Truck won't start unless primed

Redkliney

New member
Apr 10, 2020
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Pa
Ok need some help diagnosing. Did cp3 and injectors last week. Truck ran awesome for 4 days. Took the wife and kids to pick up the car at the garage for inspection and gave the gogo pedal a good push. Fell on its face and shut off. Figured a fuel line collapsing. I had to reprim the truck to get it to start ever since then. Put clear line from cp3 to the junction block and not getting air. Put on a vaccum gauge and with the truck idling will pull 2inhg at idle and 4inhg full throttle parked. Shut it off and let the rail pressure bleed down. Recrank and the rail pressure doesn't even budge. Prime it up and if fires right off lickity split. Tried unplugging the fpr and at idle will run about 25.5kpsi. Its an lbzsupersport pump. Was retuned and the fuel pressure desired and actual follow suit. Just does not seem to be drawing fuel to start unless its primed.
 

Redkliney

New member
Apr 10, 2020
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Pa
I had to bypass the lift pump. Caused my rail pressure at idle to go to 11500. The truck won't strat till i prime it to 10 psi though. Was told to regulate my lift pump to 4-5 psi so I'll have to find a regulator.
 

torqued2dmax

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Mar 26, 2017
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Brookville, PA
I hope you did not hurt your new cp3 with too much pressure on the low pressure side before you realized it and removed it ! Do you know what the pump was putting out ?
 

Redkliney

New member
Apr 10, 2020
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Pa
The first time i started the truck i saw it was at 11500. Saw my desired and actual Ma for the regulator way off. Thought about it and remembered the lift pump thing so i pulled the fuse and it ran with desired perfectly. Ran it for a few trips over a few days. When it fell on its face and i saw the line wasn't kinked i figured the extra pull through two filters and a off pump did it. So i removed it. Its still on the truck but no fuel lines hooked up. I still have my test gauge hooked to the test port line so i may hook it up just to see what pressure it was running at. If it was high what does it damage in the pump? I've been reading up about the cascade overflow valve and am wondering if it could have stuck open causing too much fuel to go to the return and not the fca?
 

DAVe3283

Heavy & Slow
Sep 3, 2009
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Boise, ID, USA
ReaperLegion.net
I don't think you can hurt the CP3 with too much inlet pressure. Well, maybe something extreme like 25+ PSI could cause the seals to leak, but you're probably going to be pissing fuel out of your FICM (assuming you didn't bypass it) first.

When you crank it without priming first, what does rail pressure do? If you unplug the regulator and crank without priming, what does rail pressure do?
 

Redkliney

New member
Apr 10, 2020
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Pa
Rail pressure doesn't budge. After i shut the truck off it drops to around 200psi, will stay that way even over night. Go to start the truck and fuel rail pressure doesnt budge. Gonna get some clear 5/16 hose to put from the junction block to cp3 to make sure there is definitely fuel there. Honestly seems like for some reason it's just not sucking like it should till its at full running speed. Haven't checked cranking rpm but it sounds healthy.
 

Redkliney

New member
Apr 10, 2020
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Pa
So hooked lift pump back up. Pressure gauge at port reads 5 psi. Really starting to thing the cp3 itself is a dud. Put 10 psi to it starts and runs like a champ. Gonna try a clear return line yet to see if a seal in the pump is bad yet. From what I've been reading a cp3 should pull at least 12inhg while cranking. With a vac gauge on just the cp3 inlet its only drawing 4.
 

Dozerboy

Active member
Jun 23, 2009
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TX of course
4" is the restriction in that factory setup with new filters. Unless you pinch off a hose or have old filters you won't see more then that.

Sent from my SAMSUNG-SM-G900A using Tapatalk
 

Redkliney

New member
Apr 10, 2020
7
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Pa
Thats why i hooked the vaccum gauge into the cp3 feed hose. Only got 4. Put all clear lines on today and i have no air in the fuel entering. But it sure is coming out.
 

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