Gear Pump Testing
10-17-2021, (Subject: Gear Pump Testing ) 
Post: #1
Gear Pump Testing
I wish there was a few more threads or more testing info on the gear pump for the CM871, I have been fighting fuel milage issues since I got the truck, I ran down the whole list of everything, boost leaks, EGR tune-up, injectors, sensor's filter, blah blah blah,and finally just decided to put a new lift and gear pump in and they made the most difference from any other repair, I went from 5 mpg to 6.6, and pretty sure theres a burnt valve still, granted there was alot of other issues along the way, and there never was any codes for it and the pressure was always within spec, even with a mecahical gauge on the old pump to the new pump no high pressure difference were noticed, but on the lift pump I went from 12 psi to 20 psi, and need alot less throttle going everywhere, it's kinda nice. Hope this could help someone out.
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 Thanks given by: hookliftpete
10-18-2021, (Subject: Gear Pump Testing ) 
Post: #2
RE: Gear Pump Testing
Simply replacing a worn gear pump and electric lift pump on a CM870 or CM871 is not going to make a 1 mpg difference unless one of them was sucking some air... or you were getting low pressure fuel problems that were noticeable, causing CEL lights to come on. Something does not add up properly in your statements there.

I have more than 1.4 million original miles on my gear pump and electric lift pump, and I still get 9+ mpg with the truck while loaded heavy, everywhere it goes.

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Also if you suspect a burnt/leaky valve causing compression loss, then you need to remove all the rocker arms and pressurize the intake manifold up at 30 psi and listen/check for leakage while all the valves are shut... and then do the test at the exhaust manifold.

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You also need to do an overhead adjustment on it and do a proper injector leak test on it...
http://rawze.com/forums/showthread.php?t...8#pid67948


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10-18-2021, (Subject: Gear Pump Testing ) 
Post: #3
RE: Gear Pump Testing
I know I didnt think it would make that much of a diffeance but it did, so far I'm up 1.5 mpg, I pressure and vacuum tested the fuel system several times and never found a leak, watched my pressrues under load and empty at idle, even took it to the shop. It helped, and I should've know it was hurt from having fuel lines coming apart in it for so long.

I did pressure test and smoke test the intake side when i did the injectors and has very low pressure coming out of cylinder 1, but did not do the exhaust side, and cylder one was very wet and carboned up.

still trying to figure out if i want to take on the head, or take it to haggie or a dealer.
Just got a few more things to do to the new back up truck so this one can be down.
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