Engine Misfire after changing coolant tank

So I spent the last 4-5 hours wrestling with removing and replacing the coolant tank. Got it all back together and went to flush the coolant (drained old coolant, filled with water and flush fluid). Was running the engine at idle, and everything was going fine but then as temp started coming up after 5 minutes or so to about 100-110, the engine started running rough, followed by check engine light and the following codes... P0300 - Random/Multiple Cylinder Misfire Detected P0301 - Cylinder 1 Misfire Detected P0302 - Cylinder 2 Misfire Detected What should be some of the first things I should check? Thanks in advance

you may have got something wet...coil etc. let it dry out ?check your vacuum lines ,may have disconnected due to the work done.i hope you did not overheat and pop a head gasket

You really have to over heat and idling engine to warp the head and blow the gasket. Since there is no load on the engine, it heats up evenly, even during over heating and nothing warps. Chances are the # 1 &#2 coils got wet. Since they are probably cracked from age, the water/coolant shorted it out. Let it dry up anf see if the mussfire goes away. However, this is a sign that the coils are due for a change.

funny (not haha but hmmm) i did the exact same as the OP. finally got er all hooked up yesterday and she ran really rough. it didnt pull out any codes yet but the check engine light did flash. thought maybe i did something when i dropped the engine. so on monday will check codees and thinking its the coils, or else a vaccuum line...could the maf sensor affect this as well?

So... after letting the car sit for 4-5 hours, I cleared the codes and started it up.... once again, everything was smooth (just idling in the garage), until the temperature reached about 120F after maybe 5 minutes, and then started to run rough with a misfire on cylinder #1. doesn't sound like coils being wet.... would that be a symptom of loose vacuum line? I'm actually not sure where to check for this... I'll be searching google in the morning, but if anyone can point me in the right direction I would appreciate it. FYI - 2002 C4 Cab.

Have you disconnected the evap line that goes into the evap purge valve? Any air in the cooling system? Vacuum refill tool or manual bleeding?

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Bingo.... Air in the cooling system.

Weird...air in the cooling produces misfire codes?

Possible the air pockets affect the temperature pickup of the coolant temp sensor, which then throws off the fuel trims.

I haven't had a chance to run the car for an extended period since, but I opened up the bleed valve again once idling, and saw color of "flush" coolant change... In other words I wasn't circulating the fluid... Probably causing water pump to cavitate.

Makes sense. You should definitely perform the manual bleeding procedures that involves cycles of revving the engine to higher rpm once warmed.

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Well.... Got out there again and more misfires on cylinder 1. Ran smooth for about 10-12 minutes... Temp got up to 160 then misfire... I'll let everything dry out and try again in the morning.... On pelican website it says to rev to 5000 rp during flush, but in park, only can get up to 4000.... Seems to be limited there... As that because I have a tip?

Yes, most likely limited by the tip. However, 4k should be plenty anyway. Maybe trace back what you disconnected and make sure all connectors, hoses are seated correctly and no air leak? If #1 misfire persists, you may want to remove the coil and plug to inspect them carefully. If multiple misfires, I would suspect wrong fuel/air mixture because any wetness on cracked coil should have dried up by now. You connected back the evap purge line, right?

Not sure I disconnected it?? Sorry, kind of a newb at this. Do you have a picture of what it looks like and I can check whether It's connected securely or not?

another quick question..... if I was running the engine for 5-6 minutes without the water running through the engine, could it have caused any catastrophic damage which is why I'm still seeing check engine light? Though after I got the air pockets out, I was running for 10 minutes or so until it started to run rough again.

Anything is possible but not likely. You'll have to start systematically check everything.

+1 Evap line is the one that says "Disconnect" in the photo borrowed from 6speed Coolant5 (Medium).jpg

Just an update.... Talked to the mechanic, Plugs in cylinder 1 was completely fouled up, and all 6 were pretty bad. He said he's never had such a hard time pulling them out - really seized in there. Also coils on 1,2 and 6 were bad (6 was extremely corroded), so he is replacing those 3. Also performed a leak down test and there were no issues. He's going to take it for a drive to ensure everything is sorted, but hopefully that fixes the problem!

Sounds like good news! It's quite a coincidence all these problems popped up after coolant change though.

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That's what I thought.... Hoping it's that I got some coolant on the coilpacks combined maybe with the car overheating when I didn't have good coolant flow causing poor combustion which fouled the plugs????? Anyways... he took it for a 15 mile drive and said it ran like new, no more misfires.

thank you for the report back.

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That's good news.

Nah, plugs don't foul because of missfire from a soaked coil. They were probably just old amd/or the end gap was too large.

This happened to me today! P0301, rough idle - after coolant tank changed. Could there be air in my coolant system? Will it work itself out, or do I need a full flush?

Did the coils get wet?

nm

I changed out my coolant tank in a 1999 996 tiptronic. Got a misfire in cylinder #1 and the temperature light would not stop blinking. I pulled coil pack and spark plug in cylinder #1 and they both looked great. The only thing was the spark plug came out way too easy, so I think it was very loose. I reinstalled the plug at 22 ft lbs and reinstalled the coil pack. By the way getting those out of cylinder #1 is no picnic. Started the car and everything runs great! The coolant light kept blinking though. After purging the system for air, the coolant light just kept blinking. So I thought to myself, dang it, I am going to have to pull that tank again to get at the coolant level sensor. I installed a new sensor so logic was to reinstall the old sensor to see if the temperature light would go out. Well, I did not have to remove the hoses from the coolant tank to get at the coolant level sensor. All I had to do was remove the fuel return line and the smog pump along with the air cleaner, and I moved the tank to the right and I was able to access the coolant level sensor at the bottom of the tank. It is extremely tight, and I have big hands, but I was able to do it. I removed the new sensor and reinstalled the old sensor. I put everything back together keeping an eye out for fuel leaks. Started the car up and the temperature light stopped flashing! Everything is fixed and I am a happy camper.