#po301

Sajeev,

I recently bought a 2002 Miata, manual transmission, in silver. The prior owners appear to have been followers of the sans souci school of maintenance, so I have been wrenching on it quite a bit. It has only one problem I can’t solve: a persistent P0301 code, showing a misfire in Cylinder 1. The actual experience of driving the car is fine — I don’t feel a miss or a drop in power. That light, though… it isn’t constant. It doesn’t come on instantly; if I clear it, I might get a few minutes of light-free driving, or an hour, or a day. But after that, the CEL goes blinky-blinky.

Logic suggests that the misfire can only come from spark, air, or fuel, so I went at each as follows:

• Spark: I’ve replaced the spark plugs (NGKs), plug wires (ditto) and boots. I swapped ignition coils to see if the code would move; it didn’t. The ignition wiring harness has some broken protective tape, but I don’t see any broken wiring.
• Air: I’ve replaced the air filter and checked for vacuum leaks.
• Fuel: I replaced the fuel filter, and, to make sure I didn’t have a fuel injector problem, I swapped the injectors between cylinder 1 and cylinder 4. I spilled a bunch of fuel, but the code stayed put.

I’ve been busy fixing other issues (leaking valve cover gasket, cracked radiator, soft top made of cheesecloth) on this Miata, but the P0301 has me stumped. I checked compression, and it’s good across all four cylinders. Forums mostly argue in favor of ignition problems, but I feel like I’ve covered that area.

The big question is this: Do you think new driving shoes will fix the problem?

Hi Sajeev,

You asked for some emails, so here’s one from me. It may not be Piston Slap worthy, but it’s got me confused. Here’s my problem:

I have a 1998 Nissan Frontier. 150k miles, 2.4l four banger. It threw a Service Engine light on me the other day. The code is a P0301, i.e. cylinder #1 misfire. Figuring it was a spark plug issue, and since I was about due for a tune up anyway, I replace the plugs, wires, distributor cap and rotor. I cleared the code with my scanner, and….it came right back. I did a little creeping on the Nissan forums, and the consensus seems to be that this results from clogged EGR passages. So this past weekend I decided to clean them. I was lead to believe that this would be a cake walk. All that was required was to remove the set screws between the intake runners, spray some carb cleaner in there and scrub them out. Easier said than done. Removing the screws was not too bad, but putting them back in after cleaning was nigh impossible. 5 hours and sawed off 8mm Allen wrench later, I had the plugs back in. My truck ran great! For 20 minutes. Then the code came back. Now I’m pretty much flummoxed. The way I see it, my options are:

1. Remove the air cleaner assembly and manifold screws again and try cleaning them more thoroughly with a pipe brush and more carb cleaner
2. Try something like Seafoam through a vacuum hose. I am reluctant to do this as I’m not 100% sure which hose to use and opinions on Seafoam are mixed
3. Take my vehicle to a mechanic for a more professional diagnosis. I do have access to a reputable independent mechanic who specializes in Nissans and Toyotas

So, what do the B&B think? Anyone else had this problem with a Nissan KA24DE 4 cylinder?

Thanks for your help.