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Need help with hard miss with cylinder balance fault codes

dbrannon79

dbrannon79

I'm getting there!
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I figured I better start a new thread rather than keep going on this thread so it would be all in one place.

Here is the link where I started talking about what happened.

What did you do with your GMT400 today...or yesterday....

Well hoping this will be the final saga on my steering for my rig. I had been hearing some sounds from the power steering pump in sharp turns that sounded like it was starving for fluid but it's wasn't low. I went out into my garage digging around, I knew I had another pump in there...
www.thetruckstop.us

this morning on my way to work, everything was fine. got onto the freeway and as soon as I was exiting my truck started sounding funny and began to misfire. the sound it was making sounded like a hollow thumping along with the smell of raw diesel going out the tail pipe. I made it another mile and half into work for the day. Upon leaving, I popped the hood, checked the oil and fired her up. she was missing bad and bellowing smoke smelling of diesel.

@ak diesel driver and @Paveltolz suggested the rocker buttons which I have never touched since I have had this rig.

I made it home slow and easy, got out my laptop and checked for codes and tried to run the injector cut out test to isolate which cylinders were not fireing. when idling she tries to occasionally fire on all 8 but that only happens for about a second or two.

I tested all the injectors one by one and all seem to lower the RPM or make things worse. #4 seems to be the weakest to make any noticible changes. turning on the high idle switch and then you can feel the difference on #4.

there are two codes showing in both current and historical.

92 - Cylinder Balance Fault #2
93 - Cylinder Balance Fault #6

where should I start here. this I have never seen before!


1692229650231.jpeg
 
Per this thread, sounds like you’ve got a fuel or air leak somewhere:

www.dieselplace.com

DTC 92,96,97,98 Cylinder balance

What does "cylinder balance" mean, anyway? I just got this poorly-maintained engine running, and it was fine for a week or so. Now seems like it's missing on a cylinder. Some white smoke, and rough. I had the front off to replace the timing chain, and it started right up and ran perfectly, to my...
www.dieselplace.com www.dieselplace.com
 
That thread also shows a rocker button broken too. I guess I will start making plans to tear this thing down soon. in the mix of things I can swap around the injectors from left to right too since the PCM is saying something about #2 and #6. that way if they are suspect they can be changed lots easier.

I hate the fact that it has been running really good and this happens all of a sudden out of nowhere! I keep getting the thought in the back of my head that I could be throwing the towel in sooner than I think.
 
#2 and #6 are next to each other in the firing order. I would confirm its not a mechanical issue first by testing both cylinders. But it could be a injection pump issue. Normally air in the fuel with cause misfires on all cylinder randomly. I always confirm what cylinders are actually misfiring on the scanner by watching live data and checking misfire counters. I've had multiple cylinders set codes when in realty only one cylinder was misfiring. Then check then confirm its not a mechanical issue on any of the cylinders that showed misfires. If I feel confident I can swap injectors without issues (Thanks Ohio rust) I will do that normally too. If its still misfiring and everything test good, more than likely its an injection pump issue.
 
It will most likely be okay after a fashion.
If there will be new injectors involved, be sure to test them before installation. Let us know those results too.
I did the hardened bolts, thick washers and self locking nuts on My truck, to replace them plastic buttons, happy that I did.
The only thing different that I think I would do if I was going to do it again, place the washers on a bolt, then, take them to a belt sander, to get a finer finish than a grinder wheel, and let the washers spin against the sanding belt to slightly reduce the OD of the washers.
They all worked out okay as is but I think a slightly looser fit in the valley of each rocker arm might be a little nicer.
Check the fit though before You do as I suggest. Might be that the brand of the thick hardened washers You get could be slightly smaller OD than the ones from the HW store over here.
 
what I thought was interesting is when doing the cut out test. both 2 and 6 both seem to be firing or at least the engine tone and rpm changed turning them off.

I'm curious if a bad batch of fuel could have caused this. I have a clear bowl on the filter but it looks clean without opening the filter up. no FFM, that was removed a while back.

I will have some time to play with it tomorrow. since my schedule change I get three day weekends off now.

so here's my plan... let me know if there is something I missed or should do before the other.

1. reinstall the clear tube on the return of the IP and check for air.

2. connect the fuel pressure tester and check the LP operation.

3. look over the live data on GMTD. not sure if it shows misfire counter but will check.

4. if I don't see anything else, begin teardown to pull valve covers and check rocker buttons.
 
Ted (the newly wed) once pulled up with number 6 out but was coding a different oil. His oil level was over the full mark and the oil very thin. He’d already noticed that issue earlier and had done a couple of oil changes while limping to my place pulling a Duramax. We got him new nylon buttons and (pun alert) buttoned back up and on the road.
Check the oil for level and diesel smell.
During discussions over the course of my last saga I learned that the ECM programming will try to balance out an underperforming cylinder by adjusting the others. When things get to the point that the ECM just can’t do it, it will code such as yours, mine and others have discovered. However, the code may not be for THE bad cylinder, rather, the one that can’t keep up. I was initially getting cylinder 3 and 5 codes when doing a timing resets (sometimes 5 & 7) and the engine was running like it had gone to hell in a hand basket. Some other’s I talked to had coded Cylinder 3 when when going in to investigate discovered it was actually 5 with the issue.
 
Paveltolz said:
Ted (the newly wed) once pulled up with number 6 out but was coding a different oil. His oil level was over the full mark and the oil very thin. He’d already noticed that issue earlier and had done a couple of oil changes while limping to my place pulling a Duramax. We got him new nylon buttons and (pun alert) buttoned back up and on the road.
Check the oil for level and diesel smell.
During discussions over the course of my last saga I learned that the ECM programming will try to balance out an underperforming cylinder by adjusting the others. When things get to the point that the ECM just can’t do it, it will code such as yours, mine and others have discovered. However, the code may not be for THE bad cylinder, rather, the one that can’t keep up. I was initially getting cylinder 3 and 5 codes when doing a timing resets (sometimes 5 & 7) and the engine was running like it had gone to hell in a hand basket. Some other’s I talked to had coded Cylinder 3 when when going in to investigate discovered it was actually 5 with the issue.
Click to expand...
Thanks for that info. something I did notice was slightly off to me was our trip to and back from the coast. was about 350ish miles round trip. I had topped off the oil before our journey, expecting to have to add some while out there and then again once we returned, I never had to add any the whole trip and to this day the oil level is right on the full mark still!!

I know it looses a little oil here and there so I think your right, I am making oil! LOL I will give it the sniff test when I get home tonight.

Question: if I indeed lost a button I am sure the push rod had come off the lifter too. what or how can it be recovered if it hasn't slipped past the cam into the rotating assembly? and what other damage should I expect to have to be repairing?
 
@Paveltolz your explanation of the PCM not keeping up with trying to balance out the engine and coding those two cylinders makes sense now. when I did the cut out test and seeing that #4 seemed really weak for making any difference until I turned on the high idle makes me wonder if I lost the button and the rocker slipped off the #4 intake valve. the compression of the engine being able to "suck" open the intake valve just enough to get "some" fuel but can't do it at idle. LOL just thinking out loud here.
 
dbrannon79 said:
Thanks for that info. something I did notice was slightly off to me was our trip to and back from the coast. was about 350ish miles round trip. I had topped off the oil before our journey, expecting to have to add some while out there and then again once we returned, I never had to add any the whole trip and to this day the oil level is right on the full mark still!!

I know it looses a little oil here and there so I think your right, I am making oil! LOL I will give it the sniff test when I get home tonight.

Question: if I indeed lost a button I am sure the push rod had come off the lifter too. what or how can it be recovered if it hasn't slipped past the cam into the rotating assembly? and what other damage should I expect to have to be repairing?
Click to expand...
 
It seemed that looking into the heads with the covers off it was quite wide open.
If the lifters are such that the wheels are no bigger than the OD of the lifter in the bore, lifters could easily be changed through the gap. I dont remember what kind of a gap there was going downwards into the lower unit of the rotating assembly. I didnt look it over that closely.
Maybe someone with a spare opened engine could give us that information, or someone in the know.
 
Welp. Got home and began testing. Connected clear line and fuel pressure gauge at the IP. All looks ok I think. I videoed the second startup. Does this seem like a rocker button? Just curious before I tear into this

 
upon re-watching my own video. mind you im only letting idle for a minute or so, but I noticed it building close to 8 psi with the key on then on startup it starts bouncing from 3 psi to 0 as if it's just dumping fuel and the LP can't keep up or it too is bad. I suppose that is where the injectors are dumping it out.
 
I will do that. I'm gonna quickly move it into the shade in the back yard where it's cooler to work and try that. if one or more are just dumping I am assuming I will see solid streams rather than pulses of diesel? it will be fun to get to #'s 4,6 but If I have to pull the turbo I will.
 
dbrannon79 said:
upon re-watching my own video. mind you im only letting idle for a minute or so, but I noticed it building close to 8 psi with the key on then on startup it starts bouncing from 3 psi to 0 as if it's just dumping fuel and the LP can't keep up or it too is bad. I suppose that is where the injectors are dumping it out.
Click to expand...
That is pretty standard fuel pressure levels and reaction with an OEM style lift pump.
 
Just got her moved to the back yard. Only ran for about 3 minutes. She is smoothing out on the miss but that hollow thump sound is very strong in the air cleaner or the passenger side area of the engine and in the exhaust
Thought I’d post this Before doing much more

Edit: I just pulled the air cleaner and it’s not coming from there. Sounds more like a bad exhaust leak but no smoke or soot anywhere around the engine

 
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I’m gonna start pulling it down to get at the valve covers and see what I find. If nothing there , check injectors and maybe compression test and see from there. I’ve invested too far to scrap it out but when I do y’all here will have dibs on it
 
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