Rep Power: 0

2002 Civic EX Coupe, Automatic. 170,000 miles.

When I bought the car, it had a check engine light on (I don't remember all the codes), and no maintenance records. I did the following mileage maintenance.
- new timing belt.
- 100,000 NGK spark plugs.
- cam / crank seals.
- v/c gasket & spark plug tube seals.
- water pump, etc...

I got the car down to one code, a PO302, Cylinder 2 misfire. I switched out the ignition coil, because I had afew Denso / OEM ones. At the same time I put in 95 Octane fuel, the highest grade available to me. I've run several tanks of 95 Octane fuel through the engine (4,000 miles worth). Now, as soon as I put the cheap 87 Octane fuel in, with in 100 miles & several start ups, I've got the PO302, cylinder 2 misfire back. I don't notice any performance issues / misfires. In fact, if it wasn't for the check engine light, I wouldn't know there was a misfire.

I'm thinking about running a can or two of SeaFoam through the upper intake, but I've never been a fan of "a solution in a bottle".

- I'm wondering if I could have a carbon build up in that cylinder?
- Is there a better "solution in a bottle" to de-carbon an engine?
- I imagine I could move / replace the number 2 fuel injector, but this appears to be Octane fuel related.
- I can't justify pulling / replacing the cylinder head when fuel grade seems to affect the check engine light. Convince me otherwise, maybe...

There are no performance parts on this car.
- By any chance is there a fuel injector upgrade that gives a better spray pattern?

 
Rep Power: 511

any reason you've been using 95 octane vs 87? Unless you're running boost or high compression in that D17A2, there is zero reason to put anything more than 87 octane. Just because it's premium fuel doesn't mean it'll make your engine run better, stronger, or cleaner.

I'm actually thinking this is more of a correlation =/= causation thing. Might be purely coincidental.. These D17s are notorious head gasket fiends. You may want to do a compression and/or leakdown test to see if anything is funky with cylinder 2.

 
Rep Power: 367

higher octane means it will be harder to detonate by itself without a high compression.
carbon build up increases compression, so the opposite of the issue
head gasket leaking could be a potential culprit
https://www.civicforums.com/forums/3...reference.html

 
Rep Power: 0

I've been running the 95 octane in the car, in the belief that it has more detergents to clean the combustion chamber.

I'll get with the local mechanic to see if he has the hydro-carbon purple changing liquid detector stuff. This will take afew weeks to get done. I'll report back on this.

 
Rep Power: 367

that test does not work for the D17 engines.
read the link i posted. There is a video there showing how to test

 
Rep Power: 511

Unfortunately, contrary to popular belief, that's not what octane rating is. It has to deal with the amount of heptane and 2,2,4-trimethylpentane (an isomer of the hydrocarbon octane, C₈H₁₈ -- "oct" referring to the fact that there are 8 carbon atoms in the molecule, and where the "octane" determination really comes from). Yeah, I was a science major in college. lol.
In simple terms, the larger the relative concentration of 2,2,4-trimethylpentane, the higher the octane rating. 2,2,4-trimethylpentane has a high resistance to pre-ignition, and, particularly in high compression ratio and forced induced engines, reduces preignition, or knock. Otherwise, fuels of the same brand will have the same detergents in them.

Engines rated for lower octane ratings are designed with that bit of pre-ignition in mind.