White smoke on startup and code P0300?

[Texas Dave]

My 2007 Expy with the 5.4L and 300,000 miles has recently started doing strange things. On the first startup of the day it emits thick white smoke for about 5 seconds. After that, no smoke the rest of the day. It has a rough idle and obvious misfires at low speeds. However, at highway speeds it runs very strong. Accelerates to pass like a beast. Scan shows a P0300 code. My thinking is a vacuum leak due to the fact that it runs perfect at high speeds. Just for grins I changed the MAF sensor which did not help. Any ideas what to look for?

 

[99WhiteC5Coupe]

My 2007 Expy with the 5.4L and 300,000 miles has recently started doing strange things. On the first startup of the day it emits thick white smoke for about 5 seconds. After that, no smoke the rest of the day. It has a rough idle and obvious misfires at low speeds. However, at highway speeds it runs very strong. Accelerates to pass like a beast. Scan shows a P0300 code. My thinking is a vacuum leak due to the fact that it runs perfect at high speeds. Just for grins I changed the MAF sensor which did not help. Any ideas what to look for?

Has your engine coolant level dropped?

Some have posted on this forum about a heater-hose (or connector fitting) leak on the right rear side, causing coolant to enter the spark plug tube(s) and cause a misfire.

The thick white smoke may indicate a head gasket leak.

 

[Texas Dave]

The coolant level is normal. The smoke disappears after about 5 seconds. The rough idle and misfires at slow speeds continue all day.

 

[GlennSullivan]

Start the engine, let it smoke for a few (2) minutes, shut it off, then carefully run a gloved finger on the inside of the tailpipe and examine what comes out for smell and feel - It should not be very hot after only a few minutes. It should tell you if it is oil or coolant.

 

[Texas Dave]

It only smokes for 5 seconds. I let it run for a couple of minutes and did what you said. It was wet but had no smell. Perhaps just water vapor?

 

[Pilgrim]

White smoke generally indicates water and/or coolant in the cylinders. Possibly head gasket or?? P0300 is random misfires which could be connected to the smoke or other things like plugs, coils, ....?

 

[Texas Dave]

PROBLEM SOLVED: It was a camshaft position sensor on the passenger side. $25 and about 30 minutes work and no rough idle, no codes, and no check engine light. Runs great.

 

[Rexpedition]

Congrats -- but what exactly lead you to this conclusion?