Injector replacement and bleeding.

[Andres]

Where does the air go?



Over the weekend I decided to replace my DDP stage 2 injectors with the stock ones. This is in an offroad truck (Hummer H1) and stage 2 injectors seem to work great if your RPM's are at 1800 or above. EGT's go through the roof if you are at 1400-1500 rpm. So you need to run in low lock to keep the RPM's up if in a under 30 mph enviroment.



Took about 7-8 hours to do the job, not a big deal. I had to lift the body to remove the valve cover, the injectors themselves were easy.



I replaced the fuel filter and bled the system (to the filter anyway) before crank - did so to keep the CP3 somewhat lubricated while cranking on an empty fuel filter canister . The system past the CP3 is full of air (since you pull the fuel tubes).



I expected, and got a long crank and used a bit of ether - works every time.



How does the air get released from the system? I'm "assume" that the CP3 builds up fuel and air pressure to near 3000 psi and the ECM fires 12v to the injectors, releasing air first (to bleed) then fuel?.



Does the ECM open the injectors in absence of rail pressure? Is that how the air gets bled?



Anybody want to buy a low mileage set of +90 hp nozzles? They will be on eBay.

 

[cerberusiam]

When you turn the key on you should here a clicking on the engine, thats the ECU bleeding the injectors.



Along with the injectors, the CP3 bleeds air out using the COV so when it starts building pressure its pure fuel pressurizing the rail.



Once the air is out and rail pressure starts rising the bleed stops to build start pressure. Once you have fuel to the CP3 inlet the rest of the system is self bleeding.