Misfire in Cylinder#8

[AkursedX]

Well I will first start off with some background.

Over the weekend, I replaced my passenger side exhaust manifold gasket and fixed and extracted a broken header bolt by cylinder #8. Although a bit of a pain, everything seemed to go well and I got the bolt out and everything reassembled.

I then took the car out for a drive to the grocery store and back with no issues.

Fast forward to this morning. I had to take my kid to the doctor and I fired the Tahoe up and noticed right away that it was not firing on all cylinders. After I got back, I pulled up my codes and did a quick scan via HPTuners. I got a misfire code for Cylinder#8. My scan showed misfire counts around 180 at idle and the O2 sensor and fuel trims indicated to me that fuel was being injected and then unburnt. That seems to indicate that I have no spark in that cylinder.

I swapped a spare wire I had and also replaced the plug and there was no difference. My next step is to switch the coil-packs around.

I should also add that the Tahoe spent the night sitting out in a fairly heavy rainstorm and got very very humid, things that normally don't get along with electrical systems.

So my next step is to put in a new coil-pack and see what happens. I am hoping this will remedy the issue.

If this doesn't rememdy the issue, where should my next step be?? Compression check? Fuel injector? I don't know and could use some direction.

 

[AkursedX]

So I just thought I'd update.

I went to the parts store and picked up a new coilpack. I changed it out in the pouring rain and voila! she's back up and running again.

I'm glad it was just the coilpack and I didn't have to go any further....

 

[AkursedX]

Dammit......


I drove my Tahoe into work today. For most of the ride it was running fine. I was almost to work and was sitting at a light. I started noticing the same sputter again.

I stepped on the gas and the truck started shimming again and the SES popped back on.

I can't check the codes yet, but I'm willing to bet it's the same cylinder misfire. If that's the case, I'm leaning torwards a leaking injector. Considering that it was running fine with the new coilpack tells me that it had a strong enough spark to ignite the extra fuel, but as time went on, the extra fuel probably fouled out the plug.

Next in line, a fuel pressure test and probably a new injector.....

 

[Mac]

What's the code?....

How did you get the broken bolt off?
Drill extrator or Drill Tap?..or?

 

[AkursedX]

What's the code?....

How did you get the broken bolt off?
Drill extrator or Drill Tap?..or?

The code is P0308 I believe. Misfire cylinder#8.

Only the bolt head was broken off therefore I was able to get an extraction socket on it. I had a very good amount of thread sticking out to get on.

 

[Mac]

I guess all you could do is try narrowing it down.
Since you changed the coil, and now suspect the injector. Why not clear the code, and swap injectors to see if it pops up on the other cylinder.

If that don't work. keep swapping the other suspected parts..wire,spark plug...eventually working your way down to the ..O2, and checking the CAT, Compression and valves.


Back to the broken bolt....after removing all the bolts could you fry off the exhaust manifold easily, or is it being held on by the damage bolt?.

(Just gathering info. I'm missing head bolts, might wanna tackle it sometime soon.)..Bloody GM....

 

[AkursedX]

Back to the broken bolt....after removing all the bolts could you fry off the exhaust manifold easily, or is it being held on by the damage bolt?.

(Just gathering info. I'm missing head bolts, might wanna tackle it sometime soon.)..Bloody GM....

I was able to pop the manifold off the broken bolt no problem. I was not able to break the bolts that hold the y-pipe to the manifold free so my room to work was a bit tight. Freeing the dipstick tube, and working through the wheelwell made the job a bit easier.

 

[BOSS]

I guess all you could do is try narrowing it down.
Since you changed the coil, and now suspect the injector. Why not clear the code, and swap injectors to see if it pops up on the other cylinder.

If that don't work. keep swapping the other suspected parts..wire,spark plug...eventually working your way down to the ..O2, and checking the CAT, Compression and valves.


Back to the broken bolt....after removing all the bolts could you fry off the exhaust manifold easily, or is it being held on by the damage bolt?.

(Just gathering info. I'm missing head bolts, might wanna tackle it sometime soon.)..Bloody GM....

Is this guesswork? Or troubleshooting...

Sorry bro

Mac has a good point, swapping pieces to isolate and/or eliminate variables. *Edit I would clear codes, and disconnect the exhaust manifold from the cats if you end up with a multiple cylinder misfire code...not that I'm predicting it

On the broken header bolt, it's common:
http://www.tahoeyukonforum.com/forum/showthread.php?t=14909

B