P0300 code random misfire...

**MagicMan** · 10-10-2006, 11:05 AM

Thats what my car is throwing.

I have changed the plugs a few times and it is still there. I also changed the wires & still there. I had it scanned at Autozone & the scanner did not say which cylinder(s).

I can feel the car is down on power, but at 70+ it'll shake pretty bad.

I know the wires are all on properly and the plugs are good. That leaves coil packs & what else?

Anyone in South NJ with software that says which cylinder(s) it is want to help?

**2001NBMZ28** · 10-10-2006, 01:22 PM

My car has thrown P0300 a couple times over the years, just cleared the code and doesn't come back. I'd try resetting the PCM first, if that doesn't work see www.gearchatter.com/viewtopic8880.php

**MagicMan** · 10-10-2006, 01:26 PM

Originally Posted by 2001NBMZ28

My car has thrown P0300 a couple times over the years, just cleared the code and doesn't come back. I'd try resetting the PCM first, if that doesn't work see www.gearchatter.com/viewtopic8880.php

I've cleared it & it comes back. The car is not running at full power. I can feel it + it shakes at 70+

**2001NBMZ28** · 10-10-2006, 01:36 PM

Try resetting the PCM, think I read somewhere that'll reset the crank position sensor - easy to do and won't hurt to try, just grumpy idle for a few minutes until it relearns. Just in case you need it:

PCM Reset
Turn key on, don't start car
Pull PCM BATT aand PCM IGN fuses in engine compartment
Wait 5-10 min
Turn ignition off
Replace fuses

**MagicMan** · 10-10-2006, 02:20 PM

I have reset the PCM. It does nothing.

**MassGaskets** · 10-12-2006, 02:44 AM

Originally Posted by Loco

I've cleared it & it comes back. The car is not running at full power. I can feel it + it shakes at 70+

No fouled plus when you swapped em? If the PCM is cleared, will it throw the code sitting at idle?

Does it vibrate if the car is at higher RPM when stationary and in neutral/Park?

If so, sounds like it could be a miss, harmonic balancer, etc...
If not, then you've got drivetrain/wheel-tire balance, etc (aka "everything else")

I always hate all this troubleshooting... LOL!

**MagicMan** · 10-12-2006, 06:15 AM

Originally Posted by MassGaskets

No fouled plus when you swapped em? If the PCM is cleared, will it throw the code sitting at idle?

Does it vibrate if the car is at higher RPM when stationary and in neutral/Park?

If so, sounds like it could be a miss, harmonic balancer, etc...
If not, then you've got drivetrain/wheel-tire balance, etc (aka "everything else")

I always hate all this troubleshooting... LOL!

Still shakes in N.
Plugs were not fouled.
Once the car warmed up the code came back.

**GatorSS** · 12-13-2006, 06:33 PM

I'm dealing with the same issue right now. All plugs and wires have been checked and are fine. Fuel pressure is fine, a steady 58 psi from idle to redline. The only code thrown is P0300.

It started as an intermittant misfire several days ago. It has progressively become worse. The misfire is evident at idle, and gets progressively worse with any load. It is so bad now, I can hardly drive it at all...severe misfire is now virtually continuous.

Anyone else had this problem? Suggestions? Possibly the 02 sensors? Crankshaft Position Sensor?

**9t8z28** · 12-13-2006, 07:11 PM

Check the coil voltage. Just one coil bad could make it run like shit!

**GatorSS** · 12-13-2006, 07:39 PM

Thanks for the response. But wouldn't it throw a different code if it were a coil (P0350 - P0358)?

**Steve Crowe** · 12-13-2006, 08:54 PM

Folks, the random misfire code can be caused by two things - your ignition or your fuel delivery.

First thing of course is to make sure your plugs and wires are in top condition. Many people ignore their wires or think what they've bought is bulletproof. This is not always the case and I'd prefer you read this entire website: http://www.magnecor.com

I have no association with these people except for countless years of flawless performance.

The coils on GM cars have been known to fail but rarely do they fail without biting the dust in a couple of days, then you'll get a hard code.

If you've ruled out your ignition you may need to clean your injectors and I don't mean by pouring a few bottles of injector cleaner in the tank. There are times it needs to be done right. You can find more info in the sponsor's section.

[edited for sp? - sorry.]

**YoMommasTA** · 12-13-2006, 09:15 PM

look for rust in the fuel system

**GatorSS** · 12-14-2006, 06:14 AM

My plugs and wires are in top condition (wires are Magnecor 8.5mm). Fuel system has no rust. I was thinking it was a coil, and that it would be relatively easy to isolate the bad one. However, the code P0300 displays as "random/multiple cylinder misfire detected" which means its more than one.

The symptoms are just like I've experienced on outboard motors when I've had a coil go bad--intermittant misfire and then within a few days it gets worse to where it totally fails. But it was always easy to tell which coil it was by inspecting the plugs. In this case, all my plugs look virtually identical.

I was thinking of replacing all eight coils, since if one or two fail, how much longer before another one goes? But that is pricey troubleshooting. Nevertheless, if I have to do it, I will.

Thanks for your help.

**GatorSS** · 12-14-2006, 06:17 AM

Before I start checking, anyone know where to get the best price on coils?

**9t8z28** · 12-14-2006, 06:45 AM

I dont know what they cost new but someone is selling a set for $220 is the for sale section.

**GatorSS** · 12-14-2006, 07:17 AM

I didn't see it, but I assume that set for sale is used. I don't want any used coils. But thanks anyway.

**9t8z28** · 12-14-2006, 07:20 AM

Not that you would want to but, do they sell the coils individually. Just throwing that out there

**Steve Crowe** · 12-14-2006, 09:14 PM

I wouldn't start throwing coils at a problem until you know more, Have you read the LTFT from your PCM lately? That might tell you something.

**GatorSS** · 12-15-2006, 07:05 PM

So, you're thinking maybe a fuel injector or two?

**0rion** · 12-15-2006, 07:37 PM

sounds like you've covered most of the bases so far. I would maybe look at the crank shaft position sensor next but that would be just taking a stab in the dark. Looks like you've already checked most of the stuff I would've looked at first. Be sure and keep us posted and let us know what it ends up being. Keep after it and I'm sure you'll get it.