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PostPosted: Sat Oct 10, 2009 5:34 pm 
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When I power up my fuel pump, it goes to 50+psi (where it should stay until I actually turn the car over) and I immediately hear a hissing noise. The sound of pressure being released, and the fuel pressure gage drops to the 40s and holds. I thought it was the EVAP purge valve, but its actually coming out of the main fuel line where it connects to the fuel rail.

First, I'm assuming this is not good, and want to fix the connection. And I don't want to screw up any parts while I'm getting this off.

The connection looks like a metal version of a quick-clip with another type of clip involved, holding it on the rail.

First, is the metal "quick-clip" part of the rail or the fuel line?

And how do I get this disconnected? (There isn't a clip left in the automobile industry which I haven't ruined trying to get it off.)

Thanks for any help.

.

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PostPosted: Sat Oct 10, 2009 5:51 pm 
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You need a special tool to get them off. Most auto stores have them. I got mine at Napa. The fitting will stay on the line side, and the tube on the fuel rail slide out of the fitting.

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PostPosted: Sat Oct 10, 2009 5:52 pm 
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even with the tool its kinda tricky sometimes. be patient

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PostPosted: Sun Oct 11, 2009 2:13 am 
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PostPosted: Sun Oct 11, 2009 7:32 am 
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charliemax wrote:
First, I'm assuming this is not good, and want to fix the connection. And I don't want to screw up any parts while I'm getting this off..


I wouldn't assume this. Is any fuel leaking out the connectors? Unplug the vac fitting on the regulator, is any fuel coming out the fitting? What you are probably hearing is excess fuel being returned to the fuel tank, which isn't a problem as the system is supposed to recirculate fuel by pushing open the valve on the regulator.

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PostPosted: Sun Oct 11, 2009 10:25 am 
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clm2112 wrote:
charliemax wrote:
First, I'm assuming this is not good, and want to fix the connection. And I don't want to screw up any parts while I'm getting this off..


I wouldn't assume this. Is any fuel leaking out the connectors? Unplug the vac fitting on the regulator, is any fuel coming out the fitting? What you are probably hearing is excess fuel being returned to the fuel tank, which isn't a problem as the system is supposed to recirculate fuel by pushing open the valve on the regulator.


No fuel. No fuel smell. No fuel smell when i remove the T connector from the regulator.

I'm new to the fuel system. So, the three lines from the tank.. one is the vapor line to the EVAP, one is fuel to the rail and FPR. When the FPR exceeds the pressure it wants, it closes, and the fuel is diverted to the third line, which is a return.?

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PostPosted: Sun Oct 11, 2009 3:37 pm 
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More or less. The regulator is always returning fuel to the tank through the return line when the engine is running. It just releases some of the pressurized fuel into the return line. How much fuel it returns depends on how much the engine is using. The regulator is most likely what is making the noise you hear. This is fine as long as it is not releasing too much. But the way your pressure is reading, it may be returning too much.

What are the fuel pressure specs for your car? If it is 50-55 psi, then the pressure should hold in that range for at least 5 minutes. If it builds to spec then falls and holds below spec, you have a problem. Could be the pump (but you just replaced yours), the pulsator, or the regulator. Beings you can hear a pressure release at the fuel rail, I would suspect a bad regulator.


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PostPosted: Sun Oct 11, 2009 7:10 pm 
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charliemax wrote:
No fuel. No fuel smell. No fuel smell when i remove the T connector from the regulator.

I'm new to the fuel system. So, the three lines from the tank.. one is the vapor line to the EVAP, one is fuel to the rail and FPR. When the FPR exceeds the pressure it wants, it closes, and the fuel is diverted to the third line, which is a return.?


Leave it alone, you don't have a problem.

You have a high pressure line from the pump to the rail. The regulator is on the return line back to the tank to dump the excess fuel pressure. The vac fitting raises the rail pressure at high rpm (low vac) to help the system compensate for the large volume of fuel needed be the injectors at high rpm.

The fuel needs to circulate, which is what cools the electric fuel pump. The pump pressure and volume are always supposed to be more than the engine needs, so it is always flowing fuel back to the tank through the return line.

You can tell the two apart by the diameter of the lines. The supply line is always bigger than the return line. GM even put different size connectors on the lines to keep someone for hooking them up the wrong way.

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Last edited by clm2112 on Sun Oct 11, 2009 7:12 pm, edited 1 time in total.

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PostPosted: Sun Oct 11, 2009 11:16 pm 
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1fatcat wrote:
More or less. The regulator is always returning fuel to the tank through the return line when the engine is running. It just releases some of the pressurized fuel into the return line. How much fuel it returns depends on how much the engine is using. The regulator is most likely what is making the noise you hear. This is fine as long as it is not releasing too much. But the way your pressure is reading, it may be returning too much.

What are the fuel pressure specs for your car? If it is 50-55 psi, then the pressure should hold in that range for at least 5 minutes. If it builds to spec then falls and holds below spec, you have a problem. Could be the pump (but you just replaced yours), the pulsator, or the regulator. Beings you can hear a pressure release at the fuel rail, I would suspect a bad regulator.



clm2112 wrote:
charliemax wrote:
No fuel. No fuel smell. No fuel smell when i remove the T connector from the regulator.

I'm new to the fuel system. So, the three lines from the tank.. one is the vapor line to the EVAP, one is fuel to the rail and FPR. When the FPR exceeds the pressure it wants, it closes, and the fuel is diverted to the third line, which is a return.?


Leave it alone, you don't have a problem.

You have a high pressure line from the pump to the rail. The regulator is on the return line back to the tank to dump the excess fuel pressure. The vac fitting raises the rail pressure at high rpm (low vac) to help the system compensate for the large volume of fuel needed be the injectors at high rpm.

The fuel needs to circulate, which is what cools the electric fuel pump. The pump pressure and volume are always supposed to be more than the engine needs, so it is always flowing fuel back to the tank through the return line.

You can tell the two apart by the diameter of the lines. The supply line is always bigger than the return line. GM even put different size connectors on the lines to keep someone for hooking them up the wrong way.


Thanks for taking the time to explain this, clm2112 and (again) ifatcat. I have been reading the FSM, but it wasn't coming completely clear, because I have/had 3 problems.

1-Had a small vacuum leak. At idle and in gear, my boost gage was up. Any stress from an accessory would send it higher. The MAP pressure would go up, but the MAF wouldn't see any additional air. EGR pipe and TB reseated, I believe the leak is taken care of. the MAF always trends with the MAP. They are in synch and I idle at -10 on the boost. But...

2- At idle and in gear, adding accessories moves the boost up. The battery is new, the alt ain't. Connected a multimeter and taped the gage to the windshield for a full operational run. The alternator can't take stress. The charging circuit pegged at 14.2v. But as I added accessories it dropped briefly and significantly as far as below 13.0v. It also eroded the steady state down from 14.2v. Meanwhile, as voltage went down MAP/boost went up. Added an 8AWG wire between the alt and the post at the fuse relay, to make it easier on the alternator. Slight but definite improvement, so the new alternator goes in tomorrow.

But that leaves me with my real or imagined fuel problem. Actually there is a fuel problem, I just keep changing imagining where the problem is, :roll: as i learn more and solve the other issues.

-My LTFT pegs at the max 16.4 at idle and until I get past slight throttle. When I had the leak, the STFT would jump after that air, and I would go over the cumulative max and get p0171. Which is what started all of this. 16.4 is a fat push, that's fighting some weakness in baseline fuel pressure (?). And when I make myself drive like the grandpa I am, I still have trouble pushing over 20 mpg.
-Post ignition, my steady state pressure is 44psi (and reacts to throttle just fine, as best as i can tell). The problem is that when i turn the car off, within an hour the pressure drops to nothing. That's not good, according to Chilton's and the FSM, as well as the knowledgeable wrenchers here.

My KEY ON pump power-up is supposed to be 48-55psi (this is higher than prior yr models). It does for a millisecond, but the pressure release immediately takes it down to 44psi and holds. Same place every time. And 44psi is well within normal running operating range, (and actually kicks the engine over fine, too). It is so fast, precise, and exactly repeating.. I have to agree (and hope) that it is the work of the regulator, opposed to some random leak in the system. Now that I understand that the system is pressure/release and not pressure/bypass, a weak regulator could explain the power-off leak down of fuel into the return line. It's not leaking back in the supply line, as my other theorized gremlins in the system would allow.

I'll replace that and we'll see. Thinking about the issues it re-raises, if it doesn't work, just makes my head hurt. So I'm going to stop doing that.

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Last edited by charliemax on Sun Oct 11, 2009 11:26 pm, edited 1 time in total.

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