*HELP* P0300 Multi Misfire

[shwagg]

I was out today on the freeway at different speeds and I have never missed a gear. then I get off and get to a light and the engine is running ruff with a definate miss. I mean the shifter is shaking my hand off at low rpm take off speeds. Then the ses light comes on and flashes. I limp it home and get the predetor on it and it gives me p0300. multi misfire. I do have a sqeeky belt that only starts after its up to temp and its more of a ringing kind of noise. I do not have a K&N, have not washed the engine bay in awhile. I have not had any problems up til now. I do realize the predetor is not the cause but i still went back to factory tune just in case. The car is bone stock except for the SLP Lid and Skip shift eliminator. I have not changed the plugs or wires the car only has 26,600 those wires and plugs should have plenty of life. If it was a crank sensor wouldnt the car be dead in the water? If all else fails I just talked to my neighbor who is the service manager at the local pontiac dealership and he said he could get it in and charge me 35.00 an hour.What could this be at 26,600 miles? Any insite would be great, especially if you have seen this before. Thanks in advance for any help.

[Redphoenix1998]

That's a hard one to diagnose cause it could be a number of things. You said a ringing noise is heard though right? Did you just recently tune it with the predator? If you did then bring it back to stock because maybe you threw the timing in the PCM off, that's just a guess though but the code is for 2 or more cylinders misfiring, so just in case it isn't just the tune, check your plugs and make sure none of your wires have any gashes in them. The plugs should have a brownish tip and if it's oily or burnt to a crisp, you have a problem.

[shwagg]

I just finished going through the plugs and all have what seems to be spark. I used a spare plug and unplugged one spark plug at a time and all had spark but this is now way to be sure there is enough spark though. I then removed the plug and two of them looked wet but all had a tan color and where the stock Denso. The gap was set to .060 (looks large). What is the the flow rate of the stock injectors. I might have to go with the ford SVO injectors but I am not sure which ones to get without having to change the fuel pressure regulator. Rechecked the troubles and it did not give any cylinder number just the P0300.

[0rion]

Put a fuel pressure gauge on the end of the rail to see what your fuel pressure is(stock is 58psi). Might have some trash in the filter. Misses are hard to diagnose without going over the car. The very first thing I check on a car that's missing are the plug wires. Might just be me but it seems like 80% of the time it's a plug wire problem. Was it raining when you were getting the miss? Might need dielectric grease in the boots.
I'd be tempted to get some electrical cleaner and clean your MAF even though you aren't using a K&N. What 2 plugs looked wet and could they have been wet from the way you were testing for spark?
As with everything I do just start cheap and work your way up. I would say 26k is early to need plugs and wires but it's not completely unheard of. Check your plug wire boots really good and make sure none of them are dried out. My buddy had a problem with his vette missing. He had 2 plug wires that were burned ever so slightly from his headers. If you just pulled the wires and looked at them you would've never caught it but when I bent the boot to the side it split. If you have the stock shields on make sure one hasn't chaffed a wire or something. Just ideas.

[shwagg]

Alright, I found the problem to be two bad spark plug wires, #1 cylinder coil pack, and a bad spark plug. Thanks to everyone who helped. Take care and be safe.