[quote author=BigBlue link=board=4;threadid=16913;start=0#158747 date=1057912575]
I'd sure hope it didn't show any signs of wear. With only 400 miles on it. What do you think could be the cause of such low pressures from the factory? Different machining tolerances?
[/quote]

I would suspect manufacturing tolerance - and there are many possible contributors - weak bypass spring would be a prime suspect, off-tolerance clearances in the pump rotor and/or vanes, too much end clearance between rotor end plates - or there could be minor problems in the motor itself, brushes need to seat in better for maximum power/RPM in the motor - binding in the motor bushings or poor clearance that slows the RPM - many possibilities - but *I* would bet that simply running that pump for a while would see the PSI slowly increase as individual components seat against each other - no problem in my case, since my pusher pump would take up the PSI slack - but COULD be a problem for guys with engine mods, but stock fuel delivery systems who really NEED all the PSI they can get while under heavy loads... I'll get a better idea when I run a pressure/flow test later...

Alpine - yeah, I'm familiar with the PSI in/out differential bit, but am hoping that since my system is running a modded pusher that reduces/bypasses the pusher, and is intended primarily as a low pressure priming and flow assist rather than an all-out pressure booster, that it's milder impact will not radically overboost flow to the stock pump, but rather help it to run at optimum capacity, and still maintain proper internal bypass flow. Unfortunately, I have no way to actually test as to whether that is actually happening or not - again, only time and miles will tell...

Here's a pic of my modded Carter 4600 pusher:

 

I suppose that to head off questions on the pusher bypass, I should explain - the shown bypass includes a "flopper" valve that SLIGHTLY reduces PSI when functioning normally - reducing max PSI output by about 3-4 psi - this was done because without this arrangement, PSI at the VP-44 was sitting at about 26 PSI at idle - too much for my comfort. Second, I wanted some protection in the fuel delivery in case the added pusher failed for any reason - so if/when the pusher is shut down, the flopper valve reacts to the suction of the stock LP, opens, and allows nearly full normal flow around the pusher as though it wasn't there - actual test shows that I still get 15 PSI at the VP-44 even with the added pusher shut down...

On the other hand, if the stock LP should fail, there SHOULD be enough PSI provided by the added pusher to overcome losses thru the failed stock LP to still allow operation of the Cummins... Details of how the flopper valve was made are displayed in the "pusher pump" section in the web pointer at the top of my sig...

 

[quote author=vegasbound link=board=4;threadid=16913;start=#158859 date=1057945023]
Gary, Do You wire the pusher into the stock LP pump wire. so it operates in unison with stock pump? I'm new here, but learning alot of things about these trucks and engines.
[/quote]

I got a lift pump extension wire harness about 6 inches long from Cummins - part # 4025182 - costs about $7, and spliced into that for a control voltage that operates a low-current coil Radio Shack relay with contacts good for 20 amps - THAT relay takes fused power off the main fuse panel to operate the remote added pusher pump - I didn't want to place the additional load of the added pump in parallel with the existing pump and chance damaging its control circuit, this way the added relay and pump is controlled right off the stock LP - here's a pic of the relay and its placement:

 

[quote author=Mark Thomas link=board=4;threadid=16913;start=15#159068 date=1057979776]<br>Is the carter available for the 03' so cummins if yes where can I get one?<br>[/quote]<br><br>Carter makes a fairly wide selection of pumps in varying PSI and volume - your '03 uses a different fuel system than prior years, so not sure if an added pump would have any useful benefit...