Duramax Diesels Forum Truck of the Week
  #1  
Old 10-18-2017, 08:03 PM
N2BRK N2BRK is offline
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Default low idle lift pump pressure

I'm not really sure what's going on. Maybe someone here has an idea that I haven't considered.

I have a MITUSA lift pump. It's not as strong at idle as it was when brand new, but still pumping a good 10psi or so. The regulator is a 12psi fixed regulator.

I ditched the stock cp3 for a 12mm Exergy stroker, and when I started up the truck everything was great except the lift pump gauge was whacky; like I was looking at vacuum not pressure. When I'd give her a little throttle, I would see the pressure come up just fine. WFO she was holding a good 8psi or so.

It was decided that the MITUSA pump was around 100k and 7 years old, and time for replacement.

I bought a new pump from Glacier (Rich is a huge help!) that is very similar to the MITUSA. Results are exactly the same! So, could there be a failure of the new CP3 creating excessive return at idle? It's the only change that was made taking me from pressure to vacuum at idle immediately after installation. Other ideas are a regulator sticking (highly unlikely in my opinion), or a pinched feed - also unlikley but I'll look again tomorrow more carefully. OR does a 12mm suck so much more at idle that this is common? The last seems absurd to me, but I'm just a hobbyist here so WTF do I know

I'd like to resolve this before I drive all the way to Mark in a couple weeks for a retune!

Thanks in advance,
Wally
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Old 10-19-2017, 05:58 AM
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Dozerboy Dozerboy is offline
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Default

I saw no change in fuel pressure at idle when I went to a stroker. I have dual Kennedy pumps. Are you maintaining pressure under throttle? WOT? It so I wouldn’t worry to much, but check out those other possible issues.


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Old 10-19-2017, 07:29 AM
N2BRK N2BRK is offline
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I hammered my tune 4 (around 600hp) and held 28k just fine, while showing 7-8psi on the lift pump gauge. My only concern is at idle.
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Old 10-19-2017, 09:17 AM
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kiwilml kiwilml is offline
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I'm just remembering something on my lml I had.. I swapped in a 10 mm cp3 and I lost about 3 to 4 lbs of lift pump pressure..

But that was going from a cp4 to a 3 so I figured that was just the difference in them..

I'd say what you have going on isn't normal though but I sure wouldn't know what would be causing that for you..
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Old 10-19-2017, 09:59 AM
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Burn Down Burn Down is offline
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Stock fuel lines on the lmm like to kink. You could unhook your supply line and stick it in a gallon of clean fuel, to eliminate a line restriction problem.
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Old 10-19-2017, 11:15 AM
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I had a similar issue. I had to turn my AD up a couple psi when I put the stroker pump on.
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Old 10-19-2017, 11:29 AM
N2BRK N2BRK is offline
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thanks Kyle!

Exergy just sent me a reply that this is normal. They flow extra for cooling. I'll either accept it as normal or need to run a different pulley on the pump for additional RPM.
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Old 10-20-2017, 01:16 PM
N2BRK N2BRK is offline
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in case anyone ever lands on this thread with a similar question, I'll post a bit of infrom from Exergy on the 12mm:

Quote:
The total required supply flow at idle (700 rpm) is 2.5 lpm or 40 GPH. This includes both return flow and the high pressure flow to the injectors. To show the other extreme: at 4500 rpm & MPROP (FCA) all the way open(<600mA), the required supply flow is 8.5 lpm or 135 GPH.
I'm going to get a new pulley and spin my pump faster.
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