cm871 help---
04-16-2021, (Subject: cm871 help--- ) 
Post: #1
cm871 help---
background-- we have a cm871 450 hp 390k miles. driver came into our shop complained of low power. diagnosed to turbo not functioning properly. in sake of time, we replaced with a new turbo from peterbilt along with vgt controller. restarted truck, #6 injector code, replaced injector along with cam and 2 rockers(6 intake and 2 intake). the cam and rocker looked scarred when we removed the valve cover so we replaced while apart. truck restarted, idles fine with a bit of black smoke at idle. when the truck is revved up, occasional pop like a back fire, along with a tap sound and tons of smoke. checked egr, cleaned it. have not drove it after reassembly.
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04-16-2021, (Subject: cm871 help--- ) 
Post: #2
RE: cm871 help---
Does the truck have the emissions? Has it been deleted? Year make and model of truck too. Is it still running the factory sensors? Are they still painted red? Sounds like it needs a cleaning and EGR Tuneup. How about the fuel doser, was that replaced or at least inspected?


User's Signature: 2008 ProStar, OEM 600hp CM-871, 18spd, 3:42, in framed in Rawze's driveway. Every day is a fresh new episode of, "The Twilight Zone"... Rod Serling lives rent free in my head. I can smell the Chesterfields.
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04-16-2021, (Subject: cm871 help--- ) 
Post: #3
RE: cm871 help---
2009 peterbilt 389. ecm was replaced about 8 months ago. most sensors are factory. egr was removed and cleaned. we have not looked at the doser. there are no active codes.
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04-16-2021, (Subject: cm871 help--- ) 
Post: #4
RE: cm871 help---
The truck needs an EGR tuneup, go to the video tab at the top of the page, do that. Odds are that is your issue, old sensors. The smoke, if the truck is still stock, no delete, the cans need to be replaced, as I am sure they are originals, the DOC filter is more than likely face plugged, and I would surmise, it and or the DPF filter are cracked. Doubtful it needed a turbo, that is the first place everyone goes when there are emissions problems. The turbo cannot perform due to the damaged DPF and DOC filters. The cam and rollers were damaged from the soot...

EGR tuneup, replace fuel doser, I am sure it is factory original, drop the DPF/DOC cans. Start there, post photos of both can faces. There is a core charge on the doser, so do not throw it in the trash.

Here is the link to the EGR tuneup on the CM-871, there are six videos in total... https://www.youtube.com/watch?v=FhJxpyS5MpY

The tick, redo the overhead, odds are something was missed.


User's Signature: 2008 ProStar, OEM 600hp CM-871, 18spd, 3:42, in framed in Rawze's driveway. Every day is a fresh new episode of, "The Twilight Zone"... Rod Serling lives rent free in my head. I can smell the Chesterfields.
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 Thanks given by: hhow55
04-16-2021, (Subject: cm871 help--- ) 
Post: #5
RE: cm871 help---
Sounds like maybe your static timing is off as well. You sure you used the right wedge for that cam?


User's Signature: Warranty??? Yeah right, I am the warranty!!!
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 Thanks given by: Waterloo
04-16-2021, (Subject: cm871 help--- ) 
Post: #6
RE: cm871 help---
On a side note, looking at the age of the truck, the crankshaft damper should be replaced too. They have a 500,000 mile lifespan, but that is under normal use. This truck has not seen that, and I would bet the viscous fluid internally is hardened, something you may want to discuss with your customer. The damper, when in this condition can and will do damage to the accessories and eventually the motor, especially if it fails. When a damper fails, it blows apart, sometimes catastrophically, taking the front structure and motor with it. They run around $700 from Cummins, paint them and highlight the timing marks. I would replace if my truck.


User's Signature: 2008 ProStar, OEM 600hp CM-871, 18spd, 3:42, in framed in Rawze's driveway. Every day is a fresh new episode of, "The Twilight Zone"... Rod Serling lives rent free in my head. I can smell the Chesterfields.
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04-16-2021, (Subject: cm871 help--- ) 
Post: #7
RE: cm871 help---
(04-16-2021 )tree98 Wrote:  Sounds like maybe your static timing is off as well. You sure you used the right wedge for that cam?

That tick, when I last did my overhead, I fired her up and had a tick... I had to redo it, tick gone, but good call on the wedge, I forgot about that.


User's Signature: 2008 ProStar, OEM 600hp CM-871, 18spd, 3:42, in framed in Rawze's driveway. Every day is a fresh new episode of, "The Twilight Zone"... Rod Serling lives rent free in my head. I can smell the Chesterfields.
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04-16-2021, (Subject: cm871 help--- ) 
Post: #8
RE: cm871 help---
* anyone verify the turbo was re-calibrated correctly after its replacement, and checked that it was not going to high positions, choking the engine off?

* Anyone verify that any of the metering and timing actuator plugs did not get knocked loose?

* Anyone verify a second time that the replaced cam did not slip? and that crank was pinned properly, and the #4 (for injector cam) and #6(for valve cam) wedge was used?

* Anyone bother doing an injector leak test?

* anyone set/verify again, the overhead valves correctly and engine brake after the repairs?

* Anyone check the detent clearance on the engine brake rockers after the re-assembly of everything in the top end?

- There are a lot of things that can cause what you describe... from improper injection timing due to one reason or another, all the way up to, and/or including a burnt valve.

-- Also, if it is not deleted ... then WHY is there a lot of black smoke?. - Cracked DPF unit perhaps?. I know that it can black smoke even with the DPF in place... but it would have to be a very, very severe condition to allow it to get past the DPF.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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04-17-2021, (Subject: cm871 help--- ) 
Post: #9
RE: cm871 help---
We checked most of these items this morning. After doing a cylinder cutout, #6 seems to be the culprit. Truck will run on all except #6 when cutout. That is also the injector we replaced. We will keep everyone posted. Thanks for the input.
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