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Old 04-26-2017, 09:24 AM   #3 (permalink)
Ramblinrodney
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Join Date: Sep 2006
Location: Midland, MI
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Something as expensive as a CP3 to replace just for mantinance is unheard of. If that's all that was done put your known good one in.
The only thing electrical with your CP3 is your FPR valve. Is this plugged in?
GM Part 97728979 FPR, REGULATOR KIT, Fuel Injection, REGULATOR KIT,FUEL PRESSURE(PART OF 1
Did you disconnect your batteries? You didn't short out your TCM?
It takes approximately 2500 PSI rail pressure to start.

High Pressure Injection Pump (CP3 Pump)

Before condemning the pump for a starting issue you need to be certain that the high pressure fuel system is not leaking the pressure. Perform the injector return flow test.
If there has been a major contamination issue with dirt and or water then it is very likely that the high pressure pump will need to be replaced. However, the injectors are typically damaged first, but any contamination that got into the injectors went through the CP3 pump first.
The most common failure of the high pressure pump is the inability to keep up with high fuel demand such as towing a trailer up a hill. This problem will usually set a low rail pressure code.
Other Notes:
• If the vehicle has starting issues then the injectors are the most likely cause. Perform the injector return flow test.
• If the vehicle only acts up during a hard pull with a load and there are no restriction issues then it is more likely a HP pump causing the problem. A limit valve could also cause this problem.

No Start or Hard Start

Excessive fuel restriction, check or change fuel filter
Use vacuum gauge, check the suction, you should have no more than 5 inches Hg at WOT (wide open throttle) or 7-8 inches Hg under load. If you have too much suction, after changing the filter, the restriction could also be the sock in the tank. Too little vacuum (less than 2 inches Hg) means that it could be sucking air.
Check for air in fuel system, install clears lines before and after the filter housing to check for air in the lines.
Confirm actual versus desired rail pressure, even under crank no start conditions
If the above are ok, then it comes down the following.
a. fuel injectors (see injectors for more diagnostic information)
b. high pressure injection pump
c. Fuel pressure regulator, check to make sure it is not stuck.
d. fuel pressure relief valve (high pressure limit valve), check to make sure it is not leaking into the return system when rail pressure is 160 MPa
Before condemning the high pressure pump you need to make sure there are no high pressure fuel leaks. Use the EN-47589 (same block-off caps as #9011 SPX Miller tools) cap set to cap off the injector rail to isolate the injectors from the injector return system.
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Last edited by Ramblinrodney; 04-26-2017 at 09:39 AM.
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