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Experience:  ASE Master Technician/Advanced Automotive Diagnostic Technician
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1999 Suburban: 4wd 5.7L..oil pressure switch/sensor, fuel injectors

Customer Question

Have a 1999 Suburban 4wd 5.7L 350. I replaced the fuel pump, oil pressure switch/sensor, fuel injectors (8), included an MSD spark enhancer(plenty of spark). The fuel pump will not run when you turn the key on. I jumpered the pump to 12V and had to hit the pump to get it to run. Is there something in an electrical circuit that is keeping my fuel pump form running when it should !!! Help 5 weeks on this problem!!
Submitted: 11 years ago.
Category: Car
Expert:  Davo replied 11 years ago.
 Check the fuse under the hood called ecm b it provides the power to the fuel pump relay.Also see if the relay clicks when the key is turned on.See if you have battery voltage at the gray wire at the fuel pump connector while cranking and ground on the black wire.Let me know what you find.    
Customer: replied 11 years ago.
Reply to Davo/diablo666's Post: I did check the underhood fuses and they are all good ECM, ENG and others, I know I'm getting voltage to the connector grey to black since I checked it before I put the pump in and put the tank back on. If I jump the power to the pump from the relay connector underhood it does not run until I hit the pump with something. It seems it is sticking but I am wondering if there could be an intermittent electrical circuit I don't know about?
>
> Thank You,
> Dave

Expert:  Davo replied 11 years ago.
 I have run into several cases where pumps have been replaced and towed into me for a no start,fuel pump won't run.I remove the connector from the top of the tank for the pump and look very closely with a magnifier and a bright light.Any lack of bright shine(dull finish)to the terminals in the connector or a slight brown tint is no good.You should be able to buy a new replacement harness at the local GM dealer.All the wires will be white so you will need to match them for their prospective position in the connector.If you do have power and ground this is the most likely cause of the inoperative pump.Don't attempt to repair the connector thats there by reforming the terminals it won't last for long and may cause a repeat pump failure.The possibility also exists that your new pump is faulty/defective out of the box. 
Customer: replied 11 years ago.
Reply to Davo/diablo666's Post: Hi,

I will be accepting these answers soon. I just dropped the tank again and replaced the pump since it was under warrenty. I checked the voltage at the connector. I have +5 volts on the grey and green wires using the blk/wht wire as the ground. On the other connector I have 5 volts on 3 wires the blk, blk and grey wires with respect to the blk/wht wire on that connector. When I check the voltage at the relay it has 12 volts applied to it. Where is the 5 volts comming from when I turn the key on and is the pump supposed to have 12 volts or 5 volts applied?
Expert:  Davo replied 11 years ago.
 Object Number: 258300  Size: CHB =12 volts C =ground
Expert:  Davo replied 11 years ago.
 That is the fuel pump connector.B is gray and C is black.Disreguard the other 2 wires they are for the gas gauge.Check for voltage while cranking not just with the key on.5 volts is referance voltage for computer sensors.
Expert:  Davo replied 11 years ago.
Object Number: 376148  Size: MF 
Expert:  Davo replied 11 years ago.
 Check #5 in the above pic it is an inline harness connector.The fuel pump feed goes through it.Its located under the master cylinder.

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