cm2250 rough idle

[JimT]

Ok, guess it's time for a new problem.

2012 pete 587, cm2250 537,000mi

Started the truck up the other day, cold, and after a couple minutes at idle it started to run rough, like a cylinder is cut out or missing. At the same time the engine had entered SCR catalyst warmup and the turbo spooled up accordingly. Once the SCR warmup was complete the engine returned to a normal smooth idle (set at 720-725 rpm).

Since that first occurrence it has happened 2 more times. They all occurred while the engine was still cold (first morning cold start, outside temps around the freezing point), fairly soon after starting the engine. Once the engine is warmed up it does not happen at all, regardless of operating state.

When it occurs the rpm's will slowly start to fluctuate. At the peak the gauge shows that it'll drop down to 710 rpm then up to 730 rpm in about an audible 1.5-2 second cycle. Never lasts more than a few minutes.

Less than a week prior to this I had performed a cylinder cutout test with no issues. Each cylinder ran by itself and they all leveled out roughly the same. Injector performance test passed 2 times in a row and fuel pressure test held at 30,000psi for over 5 minutes before I restarted the engine.

I did manage to get Insite up and running during one of the occurrences and tried another cylinder cutout test while it was running rough, all cylinders operated independently with no noticeable difference between them.

Last oil and filter change was about 1,000 miles ago. davco filter is not clogged up. Recent EGR tune-up, EGR valve replacement and DPF/DOC cleaning. Crankcase pressure reads pretty steady at about 1.5 inHg through insite. DPF has been operating normally since the repair. No fault codes.

I have not tried taking anything apart yet as I'm not sure where to look. My initial thought was an injector or something with the turbo, but other then these isolated incidents the engine has been operating normally.

Suggestions?

[Rawze]

will it pass this injector leak test?

how many psi does it loose in one minute?.

[JimT]

(02-13-2020 )Rawze Wrote:  will it pass this injector leak test?





how many psi does it loose in one minute?.

0 psi loss. Baseline was like 29,890 or something. When I shut the engine off it jumped to 30,500psi or so, then ended the test just over 31,000psi. It continued to hold that pressure until the engine was restarted about 5 minutes later.

Edit: this test was performed less than a week prior to the first occurrence. I'm currently heading to get fingerprinted for cdl/hazmat renewal so I can try it again later if needed.

[Rawze]

could also be that the turbo is overspooling when in warmup mode, but not quite enough to make it chough yet?
some related info: http://rawze.com/forums/showthread.php?t...8#pid22458

maybe look at the turbo position while it is doing this. Compare it to other ppl's trucks who's system is running properly to get a base line?

[JimT]

(02-13-2020 )Rawze Wrote:  could also be that the turbo is overspooling when in warmup mode, but not quite enough to make it chough yet?
some related info: http://rawze.com/forums/showthread.php?t...8#pid22458

maybe look at the turbo position while it is doing this. Compare it to other ppl's trucks who's system is running properly to get a base line?

Off the top of my head, Insite reports turbo position commanded/measured to be 86/87 percent during scr warmup. This is from memory, so if that sounds way off then it's probably just me.

I do notice a slight fluctuation in boost while it's doing it's scr warmup. It is only about 1psi so I didn't think much of it. Turbo is a reman but actuator appears original.

[Rawze]

with 500k+ miles on that enigne,.. how old is the egr cooler? - When is the last time it was pulled off and cleansed out thoroughly?

Personally, I would have axed the system it a long time ago, or at least made the system more lenient, as there is no way to keep those systems happy any ways with 500k+ miles on the engine without tearing the whole systems off it, cleaning it all up + clean-out and acid bath on egr cooler, egr valve, replacing all the sensors, baking the cans all out, replacing the SCR element at this point, and spending a whole lot of money and time on getting the engine to run well again with new valve guide seals, fuel system in tip-top shape, new injectors, and the list is very long to make that system happy like it is with an engine that is on the back half of its prime.

such is exactly why everyone hates these systems and wants to rid the engine/truck of them. - I don't blame them one damn bit@.

[JimT]

I'm considering removal, but I figured I'd wait until a good reason presented itself before doing that.

As for the EGR cooler, it was replaced at some point in the past. Based on logged data in the ECM I'm estimating it was done somewhere between 200,000-300,000 miles. Though I can't be sure.

As of late December when I replaced the EGR valve it was dry inside. There was some soot buildup, but not extreme. I did not remove the cooler or attempt to clean it in any way.

[JimT]

So, after posting this the issue did not present itself again until this morning. This time it was NOT in SCR warmup mode.

720rpm idle, outside temp was 15F when i started the truck. around the time it got up to 150K on the coolant (give or take a little) it started to bog down to 710 for a brief moment then up to 730 and back to 720. It took about 1 second to do that then the cycle would repeat every 3 seconds. It had a nice rhythm going. Did this for about a minute or 2 then returned to idling normally. Experiencing a few one-off occurrences still, temp is currently up to 180F.

As I mentioned in this post last night I got one occurence of fault code 2321 Crankshaft Speed/Position - Data erratic, intermittent or incorrect. It was inactive when I had Insite up. Never had that or any other Crankshaft codes before. I'm wondering if this could be the cause of the rough idle?

[Rawze]

(02-21-2020 )JimT Wrote:  ... I got one occurence of fault code 2321 Crankshaft Speed/Position - Data erratic, intermittent or incorrect.
...

I have never seen that error on an ISX unless there was a problem with the crank or cam position sensors, the tone wheel was loose, and/or the overhead cam had slipped. <- that is not an error to take lightly at all.