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gatliff
User
Sep 11, 2005, 4:53 PM
Post #1 of 6
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Fuel Pump Relay
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would a Fuel Pump Relay make a motor idle poor or stall out at idle if the relay is good should you hear it click it you unplug it then plug it back in with the key on ? also the same thing with the IAC should you be able to hear it work ? the truck is a 93 chevy 1500 4.3
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DanD
Veteran
/ Moderator
Sep 12, 2005, 4:05 AM
Post #2 of 6
(3163 views)
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Re: Fuel Pump Relay
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The short answer to your questions is no.
If you want an explanation as to why post back.
Dan.
Canadian "EH"
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 12, 2005, 8:46 AM
Post #3 of 6
(3158 views)
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Re: Fuel Pump Relay
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Not the highest on the list but possible. The older and maybe newer Ford ones use points inside them and they may NOT transfer enough power.
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gatliff
User
Sep 12, 2005, 10:08 AM
Post #4 of 6
(3156 views)
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Re: Fuel Pump Relay
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got a ohm/vote meter been checking anything I can all check good it got me
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harleyguy
User
Sep 14, 2005, 12:12 PM
Post #5 of 6
(3139 views)
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Re: Fuel Pump Relay
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I have a '93 GMC Sierra with a 4.3 and my experience with the fuel pump relay is; it's either actuated or not. Check to make sure you have good fuel pressure on the rail. Your fuel filter could be clogged. The fuel pump could be weak. You may have a bum rotor or dist cap also. It is usually the simple things that we pass up that come back to haunt us. Or at least me anyway. Sometimes it seems my luck with vehicles is worse than my luck with women. 
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DanD
Veteran
/ Moderator
Sep 15, 2005, 4:53 AM
Post #6 of 6
(3126 views)
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Re: Fuel Pump Relay
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Ok maybe if we explain how the fuel pumps relay and its circuit works, we’ll be of more help getting to your truck problem.
When you first turn the ignition to the run position and wake up the computer the computer will apply ground to the pull-in coil of the pumps relay which in turn closes the contacts in the relay allowing the pump to run.
This is called the prime cycle, the computer will remove this ground after about 2 to 3 seconds if there isn’t an ignition pulse from the ignition module.
As you continue to turn the ignition switch to the crank position the ignition module will start to create a pulse (due to the engine turning), that the computer recognizes as spark and again applies ground to the fuel pumps relay allowing the pump to run.
They also incorporate a back-up way of turning on the fuel pump through the oil pressure switch if the fuel pump relay fails.
Let’s say the relay will not close for whatever reason. You start to crank the engine sooner or later oil pressure will start to build. As this pressure is applied to the oil pressure switch it closes a set of contacts and applies 12 volts to the fuel pump feed wire again allowing the pump to run.
So if you have a constant 12 volts being applied to the fuel pumps gray feed wire then electrically it’s not the pump.
Electrically and mechanically are two different things and that’s where you need to connect a fuel pump pressure gauge the system. Tee the gauge in, I’m pretty sure there is a shraider (sp?) valve on the fuel rail to connect to, back by the distributor. That way you can drive this thing down the road and watch the pressure while the truck is doing its thing.
The pressure should be 55 to 60 psi and with this style of injection 50 psi doesn’t cut it, that’s not enough to open the poppet vales of the injector nozzles. But this takes us to a whole different story. LOL
Dan.
Canadian "EH"
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