MFJ

iTrader: (4)

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. I get a P0300. 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. 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 temporary 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 when the plug in the #7 cylinder wasn't firing before. 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 Tuesday. I drive the car to work so I can scan it and see what's going on. On the way there the CEL flashes again (one time) but does not stay on. When that happened my t/c 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.

So I pull out the scanner at work and I have another P0300 code pending. But this time it wasn't misfiring on #7 or #2 at all.
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.

What to do next? The vacuum line that Chevrolet got was wrong of course. So I'm not moving the car until I get a new vacuum line.

So yesterday I cleared the pending code and reset the pcm once more. The car is idling better than it has in a while.

Attached are pictures of the LTFT and STFT . Bank 2 shows 0 in the pictures but it is reading between -1.5 to 2.2. It just happened to be on 0 when I took the pictures. Car idles at 550 rpm per the tune put in it. Just an FYI.


Any ideas? The car is running fine and idling smooth but it was when the P0300 came on last time too.

MFJ

iTrader: (4)

Ok. Car has been running fine after clearing the codes and resetting the pcm until today at lunch. I'm sitting idle in the drive thru and all of a sudden it starts skipping and went really rich. Like sitting in the car was unbearable. I limp it 3 blocks back to the shop and as I go to back into my parking spot it completely cleared up and starting running fine again.

Of course the code was another P0300

Any ideas?

LSX Power Tuning

iTrader: (4)

Almost every time I have seen a P0300 and the check engine blinking its been from a vacuum leak. I had truck one time ran perfect except at WOT the check engine light would blink, ended up have a leaking intake gasket. It wasnt bad enough to make it run bad though.

MFJ

iTrader: (4)

Chevrolet is supposed to have the right vacuum line that broke on the car this time. They've ordered 3 of them and all of them have been wrong. So I'll put that on reset the pcm and see if that does the trick but I checked and now I have another pending P0300 and another for brake switch low circuit. If I remember right that and the crank position sensor wiring all run by the starter which is close to the headers so I'm gonna get under the car and see if any of the wiring is touching or has touched the headers and is burnt or grounding out.

I have the same experience with the P0300 and the flashing CEL being a vacuum problem 90% of the time, but vacuum leaks don't clear up on their on and it cleared up yesterday just when I got back to work and I ran the car for 20 minutes after work and it ran perfect again. Which is what makes me think wiring now.