a87bronco2

Okay, I have a 2007 F150 with the 5.4L flex fuel engine in it. Has anyone ever had a problem where the engine misfires and runs extremely rough the first time they start it in the day? It seems to be worse when running the truck off ethanol than dino gas. It doesn't matter if it's 90 degrees out or 50, the first time that I start it it misfires and runs rough. I've changed all eight coils and plugs in the past couple weeks, and that didn't fix the problem. Oh, and it's thrown a couple misfire codes, usually the #8 cylinder. Anyone ever had this problem or know anything about it?

Thanks for the help.

-Mark

BassAckwards

I have an 06 f150 with 5.4 but not flex fuel. It will misfire in the cold if you romp on it before the engine is warm. I think your problem is running ethanol. Ethanol has a fairly high octane, but not as much BTU as gas. So higher octane fuels are more likely to cause misfire when its cold, so stick with regular during the cold and you should be fine.

Edit: Didnt see the part about it misfireing even if its warm outside, you may want to go in to the dealership and explain to them whats goin on and get it looked at. Shouldnt misfire when its warm outside even if your just starting it up.

a87bronco2

Yea, I'm not sure. It has 90,000 miles on it...but it runs fine when it's warmed up. It doesn't just miss when you get on it when it's cold, you can hear it misfiring and feel it running rough at idle. I am kinda trying to avoid going to the dealer, as I usually fix things myself, but this problem just has me stumped. I am wondering if the #8 fuel injector could be partially clogged or something, as it always seems to throw the #8 cyl misfire code. It sometimes misfires on regular gas when the engine is cold, but not nearly as bad as on ethanol. But I don't know. Thanks for the advice Bass...anyone else?

BassAckwards

I totally understand your not wanting to go to a Dealer, I'm a do-it-yourselfer as well. I can't think of anything else accept maybe buy a bottle of fuel injector/valve cleaner that your poor in your gas tank to fix the #8 cylinder. Your predicament stumps me as well.

a87bronco2

Okay, so the problem got where the truck was missing a lot worse and even when it was warmed up yesterday. I switched the #8 and #5 fuel injectors to eliminated a faulty fuel injector from the problem and the code thrown was still #8 cyl misfire.

So I decided to pull the plug and inspect it, even though I just changed them less than a week ago...I figured if the plug was okay that the next step is to do a compression check. This is what I found:



Apparently the insulator broke in the middle of the plug, allowing it to slide down over the electrode. I'm glad it wasn't a bigger problem...still, cost me a $22 spark plug from Advance...maybe I'll write the online dealer that I got the plugs from and see if they'll replace it.

BassAckwards

Wow! Thank goodness thats all it was, and yeah definately write up the dealer and show them that pic and have them replace it.

rick99601

thatll do it, glad you figured it out.