First time posting but Ive been reading and educating myself on this forum for years!

Ill start off with my vehicle: 2003 F-150, 5.4, 4x4, (Kingranch, supercab, flare-side) 280k miles

Ive been having misfire on cylinder two codes for a couple of weeks. Since then, I replaced all of my plugs with motorcraft plugs and changed the cylinder two coil with a motorcraft as well and cleared the code. It keeps coming back. The misfires only occur within the first 20 seconds of start up and then the idle smooths back to normal. I have another issue that I fear is related. After I start up in the mornings and drive for a few min. The engine temp gauge will rise a quarter inch before the red zone and then suddenly fall down to normal almost like there is air in the system. I slowly filled the antifreeze with the truck running for about 25 min to ensure that this was not the case. I eventually discovered that the Reservoir cap is spurting antifreeze. I have ordered a new cap but I do not think that is the issue. Here is the kicker, the coolant tank has a STRONG odor of exhaust.

Don't bash me or call me dumb or anything because I'm no mechanic, but I have a theory and I want to know what y'all think. I think there is a tiny leak in the head gasket and when its running, it causes pressure to build over 16 psi in the system and causes the valve on the reservoir cap to open. When the truck is turned off, The same pressure built in the cooling system forces a little antifreeze into the cylinder cause a horrible idle/ misfire for a few seconds upon startup.

Any input is appreciated! Thanks in advance!

 

I think you are on the right track. Do a compression test to verify, the affected cylinder/s will have a lower reading than the others.

Before doing the test, you could put a borescope down each cylinder and look for evidence of coolant in the cylinders.

 

Man, I was hoping that I wasn't on the right track. haha
I know I can rent a compression test kit from an auto parts store but what about a borescope?
Thanks for your help

 

All of your symptoms, as reported, point to a blown head gasket (or similar).

 

I would suggest instead of having to tear the spark plugs out and all that BS for a compression test, just find somebody with a CO/CO2 detector. All that's required is pulling the radiator cap off and let the instrument read if there are any CO/CO2 gases in the system. By far easier. Most ASE shops will have a detector as well most HVAC techs. HVAC techs use one to test the heating system of a home for any combustible gases and CO/CO2 gases that might get passed the heat exchanger. If you have a bud in the HVAC industry, he probably has one.

 

Some parts stores loan or rent borescopes.

Labnerd, we already know there are combustion gases in the cooling system, he can smell it.

"Tearing the spark plugs out and all that BS" is something that's going to have to be done to repair it anyway, with that many miles on the engine I think it would be beneficial to see what the compression is like in ALL cylinders.

To the OP - I think you should be prepared to buy a rebuilt engine, at the very least one of the heads has to come off. With 280k on it, it doesn't owe you anything and who knows when the other head gasket is going to go or the rings and bearings start to fall apart.