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08 1500 problems

fuel pump wont kick on

08 1500 problems

Postby 2008-silverado [OP] » Apr 23 2013, 6:42pm

i have an 08 silverado 1500 4x4 extended cab with about 133k on it. its pretty heavily modded but nothing is done to the motor, ive got it jacked up on 35s with halo headlights smoked tails, led cargo lamp, touch screen in dash, ect ect and recently the truck began to just fall apart but never had a proble with it not starting. ive replaced every front end component almost on a monthly basis until i finally fixed what was causing it all to go bad, replaced the steering rack, went thru 3 rear ends and much more but it always started no problem.. until a few weeks ago i pulled into my driveway and before i could shut the truck off it started spitting and sputtering like it was out of gas(it wasnt) then shut off and wouldnt start again. if i waited a few hours it would start but just shut back off again. so i realized i wasnt hearing the fuel pump prime when i turned the key. i pulled the bed off and replaced the fuel pump and it still wouldnt start.. so out of curiosity i hooked a battery charger directly to the old fuel pump and it started no problem.. the fuel pump was never bad.. i replaced the fuse and relay and it still wont start.. checked all wiring and its all good.. so i temporarily have it hooked to a toggle switch that way i can still drive the truck cuz i need my truck for work, school and to get my gf. well a mechanic had told me that if it starts and then shuts off then wont start again for a little while that its my crank sensor.. so i replaced the crank sensor and the truck fired right up... then did the same thing it shuts off after a minute or so and wont start back up for a few minutes.. if i turn the key i hear the pump prime, i start the truck and after aminute or 2 it slowly bogs down and shuts off, then ill turn the key agaain and the fuel pump wont prime.. if i wait a little while and try it again it primes, starts then shuts back off again.. what could be the problem?
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Re: 08 1500 problems

Postby ASTE25 » Apr 26 2013, 7:11am

So, when you have the pump straight wired it runs fine? If that is the case, it's either going to be a problem with the factory power supply to the pump, the ground to the pump or possibly a problem with the security system. It's not going to be anything like a camshaft or crankshaft position sensor. I'm get a wiring diagram for it and start tracing wires.
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Re: 08 1500 problems

Postby Wade_660 » Apr 26 2013, 12:12pm

I'm thinking security system. Does it not throw a code?
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Re: 08 1500 problems

Postby 2008-silverado [OP] » Apr 29 2013, 1:55pm

i apologise i forgot to post the codes im running quite a few actually. and it runs fine when its wired to a toggle switch, when is not hooked to the toggle switch it starts up, i hear the pump prime when i turn the key, but then it shuts off after a few seconds then wont start again unless i wait a few minutes then it shuts off again, so basically the pump primes, but ssomething is keeping the pump from running once it starts.. im thinking maybe the fuel system control module? heres all my codes

p0131(o2 sensor)
p0232
p0171(probably caused by the o2 sensor)
p023f
p0230
p025a
p069e
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Re: 08 1500 problems

Postby Spodijr » Apr 29 2013, 2:10pm

Looks like you have done quite a bit of homework on this but could it be something as simple as a clog or gunk build up in the fuel line??
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Re: 08 1500 problems

Postby Wade_660 » Apr 29 2013, 2:14pm

Where did you get the fuel pump? It sounds like its not keeping adequate pressure when not on the toggle switch. It could be losing a slight amount of voltage therefore losing a little pressure.
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Re: 08 1500 problems

Postby wildchevy » Apr 29 2013, 2:20pm

Some NNBS have a fuel pump drive module located by the spare tire.

Circuit/System Description
The engine control module (ECM) supplies voltage to the fuel pump control module (FPCM) when the ECM detects that the ignition is ON. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in Crank or Run. While this voltage is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel rail pressure.

The fuel system is an electronic returnless on-demand design. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump is contained by the fuel pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pump module contains a reverse flow check valve. The check valve maintains fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

 1. Ignition ON, engine OFF, command the FPCM Fuel Pump ON with a scan tool and observe the fuel pressure gauge while the fuel pump is operating. Verify the fuel pressure is between 345–690 kPa (50–100 psi).
⇒ If the fuel pressure is greater than the specified range, replace the fuel tank fuel pump module.
⇒ If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank fuel pump module.
◦Restricted fuel feed pipe
◦Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
 2. After the fuel pump is turned OFF, verify the fuel pressure stabilizes between 500–599 kPa (72–87 psi).
⇒ If greater than the specified range, replace the fuel tank fuel pump module.
 3. After the fuel pump is turned OFF, verify the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.
⇒ If the pressure decreases more than the specified value, perform the following procedure:
3.1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief.
3.2. Install the J 37287 Fuel Line Shut-off Adapter between the fuel feed pipe and the fuel rail.
3.3. Open the valve on the J 37287 Fuel Line Shut-off Adapter .
3.4. Ignition ON, command the FPCM Fuel Pump ON with a scan tool and bleed the air from the CH-48027 Digital Pressure Gauge .
3.5. Command the FPCM Fuel Pump ON and then OFF with a scan tool.
3.6. Close the valve on the J 37287 Fuel Line Shut-off Adapter .
3.7. Monitor the fuel pressure for 1 minute.
⇒ If the fuel pressure decreases more than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injector(s).
⇒ If the fuel pressure does not decrease more than 34 kPa (5 psi) within the specified time, replace the fuel tank fuel pump module.
 4. Relieve the fuel pressure to 69 kPa (10 psi). Verify that the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 minutes.
⇒ If the fuel pressure decreases more than the specified value, replace the fuel tank fuel pump module.
 5. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 Digital Pressure Gauge . The fuel pressure should not drop off during acceleration, cruise or hard cornering.
⇒ If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank fuel pump module.
◦Restricted fuel feed pipe
◦Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
 6. If the fuel system tests normal, refer to Symptoms - Engine Controls.
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Re: 08 1500 problems

Postby 2008-silverado [OP] » Apr 29 2013, 4:47pm

it cant be a clogged fuel line because ive been driving the truck for almost a month with the fuel pump hooked to the toggle switch.. im pretty sure its the FSCM considering the truck was running fine and then just shut off out of nowhere like it was out of gas... initially i thought the fuel pump went thats why i replaced the pump but the problem was not fixed after replacing the pump and the crank sensor. i turn the key and the system primes, the truck starts up perfectly and i can revv it up but then it shuts off sometimes a few seconds after starting and sometimes it stays running a little bit longer but never long enough to drive anywhere. ive checked all connections, i even cut the plug off the end where it plugs into the fuel pump thinking it was a faulty plug and i used connectors and shrink tubing to reconnect the wires to the fuel pump. i do have the FSCM by my spare tire.. i took the cover off that and checked all wires in that and that thing is spotless inside, no messed up connections or connectors, all the pins are good and there were no obvious burn marks or anything that might show that it overheated or antything. i dont have a scan tool that i can use to command the FSCM or fuel pump..
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Re: 08 1500 problems

Postby ASTE25 » Apr 29 2013, 6:08pm

It's obviously either a power to the pump or a pump grounding problem. My guess would be the security system is not allowing it to get power of possibly as stated above the fuel pump module is bad.
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Re: 08 1500 problems

Postby 2008-silverado [OP] » Apr 29 2013, 6:55pm

how do i know if its a security issue? no security light is on.. also the ground on the pump is fine im still using that ground to ground the pump when its on the toggle switch.. if it were security wouldnt my security light be on and wouldnt it not start at all? if there a way i can bypass the FSCM to tell if thats the culprit or not?
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