2012 ISX 12 CM2250 - rough under throttle

[Alan50gt]

Greetings,

First time poster/new member. Long time lurker/reader.

Apologies in advance, this may get long winded.

My issues pertains to a 2012 ISX 12L CM2250 in a Peterbilt 579 790K miles (U.S. based, ALL AFTERTREATMENT INTACT AS MANDATED AND INSTALLED BY MANUFACTURER)

I have 50+ hrs into it so far with no definitive cause. Lots of data/testing. If I forget to list something that may help, I probably have the info, just maybe not immediately.

I was tasked with diagnosing a rough running issue with this truck. It happens ONLY when the truck has not been running for 30+ minutes. NO FAULTS, CEL, OR MIL.

Under throttle, via peddle or Cruise C. idle up, the engine will stumble, choke, shake, seemingly miss, and is believed to be heavily overfueling. (Turbo is spooling CONSTANTLY during this time)

From the beginning:

- I started with fuel. Boss thought it was injector(s). HP fuel testing revealed leaking FPRV off the jump. Replaced. Once that was addressed, it will build and hold pressure the best Ive seen across any of our fleet. (30K PSI for well over 10 minutes) Moving on from there pump leak, injector leak all checked well under acceptable values. Injector test passes. Cylinder balance shows no obvious deviation.

- From there I did several hours of monitoring and logging values. Noticed variance in the Commanded vs Actual Turbo position and surging turbo speeds. Got it to trigger a VGT actuator mechanical malfunction.

- On to the turbo. Pulled VGT actuator. Sector gear was binding, harsh scraping/noise from turbo. Actuator very noisy, loose bearing on the gear. Both were original. REPLACED BOTH. No fix to the issue, but turbo values now appropriate.

- Aftertreatment checked. DOC and DPF cleaned/baked last year after an EGR cooler failure. Checked again to be sure. Regens check out. Analyzer values all within spec. Differential values low. Builds to appropriate temps, runs about an hour. Filter restriction passes. Discussed my logs/values with our local Cummins rep, who didnt see any issues.

- checked EGR system. Pressure reference tubes/ports clear. Some soot on walls but no excessive buildup blockage. Differential values check out. Pressure values in spec in comparison with ambient pressures. IMAP sensor replaced.

BEHAVIOR: Truck will run fine post regen. (When its nice and warm) Let it cool down for an hour or 2, problem returns. In the time window this occurs, it wants to constantly go into SCR Warmup mode. Discovered this when monitoring to figure out why the turbo wanted to constantly spool up. If I slowly up the rpms I can sometimes get it to go into PTO mode (via cruise) or normal operation (via peddle) without stumbling, at which point it will run fine. Once I come back down in rpms, within about 5 seconds, SCR warmup will start again and turbo will spool back up. ** This will happen within 1 minute of running but also after 20-25 minutes of running with coolant temps at 180-200/SCR temps 400+. Some of this may be normal operation, but it seems particularly extended and repetitive. WHEN IT STUMBLES/RUNS ROUGH, A STEADY OUTPUT OF GRAYISH SMOKE OUT OF THE STACK. FILLS OUR 2 BAY GARAGE WITH A NEARLY UNBEARABLE/UNBREATHABLE EXHAUST CONCENTRATION. (which I interpret as overfueling or incomplete combustion)

This is the only ISX 12 CM2250 we have left in the fleet. The last one locked up a main bearing during an injector test about 2 years ago, so I have nothing to compare it to. Ive spent most of my time/experience on newer cummins and MX based engines.

The magic plug: Disabling the EGR system via EGR temp or EGR valve makes the problem go away 100%. Obviously disabling this changes/disables other systems, so it hasnt helped pinpoint the particular issue.

Thanks in advance for any thought and/or input. I will try to provide any additional information as needed. Probably forgot some things up front.

[Alan50gt]

One thing I forgot to mention, EGR is verified closed as commanded. Real time monitor of position as commanded. Crossover plated at intake side. Egr temp sensor removed from port. Plugged in and unplugged (disabled) position 0 has no flow or leakage. Flow increases seemingly as position increases.

[tree98]

One thing that stands out to me is that it puts out this grayish unbearable smoke. The dpf should be gobbling that up, it shouldn't be getting through if the dpf is in good working order.

Have you pulled the exhaust pipe off behind the turbo before the dpf and ran it to see what it looks like?

I don't know how it could be overfueling if it passes a leakdown test, is it using oil? Or making oil?

[Rawze]

it could also be valve guide seal leaking on it causing all of the grey smoke. That is a common issue of valve guide seals leaking and causing that grey-ish smoke with the newer ISX engines.

part of what your describing sounds also like maybe the egr cooler is partially restricted or not cooling the exhaust gasses enough and it is causing the turbo to get over-worked at idle. That or you have a poorly-rerading egr pressure sensor or possible clogged up Delta-p sensor or piping feeding it etc.

[schISM]

Is there any CEL’s for high NOX or PM after the hazy smoke episodes? What you’ve described regarding SCR warm-up mode is normal for this engine. It will run in this mode until it’s reached operating temps and the DOC is converting hydrocarbons into CO2 and H2O. Now this is purely speculation on my part, take it with a grain of salt. If the EGR cooler failed and contaminated the DOC no amount of cleaning will bring it back...it’s dead. The ECM wants that DOC to light off so it closes the turbo forcing more O2 through the engine and raw fuel into that oxygen rich exhaust stream via a post injection pulse trying to get that catalyst to light. Now that in and unto itself won’t cause a healthy engine to stumble and perhaps this is where your engines mileage may come into play. If the ECM is commanding more and more fuel to light the DOC that isn’t going to light on an engine with 790k that more than likely is getting a bit low on compression perhaps it would cause it to stumble. Again I’m just thinking out loud, as it sounds like you’ve covered your bases. Good luck and let us know when you get it figured out

[Alan50gt]

Its not triggering any faults. Most of it happening before Nox sensors are up to operating temps im guessing. The problem reconciles itself after the truck runs awhile.

Im currently into the top end. After rechecking some auxilary systems, Monday morning this thing started up after a long cold soak and ran like a complete dog.

Pulled the turndown pipe behind the doser and did some snap tests along with some high idle tests. Not saying the aftertreatment is perfect, but the base issue has to be up front. No excessive soot or black smoke comimg out. When it stumbles and misses, the engine is pumping out a ton of medium gray smoke. (Burns my eyes as it finds its way into the cab) If it doesnt stumble in the range I put it through, it will put out a little puff of the same color smoke when it comes down to idle.

Tried to recheck injector leak when somewhat cold (100 -125 degree coolant temps) but it runs like crap, nearly stalls, knocking, shuddering, surging, all you can imagine. Seems to start in the 17k - 20k psi range when High Pressure Fuel Test is running. Itll get to the 29k limit, but it get real sketchy there for a bit.

Tried blocking off injectors individually and in pairs. No improvement anywhere.

Pulled the cover. Jake and overhead seem ok, I will run it all when I put it back together. Pulled it all to take a good look at everything. Nothing obvious yet. Pulled the injectors. Some carbon on the tips but not too bad. O rings good. Cups look clean and straight. No staining. No coolant loss. No contamination. Cylinders look clean, only fuel in the dish from pulling injectors. (All 6 Injectors replaced ~200k miles ago when 4 of them were on their way out)

Only high pressure test I hadnt run was pump performance, as we did not have the proper fitting for the rail. We're trying to find someone local to test the injectors at a reasonable cost. Sometimes they want 2/3 the price of a new one... but theyre upwards of $900 a piece now. If this all checks out I suppose Ill look into the pump. Sometimes its tough enough with faults, a real nightmare without any.

Thanks for the insite (Pun Intended)

[tree98]

So when the rail pressure was at 29k did you shut the engine down and see how fast it would leak off? What you want is less than a 4000 psi drop in 1 minute.
If it falls off quicker than that, you start capping injectors and running the test again. If the leakdown rate improves, you know the injector you capped off is bad.
Maybe you have an injector or 2 hanging open? You say they were replaced 200k ago, do you know if they were replaced with factory cummins or some ebay junk?
Is the engine making oil?

I forgot to mention, you need to open a separate data monitor window in insite to watch the rail pressure.

[schISM]

Are you able to run a compression test or boroscope the cylinders? Without any faults showing up that would be my next course of action.

[Mikanic]

Grayish smoke.. makes me think of exhaust valves staying open maybe... engine brake actuator bypassing excessive oil pressure in rocker shaft when deactivated? Loose or stuck exhaust brake plunger when cold. I dont know if cummins have a procedure to monitor oil pressure in rockershaft, I know volvo does. You did a top set but maybe it would be good to take apart the engine brake rockers aswell.

Also if turbo is acting up, monitor exhaust gas pressure, is it stable when turbo is stable? Is it acting up before the turbo? I seen bad exhaust gas pressure connector make the value unstable but still valid and the turbo was acting up weird without setting faults for hours of operation before setting a fault.