CM 871 Injector Issue

[Hammerhead]

(09-09-2017 )graysonlogistics Wrote:  I only swapped the metering actuators. I replaced #1 and set the overhead. (Thanks for your videos by the way.) Still running rough, Did the cylinder test and the front bank failed. So, I will swap the timing actuators(which I should have done first) and see if the problem follows.

Swapping the timing actuator to see if the issue follows is how to diagnose a timing actuator issue, but if it was a timing actuator you would have probably had a similar issue with all 3 front bank injectors. It's a good idea to verify it anyway.

Ok, I'm not sure how much knowledge you have of the 570, 870, & 871 fueling system so here is a brief rundown.
The fuel rail in the head is actually 3 separate rail paths.
The upper is timing fuel in.
The middle is timing fuel return.
The bottom is metered fuel in.
The metering actuators control the fuel load to be injected into the cylinders for combustion, so this is a one way system. All fuel flowing through this system is burned.
The timing actuators on the other hand control the variable timing advance and retardation as determined by the ECM. This system has two fuel paths, in and return from the injectors/head. The more fuel timed into this top part of the injector, the earlier the upper plunger comes into contact with the timing fuel volume and uses hydraulics to push the lower plunger which injects the metered fuel into the cylinder. Inverse for retarding the timing. After the injector hits bottom and completes the injection of metered fuel, the port opens to relieve the timing chamber of pressure and that fuel returns back from the injector/head to the IFSM and the excess to the fuel tank, where the cycle begins again. This high pressure hydraulic action of the injector is where the asphaltene is formed.

So an injector has two partitions where it can fail or leak, as previously stated. Combustion gasses from the cylinder into the metering or fuel load portion and into the bottom fuel rail. This will potentially affect other injectors fuel loading if there is a large enough volume of gas that compromises the ability of the fuel pump to evacuate it before the next injector opens the metering port. The front and rear banks are separate, so therefore this is why #1 can affect #3, but not #5, and rarely affects #2 because the duration from 1 to 2 is long enough to evacuate the air from the front bank. It is these compression gasses forced back through the injector that produce the bubbles in the bubble test.

The other partition is of course the timing portion. If this side of the injector leaks, it does not create "bubbles". The fuel that is supposed to create a "hydraulic block" to push the lower plunger from the upper plunger leaks past internally and does not fully inject the metered fuel load in either a spray pattern to properly combust, or injects it way too late because of the loss of timing from the leak, that the combustion is now happening after the piston is already on its way down and it doesn't produce any force on the piston. The same result would also take place if the o-ring between the upper and middle fuel rail of the injector fails, or if a small crack opens that separates these two rails. The ECM cannot predict or control these as they are a mechanical deficiency that may not be detected to throw a CEL. This is where the injector cut out and bank tests in Insite diagnose injector issues.