School me on CP3 conversions

[ikeG]

I've never had to deal with cp3 conversions A few have came thru that were already done, no issues I've been just purchasing the AC Delco pump kit and replacing the whole shebang OE
Do all cp3 conversions require a retune? I've heard of possible priming issues when converted??

 

[Josh154]

Mine was a bitch to prime. I deleted factory filter head as well. Ended up shoving a air hose in fill neck while cranking and got her to fire. SDP has the best conversion kit in my opinion. I did mine 2 years ago about 40k miles later and have never had to go back in there once

 

[Josh154]

Also I think s&s has a kit out now that is emissions legal and doesn’t require any tuning

 

[slowlml]

Correct s&s has a kit out that does not require tuning. i haven't had any issues priming them but i left the filter housing on the truck. i could see why you'd have issues priming when doing both at the same time. I've used scotts and wehrlis kit and cant say anything bad about either.

 

[Dallas S]

The non emissions compliant kits remove the back flow valve from the injector return line system. If the truck is ran out of fuel and the injectors loss return pressure, they will NOT fire. Rail will be perfect while cranking yet no opening of injectors. We have had luck putting shop air in the return lines and the injectors will start to fire and then prime the return.

The compliant kits keep the back flow valve which will prime the return just like stock.

 

[Josh154]

Doesn’t that same procedure need to be done when swapping injectors?

 

[Dallas S]

I cannot explain why, but it only seems to be an issue if the truck is ran out of fuel. Maybe the injectors keep some pressure internally.

 

[$chultz38]

The non emissions compliant kits remove the back flow valve from the injector return line system. If the truck is ran out of fuel and the injectors loss return pressure, they will NOT fire. Rail will be perfect while cranking yet no opening of injectors. We have had luck putting shop air in the return lines and the injectors will start to fire and then prime the return.

The compliant kits keep the back flow valve which will prime the return just like stock.

What backflow valve are you taking about?

 

[slowlml]

Doesn’t that same procedure need to be done when swapping injectors?

Ive only had to do this once. I know guys who have probably installed 100s of sets and only had to do it a handful of times.

 

[Dallas S]

What backflow valve are you taking about?

There is a low pressure line that feeds the 9th injector. That line has the valve that will charge the return line. Thus, the compliant kits keep the 9th injector so the backflow valve is retained.

 

[JoshH]

There is a low pressure line that feeds the 9th injector. That line has the valve that will charge the return line. Thus, the compliant kits keep the 9th injector so the backflow valve is retained.

If you're talking about the return line fuel pressure regulator, I've never seen a CP3 conversion that doesn't keep that part.

 

[Dallas S]

If you're talking about the return line fuel pressure regulator, I've never seen a CP3 conversion that doesn't keep that part.

That regulator is too keep pressure on the return side of the injectors. The piezo injectors need that regulator.

On the non compliant kits, they give you a small plug that clips in place of the backflow valve on the passenger side return line. That is the valve that will recharge the return line using fuel pressure supplied to the 9th injector. Notice all the compliant kits have a soft line coming off the CP3, just like the CP4s, too feed the 9th injector.

 

[Dallas S]

The fuel tank (5) stores the fuel supply. A mechanical high pressure fuel injection pump (13), located below the engine intake, includes the fuel supply pump and the high-pressure pump. Fuel is drawn through the diesel fuel conditioning module (8), which combines a water separator, hand operated fuel prime pump, filter element and then through a fuel filter vacuum switch (9) to the fuel injection pump. The engine control module (ECM) controls the fuel pump pressures by using two fuel pressure regulators, fuel pressure regulator 1 is located on top of the fuel injection pump and fuel pressure regulator 2 (7) is located on a fuel rail (2). The fuel pressure sensor (4) provides a voltage signal to the ECM to indicated fuel rail pressures. The high pressure fuel is supplied to the fuel injectors (1) through separate high pressure pipes. The fuel injectors supply fuel directly to the combustion chambers of the engine. The fuel that is not injected into the combustion chamber is used to help lubricate and cool the injector and is routed back to the fuel tank. The fuel injector return line pressure regulator (14) maintains fuel pressure on the return side of the fuel injectors. This is required for proper fuel injector operation. In the event the vehicle runs out of fuel a check valve (11) in the exhaust aftertreatment fuel injector (10) supply line opens and the fuel supply pump back fills the return side with fuel. (Courtesy GM)

(I can’t get picture to load. But I am talking about item 11)