Yeah, I washed my engine this morning (2001 4.6l F150) at the car wash and now I have a HORRIBLE MISFIRE! I drove the truck to get the motor dry, and it hardly wanted to go I then ran some Sea Foam through the brake booster hose hoping that this would help. It didn't help at all. At first the CEL started flashing, then it became constant. I scanned the OBD2 with my scanner and pulled a code "PO308." My booklet says that this means cylinder 8 misfire detected. My plugs have about 5,000 miles on them and the coil packs are OEM. I have to have this truck going by tomorrow because I have a Dr. appointment that I can't miss. Please help!

 

I would suspect that the #8 coil pack is bad. The water probably cracked it.

 

can I test the coil pack?

 

I got liquid in one of my cylinders (just an ounce or two) and the next day the truck ran really really bad. It ended up ruining the COP(coil over plug?), -the secondary impedance was too low. I wished I could remember the correct values. But anyway I needed to purchase a new one at autozone or advance for like 75-80 bucks. They're easy to get out on the 5.4, just one screw, but don't know about the 4.6

 

Here I found the way to test the coil


You can test the COP's easily with an ohmmeter. The primary coil should read .55 Ohms, secondary(spark plug tip and pin 2) should come in close to 6K ohms.

even a slight difference in the primary will throw a code. My (defective) primary was actually .3 ohms - to show how much it matters.

 

So, to test the COP, I would place a probe on the spring inside the boot, and the other probe on either of the electrical prongs at the connector?

 

The easiest thing to do would be to remove the COP, and make sure there isnt any water in the plug well. Make sure the COP is dried out, and then reinstall it, see what you get.

 

I just removed the plug from the rear most cylinder on the passenger side and the front most on the passenger side, and I did see a slight moisure residue on the rubber boots. As I was looking at the plugs, I noticed that the one up front was a lot darker in color than the rear. I'm using Bosche Platinum tipped plugs, and the electrode is bright white when new. I then checked the resistance of these two COPs (to the best of my knowledge) with my multimeter. On both COPs the resistance between the spring and either pin on the connector was .58 (+/- .02). Does this tell me anything? Am I checking the right cylinder
?

 

an 01 4.6 has COP's

 

Try letting it dry over night

 

Yes, my 01 4.6 F150 has COPs. I went ahead and replaced the # 8 cylinder(driver's rear) spark plug and cop. This seems to have helped, but only slightly. I cleared the cel code and drove the truck for about 10 miles. The cel hasn't come back on yet, but my truck shakes like hell at 1500-2000 rpms. I'll let it dry over night, maybe it'll be ok...I'll post results

 

Please remember that a coil pack can ohm out statically okay, but that doesn't mean that it won't break down under load.

And I wish y'all would quit washin' yer engines.

 

I'd check the rest of those COP's too, moisture seems to really just ruin these guys' days. This type of thing pops up almost twice a week. I think you will be okay with .03 ohms off, some multimeters aren't within spec on something that low.

 

I have to drive about 50 miles today, and being that I still have a misfire, do you think that I will cause any severe damage? As I said, after I hit 2000+ rpm, it seems to be lacking power, but it feels O.K.

 

I hate to rub it in but have you learned not to clean the engine in that manner?
You did more damage by driving the truck after the wash job.
The spark has punched thru the boots as well as ruined coils.
Replace everything or you just go round and round with it.
The only time you might get away with washing down the engine is after all boots have been inspected as good, not hard or split and sealed both at the plug and at the seal surface around the valve covers. Then even then the seal won't last forever.
Even the old dist system will fail if sprayed with water but that system is not in danger of extra damage and dries out without damage.