Over the last few months I have been occasionally experiencing a misfire. Not noticeable at startup, no long/hard starting, not low on compression, valves cleaned, spark plugs replaced and gapped properly. It happened today while going down the highway at 65, but didnt happen at all yesterday when i drove 225 miles to minneapolis and back on the interstate. A month ago it happened after driving 200 miles to milwaukee. The spark plugs looked a little fouled, and the gaps were a bit larger than they should have been. Most likely from the last time I had it at the dealer. I replaced the spark plugs with oem plugs, made sure all were tapped properly. I had no issues since that point....until today. I'm drawing a blank as to what it could be. I'm not getting any code pointing me to the hpfp, and checked compression which also left me stumped. The only codes I have seen was misfire related, and had a momentary lean bank one a few weeks ago which resolved itself in a few miles. What I've experienced so far has been occasional sluggishness off the line (like it was getting too little or too much air) however it was only once every couple weeks, random misfire (felt like I had zero power and was completely audible, almost as if it were in momentary limp mode or out if fuel).....any info would be great. 102k, mostly stock, 1200mi on oil, 800mi on transmission oil, valves cleaned 5k ago.

 

Have you cleaned the MAF sensor?

There's an electrical connector on the intake snorkel just before the air filter box. Inside that tube us a metal filament that measures airflow to tell the ECU how to regulate air/fuel ratio. That filament gets dirty over time.

Get some Mass Air Flow Sensor cleaner at the auto parts store. It's near the other spray cleaners. Do NOT use brake cleaner, WD-40, or anything else.

Follow the instructions on the can. Basically, disconnect the electrical connector, remove the hose section. Spray liberally with MAF cleaner. Let it dry completely. Reinstall and go.

 

Suggest you replace the ignition coils. They get hot and deteriorate causing misfires. You can buy after market coils made to withstand the heat. Made by Ignition Projects. $250 from minimania. But what do I know

 

Can you monitor HPFP pressure? Can you data log off the OBD II port at all?