2005 buick rendezvous, low fuel pressure.

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4 years 5 months ago - 4 years 5 months ago #138000 by bryanwarden
2005 buick rendezvous, low fuel pressure. was created by bryanwarden
I've been having problems with poor gas mileage and lack of power even after i practically rebuilt the upper part of my engine, new injectors, fpr, plugs/wires, front 02 sensor, head/intake/exhaust gaskets, new maf sensor, cleaned up throttle body, new pcv valve, crank position sensor, radiator, thermostat, water pump, fuel filter, air filter and even ran fuel injector cleaner through multiple tanks. the fuel pump reads 40 psi on my cheap harbor freight fuel pressure tester, thought maybe it wasn't working properly so i borrowed a nice one from a mechanic friend, it reads 38.3 psi at idle, and reaches 47.2 max driving down the highway. with the fuel pressure regulator's vacuum line disconnected, the gauge reads 48.1. when i reconnect it drops back to 38.3. when the engine is turned off the gauge read 46.4 and dropped to 46.2 after 45 minutes of resting. i'm not sure if its a bad fuel pump or a bad fuel pressure regulator(which now has maybe about 1,000 miles total on it.) any help would be greatly appreciated. almost forgot, 2005 buick rendezvous cxl(i think), 3.4l 2wd 120,000 miles.
Last edit: 4 years 5 months ago by bryanwarden.

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4 years 5 months ago #138007 by cap269
Replied by cap269 on topic 2005 buick rendezvous, low fuel pressure.
The FPR behavior seems normal, so I doubt that is the problem. Remember that fuel pumps do not create pressure, they create volume. The pump pushing the volume of liquid through the lines and filter and small orifices are what creates the pressure. Fuel injected engines are very sensitive to fuel pressure as well as fuel volume. Low pressure will cause starting and driveability problems. A pump that can deliver adequate pressure but not enough volume may allow the engine to start and idle normally, but it will starve the engine for fuel and cause a loss of power when the engine is under load, accelerating hard or cruising at highway speeds. Therefore it is quite possible to have proper pressure but reduced volume. This could be due to a failing pump or a clogged in-tank strainer. To test pump volume, disconnect the fuel line past the filter and run it into a clean container (attach a hose to the line if necessary). Make sure there are no ignition sources near the testing area. Turn the key on (do not crank), wait 30 seconds, turn key off. In the container, the pump should have expelled approximately one quart of fuel. The fuel can be returned to the tank.

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4 years 5 months ago #138009 by bryanwarden
Replied by bryanwarden on topic 2005 buick rendezvous, low fuel pressure.
I will do this, but I do have a question, you said for 30 seconds but if I'm correct in my understanding, without the car running does the fuel pump not shut off after a few seconds? I guess I will find out in a few but if that's the case how do I measure the volume without a decent amount of data to collect.

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4 years 5 months ago - 4 years 5 months ago #138010 by cap269
Replied by cap269 on topic 2005 buick rendezvous, low fuel pressure.

bryanwarden wrote: I will do this, but I do have a question, you said for 30 seconds but if I'm correct in my understanding, without the car running does the fuel pump not shut off after a few seconds?

Many GM vehicles do not shut off after 2 seconds, but some do. The ones that have a timer also have a fuel pump test connector under the hood that can be shorted to battery voltage for testing and priming the fuel system.

I guess I will find out in a few but if that's the case how do I measure the volume without a decent amount of data to collect.

One way I do it is to take a container, measure 16 oz of water and pour it in the container, then make a mark on the outside of the container with a permanent marker where the water line is. Then I add another 8 oz of water and make another mark, and repeat adding 8 oz and making additional marks 2-3 more times. This gives a graduation to measure the amount of fuel collected. Obiviously you do not want a very large container or it will be hard to discriminate the liquid levels. 1/2-gallon to 1 gallon container is a good size. I use an empty 1/2-gallon glass pickle jar. You do want to make sure to dry the water out of the container before collecting the fuel if you want to return the fuel to the tank.

Current vehicles:
'88 Toyota Truck 2.4L I4 (22RE)
'05 Hyundai Accent, 1.6L I4
'06 Volvo S60 2.5T I5

Previous vehicles:
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Last edit: 4 years 5 months ago by cap269.

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4 years 5 months ago #138024 by bryanwarden
Replied by bryanwarden on topic 2005 buick rendezvous, low fuel pressure.
It shuts off after a few seconds, where would one look for this test connection to short to battery positive

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4 years 5 months ago #138028 by cap269
Replied by cap269 on topic 2005 buick rendezvous, low fuel pressure.
It should be a single gray wire, not connected to anything, behind or near the alternator. You can short it to positive by touching it to the post on the alternator where the battery cable connects.

Current vehicles:
'88 Toyota Truck 2.4L I4 (22RE)
'05 Hyundai Accent, 1.6L I4
'06 Volvo S60 2.5T I5

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4 years 5 months ago #138031 by bryanwarden
Replied by bryanwarden on topic 2005 buick rendezvous, low fuel pressure.
So, I can't find the wire your referring to, could I simply put voltage to the fuel pump relay?

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4 years 5 months ago #138032 by cap269
Replied by cap269 on topic 2005 buick rendezvous, low fuel pressure.
Yes, that is another option.

Current vehicles:
'88 Toyota Truck 2.4L I4 (22RE)
'05 Hyundai Accent, 1.6L I4
'06 Volvo S60 2.5T I5

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4 years 5 months ago #138037 by bryanwarden
Replied by bryanwarden on topic 2005 buick rendezvous, low fuel pressure.
I've tried apply voltage to the correct pin but it doesn't effect the fuel pump, I don't know what to try.

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4 years 5 months ago - 4 years 5 months ago #138040 by cap269
Replied by cap269 on topic 2005 buick rendezvous, low fuel pressure.

bryanwarden wrote: I've tried apply voltage to the correct pin but it doesn't effect the fuel pump, I don't know what to try.

Here is the wiring diagram specific to your vehicle:


There is nothing between the relay and the pump. If you apply voltage to the relay, the pump should work. If the pump runs when you turn the key, the fuses and wiring are good.

If you place a jumper where I drew the red line the pump should run:

Current vehicles:
'88 Toyota Truck 2.4L I4 (22RE)
'05 Hyundai Accent, 1.6L I4
'06 Volvo S60 2.5T I5

Previous vehicles:
Too many to list
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Last edit: 4 years 5 months ago by cap269. Reason: added second pic with jumper drawn

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