procharged HP500 fuel pressure not coming up with boost.long post
 

it has the red aeromotive pump with the boost refrenced regulator.the line is hooked up on top of the regulater to the boost box but no increase in pressure when i bring up the rpms.the blower does have boost pressure.i took the regulator apart and nothing looked clogged or bad to me still no increased fuel pressure with boost.the regulator must be bad im thinking if i set the fuel pressure at 9psi with the motor off and start it it goes down to about 6 at idle and dosnt increase.im being very carefull and just did a quick check so i dont lean i out.maybe the regulator is shot?

definitely something weird with the regulator, make darn sure you have the lines all connected properly - it wouldn't surprise me if it were inadvertently plumbed in backwards or something.

it cant really be routed wrong or backwards (i dont think)its just a line from the air box to the top of the regulator.

The Aeromotive fuel pump is a positive displacement pump. It has to be used with a regulator that has a bypass fitting. The fuel goes in the regulator, the fuel goes out of the regulator to the fuel rail/carb, the pressure tap in the carb box goes to the pressure sense fitting on the regulator and the bypass dump on the regulator goes back to the tank.

The regulator should index 1:1 with the boost pressure. If you start at 9 psi with the motor off, you should see 9 psi with the motor running, and 10 psi with 1 psi in the box and 19 psi with 10 psi in the box.

you should be measuring fuel pressure from a tee just outside of where the fuel line goes into the box, OR on the far side of the carb coming back OUT of the box (most don't do it that way but it is considered to be the most accurate).

It is significant that you say you have 9 with the motor not running but it immediately drops to 6. This is not correct.

Check the line from the box to the regulator. I had the same problem. Turned out to be a hole in the line.

Also could your guage be bad?

thanks for the replys.the fuel pressure gauge is plumbed from a port for it on the regulator it has a electric sender.im going to try a new line and im going to try the outlet line from the blower box that goes to the boost guage and put it to the regulator i know that line has pressure.the actual line that goes to the regulator is under the boost box its hard to see but looks like its to the top of the manifold.it is working opposite with the motor off 10/11 psi start the motor at idle and it has around 6psi and dosnt increase with blower pressure pull of the line on top of the regulator and pressure goes up to around 9psi.im going to check that line its almost like it has vacume instead of boost.i just bought the boat and the motor just came off the dyno but the previous owner installed it not sure what this guy did.

Sutphen 30 is right you should see a drop in fuel pressure when the motor goes into vacuum, only by a couple of pounds, though. Check your fuel pressure at the same port with a mechanical fuel pressure gauge. See if you get the same readings.

The boost reference line on a blow through carb application needs to be hooked to to air box, if it is connected to the manifold it is seeing vacuum at idle (that is why the pressure drops when you start it) and will not see any pressure unless the engine is under load at full (or mostly full) throttle. Your boost gauge on the dash however should be hooked to the manifold. I think you have the reference line in the wrong place.

WRONG PLACE WRONG PLACE.

Bam has it right.

regulator must sense the same pressure that the float bowl vent sees. This is the BOX pressure. Fuel line pressure must remain 5 to 8 psi AT THE CARB INLET in relation to the pressure ABOVE THE throttle plates (in the box).

Boost gauge should reference the intake manifold UNDER THE CARB.

Regulator should NEVER see a vacuum signal. Depending on which brand of regulator it is, it can damage the diaphragm.

You will also need to rejet your carb for the proper float level. It's a wonder that the motor didn't eat itself running on a long pull with such low feed pressure under boost.

I'll further explain my post. The line I am talking about is the small line that connects from the carb box to the barbed fitting on the regulator.