question about fuel pressure regulator

[jsmith]

Hey guys, Can someone explain to me the purpose of the vacuum source on top of the fuel pressure regulator. I know we check or set the fuel pressure with the line off and then when you put the vacuum line back on the pressure drops but why, and what purpose does that serve.

what would happen if that vacuum was being somehow interupped during engine operation. Would or could it cause a fault within the FPR.

Thanks

Jeff

 

[TR87386]

This is not only for vac we have boost referencing regulators in these cars to increase FP as boost increases.

 

[ijames]

By referencing the top of the regulator to the intake manifold it will keep the fuel pressure at a constant amount above the manifold pressure. That way the amount of fuel the injectors deliver at some amount of open time is always the same, so the ecm knows how long to open the injectors for whatever amount of fuel it has calculated the engine needs. If the manifold is under vacuum and the hose comes off the fuel pressure will rise, but if you are making boost and the hose comes off the fuel pressure will drop and the engine will go lean - maybe enough to hurt a head gasket or worse. Won't hurt the regulator itself, but lots of other stuff.

 

[jsmith]

Thanks carl for the explanation. The problem isn't with my t type but with the boat. Maybe some here has an idea. It's driving us nuts. It's a ski boat with a fuel injected 454. sits under a dog house. has run perfect for 12 years this summer seems to be vapor locking when it heat soaks. I up a fuel pressure gage on it and when it quites running or won't start it has 0 fuel pressure. We installed a new fuel pump assembly, cleaned the tank pickup, had ecm checked, pump relay checks good, Even jumped battery direct to pump(electric high pressure pump) can hear pump running but no pressure. This problem is deffinately heat related. can heat effect the Fuel pressure regulator? or it also has an engine driven pump that supplies the high pressure fuel pump, could that be effected by heat? It's just a diapram pump I wouldn't think it can get effected by heat. We are ready to sink this thing, anyone have an idea? are we on the right path with the FPR?

Thanks

Jeff

 

[bmackinnon]

I up a fuel pressure gage on it and when it quites running or won't start it has 0 fuel pressure. We installed a new fuel pump assembly, cleaned the tank pickup, had ecm checked, pump relay checks good, Even jumped battery direct to pump(electric high pressure pump) can hear pump running but no pressure. This problem is deffinately heat related. can heat effect the Fuel pressure regulator? or it also has an engine driven pump that supplies the high pressure fuel pump, could that be effected by heat? It's just a diapram pump I wouldn't think it can get effected by heat. We are ready to sink this thing, anyone have an idea? are we on the right path with the FPR?

Thanks

Jeff

I have a MasterCraft, so I'll ring in... :biggrin: If your sure the electric pump is good, must be either the mech. supply pump or the FPR dying. Both have rubber diaphrams, so I suppose it's conceivable that one of them could be leaking when warm? See if you can pinch off the (rubber part of) fuel return line with a pair of pliers (carefully) when experiencing the zero fp problem, and see if the pressure comes up. If so, then the FPR is bad.... If not, must be the mech supply pump is not supplying...... my money's on the mech. pump....

Edit: uhh... you changed the water separator/filter, correct?

 

[corsair231]

Most electric pumps won't cause a vapor lock problem but mechanical pumps can. I don't know much about boats but assuming that it is an engine mounted pump like a car set-up then they put a lot more heat into the fuel than an electric pump. If that's the case the mechanical pump would be my bet as the culprit too.

 

[unix_punk]

Worth noting that if it is electric then it is possible that the output hose INSIDE the tank could've popped off which is just causing the pump to blow the gas up at the top of the tank and right back down instead of through the output line in the hanger, if there is one not too sure how boat tanks are setup...