I know this has been ask before sry for asking again. I was needing some information on fuel pressure reading. My setup is Holley Blue pump and regulator no return I set pressure to 7 psi. I took boat out and after a while pressure drop to 3.5 psi. I brought boat back home after a few hour I went out to mess with it and pressure was back up to 7 psi. Any idea what causes this? Any information would be helpful thanks. Also fuel pump is wire on a toggle switch with a and fues relay not on ignition switch.

The pump is burnt up. Where do you have it mounted?

dont know how old the pump is but the quality of those pumps is not so great.

It was a brand new fuel pump and regulator first time out with it. it mounted in the engine compartment against the back seat about a foot or two away from the engine.

As I understand it, most electric pumps are designed to push fuel rather than pull it. So you need to mount the pump as low as possible so that it can develop a good siphon from the tank pickup. It is not going to be able to suck the fuel out of the tank to a level very much above the level of the tank. I have mine mounted on the stringer right in front of the engine - it is the lowest point I could mount it. You may have burned up the pump by not allowing it to get a good prime. It's also possible that it is just cavitating from being mounted so high. Try a lower location and see if that helps.

As mentioned, may be mounted to high. Inadequate power supply or ground. Lack of tank venting. Make sure there is a good filter before the pump too.

If you have a liquid filled fuel pressure guage on the engine somewhere, this could be it.

They are filled with glycerin I believe - anyway, when the liquid heats up it expands and puts pressure against the diaphragm on the opposite side the fuel is pressurized. This causes the guage to read low, even if the fuel pressure hasn't changed.

Edit in: believe me, I manufacture/sell a fuel psi guage adapter for a certain application and when I first sold them I supplied a liquid filled guage. I had to eat about 200 of them when i figured this out. Calls to Autometer, Mr gasket, etc,etc led me no where. i figured this out finally in the shop.

Life's a beatch right ?

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Just read where fuel pump is mounted....I agree...that is not in good location. In a perfect world it should be mounted lower than fuel level.

Why do you think Merc had to use mechanical lift pumps for many of their EFi systems with electric pumps which were mounted on the engine. Same reason.

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Antisipon valves can play havoc with electric pump fuel systems because of their small ability to 'pull' fuel.

thanks for info I will look and see if I can lower it closer to the tank

SB , who in your opinion has the most accurate fuel pressure gauge ? This is the style I'm referring to . http://www.ebay.com/itm/like/331164469013?lpid=82 Feel free to PM me .

I just wanted to add that I've had the face plates crack during the winter months on liquid filled fuel pressure gauges . That's not supposed to happen but it did .