P0016 Maybe VVT Gear Malfunctioning????

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
Hi. Long time lurker. I have been in the process of swapping a blown motor(hydrolocked and cracked a piston) out of a 2004 Trailblazer EXT LT 4.2l 4x4 that was given to me. Low mileage swap with brand new seals all over. I've replaced a lot of the internal parts inside as well . I did't wanna mess with this thing for awhile. Lol. In the process of finishing things up this code has been consistently coming and going. Today it started dying when coming to a stop. Started up immediately and wouldve died again but I gave it the power brake and got it back to the shop.
Got my TB on the scanner and the only code I had was P0016. Then the longer I let the truck run the more more open it would die at idle. I've worked thru everything else it could be at I believe.
When I watch my live data for the VVT system it shows my desired is 0 and actual at 0 when the code is stored. When the code is live(pending), desired is 0 and actual will start climbing all the way to 15 degrees till the engine stalls. I attempted to see if my scan tool would let me command while it was malfunctioning but all it did was maybe make it take longer to stall out.
This leads me to believe that it's something internal with the cam gear.
I've been doing this professionally for 3 years. Did kind of a mentorships thing for 2 year before the three years professionally but am starting to realize my need for knowledge is either outpacing my mentors understanding or he just doesn't care anymore. He just seems to thing its an oil related issue but I don't which is why I'm here. Anywho.
Any help would be greatly appreciated.
 
Last edited:

Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
Hi and welcome young Padawan
:biggrin:


I've replaced a lot of the internal parts inside as well .

We'll need to know exactly what you've changed in the engine.

Have you checked the actual oil pressure? The gauge on the dash is fake. The sensor is actually an on/off switch like for idiot lights. You would need to put an real gauge at the oil filter boss.

 

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
I've replaced the timing chain and oil pump. Ok you got me. Maybe that wasn't a lot of internal parts. I was extremely disappointed when I found out that Chevy put Ford oil pressure gauges in these. 😂. I don't remember the specifics but everything was in spec on the mechanical gauge when I checked the oil pressure yesterday.
 

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
I would think the solenoid commands and that changes the desired. The actual changes when the cam gear starts to move. Leads me to believe the locking pin is having an issue or the tension spring on the cam gear is bad. Sorry if my terminology is incorrect.
 

Mike534x

Member
Apr 9, 2012
997
Cheapest easiest fix to try would be replacing the VVT Solenoid (the one that requires moving the PS Pump out of the way), like TJ suggested. Probably would be a good idea to swap the CPS (Camshaft Position Sensor, front of the block above the VVT), the I6 is very picky/sensitive when any sensor is flaking out. If the VVT is the original, those were notorious for the small screens falling out and allowing whatever crap/gunk circulating the oil to gum up the internals.

Dorman (917-010) makes a cheap/"good" replacement for $30 bucks, and the GM/Delco CPS is $30 as well.
 
  • Like
Reactions: Mooseman

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
To give some more information. I have a donor trailblazer with a toasted transmission as well that was given to my shop so I have a few parts I have been able to swap around to help rule things out and it has the same symptoms. Everything is testing good voltage wise as well which is why I'm kinda scratching my head on this. I have put a new VVT Solenoid in and since my cam sensor is reading fine(compared to the other ones I have on hand) and there's no code associated I really see no need to replace it.
 

TJBaker57

Member
Aug 16, 2015
2,963
Colorado
I would think the solenoid commands and that changes the desired. The actual changes when the cam gear starts to move. Leads me to believe the locking pin is having an issue or the tension spring on the cam gear is bad. Sorry if my terminology is incorrect.


The VVT solenoid is commanded by a PWM signal. The valve is spring loaded to a default state where no oil pressure should flow to the phaser circuit that activates the mechanism. If for example the spring loading mechanism is failing the solenoid valve might allow some oil flow and thus the phaser may activate when it is not being commanded to do so. This would result in the desired value to be zero and the actual value to increase.

Just a thought.
 

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
The VVT solenoid is commanded by a PWM signal. The valve is spring loaded to a default state where no oil pressure should flow to the phaser circuit that activates the mechanism. If for example the spring loading mechanism is failing the solenoid valve might allow some oil flow and thus the phaser may activate when it is not being commanded to do so. This would result in the desired value to be zero and the actual value to increase.

Just a thought.
Thank you for explaining it like that. I might see if I can either find my old VVT Solenoid(unlikely). Lol. I could probably pull the solenoid from my donor trailblazer and see if that makes a difference at this point. I've already installed a new Echlin solenoid from Napa. I've never had problems with Echlin VVT solenoids on other cars. I just know to stay away from Dorman unless necessary.
 
Last edited:

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
Update: Tested the solenoid again today it's definitely having intermittent problems. Have ordered a replacement and will install it tomorrow.
After doing more research I see, while not impossible, it's highly unlikely I have a bad timing gear. Especially considering I don't have certain codes that seem to be associated with a malfunctioning gear. The only code I have in the system is P0016. She also runs to good otherwise to be anything else honestly. Thanks for setting me in the right direction @TJBaker57 . I was overlooking something so simple. I will update again tomorrow once I get the new part installed.
 

Aroc

Member
Jun 1, 2023
26
NY
When you swapped the donor engine into the '04 did you change out the cam phaser (cam actuator gear) or leave it as is?

What year is the donor engine?

I ask because the '04 models had the helical spline cam actuator gear which do not have a lock pin and depend on oil pressure to hold full advance. Also if you unplug the cpas (vvt solenoid) at idle the default is full oil pressure to the advance state and minimum valve overlap so vehicle should not stall or hesitate at all. If this follows from your above description the drift to retard could be errant solenoid movement at idle or inadequate oil pressure and malfunctioning gear lockpin to hold position at idle (if vane style).
 

Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
There were some small differences between 04 and 06 but nothing to make the swap impossible. The coolant temp sensor moved from above the thermostat to the right side of the head on the 06 requiring extending the plug wire to it, and the fuel system changed from a return to returnless system requiring you keep the 04 fuel rail.

Yes, the VVT cam gear (or phaser) did change as @Aroc explained however the 04 PCM handles it fine and the CPAS was the same from 02-09.
 

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
The coolant temp sensor moved from above the thermostat to the right side of the head on the 06 requiring extending the plug wire to it, and the fuel system changed from a return to returnless system requiring you keep the 04 fuel rail.
Yeah I discovered all that during tear down.
Yes, the VVT cam gear (or phaser) did change as @Aroc explained however the 04 PCM handles it fine and the CPAS was the same from 02-09.
Makes total sense why the phaser looked different between the two.
 

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
Update: Replaced the solenoid with an AC Delco from rock auto. Check engine light cleared and I thought I was good. It stopped stalling at idle. Then yesterday while driving it almost died again. Lol. Guess what only P0016 again.
Solenoid tested good. Checking the live data I've got erratic movement of the phaser only at operating temp. It definitely seems like the phaser is the final part of my problem. I'm surprised I don't have other codes associated. I'm kinda at a loss of what else to do.
 

Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
I know you put a new oil pump and checked the pressure but did you check it hot?
Checking the live data I've got erratic movement of the phaser only at operating temp.
May be a pressure problem because you say it's fine until it warms up.

What was the inside of the engine like? Reading a bunch of dead end threads on this code (I hate it when people don't come back and say what solved it), seems like a lot had poor maintenance and had internal sludge. My 02 was like that and I went through two cam phaser replacements. First was an ACDelco rebuilt and second was a Dorman which lasted until the truck was scrapped for a dead tranny.

One thing that's mentioned in the manual for this code is a possible improperly torqued balancer. Did you use a new bolt?
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,982
Tampa Bay Area
  • Like
Reactions: TheOneBlazer

budwich

Member
Jun 16, 2013
2,101
kanata
not knowing much about how this system works... but since you have a few spare parts now, how about doing a "clone test"... :smile: connect up one of your spare vvt but not installed... ie, let it sit in "thin air"... of course away from any bad things like belts and such. Leave a disconnected vvt installed in the engine. What happens? I don't know whether the engine will run in some default mode but maybe you will get some differences in data or otherwise that might lead to something.
 
Last edited:
  • Like
Reactions: TheOneBlazer

TheOneBlazer

Original poster
Member
Jul 5, 2024
15
Missouri
I know you put a new oil pump and checked the pressure but did you check it hot?
Yes. I checked while hot when it first started having problems to rule out an issue with the pump.
May be a pressure problem because you say it's fine until it warms up.
At this point it might be worth a revisit.
What was the inside of the engine like? Reading a bunch of dead end threads on this code (I hate it when people don't come back and say what solved it), seems like a lot had poor maintenance and had internal sludge.
The motor I put in had sat on a shop floor for 4 years. The inside wasn't super dirty. I spent a good week cleaning out her insides the best I could before sealing her up. I reused the cam actuator on a recommendation from my mentor. Not sure why honestly.
One thing that's mentioned in the manual for this code is a possible improperly torqued balancer. Did you use a new bolt?
The balancer bolt is torqued to spec. I just reused the old bolt.
 

Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
:deadhorse:

Yeah, I reused mine too way back when I didn't know about torque to yield bolts.

Knowing what I know today, if I'm replacing one of these motors, while it's on the stand, I would replace the entire timing system including the phaser, chain, guides and chain tensioner because doing it in the vehicle is an absolute biatch.
 

Aroc

Member
Jun 1, 2023
26
NY
As a long shot and preventative maintenance you can try to spray contact cleaner at the cam and crank sensor terminals to ensure the circuit provides clear signals. It worked for me to clear a slight glitch at idle.
 
  • Like
Reactions: Mooseman

Mike534x

Member
Apr 9, 2012
997
I would spend a bit more, and get one designed specifically for the Atlas family;

Did you by chance replace the Camshaft Position Sensor too? When I had my 02 years ago, it developed a habit of stalling randomly at idle once it got to operating temp. Found a forum thread long ago with a similar issue that suggested replacing the CPS, and despite not having trouble codes the stalling did go away with the new one.


Then this for the crankshaft.

 
Last edited:

Forum Statistics

Threads
23,484
Posts
639,852
Members
18,717
Latest member
Leoliboy

Members Online