INSTALLING INLINE ELECTRIC FUEL PUMP

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?

EAKOCH wrote:
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?

Didn't pay much attention to the caps until it was pointed out and commented on.
Anyway, you haven't said whether or not the thing runs and how well it does so?

Why not redo it correctly?

You aren't listening, are you?

Hello! I just bought this 96 Sea Breeze and the motor runs fine on starting fluid but a couple years ago the original owner had a intank fuel pump failure. He went to this site and Tom (Dirt Rod) sent him instructions on not to replace the intank fuel pump but to install a inline fuel pump instead. I have not replaced the inline fuel pump which has failed because of the electrical problem that I am having. The problem is, as I previously stated, that the power shuts off after two seconds. I know that at this point, installing the new inline fuel pump will not work without the relay staying open to supply electricity. I have been told that the unit ran fine with the inline fuel pump. I will listen to any advice that will help me put my new motorhome back on the road. (ps. this last spring two young men tried to get it running, they dropped the fuel tank and flushed it out and installed a cheap inline pump from the local parts store. I bought a WALBRO 255LPH HIGH PRESSURE GSL392. I hope that it will do the job.)

That fuel pump is a high capacity unit that is used for a lot of situations, including replacing the in-tank fuel pump. What might be the problem is that it also draws quite a few amps and you may be exceeding the amperage capacity of the relay or the gauge of the wires feeding the pump. If this happens, the relay may trip.