Had code P300 P301 and P308
 

Check engine light came on in a heavy rain tonight after going about a one block. Check codes when I got home and had code P300 P301 and P308. Truck was not missing, running it regular smooth self. Has 210,000 miles, but changed plugs, wires, dist cap, rotor, distributor pick up at around 175,000. Put in new fuel pump at 207,000. New cat at 199,488.

Like I said heavy rain, but nothing under hood looks wet, never has happen before. Even with the check engine light on, it ran smooth- no missing out. I have cleared the codes and ran for about 4 miles and no codes came back.

I was just wondering if it could have been something with the rain and wet roads and something that is exposed? Hasn't even happen before and have had for around 7 years.

You could have a wire bare and with the moisture in the air it was arching

Also, is the gasket between the hood, and firewall still there? 1 and 8 are right next to each other in the firing order..... with the heavy rain, something may have gotten wet, and the distributor is very well concealed back there..... :)

Gasket seal looks really great in the middle, each side looks fair. I checked and didn't see any dampness, but by then heat would have dried it. All wires look good and are snug fitting. I would guess sitting in rain for an hour or so must have got something wet? Truck has just been running smooth, even when light came on. Only thing that gets my attention is the noise that new fuel pump makes, not terrible, but I never even heard the old original one. So far no code or pending codes. That distributor sure is well protected waaay back there. Still raining, over 7 inches last 4 days, should let it sit outside, truck is spoiled, sits in nice covered garage.

Well guess it is not a moisture problem, was at stop light and was running a little rough. Went on to get a couple tacos and check codes, had 3 pending codes, same 300 301 308. No DTC codes. Went in ate lunch and drove home and it ran fine. Checked codes at home and no codes at all pending codes were gone. All this in a 20 minute time frame.

I thought pending codes had to go X number of warm up cycles to go away? Then if problem happened X number of times it became a DTC. Not sure what X should be in those.

I would guess this is going to be hard to identify.

Moved to the tech section.

Run the engine and mist some water from a spray bottle on your ignition coil and see if you get any arching.

Thanks, I gave that a try and in the dark so it would show up better, but didn't see anything. Cheeked for codes and didn't have any. Also went around plug wires and distributor. Seems like there are so many possibilities, I still wonder about that noisy fuel pump put on a few months ago. That suggestion made me remember we use to find those kind of problems doing that.

When it was running rough today I was stopped at light, foot on brake and in drive. Check engine light didn't come on, but it ran a little rough. I checked codes within couple minutes and was same 3 codes pending, but no DTC.

I don't understand why pending 3 codes went away after driving 10 minutes and maybe 5 miles in traffic. I thought pending and even DTC took 40 cycles of warmup to go away? But I read that somewhere may not be true. May have to wait for it to just quit and leave me stranded in -0 snow storm with no cell service. So far, always code P0300, P0301, P0308. I kind of wonder if a person always get a P0300 if more that one cyl misfires? Also, seems like since 1 and 8 misfire that should be a clue. As already mention they are the first two to fire. 1,8,4,3,6,5,7,2

You might pull the coil off and test it to see if its in ohm spec and look for hairline fractures on it. Bad coils can throw the po300 and pick on individual cylinders at the same time. Did you start having the codes after hitting a pool of water? Kind of funny it still ran with no feeling of a miss when it first threw the codes though. I don't much about the stored code deal and how that works.

Think I would pull the distributor cap, and have a look at the terminals inside, and the rotor. Also make sure the cap is seated properly, and the screws are tight. Checking how much wiggle the distributor shaft has wouldn't hurt either.