I have a flex fuel Coyote 5.0 and ever since I got it every time I run E85 in it I get a code and the CEL comes on. First time I got it read and found a misfire in cylinder 6. I replaced the ignition coil and put 87 in it, and sure enough it cleared. It doesn't come on right away when I run e85, but if I put a full tank in, maybe after 1/4 a tank it'll come on. I've got 80k miles on it and figure it's probably on the factory plugs which may be overgapped and probably have a good deal of carbon on them by now. Guess I'll replace the spark plugs and ignition coils as soon as I can, then I'll try e85 again a while after.

I know e85 is about 109 octane, IIRC so it has more resistant to explosion. I'm guessing you need a real good spark to run it. I was just curious if anyone else has encountered this with their corn feed Coyotes? Also, how much are the stock flex fuel injectors rated for? Do you need to go with iridium spark plugs or are double platinums fine? I think I'll run some fuel injector cleaner with Regane too, to help make sure the injectors are flowing good. I wanted to run Seafoam before replacing the spark plugs to help clean the carbon deposits. Had good results with it in 2 previous 4.6 modular engines I've had.

 

 

 

I run E85 exclusively with very good results (power increase) and while there can be variations in ethanol concentration station to station it's octane spec is 105. If you have check engine lights and codes something else is wrong like worn out ignition components eg: spark plugs most likely, possibly cops.

You didn't state what year your truck is but these are the oem Ford plugs mine came with and should work in all 11-14 5.0 coyotes. https://www.tascaparts.com/oem-parts...gtZmxleA%3D%3D

If you don't want Ford plugs use Motorcraft.
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Not possible unless the fuel pump assembly is replaced, it's all 1 piece inside the tank.
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I thought Motorcraft was Ford's genuine parts department.

Yea, and I heard that. New fuel filters in these trucks are in the tank from what I recall. Gotta drop it and pull the assembly out to replace it.

I also didn't think the fuel mileage loss was that drastic. Especially since pump fuels are about 15% ethanol nowadays anyways. I thought it was like a 10-15% difference. Fuel cost is significantly less over here, like $2.79 vs. $3.79 for regular 87(with 15% ethanol).


Sorry, I think it might have not shown my sig since I posted the thread from my phone. But I have a 2012.

 

Yea, the Ford Parts website sells Motorcraft SP-548 as the plug for the 5.0 in my F150.

https://parts.ford.com/shop/en/us/sp...plug-7823051-1

 

Motorcraft is OEM replacement line of parts, if it has a blue oval on it, it's what they rolled off the line with. Not sure what all Ford parts they have available, it changes year to year, at one time you could also buy Ford brake pads, may still be able to.
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Also, running one tank of E85 every now and then will cause issues. Ignore the CEL and run at least 3 tanks in a row before you judge anything about the alcohol. Anything including performance, mpg, CELs., etc.

Quote from manual:
For flexible fuel vehicles, if you are operating on E85, you may
experience poor starts or an inability to start the engine and
driveability problems until the fuel trim and ethanol content
have been relearned.

 

Oh wow. I thought the learning process was pretty quick if you went with the procedure in the manual (idle 1 min with no accesories, 1 min with accesories and ac, 1 min in drive, before you actually drive off). I figured it would have relearned with over 100 miles on e85 through several startups as well. Guess I was wrong. I'll be putting in new spark plugs this week, and maybe coils not too long after, then I'll give it another shot.