CM 871 Injector Issue

[graysonlogistics]

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.

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.

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.

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?

Any input Appreciated

[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.

[Rawze]

Hammerhead's logic is sound advice...

*Perform an overhead adjustment. Also checking clearance for valves to the detent. after setting it (second half of this post ... http://rawze.com/forums/showthread.php?t...66#pid9466 )

* re-test with bubble test.

* Replace leaking injector(s) if they are still leaky and you have the head in proper adjustment.

* Do cylinder cut-out test again. If #3 is the only one failing, then swap injector to another cylinder and see if it follows injector.

If the cylinder fails repeatedly and just won't run right,.. and it does not follow the injector or anything else --- CYLINDER #3 IS LIKELY DONE FOR!!!. I have seen this for cylinder #2 many times, and #3 only a couple times but is still possible.

- If no matter what you do, only that cylinder keeps failing cut-out test, then is is loosing compression like Hammerhead said. I have seen this before. It can be the head/valves,.. but equally a broken oil ring or washed out liner / other issues too. If you have to pull the head, REPLACE IT if it is more than 450k miles old, but also,... You had better plan on an inframe just in case.

[graysonlogistics]

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.

[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.

[snailexpress]

I had same problem with 871. Mechanic took out injector and pressurized cylinder with air using injector size rubber tip on blow gun. Valves should be in close position. It was well noticeable air leak on intake side from the valve.
Lost pictures but it was posted on old forum.

[graysonlogistics]

Ok so I moved the timing actuators and ran the cylinder test again and the front bank failed, it didn't follow.

So I swapped #3 injector with #1(which is new) ran the overhead set and fired it up. Still ran rough. Did the cylinder cutout and it ran on #3 this time and Did NOT on #1....
So I pulled the #1 (which was #3) injector out made a mad dash to MHC Dallas and got another injector.

Replaced it and fired the truck up and after the air cleared up we had smooth idle.

Ran cylinder test again after the coolant reached 140, all passed eventually.
#3 pass immediately #1 and #2 teetered fail/pass for a few seconds then settled into pass.

Thanks Hammerhead and Rawze for all your input.

[Hammerhead]

(09-10-2017 )graysonlogistics Wrote:  Ok so I moved the timing actuators and ran the cylinder test again and the front bank failed, it didn't follow.

So I swapped #3 injector with #1(which is new) ran the overhead set and fired it up. Still ran rough. Did the cylinder cutout and it ran on #3 this time and Did NOT on #1....
So I pulled the #1 (which was #3) injector out made a mad dash to MHC Dallas and got another injector.

Replaced it and fired the truck up and after the air cleared up we had smooth idle.

Ran cylinder test again after the coolant reached 140, all passed eventually.
#3 pass immediately #1 and #2 teetered fail/pass for a few seconds then settled into pass.

Thanks Hammerhead and Rawze for all your input.

No problem, and thank you to you as well for the updates!
Final results feedback is always appreciated around here, it's how we all learn...