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apollo18

2007 ext 6.2l misfire at idle, stabilitrak and tc off

Question

2007 ext with 208,000 miles / 335,000 kms on original engine. I have noticed if i ever let the truck idle for 30 seconds, lets say at a long stop light or at a drive thru, the idle worses, the stabilitrak turns off and the traction control turns off as well. this only happens when the truck is idling. when i begin to drive again, the lights go away and the traction control and stabilitrak are enabled once again. i believe this misfire or whatever it is only happens at idle because the truck feels and drives amazingly above idle. when im driving in the city or highway, the engine feels and runs smoothly. I have noticed this problem over probably the past 50,000 miles and in the past it would happen once in a while, but slowly slowly its getting worse and now it happens very frequently. When this happens now at idle. the check engine light begins to flash but turns solid when i resume driving again. in the past the truck has p0300 and p0308 i believe. I had the spark plugs changed to the delco 41110 around 40,000 miles ago with MSD 8.5mm wires. 

btw i do fill 87 octane, i used to do 91 but now i just do 87. ill fill 91 today and see if it improves

ive heard its the coils going bad? im thinking just to swap all 8 coils

thanks

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14 answers to this question

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If you consistently get P0308 then just swap the coil on cylinder 8 for the one on cylinder 1.  If you now get P0301 it means the coil is likely the issue.  

You should also get a proper compression test done.  

You say you had the plugs changed to 41110, what was in there before, and why the change?  I do not know what plugs are supposed to be in it, but, if those are a colder plug you may want to try putting proper range plugs back in. 

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thanks alot for the reply! yeah i guess i have to check that/do that. 

 

theres no point in just replacing all 8 coils?

 

and the old plugs were due for a change they were black as far as i remember/whatever color needs a change, and the guys on the escalade forum all seem to use delco 41-110 for the replacement plugs

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I am not a fan of throwing parts at a problem.  Since you are getting codes for just number 8 as well as a code for multiple, it is for sure pointing to number 8 cylinder.  I would do the compression test first, and if they are all good, change the plugs(you have them out, hard part is done) and put listed plugs in.  Do the one coil swap at this time as and see what happens.  When did you last have the injectors cleaned?  Have you owned this since new? 

Edited by Doug_Scott
Spelling error that spellcheck missed

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I’m going to say valves are slapping closed harder at the higher RPM’s allowing the engine to run normally. I’m thinking you’re going to find low static compression in cylinder 8. You could do a running compression check too. Test a known good cylinder first and compare to #8


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That won't resolve the issue, it will only hide it at best. 

Something I really thought I had already suggested was to check for vacuum leak around number 8 intake runner at the manifold/head connection.  Also check all vacuum lines for leaks. You can use propane to find a leak. 

If this issue has already been resolved, please post an update to help others that may have a similar issue. 

Edited by Doug_Scott
Stupid auto correct on phone kicks me out of text enter mode.

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im guessing the p0308 cylinder is 8th cylinder which is the passenger side very back which is impossible to change and such ahah. so i have had the p0308 code for a while, it just got way worse recently and causes the engine to shake and flash the check engine light with the stabilitrak and traction control service messages at idle.

 

i swapped the coil from the 1st cylinder at the front, and i swapped with the number 8 passeneger side but i am still getting the p0308. do you think it could be a bad spark plug from a bad install? its so hard to get back there, i have msd wires and i checked the 1st and 8th cylinder wire and they seem to be around 23 ohms resistance, i also sprayed them with electronics cleaner before re installing them. what do you guys think it is?

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Pull the plug and check it.  If it looks good, you will want to check compression on all cylinders.  Sometimes hard to get at plugs get dragged through crap around the opening on the way it fouling the plug. 

 

I have found occasionally that the very hard to get at plugs would not get changed at the prior tuneup.  Late 70s Monza Spider v8 had a very difficult to access number 7 spark plug that was one that stands out in my mind.  They were a popular car around here and it seemed like everyone that came in had an older plug in number 7 cylinder.  Change the plugs in a 67-68 Mustang with a 390/428 and you will find your number 8 is a breeze. 

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swapped the #8 plug with a brand new plug, and then swapped the #8 wire with the #2 wire but still misfiring

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You are going to need to check compression on all cylinders and for a vacuum leak in that cylinders port connection to intake. 

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could this be regarding to the evap codes ive had for a while? maybe the leak got worse?

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
P0463 FUEL LEVEL SENSOR A CIRCUIT HIGH
P0308 ENGINE MISFIRE CYLINDER 8

THANKS

Edited by apollo18

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you need to look into the other codes as well.  You could clear them and see which ones come back first.  Fix the first to return first.  It may very well spawn other errors.

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my mechanic did a leakdown test and said he got 94 something and said it was good, he also did compression test and got good compression, he said he cant remember numbers but it was above 200 each cylinder. he replaced the intake manifold gasket and that fixed the problem temporarily but it seems to have came back. anything else we should try?

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