Ethanol and engine misfire?

Yesterday I filled my gas tank up with fuel with a 10% ethanol mix. Shortly after driving away from the pump, the engine seemed to start to misfire on one cylinder and the check engine light flashed on with every misfire. Took the car out on the highway and it seemed to run fine, up to speed and no misfire. Once off of highway and back to idle, misfire is back and check engine light is on. Any ideas as to what could be the problem? Is the 10% ethanol just a coincidence?

I think the 10% ethanol is a coincidence. I’m assuming this is not the first time you’ve used this fuel mixture before.

Have the computer codes read to see if there is any clue as to the cause of the misfire. Many parts stores will do this free. If the CEL was on, there is at least one trouble code stored.

Checked the computer code, bank running rich, cylinder #5. In the meantime, wife called said car is overheating. Resevoir was dry. Pulled the plug on cylinder #5 and it was “muddy”. No water in oil, but suspect a head gasket. How and what causes a head gasket to blow???

Get in the habit of telling make,model,year,engine size,maintainance history,mileage

You know what? At no time did you tell us what kind of vehicle you’re talking about!


That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here. 

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

[b] What make model and year car do you have (auto or manual transmission)?  [/b]

2000 Mercury Sable Wagon. 3.0L Automatic transmission. 90,000 miles, have had vehicle for 4 years. Do my own maintenance, regular oil changes. Have had to replace front wheel bearings and front and rear break calipers. Other than that, no mechanical problems.

I conclude no “tune-up” type maintenance has ever been preformed.

The 3.0 engine is bulletproof unless it has been abused and the Ethanol is likely just a coincidence. Overheating the engine, and continuing to operate it as 98% of most people do, can certainly cause a head gasket to let go. Besides, Ethanol is not going to pick on one cylinder.
This could be verified with a compression test, cooling system pressure test, etc.

A cylinder specific engine miss often points to a faulty spark plug, bad plug wire (which can be killed by a bad plug), faulty injector, or low compression (as in head gasket problem).

I have a '96 3.8 Mustang. If I use ethanol gas, I get a skip and a rough running engine. The Walmart near me @ Myrtle Beach (Murphys) has ethanol free gas. As long as I use the ethanol free gas my car doesn’t skip or run rough.

Finding places the sells ethanol free gas isn’t easy. I haven’t seen the ethanol free at the free standing Murphy at another location (no Walmart) or at any other brands. Every now and again when I’m traveling, I’ll see a sign advertising ethanol free gas

It would be best to start another thread to get some answers to your comments as the old thread is 12 years old. It’s easy to overlook.

That being said, I suspect the problem is not the Ethanol gasoline and the skip is due to another problem.
Consider spark plugs/wires first.

Any Check Engine Light on, codes set, etc? How many miles on the engine?