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High Oil Pressure / Misfire

Bentley

By Bentley
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Bentley Enthusiast

Bentley

Posted
Posted (edited)

I'm stumped.  .....  2017 6.2l Gen V L86: 270,000 kms (180k mi)

 

I start the engine, and it idles/runs fine for about 20 seconds. Then, (as if a switch goes off), the following:

     1) misfire (I believe), then 2) the oil pressure RISES fast 3) engine light blinks and traction light goes on.

 

OBD codes are only 0308 and P050 (rough idle)

I've replaced:

- plugs, wires, injectors

- pcv, surge valves

 

KNOWN issues: 

- broken motor mount

- slight oil leak

- Carbon: I will be giving it a walnut pressure clean

 

Questions:

1) Could it be the pressure relief valve in oil pan?

2) Does the 2 stage oil pump kick in after about 20 seconds running?

3) I cannot find a youtube video on oil pan removal for this engine (Upper & Lower Pans - 2015+) - link would be helpful?

 

Any bit of help would be great!!! I have spent way too much money on this already.

Edited by Bentley
Correction
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silveradosid
silveradosid

you need to have a balance test done or even better have some one who knows how to scope the engine. i have seen on gm v8's that miss fire on cylinder 8 was caused because cylinder 1 fires before 8 an

HawaiianRR
HawaiianRR

Pulled the head off and took out the broken lifter. Camshaft lobe is not damaged. I plan to put 8 new gm lifters and guides. Replace the 1 bent pushrod. Change the filter in the VLOM because it’s easy

Bentley Enthusiast

Bentley

Posted
  • Author
Posted

Thanks, appreciate the response.

But not that. Also:

- compression is good

- changed oil sensor

 

 

newdude Senior Enthusiast

newdude

Posted
Posted (edited)
On 12/25/2023 at 11:56 AM, Bentley said:

I'm stumped.  .....  2017 6.2l Gen V L86: 270,000 kms (180k mi)

 

I start the engine, and it idles/runs fine for about 20 seconds. Then, (as if a switch goes off), the following:

     1) misfire (I believe), then 2) the oil pressure RISES fast 3) engine light blinks and traction light goes on.

 

OBD codes are only 0308 and P050 (rough idle)

I've replaced:

- plugs, wires, injectors

- pcv, surge valves

 

KNOWN issues: 

- broken motor mount

- slight oil leak

- Carbon: I will be giving it a walnut pressure clean

 

Questions:

1) Could it be the pressure relief valve in oil pan?

2) Does the 2 stage oil pump kick in after about 20 seconds running?

3) I cannot find a youtube video on oil pan removal for this engine (Upper & Lower Pans - 2015+) - link would be helpful?

 

Any bit of help would be great!!! I have spent way too much money on this already.

 

 

I assume your codes are P0308 and P050D, seeing you missed some of the digits?

 

P0308 is cylinder 8 misfire.  P050D is Cold Start Rough Idle.  
 

My guess is the P050D is causing the P0308 so bad fuel injector or more than one bad with the P050D.  In a perfect world, it needs to be hooked up to the AFIT at the dealer to test the injectors for balance and flow.  

 

Oil pump issues you'd get a code but no misfire.  P06DD, P06DE, etc.  

Edited by newdude
Bentley Enthusiast

Bentley

Posted
  • Author
Posted

Hey thanks.

As I said - new injectors, new plugs, new wires (among other things)

 

After reading many forums, the dealers just throw money at the thing until the whole engine is rebuilt.

I am hoping that someone else has had the same symptoms and can say how they cured it.

 

 

 

rlcole321 Enthusiast

rlcole321

Posted
Posted

did this happen BEFORE all the new parts?, if yes, then it must be a mechanical issue, if not, could be a bad part, has for the oil pressure problem, I've never heard it happening before, but it's not imposable, ultra-high oil pressure could cause the hydraulic lifters to "Pump-Up" to much causing bad valve closure. (I know. far fetched!). Did this happen all at once, or gradually? Clear the codes and or disconnect batt for about 3 hours to clear memory and see if it comes back instantly. 

a lot to try to come up with!

rlcole321 Enthusiast

rlcole321

Posted
Posted

If its 4WD the front diff and Sterring rack has to come out, if 2WD then you can just unbolt the Steering rack and let it drop down being careful of the wiring. may have to remove exhaust crossover. both oil pan and front cover have to come off for the oil pump.

Bentley Enthusiast

Bentley

Posted
  • Author
Posted

rlcole321: Yeah, this happened before and after new parts. I cleared codes multiple times but disconnected the battery for only about 5 minutes. I'll try a little longer. I am actually not too worried about 308, as I think it is a by product of bad engine mounts and whatever the oil is doing.

 

As the engine warms up, the oil pressure spikes less and less. (The thinning of the oil)

I thought at first the VLOM channels might be clogged, but they allow proper flow after the engine is warm.

 

This is why I was wondering if anyone had experience with the pressure valve in the oil pan, OR if there is a pressure valve attached to the pump.

 

One other thing I cannot understand: The engine starts, everything normal, and then as if there is a specific 'click', the oil spikes.

What is the engine doing 20 seconds after it is started?

 

Thank-y'all for your input!

newdude Senior Enthusiast

newdude

Posted
Posted (edited)
On 12/27/2023 at 2:41 PM, Bentley said:

rlcole321: Yeah, this happened before and after new parts. I cleared codes multiple times but disconnected the battery for only about 5 minutes. I'll try a little longer. I am actually not too worried about 308, as I think it is a by product of bad engine mounts and whatever the oil is doing.

 

As the engine warms up, the oil pressure spikes less and less. (The thinning of the oil)

I thought at first the VLOM channels might be clogged, but they allow proper flow after the engine is warm.

 

This is why I was wondering if anyone had experience with the pressure valve in the oil pan, OR if there is a pressure valve attached to the pump.

 

One other thing I cannot understand: The engine starts, everything normal, and then as if there is a specific 'click', the oil spikes.

What is the engine doing 20 seconds after it is started?

 

Thank-y'all for your input!

 

 

These engines have a variable displacement oil pump.  Below 3500rpm it operates the low pressure stage, above it operates the high pressure stage.  It does have a gauge test/solenoid test on start up.  

 

If the solenoid fails, it will set codes.  If you aren't getting codes however, I don't think you've got an issue with the pump.  

 

Explanation on the oil pump operation:  MC-10143459-9999.pdf (nhtsa.gov)

 

 

Edited by newdude
Bentley Enthusiast

Bentley

Posted
  • Author
Posted

newdude: Thanks, that is very helpful.

I think I can rule out the oil pump as there are no codes..

 

Is it possible that a misfire would set off the high pressure solenoid, which in turn would push the oil pressure up on low idle?

As the engine warms, and if I can avoid the misfire, everything seems to work at running temperature.

silveradosid Senior Enthusiast

silveradosid

Posted
Posted (edited)

you need to have a balance test done or even better have some one who knows how to scope the engine. i have seen on gm v8's that miss fire on cylinder 8 was caused because cylinder 1 fires before 8 and 7 after 8. both 1 and 7 are afm cylinders. your high oil pressure maybe leaking through and causing 1 and 7 to be weak so the engine thinks it's number 8 because it is firing stronger, diagnosticnetwork.com is really a great resource for solving problems. so your first step is to hook to a good scanner and figure out why the ecm is triggering the oil pump solenoid to go to high pressure

 

Edited by silveradosid
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Bentley Enthusiast

Bentley

Posted
  • Author
Posted

silveradosid:

Thank-you. So your answer seems to be a good direction to go. 

 

I am about to fix:

 - oil pan leak, (replace relief valve)

 - broken motor mount,

 - and walnut blast carbon on valves.

I can do these w/o spending tons of money.

 

Just a (hopeful) long shot here: could either of these issues cause the same problem?

Bentley Enthusiast

Bentley

Posted
  • Author
Posted

silveradosid: Thanks,

The oil pressure relief valve is in the oil pan, so I will do that when I replace the gasket.

As far as the rest goes, I think I will fix the mounts, oil leak, and carbon blast, then will get back here to see if all that was successful. If not, well, then uggh

newdude Senior Enthusiast

newdude

Posted
Posted
On 1/3/2024 at 12:23 PM, Bentley said:

silveradosid: Thanks,

The oil pressure relief valve is in the oil pan, so I will do that when I replace the gasket.

As far as the rest goes, I think I will fix the mounts, oil leak, and carbon blast, then will get back here to see if all that was successful. If not, well, then uggh

 

 

The LS engines had the AFM relief valve in the pan.  These LT engines don't have that anymore.  

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