1998 Civic Hx 183k. All stock. No recent work done. Noticed a change in mpg on most recent fillup (beginning of last week), and a little hesitation it seemed at times. I almost had myself convinced the clutch might be starting to slip. There were no hiccups or rough running conditions at all.

That changed Friday on my way home from work. 65 miles each way. I was 30 miles into the ride home when I started experiencing the P0301 condition. I run a scanguage II constantly - just so I can see when the engine goes into lean burn. However, that was another thing I noted in the days prior to this problem. I couldn't feel the engine going into lean burn, and the indicator wasn't showing that it was in LB mode....at all. Now, I didn't watch this constantly, but when my last mpg calculation showed a drop (5mpg or so), I started watching, and noted that it didnt' seem to be dropping in.

I was under a quarter of a tank on Friday night...so I filled it up with fresh gas on the way home. Saturday I changed the fuel filter first because I had recently filled up at a service station I don't frequent, and started thinking maybe I got bad gas ??

Anyway, changed the fuel filter, changed the distributor cap and rotor, and no improvement yet.

I'm just not sure where to go next.

Operating on the hunch that the gas may have been an issue, I was thinking about pulling the pump and getting a look at the screen and the actual tank contents. That still leaves me with what is causing the codes now....eventually branched out to include 0300, 0301, 0302, and 0304...as well as 0000.

After replacing those parts yesterday and letting it run for a little while, I'm just showing P0301 again, nothing else.

Sorry to be so long winded. Thanks for any suggestions.
JP

 

Misfiring at low rpm with heavy throttle is almost always from weak sparks. The wires are the weakest part and you really can't tell if they're bad by looking, so just replace. OEM wires are better than most aftermarket ones, and some aftermarket wires may look great but simply don't work. Of course new spark plugs also, no reason to pay more, use the stock type NGK conventional ones.

I think the gas tank will have a drain plug on the bottom if you want to take a sample or drain and replace the gas. Older models did have the plug.