502 Efi - need for more speed
10-01-2003, 10:43 PM
#11
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Location: Spicewood, Texas USA
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Mav, I agree the cam is not a good choice. But, if the fuel pressure is falling at WOT then the engine is leaning out and you're not even getting the full performance that is available with your setup.
Formula...the regulator controls fuel pressure by routing the excess fuel back to the tank. If the pressure is dropping at WOT, then there is no fuel being routed back to the tank since all available fuel is being used. You could raise the pressure to 60 PSI, but it would still drop to 30 if the pump cannot supply the volume required to maintain the pressure. To me that is a red flag. If you set the pressure at a point and it drops at WOT, then you don't have enough volume. Reprogramming the ECU to a greater pulse width would icrease the volume of fuel required. If the pump was already maxed out then it couldn't keep up and the pressure would drop. This could be what is happening. I know they use a different pump in the VST system that is VERY small and may not keep up.
Formula...the regulator controls fuel pressure by routing the excess fuel back to the tank. If the pressure is dropping at WOT, then there is no fuel being routed back to the tank since all available fuel is being used. You could raise the pressure to 60 PSI, but it would still drop to 30 if the pump cannot supply the volume required to maintain the pressure. To me that is a red flag. If you set the pressure at a point and it drops at WOT, then you don't have enough volume. Reprogramming the ECU to a greater pulse width would icrease the volume of fuel required. If the pump was already maxed out then it couldn't keep up and the pressure would drop. This could be what is happening. I know they use a different pump in the VST system that is VERY small and may not keep up.
10-02-2003, 08:24 AM
#12
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One more question.
could my regulator have a problem?
The reason I ask is with the key on or idling the system will hold 38#.
But when I turn off the key the pressure will drop down over 2-3 seconds to 30# and hold there. ????
Thoughts??
MAV
Also, if the pump is lame ( I've already cleaned the screen/sock on the high pressure pickup in the VST tank) Is there an aftermarket pump that will fit in the VST tank??
could my regulator have a problem?
The reason I ask is with the key on or idling the system will hold 38#.
But when I turn off the key the pressure will drop down over 2-3 seconds to 30# and hold there. ????
Thoughts??
MAV
Also, if the pump is lame ( I've already cleaned the screen/sock on the high pressure pickup in the VST tank) Is there an aftermarket pump that will fit in the VST tank??
10-02-2003, 02:20 PM
#13
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fuel pump pressure
An electric fuel pump located in the VST pumps fuel to the fuel rail assembly. The pump is designed to provide fuel at a pressure greater that that required by the injectors. The pressure regulator part of the fule rail assembly regulates fuel pressure to the fuel injectors.
Unused fuel is returned to the VST....
Pressure should be 34-38 PSI and should hold steady when pump stops.
Unused fuel is returned to the VST....
Pressure should be 34-38 PSI and should hold steady when pump stops.
10-10-2003, 01:11 PM
#15
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Got the diag and will test.
I run the boat again and even though I've cleaned the filter/sock on the high pressure pump, pressure at idle is 38#, when shut off will hold 30#, running mid- range 34# and WOT pressure still drops to 30#!!!
WHat gives?????
regulator?? pump???
Help?
I run the boat again and even though I've cleaned the filter/sock on the high pressure pump, pressure at idle is 38#, when shut off will hold 30#, running mid- range 34# and WOT pressure still drops to 30#!!!
WHat gives?????
regulator?? pump???
Help?
10-11-2003, 06:27 PM
#17
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An additional electric fuel pump will only fill the VST tank faster. It won't increase fuel rail pressure. I doubt that the VST tank is running dry. Fuel pressure dropping after shutting off the engine is a injector leak. It will run dirty for a few seconds on start up.
Plug off the return line to the VST tank (from the fuel rail) and run the fuel pump in the VST tank (jumper leads from the battery), don't start the engine.
With a pressure gauge on the fuel rail, it should have 60 PSI if it is good. Don't hold it there for very long or you will burn out the fuel pump. If it will put out 60 PSI the fuel pump is fine.
Reconnect the return line and run the fuel pump. Rail pressure should go up to approximately 38 PSI (engine not running, no leaky injectors).
If you add suction to the fuel pressure regulator, fuel rail pressure should drop to approximately 30 PSI (high manifold vacuum at idle closes down the regulator to 30 PSI fuel rail pressure).
38 and 30 PSI are not concrete numbers. Many engines test slightly lower and still run fine.
Dennis Moore
Plug off the return line to the VST tank (from the fuel rail) and run the fuel pump in the VST tank (jumper leads from the battery), don't start the engine.
With a pressure gauge on the fuel rail, it should have 60 PSI if it is good. Don't hold it there for very long or you will burn out the fuel pump. If it will put out 60 PSI the fuel pump is fine.
Reconnect the return line and run the fuel pump. Rail pressure should go up to approximately 38 PSI (engine not running, no leaky injectors).
If you add suction to the fuel pressure regulator, fuel rail pressure should drop to approximately 30 PSI (high manifold vacuum at idle closes down the regulator to 30 PSI fuel rail pressure).
38 and 30 PSI are not concrete numbers. Many engines test slightly lower and still run fine.
Dennis Moore
10-11-2003, 07:18 PM
#19
Originally posted by Dennis Moore
If you add suction to the fuel pressure regulator, fuel rail pressure should drop to approximately 30 PSI (high manifold vacuum at idle closes down the regulator to 30 PSI fuel rail pressure).
Dennis Moore
If you add suction to the fuel pressure regulator, fuel rail pressure should drop to approximately 30 PSI (high manifold vacuum at idle closes down the regulator to 30 PSI fuel rail pressure).
Dennis Moore
10-13-2003, 12:23 PM
#20
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Dennis,
Thanks for the response. I've already run pressure with engine off and key on -->> 38#. Key off -->> system will hold 30# ALL of my #s are with vaccum line removed from regulator!! - so pressures should be max permitted by regulator.
Its running where the pressure drops to 30 that seems bad to me. Although, last saturday I ran the boat WOT and added positive pressure 5# (bicycle hand pump) to the regulator vaccum line - no change in performance --- so I guess more regulator resistance/pressure is of no help.
I'll try your suggestions.
Thanks.
MAV
PS Send me cost and address to get your BB chevy book. It's worth that cost to have you one the web.
Thanks for the response. I've already run pressure with engine off and key on -->> 38#. Key off -->> system will hold 30# ALL of my #s are with vaccum line removed from regulator!! - so pressures should be max permitted by regulator.
Its running where the pressure drops to 30 that seems bad to me. Although, last saturday I ran the boat WOT and added positive pressure 5# (bicycle hand pump) to the regulator vaccum line - no change in performance --- so I guess more regulator resistance/pressure is of no help.
I'll try your suggestions.
Thanks.
MAV
PS Send me cost and address to get your BB chevy book. It's worth that cost to have you one the web.
Last edited by maverick1; 10-13-2003 at 04:46 PM.
