Fuel pressure on carb 454
 

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 ?

=========================

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.

==========================

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 .

That price point Marshall guage is not stainless shell. As with any chrome guage, it rusts fast. I've used a bunch of them. Have had a few go bad out of many used. Not a bad cheap guage overall.

Liquid Filled guages where a fad. I was early in with that fad and early out. LOL.

I'm trying to ask you what do you use . Do you have a favorite for accuracy and dependability . The ones I have used were junkers .

When I use an electric pump I mount it in the bildge under the motor. If there isn't any thing to mount the pump to I just glass down a piece of wood and use some short screws. When you mount the pump above the gas level it causes the pump to over heat and it looses its tolerances it will still pump fuel but when there is a large demand it can't keep up = low fuel pressure. Once you over heat the pump one time it's done it will never be right again.

Honest ? Not really any. I prefer to run Electric Guage of your choice in dash. Temporarily install mechanical screw in guage (known to work) to see what psi it reads and then install electric psi sender for guage installed in dash. Note the difference.

When, and if, electric guage reads different or acts weird, remove sender and install known good screw in guage to determine if issue with electric one or not.

I've had most all screw in guages break at some time or another (in boats especially and race and/or serious street cars) , not too mention, you can't read them when at WOT and top speed.

Just my single person experience.

That's what I was looking for . Thank you .

These are reasons I don't like electric fuel pumps for most applications. Your basic marine engine, carbureted, even with the mercury sea pump/fuel pump deal, is more than adequate. If you have a block mounted pump, an old fashioned 6 valve style pump that cost less than 150 bucks, with 1/2'' NPT inlets and outlets, will supply 1000HP all day with carbs, and last a long time. The standard merc sea water pump mechanical will also move a good amount of fuel.

Some guys assume electric pumps are the way to go, and that they are gonna get some sort of performance enhancement from adding them. If you have fuel starvation issues with most mechanical pumps, its usually not the pump itself, but the line size, pickup size, etc.

Only time I would want to go electric is with something like a Weldon, aeromotive, with a return style regulator, on high power stuff, or EFI. I have no use for those BS holley blue/black pumps with dead head regulators..

Good advice on mounting the fuel pump below fuel level. I would install a shut-off valve just before the pump if you don't have one already. If your pump starts leaking or you need to swap out the pump, a shut-off valve will come in real handy.