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Old 11-27-2022, 01:10 PM   #1
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Location: Kempner Texas
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Fuel pump voltage

1997 pace arrow ford chassis 460 eng EFI. Last time dad used it was 2018. I tried to start it but no fuel pressure. Disconnected the fuel filter cycled the ignition and no fuel. Could not hear the fuel pump either. Drained 65 gallons of stale fuel. I put the fuel in barrels and lit them. No flash just a gentle flame for over 5 hours. Pulled the pump looked good along with the inside of the tank. Checked for power at the connector when cycling power and cranking the engine. I would get 12 volts for a couple of seconds then it would drop to 7 volts when cycling the key. I tried it with a chassis ground also the same result. When I cranked the engine I would get the 12 volts then drop to 7 when I released the key. Iím not understanding the 7 volts. Iím looking for a schematic to see if it clears it up for me. Also I took the pump and connected it to my battery it worked. Connected it back to tank connector and it works now. Placed it in a bucket of clean fuel and the engine fired up and ran good. I put welcome.
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Old 11-27-2022, 01:19 PM   #2
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There is a rollover crash switch under the dash that cuts power to the pump. It's a steel ball resting on contacts. Try bypassing it.
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Old 11-27-2022, 01:42 PM   #3
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So Ford used very same light duty engine and transmission in Ford pickups.. go online and get basic automotive repair book for 1997 Ford f250 or f350 with Ford 460.. this will walk you through repairs... same wiring diagrams and troubleshooting.. how old is fuel pump ? And did you put old one back in?
Good luck and keep us posted
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Old 11-27-2022, 04:18 PM   #4
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Quote:
Originally Posted by Doppler1963 View Post
I’m not understanding the 7 volts. I’m looking for a schematic to see if it clears it up for me. Also I took the pump and connected it to my battery it worked. Connected it back to tank connector and it works now. Placed it in a bucket of clean fuel and the engine fired up and ran good. I put welcome.
A couple of things. First the fuel pump will only run for about 10 seconds when you key on and the engine is NOT running. To me, it seems odd that you are getting ANY voltage after that 10 seconds !

Second, I don't remember when Ford started doing this, but they went to a "returnless" fuel system about the time your chassis was built. Original EFI systems would pump a large quantity of fuel up to the engine. A mechanical fuel pressure regulator would send the excess back to the tank. This caused hot fuel and excess vapors in the tank. The solution was a separate electronic fuel pressure controller that would pulse width modulate the voltage to the pump. Some meters might register this as less than 12V.

In your case, it sounds like simple corrosion on a connector that got "cleaned" from unplugging and plugging it back in.

Last, don't use a meter for this type of testing. Use an old fashioned, non-LED, 12V test light. This will put a load on the circuit. If you have approximately 12V, you will have a bright light. Less than 12V, dim. Some mechanics make up a HD test light (2 stop/turn signal bulbs). This would draw about 4-5A.
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Old 11-27-2022, 04:44 PM   #5
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This one has a fuel return line. I use a fluke digital multi meter. I will try what you said about using a test light tomorrow. I don’t Remember the contact but when I was checking where the fuel pump relay is I had the 12 volt feed voltage from the fuse but I also had 3 volts on the contact that closes the relay with the key in the run position. Can that be because of a bad PCM?
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Old 11-27-2022, 05:12 PM   #6
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Sounds like imho .. more like bleed over on relay not pcm.. that said.. Ford had problem with bad capacitors in certain pcm.. in early 90s .. I would check relay.. just replaced and re check.. I also would pull pcm.. not that hard.. and post pictures of caps .. we can tell you if bad.. well sometimes..
I am thinking more towards.. the pcm runs 7v thru f/p to keep alive the relay while key is on.. or you got chafing in harness some where.. it's very common members post that they seem to many times find chafing.. so it is time consuming.. but you are going to.. need to.. find it.. but 1st check voltage at all sides relay.. replace it.. then head to the emergency fuel shut of.. check there.. then start checking harness.. if you have a continuous tone generator on fluke or hook a old horn in harness and shake harness.. check around engine area.. because heat can partly melt wires together.. inside and unless you look at each wire.. you will never find it..
Grab a book.. and check out f/p troubleshooting..
Good luck and keep us posted
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Old 11-27-2022, 07:54 PM   #7
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Quote:
Originally Posted by Doppler1963 View Post
This one has a fuel return line. I use a fluke digital multi meter. I will try what you said about using a test light tomorrow. I donít Remember the contact but when I was checking where the fuel pump relay is I had the 12 volt feed voltage from the fuse but I also had 3 volts on the contact that closes the relay with the key in the run position. Can that be because of a bad PCM?
99.999% of the time, you don't get power FROM any electronic box. Positive voltage comes from a different source and the electronics turn it on by providing a path to ground.
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