A couple months back I got a 96 Deville, which ran nice and smooth, and my dad says, "You don't need to put premium in it, just use regular." Well, after 1 tankful of regular my poor Caddy starts running like crap, Service Engine Soon light comes on, etc. Since then I have put in ONLY premium - about 2 tankfuls worth, but it still sputters and runs rough. Will this problem clear itself out as more premium gas goes thru the system, or is there a better/different plan of action I should take?

Thanks for any assistance!

 

Need to find out what codes are stored. See FAQ section.

 

so you don't think premium gas will clean out the system?

and how do you check codes?

 

Running premium fuel through an engine that was designed to use premium to begin with won't do much of anything in terms of "cleaning out the system." It's difficult for anyone here on this forum to pinpoint the cause of the problem, even by what you yourself have posted. Given that the car is 13 years old, it could be anything, and not necessarily only caused by running regular gasoline through it.

It may need plugs, it may need new wires, or both, it's hard to say. You've answered your own question in a sense, saying you've ran two tank fulls of premium and the condition still exists. If it was me I would start looking at the electrical side of things (plugs, maybe wires) and take it for a nice long drive. We don't know the service history of the car either, it's unfortunatewe can't tell you exactly what to do to solve it but I wouldn't lose confidence. It doesn't sound too, too serious.


If the car acts like it's missing or jerking driving up a slight hill as you give it gas, I would definitely change the plugs. When the engine is under load and the plugs are bad it's usually pretty obvious it's not firing properly.

 

well, I appreciate the help anyway.

The rough running sure did seem to coincide with the regular gas I put in it.