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How To Diagnose Misfires That Don't Throw The CEL

04SS6.0

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04SS6.0 Enthusiast

04SS6.0

Posted
Posted

i have an 04 silverado ss 6.0 365,000km, do all the work on it myself, but this problem had me stumped.

 

I was getting a P0300 code rough idle flashing CEL i replaced the intake manifold gasket with a Fel-Pro one torqued to factory specs first 44 in lbs then 89 in lbs in the factory order. Then i was getting a p0303 code, moved that coil to cylinder 5, got a p0305, moved it to cylinder 1, got a p0301 code. Obliviously that coil was bad, Replaced coil. Seemed to fix it no codes being thrown but i can still feel misfires, took it to mechanic, they concluded :
(1-2 misfires every cycle or so, (normal running condition))  

 

My question is, is that a normal running condition 1-2 misfires every cycle?

 

I wish they told me if it was in bank 1 or bank 2 or both.

 

Parts that are new in the yearish or less
intake manifold gasket
all spark plugs
all spark plug wires 
all ignition coils 
all O2 sensors 
MAF sensor 
Vapor Canister Vent Valve / Solenoid
Fuel Tank Pressure Sensor
Vapor Canister Purge Valve / Solenoid

 

I wish i had the devices to look at the fuel trims graphs and 02 sensor graphs and cylinder misfires numbers. Then i could try myself. 

 

What can i try to diagnose these misfires? is what the mechanic said normal? should i find a different mechanic to actually diagnose it? 

 

Is it a vacuum leak? is the intake manifold gasket leaking? Any tricks to test those?

swathdiver Senior Enthusiast

swathdiver

Posted
Posted
3 hours ago, 04SS6.0 said:

I wish i had the devices to look at the fuel trims graphs and 02 sensor graphs and cylinder misfires numbers. Then i could try myself. 

 

Not sure about misfires being normal, would drive me nuts if they were.  I have a Tech-2 and my truck has NEVER shown a misfire on any cylinder.  There are Bluetooth adapters that work with apps on your phone that would allow you to see misfires.  Not all, so you'll have to be thorough but I would start with Torque Pro.  Scotty Kilmer on youtube recently reviewed an app that even allows remote diagnosis, you run the app and I can see the data live or recorded on a website.  Tech-2 aren't all that expensive anymore, about $350 compared to years past.  GM has moved on to other tools.

 

The diagnostic tools on the Tech-2 allow you to graph sensors and run tests on the coils and injectors and other advanced, bi-directional scan tools have the same features.  

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

I changed a negative battery cable awhile back,solved one issue,created another,g102 on left of engine,below exhaust manifold has the coil ground also,I twisted it, installing new cable,gave me a 300 code,repaired that small ground,good to go,worth a look

SILVER SLED Senior Enthusiast

SILVER SLED

Posted
Posted

Do you notice it running rough?  I've seen a few vehicles have a misfire on occasion and still run good and not set a cel light.  Also, you may try to have the crankshaft position sensor relearned.  I've seen that cure a few odd misfires. 

carkhz316 Enthusiast

carkhz316

Posted
Posted
7 minutes ago, SILVER SLED said:

Do you notice it running rough?  I've seen a few vehicles have a misfire on occasion and still run good and not set a cel light.  Also, you may try to have the crankshaft position sensor relearned.  I've seen that cure a few odd misfires. 

I second this. If one is getting a stored P0300 but no CEL or any observable driveability symptoms,  it seems a they are solved by a crank angle relearn. I've fixed this a few times, once on my last truck.

04SS6.0 Enthusiast

04SS6.0

Posted
  • Author
Posted
16 hours ago, swathdiver said:

 

Not sure about misfires being normal, would drive me nuts if they were.  I have a Tech-2 and my truck has NEVER shown a misfire on any cylinder.  There are Bluetooth adapters that work with apps on your phone that would allow you to see misfires.  Not all, so you'll have to be thorough but I would start with Torque Pro.  Scotty Kilmer on youtube recently reviewed an app that even allows remote diagnosis, you run the app and I can see the data live or recorded on a website.  Tech-2 aren't all that expensive anymore, about $350 compared to years past.  GM has moved on to other tools.

 

The diagnostic tools on the Tech-2 allow you to graph sensors and run tests on the coils and injectors and other advanced, bi-directional scan tools have the same features.  

Ill check it out. I have also heard about blue driver bluetooth. Its about $100 does LT & ST fuel trims, and engine misfires. 

04SS6.0 Enthusiast

04SS6.0

Posted
  • Author
Posted
13 hours ago, riverbanks said:

I changed a negative battery cable awhile back,solved one issue,created another,g102 on left of engine,below exhaust manifold has the coil ground also,I twisted it, installing new cable,gave me a 300 code,repaired that small ground,good to go,worth a look

For sure ill look into those ground wires. thanks.

04SS6.0 Enthusiast

04SS6.0

Posted
  • Author
Posted
11 hours ago, SILVER SLED said:

Do you notice it running rough?  I've seen a few vehicles have a misfire on occasion and still run good and not set a cel light.  Also, you may try to have the crankshaft position sensor relearned.  I've seen that cure a few odd misfires. 

I can notice the misfire just because its been my daily driver for 8 years, it isnt rough, pretty smooth not throwing a pending code or CEL light but i can feel it. 

 

Now that i look on my bill from the mechanic i can see they did a CKP variation relearn. So i guess that's not it. 

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