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gm 6.2l cylinder 8 misfiring only at idle #5444786 06/02/20 04:59 PM
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apollo18 Offline OP
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hey guys, got a 07 escalade with the 6.2l v8. its got 340,000km on it and has been running great, never had any engine issues other then the piston slap and noisy lifters


so i have noticed that over the past 50,000 km the truck has had this problem but back in the day it would only do it if i let the truck idle for 4-5 minutes (which i rarely would ever do) and it just gradully got worse and worse and now it "misfires" at idle within 15 seconds




so the thing is whenever i come to a stoplight and stay stopped for like 15-20 seconds, ill get the message that says " stabilitrak off service traction control" and then the tone of the engine will change and i guess it will sound rougher with a shake, but right when i start driving agian it goes back to normal and then message clears. if i go on the highway, it drives perfect, smooth, good power good revs and never triggers a messsage or anything, but when i come a stop light or any stop, if i wait long enough it will do its thing again.. rough idle, stabilitrak message, and also if i wait like a minute or 2, then the check engine light starts flashing as well, i believe this is because the truck thinks its misfiring or is misfiring and thats why the check engine light flashes. I have also noticed it started doing it earlier lately, like within 5-10 seconds of being stopped anywhere whether its thru the drive thru or at a stop light etc or a long stop sign, it will come up and say "stabilitrak off service traction control"" and the tone of the engine changes like it sounds different then if i wait a little longer, the check engine will begin to flash. however right when i resume driving and my revs get higher etc then the messages dissapear and the truck drives normal and no check engine flash


firstly, the codes i get are p0308 so i know there is a misfire
P0036 HEATER CONTROL CIRCUIT BANK 1 SENSOR 2
P0056 HEATER CONTROL CIRCUIT BANK 2 SENSOR 2
P0449 EVAP EMISSION SYSTEM VENT VALVE/SOLENOID CIRCUIT
P0452 EVAP PRESSURE SENSOR/SWITCH LOW
P0308 ENGINE MISFIRE CYLINDER 8




i also do have some evap codes but have had those forever


so im not a mechanic on my own but i swapped coils and tried to see if the misfire stops and it doesnt. i also swapped the plugs and wires around and still has the same problem. the plugs and wires are relatively new only 50,000 km on them. i used my code reader and traced it as a p0308 so i swapped a brand new spark plug into that cylinder and still has the same problem. but have showed it to a local indie mechanic and he did a leakdown test got 6% so he said the engine is still strong, he said compression test was above 200+ for all cylinders, lastly i believe he said he changed the intake manifold gasket but it still has the same problem. he also said the wires are good too.

i then took it to GM for a diagnosis and they said this
"PO300 MISFIRE. MISFIRE IS ON
CYLINDER 8. THE IGN. COIL AND WIRE ARE GOOD. COMPRESSION IS OK. HOOKED
UP INJECTOR BALANCE TEST FIXTURE. ALL INJECTORS ARE GOOD. SUSPECT
CAMSHAFT ISSUES DUE TO NOISE IN RIGHT REAR BANK AT HIGHER RPM. WOULD
NEED ENGINE DISASSEMBLY TO FIND "




anyone have any luck? i was reading more and someone said when the engines get gunked up and old, the vvt goes wonky and ends up causing this? but not sure if thats the truth


so i wanted to ask, any chance this could be an easy/cheap fix? if not, then whats the worst that could happen by me driving this still? like am i doing way more damage by keep driving it? like my reasoning is that if the fix is expensive i am just going to drive it till it dies because the engine already has enough clicks and i would rather spend the money on a different vehicle. but if it is a cheap fix or easy then might as welll get it fixed.

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5444790 06/02/20 05:06 PM
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eljefino Offline
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When this happened on my saturn it was the intake manifold gasket leaking a little vacuum. It only mattered at idle due to the very small amount of fuel injected.

You can spray your idling engine with something flammable to see if it gets better. Or waft an unlit propane torch. Used to say brake cleaner but depending where you live, it's not (that) flammable anymore.

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: eljefino] #5444827 06/02/20 06:06 PM
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apollo18 Offline OP
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Originally Posted by eljefino
When this happened on my saturn it was the intake manifold gasket leaking a little vacuum. It only mattered at idle due to the very small amount of fuel injected.

You can spray your idling engine with something flammable to see if it gets better. Or waft an unlit propane torch. Used to say brake cleaner but depending where you live, it's not (that) flammable anymore.



thanks! my mechanic did replace the intake gasket but sadly same thing

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5444844 06/02/20 06:31 PM
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Take the valve cover off and start it. See if #8 valves are not opening as much as the rest,


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Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5444847 06/02/20 06:37 PM
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alchargo Online Content
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Anytime you get a Stabilitrack or traction control related message, there will be an accompanying Chassis (CXXXX) related code, much like the Powertrain (PXXXX) codes you are getting. I would start with using a code reader or scan tool that will read C codes before throwing anymore parts at it.

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5444896 06/02/20 08:12 PM
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Trav Offline
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Check main power and ground cables to the battery and body. Easy to do and cost nothing to check but bad connections can cause all sort of issues with modern systems.


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Re: gm 6.2l cylinder 8 misfiring only at idle [Re: alchargo] #5444923 06/02/20 09:10 PM
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Originally Posted by alchargo
Anytime you get a Stabilitrack or traction control related message, there will be an accompanying Chassis (CXXXX) related code, much like the Powertrain (PXXXX) codes you are getting. I would start with using a code reader or scan tool that will read C codes before throwing anymore parts at it.


?? Stabilitrack disables whenever there is a engine misfire. He’s got a misfire code there, no need to be looking for chasis codes when he’s got a misfire.

You might want to start diagnosing your evap code issue. I have witnessed two GM vehicles with evap purge valve codes and the failed purge valves caused misfires. On both of those cars it was the evap purge valve on the intake manifold. I’d start by getting that corrected. And the vehicles only misfired at idle.

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5444961 06/02/20 11:28 PM
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tcp71 Offline
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Definitely evap purge valve as a starting point.


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Re: gm 6.2l cylinder 8 misfiring only at idle [Re: tcp71] #5444963 06/02/20 11:45 PM
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apollo18 Offline OP
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is that pretty easy to change out? odd that GM didnt even notice or test that at first

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: buddylpal] #5445012 06/03/20 05:57 AM
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Originally Posted by buddylpal
Originally Posted by alchargo
Anytime you get a Stabilitrack or traction control related message, there will be an accompanying Chassis (CXXXX) related code, much like the Powertrain (PXXXX) codes you are getting. I would start with using a code reader or scan tool that will read C codes before throwing anymore parts at it.


?? Stabilitrack disables whenever there is a engine misfire. He’s got a misfire code there, no need to be looking for chasis codes when he’s got a misfire.

You might want to start diagnosing your evap code issue. I have witnessed two GM vehicles with evap purge valve codes and the failed purge valves caused misfires. On both of those cars it was the evap purge valve on the intake manifold. I’d start by getting that corrected. And the vehicles only misfired at idle.


My 05 Silverado had a bad purge valve for a while, every time we filled the gas tank it would take 2 tries to start, like it was flooded.

It did occasionally have a stumble at idle that might have been the same cause, but you literally had to be standing near the tailpipe to hear it stumble when it did it.

It is a cheap and easy fix though, so it's worth trying first.

Last edited by caprice_2nv; 06/03/20 05:58 AM.

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Re: gm 6.2l cylinder 8 misfiring only at idle [Re: alchargo] #5445232 06/03/20 11:11 AM
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Originally Posted by alchargo
Anytime you get a Stabilitrack or traction control related message, there will be an accompanying Chassis (CXXXX) related code, much like the Powertrain (PXXXX) codes you are getting. I would start with using a code reader or scan tool that will read C codes before throwing anymore parts at it.


Not true that you always have C codes.... many Powertrain related codes will set the Stability/Traction messages/lights. Reason is certain engine/trans codes (such as his misfire) make it unsafe for stability/traction systems to work properly so they disable themselves for safety reasons - there is not anything wrong with those systems. Fix the P codes and they go back to working as they should.

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5445392 06/03/20 02:11 PM
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P0452 can be from a loose or leaking gas cap or a leak at the filler neck.

I got that code only on my '01 Silverado. The above 2 things didn't solve it, so I went to inspect the pressure sensor on top of the tank and found all three wires were broken or chewed through.

I have no idea how or if that code would be related to your misfire, but it can be an easy one to check out.

Re: gm 6.2l cylinder 8 misfiring only at idle [Re: apollo18] #5445450 06/03/20 03:30 PM
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