Raw gas smell to exhaust

[Mark K 2]

A few weeks ago, I started burning 91 octane, no-ethanol fuel in my ST. The MPG is better to the point where it's worth the extra cost. Well, since I started doing this, I've had two situations where after I start the truck, there's a strong odor of raw gas coming out of the exhaust pipe and the engine is surging at idle about once a second between 500 and 1000 RPM. Drives fine once the RPM gets over 1000. If I shut the truck off and restart it, the problem is gone.



Is the super fuel doing this or is it coincidental? IAC? Other? 98,000 miles on it.

 

[zaffo oxnard]

I get the same thing on my 2001 with 90,000. Sometimes the raw gas smell is terrible. I think it is a plug misfiring. There is no way the fuel injection is pumping that much extra into the mixture. It is bad as an older v-8 car with a carb that is running rich. Nasty.

 

[EddieS'04]

Maybe the knock sensor? Or the front O2's.

Something must be making it hard for the ECU to retune to 91 and no ethanol.

Im just guessing.......

 

[Gary Spann]

If you have a stethoscope you can listen to each cylinder and see if any are not firing. I JUST had this happen and it was the #3 cylinder (the hardest one to change)! You can also pull off one plug wire at a time. If the engine shudders when you pull it then that one is a good plug. If you pull the wire and there is no change then that is a bad plug.