No Pressure at Fuel Rail, Engine Starts

JeepGirl1013

JeepGirl1013

TJ Enthusiast
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Joined
Jan 12, 2024
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123
Location
Missouri
Hi, not finding clear answers on troubleshooting steps.

- jeep is slow to start. It does crank, fuel pump comes on. Engine does not start until 2nd or 3rd turn.

- tested fuel pressure at shader valve. Pressure is zero when cycling key and running the engine.

- switched the horn and fuel pump relays, no change in behavior

- traced fuel line and no leaks or rust

Am I just looking at a bad pump? can I test the fuel pressure regulator somehow? What else can I test before dropping the tank because I just filled it 😭😭😭😭
 
Does it stay running and or does it idle poorly/ feel like loss of power? I had above symptoms and my fuel pump was dead. If you think its a starting issue then id check your battery volts at off/cranking amps/ running volts etc.
 
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DylanM345 said:
Does it stay running and or does it idle poorly/ feel like loss of power? I had above symptoms and my fuel pump was dead. If you think its a starting issue then id check your battery volts at off/cranking amps/ running volts etc.
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It stays running. I can drive across town. I only got it a week ago so not too much drive time yet. But the past few days it’s definitely riding rough. It was very smooth when I got it. We just put in brand new battery and ground cable so voltage is good
 
The first time I used a fuel pressure gage I felt like I screwed it on hella tight and it still read zero. I don't remember if I had the wrong fittings or if the gauge was bad or what, but I've never had a problem reading it since. I'm remembering a gauge being bad that I rented from Autozone.... But regardless I'm having a hard time believing you're able to drive without any real symptoms if you have no pressure at the rail. It's got to be the gauge or the person using the gauge (with all due respect, of course).
 
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hear said:
The first time I used a fuel pressure gage I felt like I screwed it on hella tight and it still read zero. I don't remember if I had the wrong fittings or if the gauge was bad or what, but I've never had a problem reading it since. I'm remembering a gauge being bad that I rented from Autozone.... But regardless I'm having a hard time believing you're able to drive without any real symptoms if you have no pressure at the rail. It's got to be the gauge or the person using the gauge (with all due respect, of course).
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I would totally agree with this except when we opened the shader valve absolutely no gas comes out. If there were any pressure shouldn’t we have some leakage when the cap comes off? We could get some fuel to come out by manually manipulating the valve.
 
JeepGirl1013 said:
I would totally agree with this except when we opened the shader valve absolutely no gas comes out. If there were any pressure shouldn’t we have some leakage when the cap comes off? We could get some fuel to come out by manually manipulating the valve.
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Send some pics of the fuel gauge... specifically the end that connects to the Schrader valve.

-Mac
 
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JeepGirl1013 said:
I would totally agree with this except when we opened the shader valve absolutely no gas comes out. If there were any pressure shouldn’t we have some leakage when the cap comes off? We could get some fuel to come out by manually manipulating the valve.
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If I understand what you're describing correctly, no. Fuel shouldn't come out when removing the cap, only when pressing in the core pin in the center of the valve. It's the same as the valve on a tire-- with the cap off, nothing happens, but when you push in on the core pin, air will leak out.

In the same way, that pin has to be pushed in for the fuel pressure to be read, so if you don't have the correct adapter for your fuel pressure gauge, it may not be pushing in the pin to where it can read the pressure.

1705727127496.png
 
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WVJeep304 said:
If I understand what you're describing correctly, no. Fuel shouldn't come out when removing the cap, only when pressing in the core pin in the center of the valve. It's the same as the valve on a tire-- with the cap off, nothing happens, but when you push in on the core pin, air will leak out.

In the same way, that pin has to be pushed in for the fuel pressure to be read, so if you don't have the correct adapter for your fuel pressure gauge, it may not be pushing in the pin to where it can read the pressure.

View attachment 492879
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I will check all the adaprors in the morning. But all the videos I watched on youtube said that if the system was pressurized that there should be some leakage when the cap was removed. 🤷🏻‍♀️

‘I do hope it’s user error!
 
JeepGirl1013 said:
But all the videos I watched on youtube said that if the system was pressurized that there should be some leakage when the cap was removed.
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Lots of idiots make YouTube videos (including me.)

A working Schrader valve will not leak. The valve on my 97 doesn't. That's 25+ years old.

If the Schrader valve on your tires leaked you'd replace the valve stem.

-Mac
 
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Ok @macleanflood @WVJeep304

We didn’t have the adaptor on tight enough. Cranked on hard with a wrench and got it working.

We have to prime the pump four times before we get to 48psi at the fuel rail. when the fuel pump stopped making noise it immediately dropped to 40. Then down to 30 after 15 sec, then slowly lost pressure from there.

Thoughts?
 
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JeepGirl1013 said:
Ok @macleanflood @WVJeep304

We didn’t have the adaptor on tight enough. Cranked on hard with a wrench and got it working.

We have to prime the pump four times before we get to 48psi at the fuel rail. when the fuel pump stopped making noise it immediately dropped to 40. Then down to 30 after 15 sec, then slowly lost pressure from there.

Thoughts?
Click to expand...

Most likely a failed fuel pressure regulator, less likely leaking injectors.
 
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