Random misfire (P0300)

[Andy H]

On my way home today my 2000 camaro started running rough. I don't think it is running on all cylinders. It has no power at all. I'm getting P0300 code. I have to work tonight so I didn't get to do alot of troubleshooting. I did pull the plug wires off of the coil packs and check the resistance. I got the same reading on all 3 coil packs (6,600 ohms). BTW these are the original coil packs (110,000 miles). The plugs and plugs wires are fairly new. Also the cat converter is pretty new. It is a magnaflow converter. I checked the fuel pressure with a gauge and got 43psi with the key on engine off and 42psi with the engine idling.

That's all I got to check before I had to go to work. Luckily I just got the brake lines replaced on my truck so I can drive it to work. Anyway, I just wanted to see what ideas you all have as far as troubleshooting this problem. It will probably be Tuesday before I get to do alot of troubleshooting on it. So what do you all think?

Thanks!
Andy

[ssms5411]

Re: Random misfire (P0300)

You said you check the coils but how about the ICM, also check the fuel injectors because it will have a random misfire if one isn't working. Might check your other sensors on the TB also.

[Andy H]

Re: Random misfire (P0300)

No I didnt get to check the icm or injectors. How exactly do I check the icm?

[ssms5411]

Re: Random misfire (P0300)

Same way as the coils for ICM, injectors should have a ohm reading from 10-20 ohms, but they still could be clogged and you wouldn't know it unless it actually throws a code for that injector. I had a bad injector that took me a year to finally find it.good luck

[Rob Bell]

Re: Random misfire (P0300)

As for the ICM, you'd probably have to pull it and take it to a parts store and get it tested.

[Andy H]

Re: Random misfire (P0300)

I took the icm and coil packs to advance auto and they said they could'nt test them. Here's what I did today. Since this is not intermittent, I decided to unplug the plug wires at the coil packs one at a time and start the engine. I figured if I unplugged a wire and the miss got worse then that coil would be good. The miss got worse everytime untill I got all the way to the coil pack that fires cylinders 1 and 4. When I unplugged the wires from this coil pack, the rough idle was the same as when the wires are plugged up. So, I figured bad coil pack. I bought a new and put it on and the idle was still rough! So I thought I may have fouled the plugs so I put some different plugs in cylinders 1 and 4. They rough idle was still there (the same). I visually inspected the plugs wires and they look great. I don't know what to think now!

On a side note, The original acdelco plugs 41-921 that came factory. I had 85,000 miles on them when I changed them. I replaced them with 41-101 plugs. When I pulled the 41-101 plugs (they have 35,000 miles on them) They looked aweful bad shape. My original plugs with 85,000 miles that I saved look much better. I am going to replaced all the plugs again. I need to know what plugs to buy because I can't get 41-921 anymore. I guess they have been discontinued.

[Big_G]

Re: Random misfire (P0300)

Did you ever verify the ICM was good? I had this problem a while back. Turned out I had a bad coil pack, a bad ICM, and a bad injector all around the same time. No wonder nothing I tried seemed to fix it...

[Andy H]

Re: Random misfire (P0300)

It turned out to be the icm. I went ahead and put some new 41-101 iridium plugs in too. Thanks to everyone for their help!

[whitdog54]

Re: Random misfire (P0300)

fricken ICM and coil packs on these cars are ridiculous.

glad you figured it out