I've got a 98 F150 SC and my check engine light has popped on twice in the past year. The first time was last November, so I took it to the dealership and they checked the codes...it was 2 fouled plugs. They replaced the plugs and cleaned the injectors and it ran fine for a long while (had 44k on it then).

I had my truck in the dealership paint shop so they could fix an issue with the clear coat on one of my fenders, and on the way home, I got a check engine light. Before this, the engine shuttered a little, was running a little rough, but when I gave it gas, it smoothed out. Right after it happened, I drove back to the dealership. Turns out it fouled another plug (has 55k) so they put on a new fuel filter, replaced the plug, decarbonized the intake and sent me on my merry way.

I love this truck, but I'd like to know what the heck is going on. Should I see about replacing the coil packs or put on something other than Motorcraft plugs or should I be looking for something else wrong under the engine bay?

 

This may be off in left field, but is one possibility. Is you engine oil level correct? Not over the max. line on the dip stick? If so it "could" cause oil fouled plugs.

 

Thanks for the reply, but my oil level is at the max line. I've always had a problem with this particular engine and reading oil though...even after putting 6quarts of oil in it...sometimes it doesn't even read, while others it reads as if it has more.

 

You may or may not do this prior to changing your oil so I will mention it. Before changing your oil, if the truck is cold, you should let it run for about 5 - 10 minutes. That way the oil will drain better and any slug will come out as well.

After filling with 6qts, you should start it up and let it run for 5 minutes, check for leaks etc. After 5 mins or so shut it off let it set for 5 minutes then pull the dip stick, clean it with a rag, then put it back in pull it out and check. You should get an accurate reading of how much oil you have.

From what it sounds like if you are having a problem reading your dip stick and because of that adding more oil you could indeed have it a little over full. That can cause fouled plugs as well as seal damage. If you find it is over the max line you want to drain some out so as to get it below the max line, but not under the min line.

Don't know if that helps, but if so great...

If you continue to have a problem with the plugs I would see a dealer about it soon so your truck stays in good running order.

 

Thanks for the advice. I've been changing my own oil for quite a while now (almost 25 years) and have never heard about changing the oil warm. I'll try that next time I do an oil change.

I know that when checking the dipstick, you clean it the first time, and then put it back in to get a reading, but this one has never been all that accurate. Even when checking the oil, engine cold, on level ground, with 6 quarts of oil, sometimes it will register below the max line. It's flakey to me...

The dealership says they aren't sure what the underlying problem is. They put it on an oscilloscope to check to see which plugs are erratic...but they haven't said if anything's wrong. I'm just a little frustrated.

Might be a good reason to get a 3/4 ton truck...

 

Oil level has been discussed a few times in this forum. The manual says 6.0 qts and that the reading on the dipstick should be between min and max. It is my understanding that "max" should not be read as "full", full is 6.0 qts after an oil and filter change. There are others in this forum that disagree and put in 6.5 qts to try and bring it up to the max line as they consider the max line as "full". I'll bet I have just started an argument. Look in the engine forum under "How Many Quarts"

 

Texcowboy9: