(6.0L Vortec) Tahoe very unusual cold start

[braveheartwallace]

Wanted to post this here to get some of y’all’s thoughts on what may be going on.
Also posted in Hybrid General discussion...


This morning where I am in New Mexico it was a cool 9˚. I went to start my Hybrid Tahoe (6.0L vortec) and it had this incredibly rough idle as recorded in the following youtube videos:



Initial start:

A couple more attempts after engine repeatedly “stalling”:

Running normal after idling for a few minutes:

One thing to note about this hybrid model is that the computer cranks the engine for up to 10 seconds at a time from the drive shaft via the hybrid transmission, similar to bump/roll starting a manual car. There is no traditional starter like on non hybrid models.



In the first two videos you can see me start the car after it stalls/shuts down on its own. I am unsure if the engine actually fired or not. The engine may not have actually been running and just constantly being turned over by the hybrid’s electric motor.



At the end of the second video where I say, “I’m going to end the recording to check that engine light” the reported codes were:

P1400 - Manifold Differential Pressure Sensor

P0506 - Idle Speed Control System RPM Lower than Expected

P0300 - Random cylinder misfire detected

P0011 - Intake Camshaft Position System Performance (Camshaft Position System replaced less than 2k miles ago, code hasn’t resurfaced since then.)



I cleared the codes and restarted the engine smoothly. Drove for a couple hours with no apparent problems and check engine light never came back on.



Anyways, my theory is the roughness was the result of the computer managing the engine in an “open-loop” without any data input from the freezing-cold downstream O2 sensors resulting in improper fuel/air metering. Once it had warmed up enough, I think it switched to a “closed-loop” where all sensors were sending data thus allowing it to meter fuel/air properly and idle smoothly.



The car has been in these cold conditions before but never has ran this rough on a cold start. Any and all thoughts are welcome!


Edit: MAF sensor and throttle body were cleaned at same time when the camshaft position system was replaced.

 

[BG1988]

Wanted to post this here to get some of y’all’s thoughts on what may be going on.
Also posted in Hybrid General discussion...


This morning where I am in New Mexico it was a cool 9˚. I went to start my Hybrid Tahoe (6.0L vortec) and it had this incredibly rough idle as recorded in the following youtube videos:



Initial start:

A couple more attempts after engine repeatedly “stalling”:

Running normal after idling for a few minutes:

One thing to note about this hybrid model is that the computer cranks the engine for up to 10 seconds at a time from the drive shaft via the hybrid transmission, similar to bump/roll starting a manual car. There is no traditional starter like on non hybrid models.



In the first two videos you can see me start the car after it stalls/shuts down on its own. I am unsure if the engine actually fired or not. The engine may not have actually been running and just constantly being turned over by the hybrid’s electric motor.



At the end of the second video where I say, “I’m going to end the recording to check that engine light” the reported codes were:

P1400 - Manifold Differential Pressure Sensor

P0506 - Idle Speed Control System RPM Lower than Expected

P0300 - Random cylinder misfire detected

P0011 - Intake Camshaft Position System Performance (Camshaft Position System replaced less than 2k miles ago, code hasn’t resurfaced since then.)



I cleared the codes and restarted the engine smoothly. Drove for a couple hours with no apparent problems and check engine light never came back on.



Anyways, my theory is the roughness was the result of the computer managing the engine in an “open-loop” without any data input from the freezing-cold downstream O2 sensors resulting in improper fuel/air metering. Once it had warmed up enough, I think it switched to a “closed-loop” where all sensors were sending data thus allowing it to meter fuel/air properly and idle smoothly.



The car has been in these cold conditions before but never has ran this rough on a cold start. Any and all thoughts are welcome!


Edit: MAF sensor and throttle body were cleaned at same time when the camshaft position system was replaced.

what were the other codes ?
you should have not deleted them.. i'm sure there was some Uxxx and hybrid codes you did not cough up..




how old is the battery? Bad 12Volt battery will cause all sorts of issues(as well as the ground system)... once the temperature falls..??


The NNBS cycles the batteries pretty hard...


since you are having a bunch of engine codes as well as a random misfire this might be correct bad ground wires GM used Aluminium wires and cable lugs to cut a corner .. and when they do bad they go bad..






Just for now run it on M when making a left turn or near train tracks
minimize the risk of stalling out.

 

[braveheartwallace]

what were the other codes ?
you should have not deleted them.. i'm sure there was some Uxxx and hybrid codes you did not cough up..




how old is the battery? Bad 12Volt battery will cause all sorts of issues(as well as the ground system)... once the temperature falls..??


The NNBS cycles the batteries pretty hard...


since you are having a bunch of engine codes as well as a random misfire this might be correct bad ground wires GM used Aluminium wires and cable lugs to cut a corner .. and when they do bad they go bad..

View attachment 237525 View attachment 237526




Just for now run it on M when making a left turn or near train tracks
minimize the risk of stalling out.

Other codes were P0AC4 (hybrid aux transmission pump), P0BBD (hybrid battery pack voltage) and P0A80 (Replace hybrid battery pack). These three codes have been reported for the last 4-5 years and I've been ignoring them for the most part.

Planning to replace aux pump soon, however it should be unrelated as the aux pump doesn't have a job while starting the car.
Car is started using Drive Motor/Generator 1, and Aux Pump interfaces with those clutches, but only while in gear.

It's never stalled on me while in motion. This is the first I've seen the engine ever "stall."
I do however drive it in M to prevent auto stop from engaging at low speeds and shift to D upwards of 40 mph.

12V battery is about a year old and has correct voltage.

I'll inspect the ground wires.

 

[BG1988]

Other codes were P0AC4 (hybrid aux transmission pump), P0BBD (hybrid battery pack voltage) and P0A80 (Replace hybrid battery pack). These three codes have been reported for the last 4-5 years and I've been ignoring them for the most part.

Planning to replace aux pump soon, however it should be unrelated as the aux pump doesn't have a job while starting the car.
Car is started using Drive Motor/Generator 1, and Aux Pump interfaces with those clutches, but only while in gear.

It's never stalled on me while in motion. This is the first I've seen the engine ever "stall."
I do however drive it in M to prevent auto stop from engaging at low speeds and shift to D upwards of 40 mph.

12V battery is about a year old and has correct voltage.

I'll inspect the ground wires.

--
i plan to swap out my grounds pretty soon with heavy duty copper cables with tinned copper lugs...


i used solvents(Isopropyl alcohol 91% ) to clean mine (and scrub brush ) for now to get me by the float voltage is 13.0/13.1 and charging voltage is 14.8-14.9


before the float voltage was 12.4-12.6v and 14.4-14.6v...


just be careful with the alcohol you don't want to get your suv drunk (it's highly flammable )




there is 6 connections total from the battery to the inverter (ground wires)


on the AUX pump i would check the wires they fail on the 2008-09 models but the pump is ok
those have an issue with the negative terminal as well coming loose (check both of them they should be securely in place)



i would confirm 100% before "spending money on the AUX pump"


i don't like that oil pressure level your o-ring is busted sucking up air.. 100% sure
40 PSI on a cold start is pretty bad it means your sucking up air you can see it slowly going up as well it should pressurize quickly from 0 to 70PSI-ish in less then a second..that is something that should be on the top of the to do list
PM what it should be like


on a cold start it should be at about 70PSI(≥60PSI) @ temp below 60F(depending if you use 5/30 oil 60psi if your using 0/30 oil)...

 

[braveheartwallace]

--
i plan to swap out my grounds pretty soon with heavy duty copper cables with tinned copper lugs...


i used solvents(Isopropyl alcohol 91% ) to clean mine (and scrub brush ) for now to get me by the float voltage is 13.0/13.1 and charging voltage is 14.8-14.9


before the float voltage was 12.4-12.6v and 14.4-14.6v...


just be careful with the alcohol you don't want to get your suv drunk (it's highly flammable )




there is 6 connections total from the battery to the inverter (ground wires)


on the AUX pump i would check the wires they fail on the 2008-09 models but the pump is ok
those have an issue with the negative terminal as well coming loose (check both of them they should be securely in place)



i would confirm 100% before "spending money on the AUX pump"


i don't like that oil pressure level your o-ring is busted sucking up air.. 100% sure
40 PSI on a cold start is pretty bad it means your sucking up air you can see it slowly going up as well it should pressurize quickly from 0 to 70PSI-ish in less then a second..that is something that should be on the top of the to do list
PM what it should be like


on a cold start it should be at about 70PSI(≥60PSI) @ temp below 60F(depending if you use 5/30 oil 60psi if your using 0/30 oil)...

Are you talking about the O ring on the oil pickup tube inside the pan or the O ring on the oil pressure sending unit?


Edit: that was a dumb question on my part. It must be the oil pickup tube's o-ring.

 

[BG1988]

Are you talking about the O ring on the oil pickup tube inside the pan or the O ring on the oil pressure sending unit?

pick up tube