Engine/Transmission (1998.5 - 2002) Lift Pump Pressure Question?

[Max Wedge]

I am running the Vulcan 1/2" Line Conversion with a 'new' lift pump back by the tank--hooked up a mechanical pressure guage to the tapped elbow at the VP44 and I am getting readings from 14lbs idle to 8. 5 full throttle with EZ Pro Comp Drag Box on level '5'.



Now here is the pressure question, I can be either cruising down the highway (no load) or parked and the pump will change noise pitch and pressure will drop to about 6lbs momentarily and then recover to 13-14lbs. Or if setting still with it idling in 'park' and it drops to 6lbs, I can touch the throttle and it will recover immediately to 13-14lbs.



Any ideas?



Max

 

[monkeyman]

Where are you getting your 12 volts from? I would check with a meter to see if it is really 12 volts all the time.
Rick

 

[Max Wedge]

I am getting the 12 volts supply from the factory 12 volt supply from the original lift pump connection via the Vulcan supplied electrical connection. All connections seem to be good, as I have instpected them.



I thought that maybe the ECM is controlling the power and limiting it???]



Max

 

[monkeyman]

That is where my Fass is hooked up, I see a steady 19psi all the time. Im not to familar with the Vulcan System, Is the pump vane,piston etc? It may be affected by voltage spikes, or your gauge could be wrong also!
Rick

 

[jhoughton]

I had the same thing going on. I found that the connection to the fuel tank was sucking air and causing a lot of bubbles in the fuel. This is a slip connector with an O ring seal. Possibly the new fuel causing the O ring to dry out. I installed the draw straw mod and with the same pump now have 12-13 idle and have not been able to pull any lower than 11psi.

 

[JKinney]

I also had a stock lift pump doing the same thing. It was located back by the tank with a vulcan kit. I think that was lift pump #3 Replaced with #4 and has been great for a year. You can try dielectric grease on the electrical connector.