JimboGo

Driving 2007 is 250 and lost a lot of engine power so I limped it home. Cylinder misfire is audible and car shakes at idle. OBD 2 reader brings up P0304 for cylinder 4 misfire so I changed cylinder 4's coil pack out with cylinder 1 and tried again.

Cylinder 4 is still misfiring (P0304) and cylinder 1 is fine so I know the coil is not the issue. After switching the coils P0354 also started showing up (Ignition Coil D Primary / Secondary Circuit Malfunction). I have tried comparing resistance/voltage readings of the cylinder 4 circuit with one that is working and can't seem to find any major differences.

Does anyone have advice for diagnosing these errors and repairing them? Thanks!

MikeFig82

iTrader: (13)

Have you pulled the spark plugs? Check the wiring on the coil pack.

2013FSport

iTrader: (2)

^^ +5 Pull the plug and confirm its not shorted and or swap/replace w new. If no help continue on and ohm the failed units wires back to the ECM and verify they are good as well as inspect the ECM pins for burning, corrosion, damage, etc.

If that tests ok ohm another wire set from ground to each of the 4 wires looking for one that is different.

JimboGo

Thanks guys, appreciate the suggestions. I switched the spark plug out yesterday with cylinder one and the misfire didn't follow the switch so that seems okay.

I also went in and manually cleaned out the intake valves to reduce some of the carbon buildup that is an issue with these models but this didn't have any effect on the problem.

For checking the circuit resistances I was just connecting two contacts from the #4 circuit to the voltmeter and then comparing resistance values to the same contact combination on a working cylinder circuit. Is that how you would recommend doing it?

Couldn't find any irregularities with that method. I will check the ECU for corrosion tonight.

2013FSport

iTrader: (2)

Yes, but do these tests.
On Cyl 4, ohm the 4 connections from chassis ground and record them. Repeat in the same order on say Cyl 2.

From drivers seat bank 1 is the right side. Bank 2 is left side.
from the front back its
Bank1 1, 3, 5.
Bank2, 2, 4, 6. 6 being near the brake master cylinder on USD. That said are we talking about the same Cylinder #4?
If yes, and your ohm readings are the same between wires of cyl #2 and #4, set your meter to Volts DC and turn the ignition on. One wire should show near battery voltage with the key on. Does it on both #2 & #4?

PS I suggest you clear the codes each time and just because it still shakes, you could have moved the problem and the ECU takes like 300 misfires to say its a valid misfire. Well, unless you have a bad connection.

In this case, your codes 304 and 354 should repeat if not fixed.

JimboGo

After chasing all kinds of different things (cleaning intake valves, cleaning/switching injectors, etc.) it ended up being the plug. I guess the codes weren't clearing properly when I switched the problem cylinder out initially so I couldn't tell the misfire followed the spark plug.

Engine light is still on but power is back and misfire is gone. Going to replace the rest of the plugs this weekend when I can get the brand I want.

Thanks for all the help!