Fuel pressure testing

Nathanael Rusciolelli

TJ Enthusiast
Joined
Dec 4, 2016
Messages
118
Location
North Carolina, United States
Trying to test the fuel pressure to diagnose some hard starting issues. If I understand correctly all I should have to do is screw on the gauge connector to the test port right? When I try and do this fuel just sprays everywhere. Am I forgetting a step or is there maybe too much pressure in the system?
 
There is pressure on the line at all times if everything is working correctly. You may just be blowing the gas out of the line past the connector. Release the pressure then attach the gauge.
 
Don't know if this would work for jeeps, but to change a fuel filter on FI vehicles I pull the fuel pump fuse and crank the engine over for 15 secs or so to relieve the line pressure. Jerry?
 
I actually figured it out. Does anyone know what the pressure should read when the engine is running? Mine hit 15psi when I cycled the key a few times and didn't go up much with the engine running. I know this is pretty low but what should it be at? Also guessing this is going to mean fuel pressure regulator/fuel pump issue
 
I actually figured it out. Does anyone know what the pressure should read when the engine is running? Mine hit 15psi when I cycled the key a few times and didn't go up much with the engine running. I know this is pretty low but what should it be at? Also guessing this is going to mean fuel pressure regulator/fuel pump issue

You should be reading +/- 49 PSI at the rail.
 
Well, whether it's your pressure regulator or your pump, the TJ models put all of it on top of the tank, so you're dropping the tank either way. I would buy the entire fuel pump sending unit assembly as a whole from either Mopar or Bosch. Don't buy junk from the parts store like Airtex or any other similar brands. It's most likely the pump not putting out enough pressure, but I'd go ahead and buy the whole assembly since you're going to be dropping the tank and doing all the work either way.
 
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Well, whether it's your pressure regulator or your pump, the TJ models put all of it on top of the tank, so you're dropping the tank either way. I would buy the entire fuel pump sending unit assembly as a whole from either Mopar or Bosch. Don't buy junk from the parts store like Airtex or any other similar brands. It's most likely the pump not putting out enough pressure, but I'd go ahead and buy the whole assembly since you're going to be dropping the tank and doing all the work either way.

I will look into those. Thank you
 
Doesn't matter. The anti drainback valve is a part of the fuel pump assembly so yes you'll be getting a new one to replace your current one, but that part isn't faulty in this case unless it's the reason you're having hard starts. Either way, buying the whole unit will give you a new drainback valve and a new pump which should fix both your pressure and starting issues.
 
What brand of fuel pump did you install? Hopefully not a Spectre, Airtex, or a store brand. Bosch is the brand that holds up, who is also the OEM for the Mopar fuel pump.
 
What brand of fuel pump did you install? Hopefully not a Spectre, Airtex, or a store brand. Bosch is the brand that holds up, who is also the OEM for the Mopar fuel pump.
I was wondering, what are your thoughts on Crown Automotive? Quadratek sells Crown Automotive Fuel pumps as well and wondering if they are just as good as the Bosch/Mopar.
 
I was wondering, what are your thoughts on Crown Automotive? Quadratek sells Crown Automotive Fuel pumps as well and wondering if they are just as good as the Bosch/Mopar.
I'd go strictly with Bosch who is the OEM. So far, there's no clear good quality reliable alternative to Bosch that anyone has been able to find. I installed a Spectre years ago and it lasted 13 months before failing, one month out of warranty.
 
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So I tested my fuel pressure and I was getting around 56-58 psig. That seems a little high to me, but at one point it went down to 30 psig but then kicked back up to 56-58 psig. The engine did sound like it was struggling that second it was down there and then corrected itself. Is this a fuel pump issue? Can the CPS cause the fuel pressure to go down like that? I'm so confused on this, thanks for any and all input!
 
You should be reading +/- 49 PSI at the rail.

I realize this is an old post. My jeep stalled a few days ago about 2 miles after I got gas. Cranks but won't turn over. Changed the CPS, IAC, MAP, TPS, starter solenoid, ignition switch, and ignition actuator pin. And checked the starter brushes.

I can't hear the fuel pump when I key it on (not sure if I'm supposed to) but I checked the pressure last night and it read 44-45 when I keyed it on each time. It didn't change when I cranked it.

I'm not sure how to interpret that. And I don't know if it would be related to the stall/no start issues.
 
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