Question P0300 found and fixed. Cylinder washed?
02-26-2014, 12:22 PM
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Question P0300 found and fixed. Cylinder washed? Ok just like the title states.
I was driving my car and the CEL starts flashing. Hasn't been on it justs starts flashing. At this point the car is running perfect. I'm in the middle of nowhere headed into town. I figure I'll check the code when I get there. I'm 6 miles from town and it starts running rough. Skipping and my torque converter wouldn't lock in. So I slow down. Get to the nearest place to check the engine out. Normally on a P0300, from what I've found, a vacuum leak is normally the cause. So that's where I start. I run the vacuum line from the front of the intake back and where the two lines converge into one line behind the motor it's completely broken in half.
So I know you can't get this vacuum line anywhere but the dealer and it's Sunday. So I get a t fitting, some hose and make one that works. I clear the code and no change. So I reset the pcm to get rid of the bad things it's learned and still no change. P0300 comes up again.My shop is 2 miles down the road. So I limp it there at 1500 rpm and drop it off.
The next day I pull out our scan tool and 1400 misfires on #7 and 1200 on #2. Running rich as hell from the smell. So I know one of them isn't firing at all. I know I've fixed the vacuum leak due to the manifold pressure. So my first thought is it ran so rich it fouled a plug(s). I pull #7 first. Picture attached. So it was fouled and NOT firing at all. The other 7 plugs looked fine. So I changed all of the plugs.
Reset the pcm and started it up. No misfires, ran smooth after it relearned the STFT's and wasn't running rich anymore. So I leave it at work waiting on the factory vacuum lines from Chevrolet. The fix works but looks like ****.
Yesterday, I go at lunch to get food and decide to drive it to let the pcm relearn some more. Ran fine. Blowing smoke out of the left bank at first then it quit. I'm sure from #7 cylinder. So I take the car home and change the oil as soon as I get there. I live 40 miles from work and the car ran great. No codes, idled fine and I never got on it at all. You could smell burnt oil slightly at idle but never saw any smoke. So I changed the oil (didn't really detect a gas smell in it) because where will the gas go.....into the oil. I crank it up and after a few minutes I could smell it running rich again. I checked my homemade vacuum lines and they were still working fine.
Which brings me to this morning. I drive the car to work so I can scan it and see what's going on. On the way here the CEL flashes again (one time) but does not stay on. When that happened my converter unlocked again (misfires will cause that so I know it's not a tranny issue). I slowed way down and limped here again. (About 10 miles) The car was not running rough or didn't feel as though it was missing.
It's likely I could have fouled or be starting to foul the #7 plug again and could be causing another P0300. I'm pretty sure it washed the cylinder from the vacuum leak the first time.
What to do next? I thought about disconnecting the injector and adding a small amount of oil to the cylinder to get the rings to reseat. The vacuum line that Chevrolet got was wrong of course. So I'm not moving the car until I get a new vacuum line.
Hopefully I didn't score the cylinder wall and I need to eliminate the smoke and burnt oil smell. Sometimes it'll take care of itself and reseat the rings after getting the unspent fuel out and new oil covering the cylinder walls. But I don't want to find out that it's not going to and keep running it and do more damage.
I was driving my car and the CEL starts flashing. Hasn't been on it justs starts flashing. At this point the car is running perfect. I'm in the middle of nowhere headed into town. I figure I'll check the code when I get there. I'm 6 miles from town and it starts running rough. Skipping and my torque converter wouldn't lock in. So I slow down. Get to the nearest place to check the engine out. Normally on a P0300, from what I've found, a vacuum leak is normally the cause. So that's where I start. I run the vacuum line from the front of the intake back and where the two lines converge into one line behind the motor it's completely broken in half.
So I know you can't get this vacuum line anywhere but the dealer and it's Sunday. So I get a t fitting, some hose and make one that works. I clear the code and no change. So I reset the pcm to get rid of the bad things it's learned and still no change. P0300 comes up again.My shop is 2 miles down the road. So I limp it there at 1500 rpm and drop it off.
The next day I pull out our scan tool and 1400 misfires on #7 and 1200 on #2. Running rich as hell from the smell. So I know one of them isn't firing at all. I know I've fixed the vacuum leak due to the manifold pressure. So my first thought is it ran so rich it fouled a plug(s). I pull #7 first. Picture attached. So it was fouled and NOT firing at all. The other 7 plugs looked fine. So I changed all of the plugs.
Reset the pcm and started it up. No misfires, ran smooth after it relearned the STFT's and wasn't running rich anymore. So I leave it at work waiting on the factory vacuum lines from Chevrolet. The fix works but looks like ****.
Yesterday, I go at lunch to get food and decide to drive it to let the pcm relearn some more. Ran fine. Blowing smoke out of the left bank at first then it quit. I'm sure from #7 cylinder. So I take the car home and change the oil as soon as I get there. I live 40 miles from work and the car ran great. No codes, idled fine and I never got on it at all. You could smell burnt oil slightly at idle but never saw any smoke. So I changed the oil (didn't really detect a gas smell in it) because where will the gas go.....into the oil. I crank it up and after a few minutes I could smell it running rich again. I checked my homemade vacuum lines and they were still working fine.
Which brings me to this morning. I drive the car to work so I can scan it and see what's going on. On the way here the CEL flashes again (one time) but does not stay on. When that happened my converter unlocked again (misfires will cause that so I know it's not a tranny issue). I slowed way down and limped here again. (About 10 miles) The car was not running rough or didn't feel as though it was missing.
It's likely I could have fouled or be starting to foul the #7 plug again and could be causing another P0300. I'm pretty sure it washed the cylinder from the vacuum leak the first time.
What to do next? I thought about disconnecting the injector and adding a small amount of oil to the cylinder to get the rings to reseat. The vacuum line that Chevrolet got was wrong of course. So I'm not moving the car until I get a new vacuum line.
Hopefully I didn't score the cylinder wall and I need to eliminate the smoke and burnt oil smell. Sometimes it'll take care of itself and reseat the rings after getting the unspent fuel out and new oil covering the cylinder walls. But I don't want to find out that it's not going to and keep running it and do more damage.
Last edited by MFJ; 02-26-2014 at 12:41 PM. Reason: spelling
02-26-2014, 08:13 PM
#2
TECH Regular
Swap the injector with another cylinder and the coil with a different cylinder. Also stick that plug wire on a different cylinder. Keep track which went where. See if the misfire follows any of those. If it stays on cyl 7 then do a leak down test on that cylinder.
02-26-2014, 09:29 PM
#3
can you watch the fuel trims and see what its doing? I recently ran into a problem where one of my o2 sensors pretty much flatlined, and since p1133 and p1153 were turned off in the tune, It just dumped a shitload of fuel in bank 2, causing a misfire. Seems to run fine at first, but the misfire eventually comes. Running in open loop everything is fine.
Your problem could be different, but don't rule out the o2 sensors.
Your problem could be different, but don't rule out the o2 sensors.
02-27-2014, 06:00 AM
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It gets even more weird now.
I put the scan tool on the car yesterday afternoon. It does have another pending code for P0300. No other codes. So I checked the misfire log history. Since I reset the PCM this is from the time I drove it home and back to work.
1 0
2 0
3 2169
4 781
5 816
6 0
7 0
8 0
#7 and #2 were the misfires last time. All I did was change plugs and reset the PCM.
I also watched current misfires as it went through the hundred count cycles and every now and then 1 cylinder would misfire but never 3,4 or 5. I watched for 30 minutes.
O2's are reading between STFT's are 1.3 and 2.4
LTFT Bank 1 (3.4) Bank 2 (7.8)
I put the scan tool on the car yesterday afternoon. It does have another pending code for P0300. No other codes. So I checked the misfire log history. Since I reset the PCM this is from the time I drove it home and back to work.
1 0
2 0
3 2169
4 781
5 816
6 0
7 0
8 0
#7 and #2 were the misfires last time. All I did was change plugs and reset the PCM.
I also watched current misfires as it went through the hundred count cycles and every now and then 1 cylinder would misfire but never 3,4 or 5. I watched for 30 minutes.
O2's are reading between STFT's are 1.3 and 2.4
LTFT Bank 1 (3.4) Bank 2 (7.8)
