HELLO! MY INTANK FUEL PUMP QUIT AND SOMEONE INSTALLED A INLINE PUMP. THE PROBLEM IS WHEN I TURN ON THE KEY TO POWER IT UP, IT TURNS OFF AFTER TWO SECONDS. THE NEW FUEL PUMP RELAY IS SPLICED TO THE OUT LINE OF THE INERTIA SWITCH AND ALSO GROUNDED TO THE FRAME. BOTH INCOMING AND OUTGOING WIRES TO THE INERTIA SWITCH HAVE 12V FOR 2 SECONDS AND GOES OFF. THE FUSE BOX RELAY IS WORKING FINE BUT THE GROUND FOR THE SWITCH PART OF THE RELAY REVERTS FROM TOTAL GROUND TO 1.75 VOLTS AFTER 2 SECONDS. THIS OPENS THE RELAY AND THIS OPENS THE FUEL PUMP RELAY. SO AFTER 2 SECONDS I HAVE NO ELECTRIC TO THE PUMP. CAN I JUST RUN A PERMANENT GROUND TO THE FUSE BOX RELAY TO FIX THE PROBLEM? ALSO THERE WAS A VERY HEAVY DRAW GOING THRU THE RELAY TO THE INERTIA SWITCH AND I ASSUME TO THE INTANK FUEL PUMP. WAY OVER 10 AMPS, SO I DISCONNECTED THAT LINE AT THE INERTIA SWITCH BUT STILL HAVE IT HOOKED UP TO THE NEW FUEL PUMP RELAY. IS THIS WHAT I SHOULD BE DOING?

You might want to post what chassis you have so anybody with good knowledge of that particular chassis / model / year can offer some help.With a Chevy P30 chassis, when you first turn on the key the engine computer causes power to be applies to the fuel pump relay for two seconds to supply fuel under pressure to the fuel rail.Then when you continue to turn the key to start the engine, power is applied to the fuel pump relay once again as the engine is cranking over.When the engine starts and oil pressure comes up, the fuel pump relay drops out and a pair of contacts in the oil pressure sender close to provide power to the fuel pump. Those contacts then become power to the fuel pump so long as the engine is running and producing oil pressure. The relay is no longer providing power.Apparently you are tied into the fuel pump system somewhere that is not providing power once the engine is running.Is your problem that the engine starts and then quits once you let off the key???

Do you know how to turn off the CAPS?Posting in ALL CAPITAL LETTERS is internet yelling.As was suggested in your other posts, most folks won't bother with reading one in all caps.So if you are looking for help...turn off the caps.

It is common and a safety feature for a fuel pump to cut off if there is no oil pressure. You need a good diagnosis for your model to see what you have.

I didn't bother reading the OP. All caps is just too much work.However, it should be noted that all the electric fuel pumps I am familiar with shut off as soon as the fuel pressure reaches what it is supposed to be. Turn the key, they stutter for a couple seconds and quit. As the engine starts and fuel starts to flow, the click on and off as needed to maintain proper fuel pressure. I've never heard of an electric fuel pump that runs continuously.

Does the engine run? If it does, then don't worry too much about the voltages because the fuel pump is designed to shut off once pressure gets to the max. Has the in-tank fuel pump been disconnected completely and is out of the electrical circuit so that it is not feeding back anything to your ECM?

INSTALLING INLINE ELECTRIC FUEL PUMP | Good Sam Community

EAKOCH
Explorer
Jan 25, 2014
Okay, everyone. I apologize for using all caps in my previous posting. I didn't know that it was offensive. I am very old schooled in mechanics so the explanation of how it works now days was very helpful. My unit is built on a Ford motorhome class A chassis 1996. When I disconnected the wire to the inline fuel pump at the inertia switch it probably was a not a good idea. However there was a very high amperage draw (way over 10 amps,) and I was afraid that the intank fuel pump was malfunctioning. I guess that I should just drop the 75 gal tank and replace the intank fuel pump. I want to thank everyone that took time to try and help me.
More_To_See
Explorer
Jan 25, 2014
At this point if you would like to perhaps keep that external fuel pump I'd probably just use the existing wire to the in-tank pump to control a power relay or solenoid. Break the connection to the in-tank pump so it's no longer in the circuit. And of course pick up good power somewhere with a fused line back to that relay / solenoid. Maybe just wire up that arrangement laying out on the ground to prove it will work before doing a neat and proper "harness" job onto that chassis.

As a quick troubleshooting check, why not electrically reconnect just your in-tank pump and see whether power is maintained there while attempting to start the engine. (Of course the defective pump will not provide fuel to actually start the engine.)

Good luck with the problem. I'd be interested in finding out how you finally get your rig up and running again.
tropical36
Explorer
Jan 26, 2014
EAKOCH wrote:
Okay, everyone. I apologize for using all caps in my previous posting. I didn't know that it was offensive. I am very old schooled in mechanics so the explanation of how it works now days was very helpful. My unit is built on a Ford motorhome class A chassis 1996. When I disconnected the wire to the inline fuel pump at the inertia switch it probably was a not a good idea. However there was a very high amperage draw (way over 10 amps,) and I was afraid that the intank fuel pump was malfunctioning. I guess that I should just drop the 75 gal tank and replace the intank fuel pump. I want to thank everyone that took time to try and help me.

Before you drop the tank, check to see if you can't do a trap door in the floor above the pump works. It's been done many times with certain rigs and does save time and expense for what might be a next time and especially with so many problems arising with the pickup and hose for the genset fuel delivery system.
EAKOCH
Explorer
Jan 26, 2014
Okay "MORE TO SEE & TROPICAL 36", I like your suggestions and they are both worth looking in to. I would like to get the motorhome running (to get the wife off my back) and then go from there for the best solution to keep this rv on the road. Thanks again everyone.

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INSTALLING INLINE ELECTRIC FUEL PUMP

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