tank a little - simply go to pick and pull and find any number of them on wrecked chrysler minivans. Same part number and you can get 4 in 15 minutes for less than $10.
Damn, I must have my fuel lines reversed. I have the fuel supply feeding into the inlet that goes directly into the pressure regulator. So you are saying that is wrong?

I put them back on the way i thought made sense.
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post #4 of 10 Old 06-30-2019, 01:47 PM
Boojo35
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Quote:
Originally Posted by tdagner View Post
Damn, I must have my fuel lines reversed. I have the fuel supply feeding into the inlet that goes directly into the pressure regulator. So you are saying that is wrong?

I put them back on the way i thought made sense.
Yes he is in a nutshell. The supply side feeds the rail. The FPR returns the excess pressure to the tank.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #5 of 10 Old 06-30-2019, 03:06 PM Thread Starter
tdagner
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Thanks so much for this. I had to change my fuel lines around but the jeep fires right up. Made my day. This is a swap into a cj5 that is getting close to and end. Ran pretty fast cause I didn’t have the hole in the intake plugged where it goes to the brake booster.
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post #6 of 10 Old 06-30-2019, 03:09 PM
Boojo35
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Cool. Thanks for posting back.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #7 of 10 Old 06-30-2019, 03:45 PM
Luuca
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Not to complicate matters, but if you get a TJ style single feed rail, you can basically ditch the return line if you do not have inspections or SMOG inspections in your state.

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post #8 of 10 Old 06-30-2019, 04:51 PM Thread Starter
tdagner
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Originally Posted by Luuca View Post
Not to complicate matters, but if you get a TJ style single feed rail, you can basically ditch the return line if you do not have inspections or SMOG inspections in your state.
Thanks. I have it working right now and that is enough for the time being. haha. But I will keep it in mind for an upgrade.
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post #9 of 10 Old 07-12-2019, 12:38 PM
BaumSquadM24
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For the single feed rail, I do believe you still need a return line from your fuel pump. Otherwise your pump will just keep pumping and it will max out at the pumps max pressure and will cause all sorts of problems.
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post #10 of 10 Old 07-13-2019, 04:17 PM
Luuca
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Originally Posted by BaumSquadM24 View Post
For the single feed rail, I do believe you still need a return line from your fuel pump. Otherwise your pump will just keep pumping and it will max out at the pumps max pressure and will cause all sorts of problems.
2 years ago we eliminated the return line when we did the 4.0 swap by using a complete TJ rail. I did not change the fuel pump. I simply bent the soft return line over on itself and used 2 HD zip ties to keep it closed.

Our YJ has 36 psi at the rail. It has been driven 865 miles nonstop (well fuel and diet coke stops) 4 times since the swap along with daily driven by my daughter to and from work. Not a single fuel issue. 10mm sockets are a different story. They vex her... like most Jeepers

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