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Old 05-31-2011, 12:39 PM   #1
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Default What does a fuel pressure regulator tell a fuel pump on a Chevy GMC rear wheel drive

I am trying to identify what a FPC (fuel pressure regulator) tells/ controls a FP (fuel pump) if anything.

Background- have a Chevy S10 (Blazer, Jimmy, Sonoma, Bravada, Safari) that intermittently doesn’t start and also may die while driving. The doesn’t start may be after sitting overnight, or after coming back from a quick trip (cold or warm doesn’t matter). It will also die while driving slow. Let it sit overnight and it may start right up, or let it crank for 20 minutes and it may start up also. Then it will run without a problem for 3-8 days. When it doesn’t start, no fuel is smelled under the hood, and when it does start it does not display excess exhaust- indicating fuel was not being dumped into the intake.

Replaced the fuel pump with the DELPHI , the DELPHI has updates/ modifications to the fuel pump design and its electrical harness.

Yesterday it would not start in the afternoon. It was driven all morning, local errands. Did a visual inspection of the Schrader valve, and fuel came out when pressed. Went and purchased a FPG (fuel pressure gauge), and when returning, no fuel came out of the Schrader valve. Hooked up the FPG and it measures zero pressure. No noise came from the fuel pump. I have a Bravada parked next to the S10, so I checked its pressure (same DELPHI* pump) *** pumps are same design but slightly different between 4.3L pickups and SUVs} and it registered 60 psi. Now I know my FPG is good, my procedure of testing is good, and that I have a fuel related problem. Also, note, I swapped the FP relay between the Bravada and S10, no change in the lack of pressure.

My thought is I have a bad fuel pump, it may have an intermittent problem. But the DELPHI is a soldi product. In the morning, checked the S10, and when I turned the key the fuel pump kicked on (heard it). So I am thinking, does the FPC tell the FP to turn on? Before I order a replacement FP, what is telling the FP to pressure up?
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Old 05-31-2011, 01:13 PM   #2
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I have had a personal expierience with the same problem and the problem is your fuel pressure regulator is leaking. When I removed the top portion to the injectors I had a puddle of fuel on the left bank. I replaced the regulator and she purred like a kitten. It starts every time, when I was having problems I would need to crank my Blazer over a couple times to get it to start. After I replaced the regulator my fuel economy went from 12MPG to 19MPG on the high way. Definitley check the regulator and look for a puddle of gas inside. I hope this helps.
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Old 05-31-2011, 01:18 PM   #3
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When you get zero fuel pressure, do you hear the pump run for a moment when you first click the key to on?

If you press on the schrader do you get a spurt of fuel or a dripping of fuel?

Zero pressure all the time on the gauge says the gauge may be faulty.
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Old 05-31-2011, 01:20 PM   #4
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The fuel pressure regulator in your Chevy Blazer is used to help keep the fuel system'* pressure constant. If the regulator is bad, the result is often low pressure in the system. Symptoms can include a rough, sputtering engine, failing to start after ignition and worse fuel mileage. Replacing a fuel pressure regulator, like any fuel system component, can be a dangerous task because of the pressure within the system


Relieve the vehicle'* fuel system pressure by removing the fuel cap on the side and the fuel pump relay inside the fuse box, then run the engine until it stalls and continue cranking it for five to 10 seconds.

2
Disconnect the battery'* negative cable once the pressure is relieved.

3
Remove the air intake resonator by disconnecting all connectors, ducts and lines connected to it--the ducts have hose clamps that need loosening--removing the resonator'* mounting bolts with a wrench and detaching the ventilation hose from the valve cover.

4
Clean away all dirt and debris that is around the pressure regulator and fuel lines to prevent anything from entering the fuel system. Wipe it away with a clean cloth. If you use acetone, water or any other liquid cleaner, make sure you completely dry the area off.

5
Disconnect the vacuum line at the pressure regulator, the wiring harness at the front of the engine and the fuel return line. These should either come off easily by hand or have quick-connect fittings where you press on the tabs.

6
Remove the pressure regulator by removing its mounting screw; this can require a screwdriver or a hex wrench.

7
Make sure the replacement regulator has a new O-ring and lubricate this ring with a light coat of engine oil.

8
Install the fuel pressure regulator, tightening the mounting screw to 71 inch-pounds. Reconnect all other parts in reverse order of removal.

9
Re-pressurize the fuel system by reconnecting the fuel pump relay, turning the ignition switch to the on position for two seconds and turning it back on for five. Repeat the procedure with the switch multiple times.
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Old 05-31-2011, 02:40 PM   #5
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Zigger, Bill- thanks for the comments.

Note the problem is intermittent- that is why I am trying to understand if the FPR sends any electronic signal to the FP to send fuel.

With zero pressure- no noise from fuel pump. Schrader valve trickles fuel..... after trickle it will leak no fuel...

No noise at all from the fuel pump when it would not start yesterday. This morning noise from the fuel pump when key turned, and started right up. Since I have two like vehicles sitting next to each other, I was able to verify the fuel pressure gauge was fully opertional. I already purchased a FPR- but don't want to install it until I know for sure that is the problem. I have been shotgunning the problem and it is still happening, once per week (more or less). This is my youngest Son'* vehcile, he is a new driver and I hate to leave him stranded. I work out of state most of the time... so I am trying to truly pinpoint the problem,
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Old 05-31-2011, 03:49 PM   #6
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Last I checked, the fuel pressure regulator is an entirely mechanical component that regulates fuel pressure inside the fuel rail. On 3800'* you can actually remove it and replace it with nothing more than a set of ring pliers. The following image is of a fuel pressure regulator on a 3800: http://www.kc2jga.com/MISC9.JPG I can't imagine the 4.3 motor having a terribly different fuel pressure regulator. My money'* on either the wiring or the fuel pump itself.
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Old 05-31-2011, 03:56 PM   #7
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XRV,

Thanks- I think your post tells me either the fuel pump is defective, bad wiring on my part (I soldered it and am pretty experienced with solder/ auto electric) or.... when I lifted the bed (did it dump truck style) I unknowingly snapped a ground wire to the tank, not the tank side but the frame side.

Off to inspect the grounds on the bed.....
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Old 05-31-2011, 04:00 PM   #8
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Quote:
Originally Posted by xtremerevolution View Post
Last I checked, the fuel pressure regulator is an entirely mechanical component that regulates fuel pressure inside the fuel rail. On 3800'* you can actually remove it and replace it with nothing more than a set of ring pliers. The following image is of a fuel pressure regulator on a 3800: http://www.kc2jga.com/MISC9.JPG I can't imagine the 4.3 motor having a terribly different fuel pressure regulator. My money'* on either the wiring or the fuel pump itself.

This question was about the 4.3L in a Chevy *-10 Blazer not the 3800 in a Bonny, Lesabre or ect..
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Old 05-31-2011, 08:20 PM   #9
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Looks like the problem was identified.... a weak/bad ground from the fuel pump to the frame. This may have been the problem from the get go. I blame myself for the way I tilted the bed to pull the pump, but the wire may have been marginal causing the fuel pump to not provide pressure.

Have to question GM'* design on this. The fuel pump ground is approximetly 5 feet away from the fuel pump, tied to the frame. Yet the frame is less than 1 foot from the fuel pump.... WTF... Also want to mention the gauge wire is 16. Very small gauge for such a critical ground..... and a ground with no backup. Many have stated the wiring harness is the reason these fuel pumps fail prematurely, and I can believe it.

Glad I quit shotgunning trying to fix this, and did some basic troubleshooting instead. I can only imagine what a dealer may have charged to find and fix this...... Likely over 1k, they would of pulled the bed, charged me for a fuel pump, they would of missed the weak ground, then upon return charged me again to find the weak ground... another reason to be a active member of GMF....
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Old 06-01-2011, 11:09 AM   #10
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Glad to hear that you got it figured out.
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