CM 871 Injector Issue

[Hammerhead]

edited to add: Oh yeah, all of this is FIRST preceded by a proper overhead adjustment! If the injector preload is out of spec or not set correctly, it is very possible that injector #1's leak is not because of a mechanical problem, but a symptom of another issue...

(09-09-2017 )graysonlogistics Wrote:  So, I have an 871 that is running rough, hooked up the computer and did the cylinder test and the front bank failed. I swapped the fueling actuators and did the test again. The front bank failed again. It did not follow.

Did you move both the timing and metering actuators or just the metering actuators?

(09-09-2017 )graysonlogistics Wrote:  Next I did the cylinder cut out test. It ran on every cylinder by itself except for number 3. I thought that that was a tell tell that the number 3 injector was bad.

Then injector #3 is weak, has a poor spray pattern, or has internal leakage issues (different leak, in the timing chamber not the metering chamber, we'll get to that). Yes, if it will not run on this injector, it needs to be replaced, maybe. First read the response to the next question, then come back to this one. But first you need to confirm that the cylinder has no visible scoring on the walls with a boroscope, or has a broken ring etc. that is causing insufficient compression to produce proper combustion. Move this injector to another cylinder and verify it follows the injector, not the cylinder.

(09-09-2017 )graysonlogistics Wrote:  I next did the injector leak test.... I got bubbles during the cranking and proceeded to bar the engine over like Rawze video demonstrated and per the service manual. After barring the engine over, the bubble occurred between B and C which indicates #1 injector was leaking. No other injector leaked.

The bubble test tells us that injector #1 has a pintle sealing issue. This is an external injector leak of the metering chamber, not an internal timing chamber leak that will fail on single cylinder running tests. This means that cylinder compression gases can push past the pintle seal and into the fueling chambers of the injector and fuel rail. This injector needs to be replaced. Note that this is an external to internal fuel path leak, and is NOT the possible internal leak that injector #3 may be experiencing.
Now here's where the fun starts. The firing order is 1, 5, 3, 6, 2, 4. That means that compression gasses are passing injector #1 into the fuel rail, note that #5 is the rear bank BUT #3 is the very next front bank cylinder to fire, so it is possible that enough compression gasses are escaping past #1 and causing a large enough fuel void to properly fill #3 to fire correctly, and your inability to run only on #3 could be a ghost symptom of #1.
So change #1, and retest. Then if the problem with #3 continues, move it to another cylinder and verify the issue follows the injector or cylinder.

(09-09-2017 )graysonlogistics Wrote:  Why during a cylinder cut out test will it Run on #1 (with a bad injector) die on #3. Is it possible that injector 3 is stuck shut and not leak?
Is the cylinder cut out test trustworthy for injection issues? Is the leak test affirmation of injectors good or bad?

Both. As previously stated and from the firing order you can see that the gas void may be overcome because of the fueling/firing duration interval between 2 to 1 vs 1 to 3. We first must eliminate compression gasses from the fuel rail before we can eliminate a possible different issue with #3.