Misfire AGAIN P0300 and P0430

[nimrod.sixty9]

Well the Yukon is acting up again; original thread here.

This time it is not pointing out a specific cyl.
Only have;

• P0300 - Random/Multiple Cylinder Misfire Detected; and,

• P0430 - Catalyst System Efficeiency Below Threshold (Bank 2)

Seems to be every startup now, and then smooths out. This is hot or cold; could be running fine, turn off for a few minutes and it starts all over again; SES flashing and all.

 

[GTPprix]

My vote is for clogged cat

 

[nimrod.sixty9]

My vote is for clogged cat

It does seem to resemble that, but it doesn't do it all the time. I've never had a misfire from a a cat that was inconsistent.

 

[GTPprix]

I've seen it when the brick is breaking and shifting causing huge swings in back pressure but it's not super common.

 

[nimrod.sixty9]

Random frame capture. Not sure if I even trust this crappy app anymore tho (I was getting misfires with the truck OFF).

 

[SunlitComet]

backpressure test the exhuast system on both banks. Also if you can open your throttle and see if you can smell any gas in there. I say this cause you have 3 cylinders with current misfires as you are running your test and there are close to the fuel body. Two nearest the FPR. Is it hot where you live when you did this test? Engine seems awfully warm.

 

[nimrod.sixty9]

backpressure test the exhuast system on both banks. Also if you can open your throttle and see if you can smell any gas in there. I say this cause you have 3 cylinders with current misfires as you are running your test and there are close to the fuel body. Two nearest the FPR. Is it hot where you live when you did this test? Engine seems awfully warm.

Unless Im reading it wrong, doesn't it say Im misfiring on all but cyl 1?

For the fuel smell check; running or no?

It has been fairly hot today as well as not having the cover on the air box. I imagine that would explain the temp.

I will have to rent the tool to do the back pressure test. So is there anything else I should get while Im there?

---------- Post added at 04:24 PM ---------- Previous post was at 04:10 PM ----------

Just went to smell the TB... Open I could smell fuel, but only a little and with my nose buried into the TB. Could be old cleaner or oil for all I know.

---------- Post added at 05:01 PM ---------- Previous post was at 04:24 PM ----------

Also need to state, it does not lack power. Not like a clogged CAT, I get into the pedal and it rolls.

 

[SunlitComet]

Yes but I do not know how far back that history goes. Could be since the pcm last lost batt power. Current is live as in the past minute or so. I was talking engine temp not intake temp. For the fuel smell prime the system a few time with out starting and see if the fuel odor get stronger. If so can you borrow a boroscope to look inside the manifold?

---------- Post added at 02:04 PM ---------- Previous post was at 02:03 PM ----------

then you can probably skip the backpressure test then.

 

[nimrod.sixty9]

Yes but I do not know how far back that history goes. Could be since the pcm last lost batt power. Current is live as in the past minute or so. I was talking engine temp not intake temp. For the fuel smell prime the system a few time with out starting and see if the fuel odor get stronger. If so can you borrow a boroscope to look inside the manifold?

---------- Post added at 02:04 PM ---------- Previous post was at 02:03 PM ----------

then you can probably skip the backpressure test then.

How do I see current?

Had roomy prime the pump while I was nose deep in the TB, no change. If anything, the longer I held it open the less I could smell it.

Now what?

 

[SunlitComet]

Current as in current misfire count for each cylinder. I think a no cost thing to do is read the plugs and see if anything stands out. Did you see any spark arcing inside the dizzy cap before?