Michael

No need to purge air, it will just compress as necessary and allow the gauge to read. The problem with air is when using an isolator, as it runs out of diaphragm travel if it has too much air to compress.

The original symptoms sound like an isolator that needs to be refilled. Here are the instructions for doing that: Remove the line and fitting from the "gauge" side of the isolator. Using a skinny but not sharp rod (like the eraser side of a wooden pencil, or a chopstick), push into the isolator from the now-open side, to push the piston completely to the other side. If the isolator is mounted such that the gauge side port is not pointing straight up, temporarily remove the mounting hardware and hold it with that port pointing up. In this orientation, fill the gauge side of the isolator with antifreeze (using a turkey baster or syringe), then replace the fitting and tube. Remove the other end of the tube from the back of the gauge, and fill it with antifreeze (using the turkey baster or syringe). If you have someone helping you, it helps to have them loosen the tube at the isolator (while still holding it with the fitting pointing up), to let air out of that end while you force the fluid in from the gauge end. Re-install the tube to the back of the gauge, tighten everything up, and check for leaks. The rattle in the gauge could be due to that, or it could be the gearing just getting more loosened up with age and the pulsations that come from a VP44. If you send me your mailing address at michael at isspro dot com, I can have a replacement smaller orfice sent to you. It threads into the back of the gauge, just remove the fittings from the back of the gauge and use a small flat blade screwdriver to remove the old one and install the new one. Regards, Michael Pliska

I have seen some fluctuation still in the electric-pumped P-pump trucks, but the farther away from the P-pump that you tap into the line for the sensor, the less fluctuation you will see. As mentioned above, if you use the port on the Air Dog you should be fine.Regards,Michael Pliska

I'm a newbie here but have been around the diesel scene and other forums for a while. I am the engineering manager at ISSPRO, and I have been driving the MBRP/DirtyMax truck since 2008. I have vacated that seat now though and am building my own Pro Stock Diesel pickup. No, it's not a Cummins engine or Dodge body, but at least it is diesel! Please let me know if you have any questions about ISSPRO stuff or drag racing and I'll do my best to answer!Regards,Michael Pliska

If your gauge intermittently drops to zero then I would first check the wiring at the back of the gauge, particularly the red/yellow and green wires. Did the little black wire insertion tool have an ISSPRO logo on it? If not, it was the old version which tends to deflect too much and makes it hard to push the pins in. When using one of those I grab the wires while squeezing the connector and tool together, and pull the wires towards the orange connector, pulling them deeper into the "V" of the connector terminals.As far as the pulsations go, every VP44 truck puts them out onto the fuel supply line. As suggested, it is best to use a needle valve as an adjustable snubber. From my experience the grease gun hose offers a bit of additional smoothing when used with a needle valve, but the majority of the benefit is from the needle valve. Depending on the age of your gauge (if the "S/N" is earlier than C300) then you may have the older software version, which will allow more of the pulsations to be displayed on the gauge. Newer versions have more filtering in the software, specifically aimed at reducing the pointer motion from injection pump pulses while still showing changes like a drop in fuel pressure.Regards,Michael Pliska