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Old 11-10-2021, 02:11 PM   #1
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C9 RPM fluctuating warming up

Has anyone had an issue with rough idling at warm up. My engine starts and idles fine for about 4 mins then starts idling rough from 580-615 rpms and sounds like it's misfiring. I have checked every sensor and all filters. Runs fine after it warms up. Could it be stiction? HEUI and IAP sensor replaced. Been going on for 2 months. After warm it up it idles fine at 600.
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Old 11-11-2021, 08:22 PM   #2
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It is possible that the temperature sender is giving erratic data. To the ecm. I had one do that and it drove me crazy trying to figure it out. The gauge was fine and showed no problem but the sensor was messing up the Heui pump. Once we changed the sensor it run fine. It also would only run odd/rough for intermittently while warming up. Safe Travels
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Old 11-12-2021, 08:49 AM   #3
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Thank you so much! It's the only sensor I didn't swap out. I thought about it. It's heat related for sure. Runs fine with swapped out ECM's which isn't smart to do but I needed to rule it out. Thank you. I will report back. Once warmed up the idle is fine all day. 2 months of pulling my hair out! Gauge reads fine oh well ordering a new sensor today.
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Old 11-12-2021, 12:05 PM   #4
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Sometimes its a lot cheaper to take a guess and just replace a part rather then to pay for an hour of diagnostic time - but if you're swapping ECMs, it may have been wiser at that point to go to the CAT dealership and let hookup their CAT ET scan tool.
They could then see what the sensors are reporting/reading (like a fluctuating water temp or reading too low/high for the conditions).
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Old 11-13-2021, 08:07 AM   #5
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Cat ET was done and showed nothing but an $800 bill. IMO not the most dedicated mechanics out there.
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Old 11-13-2021, 01:13 PM   #6
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Quote:
Originally Posted by C9marine View Post
Has anyone had an issue with rough idling at warm up. My engine starts and idles fine for about 4 mins then starts idling rough from 580-615 rpms and sounds like it's misfiring. I have checked every sensor and all filters. Runs fine after it warms up. Could it be stiction? HEUI and IAP sensor replaced. Been going on for 2 months. After warm it up it idles fine at 600.


Have you tried shutting off and restarting to see what happens?
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Old 11-13-2021, 01:20 PM   #7
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So it wasn't the temp sender. I finally read that the C9's have a programmed cold mode that intentionally cuts out injections to decrease white smoke. So odd but true. Once water temp hits 157 or after 14 mins at idle it deactivates. Who would of thought.
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Old 11-13-2021, 01:35 PM   #8
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I remember C13s doing that in our Pete 320 VacCon trucks. SOP in cold weather was to fire them up, hit the high idle and go inside for a cup of coffee. After about 10 minutes they ran fine. Not so much of an issue during the summer months. I think they were 07 chassis.
Still a good idea to run supplemental lubericity additives, IMO.
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Old 11-13-2021, 06:54 PM   #9
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IMO I think, if true cutting out injection firing is bad. Warming up half a motor at a time. Also weird. I'm Having Cat ET disable Cold Mode like my port engine. Not sure why the ECM enabled this on a marine engine. Make sense it went away when I swapped ECM's....
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Old 11-14-2021, 06:22 AM   #10
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According to the Service Manual, code start mode is disabled if you step on the accelerator pedal. So it is only active when you first start engine and leave it idle. Maybe there are other strategies available that are not described in the manual.
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Old 11-14-2021, 10:17 AM   #11
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It doesn't mention the C9, I'm sure this series has it. This am after leaving the block heaters on all night I had no issues this am. Water temp was 172 before start up.
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Old 11-28-2021, 11:25 AM   #12
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So the C9's do not have cold mode. We swapped ECM's and the engines run fine which is odd. Cat redid the injector trim codes, memory and torque settings then reflashed both engines, rough cold idle returned on the one engine! Can't make this up. Swapped back to the original ECM on each motor and despite incorrect trim codes and torque settings no issues again so that is how I'm leaving it. At this point it's either the ECM doesn't like the factory settings or the injectors don't. I already swapped or replaced all sensors. 2 new HEUI pumps and pump tests fine. Cat ET Injector cutout also passed. Either way I'm leaving as be. Cat spent 6 hrs and 3 visits and can't figure it out. Cat tech said their software maybe corrupt. They are researching this.
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