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Old 08-23-2009
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Join Date: May 2005
Location: College Station, TX
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Help with electrical diagnosis

Well this isn't for my Ranger... it's for my little brother's 91 S10 with a 2.8L V6.

He was driving it down the road one day and hit a bump of some sort and the damn thing just died. Since then, we've replaced the fuel filter, fuel pump, and ECM. I've confirmed that the fuel pump works, and that fuel is getting to the engine. When I run 12v straight to the pump, the pump will run and pump. The engine will run when I directly power the fuel pump. When I jump the 12v power at the fuel pump relay, however, the pump doesn't run. I'm not getting 12v from the "battery" terminal on the relay it seems.

The 12v "battery" terminal also runs to the oil pressure switch. When I was looking under there, I saw that the oil pressure switch wires had fallen on the exhaust and gotten burned. I patched them in, but I am still not getting power to the fuel pump relay. On the dash, the fuel pressure gauge is flashing (it has digital gauges) but it still seems to build oil pressure while the motor is cranking.

Do any of you have any ideas? I may try to get a new oil pressure switch tomorrow, but I'm out of ideas. I don't think that the relay is bad, but I will get a new one tomorrow to be sure. Even then, when I jump the power and "bypass" the relay, the pump runs. Please help me out!
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Old 08-24-2009
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Join Date: Nov 2008
Location: Muncie, IN
Posts: 732
Check the grounds to the pcm, fuel relay, etc. I had this problem a few weeks ago on my ranger. It ended up being a ground connector from the battery that came unplugged.
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Old 08-24-2009
Join Date: Mar 2007
Location: Upstate,NY
Posts: 2,598
Hitting that "bump" most likely tripped the fuel cutoff switch.
On Rangers it is down in the passengers side footwell.No idea where it is on an S 10.
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Old 08-24-2009
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I thought the same thing on the fuel cutoff switch. Couldn't find anything on it though. I ended up running power straight from the battery to the relay, and the damn thing fires right up and runs like a top. I'll leave it that way for now and see if I can't find anything about a cut off switch.
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Old 08-24-2009
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Location: San Diego, CA
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Kyle, I believe the relay only sends power to the pump for about 3 seconds in the ignition run/start position to prime the system. Once the oil pressure gets over 3 psi the oil pressure switch closes and supplies power to the pump in the start/run position. Note, there is no fuel cut off/roll over switch like what Ford uses.

Power is supplied from 20A fuse to the Orange wire that goes to the relay, oil pressure switch, and ECM. The oil pressure switch may have either three or four wires depending, one Orange (12V power), one Gray (to fuel pump), one tan (from Oil Pressure gauge), Black (Ground if used).
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