I have been throwing money at my 1997 F150 XLT 4.6l 2WD Automatic – 157K miles I am suffering from reoccuring P0302 = #2 cylinder misfire after having replaced the intake manifold gasket from a “limp mode” condition due to coolant loss which pulled DTC codes P1285 Cylinder Head overtemperature detected & P1299 Cylinder head overtemperature protection active.

New spark plugs were gapped and installed at same time as intake gasket change. Since I saw a buildup of carbon deposit during the gasket change, I decided to put an additive in to help clean things up. I drove to the autoparts store 8 miles away and everything seemed fine. The first time I got the "check engine" light was within 5 miles of adding 16 oz of SeaFoam cleaner, half into the oil and rest into a half full fuel tank on the way home from the autoparts store. I reset the code and then per provided instructions added to running engine @ 2000rpm 16oz SeaFoam Top Engine Spray directly into the throttle body blade, turned off for 15 minutes to soak, then drove to purge out, again the p0302 came up after short drive.

Below is what I have done, at each change I continue to have a slight rough idle (not like it would stall) and get P0302 code after a few miles driving. I have replaced (at different times) multiple components including plug wires, both coils, EGR valve, PCV valve & cleaned #2 injector. I have also resistance checked all injectors @ 14.3-14.4 ohms, stethoscope verified all injectors are operating, swapped plug locations, swapped injector locations. I have performed a cold engine compression check with all cylinders @ 160-165psi. I completed a cold engine Cylinder Leak-down test @ 100psi and found all cylinders @ 95-98 psi (2-5% leakage) which I thought was acceptable and rules out valve & head gasket issues. Fuel pressure tested @ 32psi idle, 30-40psi driving. Only thing I can think i have not replaced is the electrical connector for #2.

Please any advice on what else to look at?
Help me Obi-Wan... you're my only hope!

 

Sounds like the harness is shorted on the Fuel injector 2 harness or not connected as it should be. Or the bad news is a sticking valve on that cylender or weak rings which then it would not hold pressure like you are talking about.

Are you sure that the injector harness is plugged in all the way and not loose on the injector?
Have seen where a harness is plugged in, but the hookup was just a little off and not connected correctly to the injector.

 

Stonedpony... thanks for the input - The only thing I have done to check was to "listen" to the "tick-tick-tick" of the injector cycling while the engine was running with a HF stethoscope... not very technical i know. I'll try this again but while reving the engine as I didn't do that! I have had that connector on and off several times and tried to crimp both the female connectors inside the #2 plastic coupler to create better contact. It seems to fit solid on the injector. I was really disappointed when I swapped #1 & #2 injectors and came up with the P0302 again. I will definitely try replacing the connector as that is about the only thing I haven't done yet. You are right on the possibility of a sticking valve after the initial overheat due the coolant loss via intake gasket

I am not upset about the funds spent as the 25 yr old truck needed some TLC... can't afford a new truck payment! This guy has been good to us!