will a loose return line cause a pressure drop

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#11

03-30-2009, 06:27 PM

justin1795

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justin1795 is an unknown quantity at this point

when i look online it lists two pumps for the same truck with diffrent part numbers

MODULE,F/TNK F/PMP(SENDER & PUMP)
Part Number: MU112
Product Notes:
[Fuel Tank Fuel Pump (Sender & Pump) Module]; Code sfg, sfu, sgj ; 4 Door ; Except Low lubricity fuel sys sender (K55); 18 gal tk (NE2)
Per Vehicle: 1; Years: 1998-1998 Suggested Retail Price: $654.56
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MODULE,F/TNK F/PMP(SENDER & PUMP)
Part Number: MU85
Product Notes:
[Fuel Tank Fuel Pump (Sender & Pump) Module]; Incls seal ; 18 gal tk (NE2) ; 4 Door ; Except Low lubricity fuel sys; sender (K55)
Per Vehicle: 1; Years: 1998-1998 Suggested Retail Price: $571.61
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the only diffreance i can see is the cheaper one comes with an extra seal

#12

03-30-2009, 07:57 PM

swartlkk

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It has been covered before.

Quote:

Originally Posted by swartlkk

They do.

To the OP, you have some incomplete information on those two pump options.

ACDELCO Part # MU85 {#25176789}
MODULE,F/TNK F/PMP(SENDER & PUMP) 4 DOOR; w/18 GAL TK(NE2); INCLS SEAL; w/o LOW LUBRICITY FUEL SYS SENDER(K55)

ACDELCO Part # MU112 {#25178731}
MODULE,F/TNK F/PMP(SENDER & PUMP) 4 DOOR; CODE SFG, SFU; w/o LOW LUBRICITY FUEL SYS SENDER(K55) or 18 GAL TK(NE2)

The MU112 has an application range of 97-98. It looks as though sometime in 98, the MU85 pump replaced the MU112. With the high likelihood of wiring changes, you really should first look at your pump to determine if it has the broadcast code of SFG or SFU on it which would identify it as being the later MU112 pump.

#13

04-09-2009, 09:24 PM

justin1795

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well i pulled the pump and drained the tank.. the pump is aftermarket so i wont be able to get any numbers..

#14

04-10-2009, 10:55 AM

justin1795

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i checked witht he chevrolet dealer and they said off the vin i need 25178731 for 585.66 so based on my research it would be MU112 he said there might be numbers on the pump or harness but i didnt see any on the harness and the pump aftermarket.

#15

04-10-2009, 09:25 PM

swartlkk

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Then I'd go with the MU112. They should be right as the VIN records can be cross referenced to when a particular part revision took place in the production cycle.

#16

04-24-2009, 11:20 AM

justin1795

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ok so i installed a new fuel pump and am having the same problem.. as long as the pumps on we got like 62 psi as soon as pump shuts off withing 5-6 seconds were down around zero.. i swapped gauges and get the same result... so i figured id remove the lines from the intake and install a piece of blocked hose and see if i got fuel pressure.. so i installed a piece of blocked hose on the pressure line.. had zero psi. removed test line off and on schrader valve a few times still had zero psi... so i loosed clamp on hose and gas started spraying out.. so wouldnt this be pressure??? im completly confused.

#17

04-25-2009, 09:25 AM

Captain Hook

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As mentioned in post #10, The only way to tell where the leakdown is coming from, is to isolate the fuel pump from the injectors after it pressureizes the system. If the pressure holds, the leakdown is in the tank. If pressure still drops, the leakdown is in the plenum.

Last edited by Captain Hook; 04-25-2009 at 09:27 AM.