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I would take it to a GM dealer and have them update the PCM with the newest version software along with a crankshaft variation relearn procedure.
 

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My 2008 3.7 with 165k km stumbles like that sometimes too. It even stalls sometimes when the RPM falls.

I am getting a P0411 code lately, as well as a P0305 for AIR System Incorect Flow, and Cylinder 5 misfire.
 

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Discussion Starter #6 (Edited)
My 2008 3.7 with 165k km stumbles like that sometimes too. It even stalls sometimes when the RPM falls.

I am getting a P0411 code lately.
Out of curiosity, did you get your code almost immediately once you noticed the rough idle/surge?

Mine has yet to throw a code and I've filled the gas tank 7 times since the symptoms started (tank fill #4 with a full can of seafoam, tank fill #7 with a full bottle of Redline SI1). No codes yet, no codes pending/stored, CEL functions properly.
 

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Discussion Starter #7 (Edited)
Update

I replaced the camshaft actuator solenoid using this write-up. For the hell of it, I also replaced the camshaft position sensor and did a complete fill-up of Shell gasoline w/ a bottle of Redline SI-1.

The gas cap seal, turns out that is supposed to be light green! It was covered with some sort of black gunky residue, cleaned that out for good measure.

If any of these solve my problem, I understand there are too many variables to single out a solution. Either way, each one is cheap enough to do and considered "routine maintenance" in some fashion. At least, from all of this, we can learn what doesn't fix the problem.

My used camshaft actuator solenoid had all the screens intact and no oil was found in the connector pins. The new model from GM looks quite updated as the screens appear to be metal (vs plastic, but i'm not 100% sure on this) and have a single metal wire holding each screen in place. So far, after 3 starts from cold, the engine idles fine with no startup issues.

To recap what I replaced:

- Spark plugs (5) - ACDelco Iridium
- Coil packs (5)
- Cleaned MAF
- Replaced PCV Hose to resonator
- Cleaned TB
- Replaced MAP
- Replaced air filter (Wix non-oil)
- Replaced upstream oxygen sensor
- Replaced downstream oxygen sensor
- Replaced idler pulley
- Replaced belt tensioner and belt
- Oil change - synthetic
- Battery check, no problems
- CT emissions test - passed
- Camshaft actuator solenoid (GM)
- Camshaft position sensor (ACDelco)
- Inspected/cleaned gas cap - seal was covered in black gunk

If I STILL have a problem, its going to the stealership. I still have no idea why the problem only exists until the secondary air injector pump kicks on, but i'd rather get all the routine maintenance out of the way just to be sure.
 

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Discussion Starter #8 (Edited)
Update

Problem still exists after replacing cam actuator solenoid. I am going to get it scanned for pending codes one more time before taking it to the dealership. If anything, the idling problem shows up more often. It was one in every five starts. Now, its every other start. Crossing my fingers for a code soon (can't believe I'm saying that, but I need a starting point apart from "routine maintenance")

On another note, this thread notes similar symptoms and points to the evap solenoid. I found lots of threads on this forum that have the same issue (especially with the 08's) and all lead to dead ends, so hopefully I can figure this out and have some sort of solution posted :)
 

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Discussion Starter #9 (Edited)
I would take it to a GM dealer and have them update the PCM with the newest version software along with a crankshaft variation relearn procedure.
Is there an update for open loop idle operation? If so, that might just be it. As for the crankshaft variation relearn, would that also affect closed loop operation? Truck seems to drive fine and has a rock solid idle once the secondary air injection pump turns on (closed loop).
 

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Discussion Starter #10
PCM updates available per my VIN that interest me:

Calibration History for: Engine diagnostic
Part Number CVN Bulletin # Description
12632111 00001DB7 - New calibration with diagnostic enhancements for DTC P0442.
12626116 00008E1F - New calibration with diagnostic enhancements for DTC P0411.

Calibration History for: Fuel system
Part Number CVN Bulletin # Description
12632120 00000B2A - New calibration with diagnostic enhancements for DTC P0442.


P0442 - Evap Emission Control Small Leak Detected
P0411 - Secondary Air Injection System Incorrect Flow Detected
 

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Discussion Starter #11 (Edited)
Not sure if this will work, might need to be home for me to get the pictures working... but my scanner says the EVAP Vapor Pressure is -0.141 (H2O). Could be negative because its a vacuum line? Even with the engine off, it registers a pressure of -0.095. Hard to find out what the normal readings are.

If the pic doesn't work, i'll type out the reading:

Engine Speed: 670 RPM
EVAP Purge %: 11
EVAP Vapor Pressure (H2O): -0.141
Fuel Sys: Closed
Ignition Advance: 7.5 degrees
MAF (LB/M): 0.68

 

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Would love for you to find a solution, I have the same problem. Have replaced pretty much everything you have except the last round you posted.
 

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Discussion Starter #13 (Edited)
It goes to the dealership today for a PCM update. I am going to ask about a crankshaft variation relearn and see how it relates to my problem without throwing any codes. This weekend, I plan on going through the list of parts I replaced to verify everything is sealed/torqued properly and inspect all the accessible electrical pins for corrosion. I am also going to inspect my spark plugs, taking pictures along the way and making sure they are reinstalled properly. Might take my throttle body off again (cleaned it last week) and see if I can access/clean the throttle position sensor.

In regards to the throttle position sensor, a few forum posts around here say that it's the plastic cover clipped on to the side of the throttle body. Held in by about 5 (ish?) clips. Not sure if it can be cleaned, never looked up its skirt, and there are no write-ups here on maintenance for that part. Either way, if it is too difficult to take off or looks like it could break easily, I might not mess with it. Probably not serviceable? There is a related service bulletin, but for the V8's only, 09+

On another note, my battery tested fine, but measures 11.5V with the truck off. 14.3V with the truck on. I only mention this because other posts around here find out that a weak battery is the root of their problems. Not sure how sensitive it is to voltage... I'd rather just throw this information out there in case anyone with experience on this issue wants to chime in.
 

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Out of curiosity, did you get your code almost immediately once you noticed the rough idle/surge?

Mine has yet to throw a code and I've filled the gas tank 7 times since the symptoms started (tank fill #4 with a full can of seafoam, tank fill #7 with a full bottle of Redline SI1). No codes yet, no codes pending/stored, CEL functions properly.
I've had the rough startup with and without the CEL on. It is fairly sporadic though.
 

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Discussion Starter #16
Just got back from the dealership with a fresh PCM update.

Wow, idle is rock solid.

Prior to the update, idle was between 620 and 670. The truck didn't shake or act up, but the needle movement was quite apparent as the idle would jump back and forth by 50 rpm.

Now, it sits quite solidly at 600rpm, +/- 6 rpm. No rough shakes, very little noise, needle doesn't move at all from 600.

I then hooked up my scan tool to check all the sensors. Seems like everything across the board is much more stable, except for the "evap vapor pressure" and the "short term fuel trim" both seem to jump around a little bit. Since I have no idea what these values are supposed to be at and there are no codes, i'll assume its normal for now.

Short term fuel trim will read between -3.9% and +2% while the idle stays constant. May be tiny fluctuations in the fuel to adjust to outside air flow fluctuations or other sources of error. Again, just throwing my findings out there in case someone with more experience chimes in to hopefully say "Yea man, looks good."

EVAP Vapor Pressure jumps between -0.2 and -0.6 in/h2o. Seems to not affect idle speed, but changes for no apparent reason. See closing statement on short term fuel trim paragraph.

So yea! Will report back if my open loop idle problem still exists! For now, that's all I got!
 

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Discussion Starter #17 (Edited)
Problem still exists after the PCM update.

Just went to go start the truck, last run was 90 minutes ago. Started chugging like before. What I noticed this time was a squeaking sound coming from the engine bay, would a loose belt do this? I replaced it early summer with a new idler pulley and belt tensioner. Every time the engine chugged, I heard a subtle squeaking noise... Maybe it's slipping?
 

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Discussion Starter #18 (Edited)
Current serpentine belt that was installed May of this year. 15k miles on it, Gates brand. Noticeable cracking on the top of the belt compared to old belt (second picture). Going to put the old belt back on and see what happens.



 

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  • Battery check, no problems

On another note, my battery tested fine, but measures 11.5V with the truck off. 14.3V with the truck on.

I only mention this because other posts around here find out that a weak battery is the root of their problems.




If a lead acid battery only measures 11.5-volts you have less than a 20% state of charge remaining and that might cause a cold startup issue.

You either have a major parasitic draw problem or the battery is defective.
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Discussion Starter #20



If a lead acid battery only measures 11.5-volts you have less than a 20% state of charge remaining and that might cause a cold startup issue.

You either have a major parasitic draw problem or the battery is defective.
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Well that's funny, guess there is a bit of a disagreement between Autozone battery testers and the source of your pictures. Either way, a voltage drop is a voltage drop. Wouldn't hurt getting another battery!
 
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