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Discussion Starter · #1 ·
So my car has been idleing rough lately and juss not pulling hard like it did. So I checked the timing and it was dead on. I pulled the plugs and noticed that they were pretty white. So I check the fuel pressure and it was at 23psi...really low. I pinched the return line and it jumped up to 33psi. This is a totally stock fuel system, shouldn't it be at 36psi at idle? I think its my fuel pump...any other ideas? Thanks for any help guys.
 

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I doubt it's your pump. It could be a dirty fuel filter. That's the easiest, first thing to change. Then, the regulator is easy to test after that. Draw a vacuum on the regulator and see if the pressure drops.

Make sure you are testing the fuel pressure with the engine off. You can jumper +B and FP in the diagnostics box in the engine compartment, and with the key on, the fuel pump will run off battery voltage. With the engine off, you should see somewhere in the 37-40 psi range.
 

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Discussion Starter · #3 ·
by checking the fuel pressure, I cut in to the supply line and put in a barbed fitting with a gauge connected to it and started the engine. It was at a constant 26 psi for about 5 seconds then i heard a solenoid open/close and it dropped to 23 psi and it held there. By blocking the return line it dead heads the pump right? so the internal return in the pump kicks in. So technically it doesn't matter what the regulator is at right? I could be way off, I'm just trying to repeat what my mechanic told me. Thanks for anymore help guys.
mike
 

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Yes, you are right. Dead-heading the pump uses the internal relief valve, assuming the pump is healthy enough to get there. Under zero flow conditions, you are taking the filter's effect out of it.

I'm assuming you are using the +B and FP jumper with the key on, engine off, right? That's essential.

If you are jumpering the +B and FP pins with the return plugged (make sure it's genuinely plugged), then you rule out everything except a bad pump, a relief valve that's opening too soon, or a clogged strainer on the pump. All of these things are inside the tank.
 

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flyboy said:
Yes, but it's not FLOWING if he's COMPLETELY shutting off the return, which I assumed he was. If it's not flowing, a clogged filter won't create a pressure drop.
If he's doing this test with the engine off, then that is correct. But he said

"...I cut in to the supply line and put in a barbed fitting with a gauge connected to it and started the engine."

A proper test of the fuel pump would be to manually energize the pump (+b to FP), engine off, and block the return line. Then the pump is deadheaded. Only the relief valve and the pump are in the equation.

bill
 

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flyboy said:
Since he was arguing with me, I assumed he realized I said to use the +B method and retested it with the same results.
Hmmm...well, I guess I'm not really clear exactly how he is doing his test either.

But I thnk you and I are in agreement about how it works.

bill
 
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