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Discussion Starter #1
Hey guys - I'll keep this as short as possible.

2003 Lb7 with 400k on it, Air Dog 165GPH lift pump, EFI live. PPE oil pans on engine, trans, mishimoto rad, deviant trans cooler lines, AFE intake, California Emissions but deleted. Last 4 years, I commute 700 to 1000 miles a week for work 8 months out of the year, and never had any issues aside from worn injectors. I baby it as its my means to make money and was a stickler on maintenance and quality of oil, fuel additives etc. I rarely pull anything of significance.

I replaced injectors for the 2nd time a few months ago, myself. Truck primed and fired right away. Idled great, ran up to 3000 rpm for a few minutes, no issues. Took it out on the road, around 50/55 mph, massive injector knock on passenger side bank, copious amounts of white smoke from exhaust, I figure injector is bad out of box and stuck open. Shut down truck, restart. No issues until highway speed, same event occurs. This process repeats 5 or 6 more times. The 6th time I stomped on the throttle (mad as hell) , engine shuts down instantaneously. Cranks but no start. Max fuel rail pressure at cranking is around 400 psi, obviously not nearly enough and something seriously wrong. I tore it back down, sent injectors in. They all passed with flying colors. Put it all back together with new o rings, seals, etc from merchant. Injector cups remained seated so assuming no problems there. Same no start condition. Cannot prime. Let my lift pump run periodically - NO EXTERNAL LEAKS. No fuel in valley. I've got everything off, taking Cp3 out tomorrow for replacement.

Any thoughts? Is it possible I locked up/blew up the Cp3? Would that lead to the complete inability to prime? No fuel in oil as far as I can tell.

Thank you for your time.
 

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Former GM Tech and parts
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Have you checked to see if the lift pump is actually pumping fuel up there? Possibly the shaft or rotor in the pump broke and isn't allowing fuel to move.
If you know for sure you have fuel flowing to the engine, then it does sound like the cp3 possibly took a deuce... Might just pull the feed to the cp3 off and make positively sure it has fuel flowing there before hand. If its getting to the feed fitting of the cp3 and you have no external leak otherwise, my assumption would be cp3
 

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Discussion Starter #3
Have you checked to see if the lift pump is actually pumping fuel up there? Possibly the shaft or rotor in the pump broke and isn't allowing fuel to move.
If you know for sure you have fuel flowing to the engine, then it does sound like the cp3 possibly took a deuce... Might just pull the feed to the cp3 off and make positively sure it has fuel flowing there before hand. If its getting to the feed fitting of the cp3 and you have no external leak otherwise, my assumption would be cp3
Yessir, the lift pump is definitely sending fuel. I'm getting plenty of fuel at the valve that's mounted on the alternator bracket.
 

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Discussion Starter #4
Yessir, the lift pump is definitely sending fuel. I'm getting plenty of fuel at the valve that's mounted on the alternator bracket.
Have you checked to see if the lift pump is actually pumping fuel up there? Possibly the shaft or rotor in the pump broke and isn't allowing fuel to move.
If you know for sure you have fuel flowing to the engine, then it does sound like the cp3 possibly took a deuce... Might just pull the feed to the cp3 off and make positively sure it has fuel flowing there before hand. If its getting to the feed fitting of the cp3 and you have no external leak otherwise, my assumption would be cp3
I'm inclined to agree with you - I'll be taking off the feed line to the Cp3 today and checking for flow. Thank you for your input.
 

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Former GM Tech and parts
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2,547 Posts
Yessir, the lift pump is definitely sending fuel. I'm getting plenty of fuel at the valve that's mounted on the alternator bracket.
If you have fuel there, then you probably have fuel to the cp3 since its fed off the same junction block. But, if somehow it got something plugging the line to the cp3 (hose came apart between the filter head and the cp3) then it could have blocked that passage. But, I would guess its a cp3 related issue if you just put injectors in it... and hopefully the cp3 didn't grenade and contaminate those new injectors...
 

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Discussion Starter #6
If you have fuel there, then you probably have fuel to the cp3 since its fed off the same junction block. But, if somehow it got something plugging the line to the cp3 (hose came apart between the filter head and the cp3) then it could have blocked that passage. But, I would guess its a cp3 related issue if you just put injectors in it... and hopefully the cp3 didn't grenade and contaminate those new injectors...
Injectors were pulled and sent to exergy performance for testing and checked out fine. I'll replace the Cp3 and put it all back together. Other than that I don't know what else there is to do. Thanks.
 
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