2014 5.3 high mileage COLD MISFIRE HELP

[Mattey MES]

2014 sierra 5.3 currently 430xxx km or around 265 miles misfire when cold feels like it’s running on 4 cylinders rough idle. When driving cold feels like it needs to break out of the misfire then goes full power. Will attach video. No major work done. Didn’t change coils. New plugs and wires. Compression test showed 230-240psi across all 8. 
Cel flashed when misfire is “over” and stabiltrak light turns on also. After the truck has its moment the misfire goes away completely while driving. 

truck is stock. DOD deleted since new 

gutted cats. They were clogged

 

[CamGTP]

Do you have a good enough scan tool that can watch each cylinder for the misfire?

 

Because that is what you really need. If you are able to narrow down what cylinder is reporting the misfire you can get more into it. If it's not spark or compression related it could very well be fuel related. Injector failures are super common on these engines.

[Mattey MES]

1 hour ago, CamGTP said:

Do you have a good enough scan tool that can watch each cylinder for the misfire?

 

Because that is what you really need. If you are able to narrow down what cylinder is reporting the misfire you can get more into it. If it's not spark or compression related it could very well be fuel related. Injector failures are super common on these engines.

 

1 hour ago, CamGTP said:

Do you have a good enough scan tool that can watch each cylinder for the misfire?

 

Because that is what you really need. If you are able to narrow down what cylinder is reporting the misfire you can get more into it. If it's not spark or compression related it could very well be fuel related. Injector failures are super common on these engines.

Yea scanned it multiple misfire code. 
Drove it with the scanner hooked up pretty well all cylinders on both banks missfire all random it bounces between cylinders. No particular cylinder misfires. Also zero misfire when warmed up. 

[richard wysong]

A good scanner will count the misfires for each cylinder to help narrow it down, my first thought was carbon build up on the intake valves, it acts like a sponge soaking up the fuel from the injectors until it gets saturated then runs normal. Are the coolant and intake air temps accurate on the scan tool? Any fuel in the oil?

Edited May 1, 2023 by richard wysong

[asilverblazer]

13 hours ago, Mattey MES said:

 

Drove it with the scanner hooked up pretty well all cylinders on both banks missfire all random it bounces between cylinders. No particular cylinder misfires. Also zero misfire when warmed up. 

Is it clearing up when it goes to 'closed loop' vs. 'open loop'?

[Mattey MES]

4 hours ago, asilverblazer said:

Is it clearing up when it goes to 'closed loop' vs. 'open loop'?

What exactly is closed vs open loop?

[newdude]

Well, sending it like in that second video isn't the greatest idea with an active misfire going on...

 

Have you scanned the codes yet?  What codes did you find (and I don't mean the description, what's the actual code #)?

[Mattey MES]

Just a multiple missfire code.

[Mattey MES]

11 minutes ago, newdude said:

Well, sending it like in that second video isn't the greatest idea with an active misfire going on...

 

Have you scanned the codes yet?  What codes did you find (and I don't mean the description, what's the actual code #)?

Just a multiple missfire code.

hard to show the problem without giving it lol 

you can actually see it “break” out of the mis 

[richard wysong]

in open loop it runs on preset parameters until it sees adequate coolant temp etc then switches to closed loop and uses data from all the sensors to manage the engine performance. that is just a basic explanation of open/closed loop

[asilverblazer]

18 hours ago, Mattey MES said:

What exactly is closed vs open loop?

 

14 hours ago, richard wysong said:

in open loop it runs on preset parameters until it sees adequate coolant temp etc then switches to closed loop and uses data from all the sensors to manage the engine performance. that is just a basic explanation of open/closed loop

 

My thinking is if it is clearing up once warmed up - in closed loop - then the sensors are allowing the engine to sufficiently determine/overcome the issue and adjust parameters accordingly. 

 

My initial guess would be an air/fuel ratio issue... I wouldn't expect a significant timing adjustment from cold to hot or open to closed loop. I also wouldn't expect a spark problem to clear up either (considering it is across all 8 plugs, wires and coils). 

 

Fuel trims would be something I watch on a scan tool, especially going in to closed loop. 

 

I would also watch fuel rail pressures. 

 

Other suspects, if the engine isn't getting a correct 'assumed' amount of air during open loop air intake system might be a culprit. Filter type, style, condition? Mass air flow sensor is probably registering correctly in closed loop.  

[richard wysong]

With gutted cats you must have a cel for cat efficiency? The clogged cats may be a clue that something is amiss with the air/fuel ratio as cats do not fail on their own.

[asilverblazer]

4 minutes ago, richard wysong said:

With gutted cats you must have a cel for cat efficiency? The clogged cats may be a clue that something is amiss with the air/fuel ratio as cats do not fail on their own.

Missed the gutted cat part... I'd bet for sure they were smoked as a result of the problem. Must be running too rich in open loop, goes to closed loop, sees the rich condition and leans out the fuel trims. For sure be looking at the air intake track. 

[Mattey MES]

On 5/2/2023 at 11:32 AM, asilverblazer said:

Missed the gutted cat part... I'd bet for sure they were smoked as a result of the problem. Must be running too rich in open loop, goes to closed loop, sees the rich condition and leans out the fuel trims. For sure be looking at the air intake track. 

Cats got clogged due to another misfire. Bad coil. Left side cat was slightly clogged and wouldn’t let enough air out at wot. 
truck was re tuned when cats were gutted.

[asilverblazer]

20 hours ago, Mattey MES said:

truck was re tuned when cats were gutted.

Your tuner should be able to assist... I would expect a competent tuner to see the issue via a data log.

 

On 5/2/2023 at 10:07 AM, asilverblazer said:

 

Fuel trims would be something I watch on a scan tool, especially going in to closed loop. 

 

I would also watch fuel rail pressures. 

 

...air intake system might be a culprit. Filter type, style, condition?

What intake are you using?

 

On 5/1/2023 at 11:19 AM, asilverblazer said:

Is it clearing up when it goes to 'closed loop' vs. 'open loop'?

Have you investigated if it clearing up is when the truck is switching to closed loop?