Good Morning,

I have a 2001 4.6L F150 Supercrew. Last night it start to buck and hesitate under normal load. I got it home and detected a burning smell under the hood. Test drove it some more and the engine light came on. Got the code read and it is P0303 which I was told was cylinder 3 misfire.

Question #1. What cylinder is #3. Is it on the left bank (drivers side). I can't find any identifers.

Question #2. I suspect a coil on plug failure. Possibly a short, seeing I detected a burning smell. Any thoughts or sugestions.

Thanks in advance for any insights.

 

Northcrew,

#3 is third cylinder back, passenger side.

If you think a COP shorted, you can remove it and using a multimeter, check the resistance across coil. Primary resistance (across terminals on top of coil) should be 0.55 ohms. Secondary resistance (between spark plug connection and top terminal) should be 5,500 ohms.

Tim

 

Thanks, Tim.

I pulled #3 cop checked the resistance. The primary across the two top terminals reads about .9 ohms and the secondary wrt the either top terminal reads around 5.56K ohms. I checked another cop across thr primary and it read 1 ohm.

I pulled #3 plug and it looked clean.

I wonder if it is really the cop maybe its breaking down under load and high voltage but checks ok resistance wise.

 

You could try a spark plug tester on the coil to see if it is throwing a good spark. Also, start the truck and put a long handled screw driver or socket extension to the #3 fuel injector and your ear to make sure it is firing (you should hear it ticking.)

I went through the same thing on my #2 cylinder and all this checked out ok. It ended up being a bum spark plug. Changed the plug and everything was fine.

Tim

 

check the rubber boot under the COP. they start to crack after a while. You can also swap out the COP with another on the engine and see if the code changes places.

 

I checked the boot and see no cracking. The plug looks OK, it has 64K miles on it. I lstened to each injector and can hear each of the 8 firing.

I cleaned the throttle body and threw a bottle of Redline Fuel System cleaner into the gas tank.

Still hesitates and feels like its breaking up under almost any load except idle. It idles normally. It reminds me of the the days when you a had a hairline crack in a distributor cap.

Tim, when you had the bad plug in #2 did it look look OK visually?

OBD II readers, I'm not too familar with their operation. I don't have one and all my other vehicles are older or in the case of the 98 Honda I can trick the codes out. I had this read out at Autozone. Could they have just given me a primary code and there are more codes underneath this code? Based on the Ford service CD I have it looks like there are a continous memory codes. I need to look into this a little more.

Could a misfire could be a result of another component failure such as an O2 sensor?

Monday I am going to go back to Autozone and have them do a re-read for me. I still wonder about the COP. I haven't done a swap yet.

I'm tempted to get a new plug(s) and one new cop and try the swap out method to see if I can isolate this.

 

Swap the coil from cylinder to cylinder and see if your misfire changes locations. Checking resistance on a coil is one thing, but it's not the most accurate way to check a coil. A power balance test or coil stress test is ideal, but this requires a Ford scan tool.

 

To potentially save the $50 on a new COP, I'd also recommend swapping them to see if the mis-fire moves. I bought a new COP instead of trying to swap them when I was troubleshooting my misfire and it didn't help me. My plug looked fine but I was getting frustrated so I thought I would buy another plug to try to eliminate variables and it did the trick for me.

Tim

 

I swapped #3 cop with #6. Drove to work this morning, with the same symptoms. At lunch I brought it back over to Autozone for another code read. I picked up a new code P0171, Bank 1 O2 running too lean and still had the P0303, which is probably left over from the last time. I am assuming codes are last in first out when read. As far as the P0171 O2 bank 1 too lean code, I wonder if I set that while I was cleaning the throttle body yesterday. I found the engine will stall out if the air plenum is diconnected from the throttle body. It stalled a couple of times before I realized it won't run with it disconnected.

Searches on this forum for P0171 indicated PVC hose problems, dirty MAF. I will check those out tonight just to be sure.

The misfire did not follow the cop swap so either its not catching the misfire or maybe it is the plug in #3.

Lastly I think the guy at Autozone reset my engine light today as its no longer on. Nothing else has changed however. I'll see if the light will reappear on the way home tonight.

 

Tonight I cleaned the MAF and checked the resistance of plug #3 which reads 4.81K ohms. According to the Ford manual anything between 2K and 20K is good. Thats not saying something isn'tr breaking down under high voltage however.

The check engine light returned tonight on the way home from work, so Tuesday back to Autozone for a re-read, we'll see if a misfire was caught again and in what cylinder, also if the O2 bank 1 too lean returns as well.

One observation at idle, in park, I detect no miss. In drive, foot on the brake and with some load such as headlights on the miss starts. As the load on the engine increases the miss gets worse. Worst case is in high gear cruising speed of about 50 mph and I encounter a hill.

 

How many miles on it??
Sounds like plugs/wires.

 

In the scheme of things the codes should be cleared each time work is done or you can't tell old history from the new in the short run.

 

Success! I got the codes read again today at lunch. This time a misfire in #6 was caught,0306, this is the cylinder I swapped the #3 coil to. Along with that two other codes were recorded, 0171 and 0174, bank 1 and bank 2 O2 too lean. I am thinking those codes were a secondary effect of the misfire. Anyway I bought a new coil, slapped it on in the parking lot, it test drove ok and was fine on the way home tonight.

I am thinking that misfires must be accumulated or steady for a period of time before the engine light comes on and the misfire code is recorded. The #6 misfire didn't get caught for two days.

I guess its time to invest in a code reader for myself. This is my newest vehicle, a 2001. I long for the days when you removed the air cleaner with one wing nut, adjusted the fuel mixture by turning your ear to the engine and tweaking the mixture screw and being a double jointed contortionist wasn't a prerequisite to work on cars.

Patience and advice from all the good folks on this forum paid off. Thanks again everyone who posted advice on my thread as well as the contributors on past posts that I searched through, all of the info is much appreciated. Hopefully this thread will be able help someone else out in the future.

Geoff

 

I just recently had the same problem p0303 misfire code pulled the plug wire for #3 inspected it looked good so i pulled the #3 plug didnt look too good so i threw in a new autolight and fixed the problem

 

To wrap up, the methods used by the PCM for fault detection are quite sofisticated.
This is why it's not so easy at times to just replace parts based on what the codes say.
The missfire detection is based on rotational time of the crank for each cylinder.
Anything that interfers with cylinder firing pressure can be a cause. Plugs,wires, COP, boots, injector, wiring, fuel can all get into the act.
One peticular fault that evades detection by the trouble shooting is bad plugs that only show up during cruise.
This is the results of plug deposits from gas or additives.
During cruise the EGR opens, the fuel cut back leaner and the ignition is advanced.
Bad plugs can misfire under these conditions and not under load or even at idle.
So store this for future reference.