Hi all,

I have a longstanding p0301 that has been mixed in with a bunch of other problems. For example, it's still around from p0300, rough idle, codes come and gone? - Blazer Forum - Chevy Blazer Forums

I am incredibly frustrated with this, and I decided to make a new thread dedicated to the p0301.

Aside from attempting to address the p0301, I've replaced the trans, the coolant temp sensor, the fuel pump, and the smog pump in the last 12 months, as well as some calipers and some front end components. Just this weekend the instrument cluster and the alternator (whose bearing was shot) were replaced. I cannot believe how much money I've sunk into this car over the last year.

In trying to address the miss, I've replaced the distributor, the cap, the rotor, the plugs, and the wires. I've upgraded to the MFI spider fuel rail. I've fixed two bad grounds. I cleaned the EGR and the MAF sensor. No improvement.

There's been a recent compression test: 175 on all cylinders.

I am pretty sure that the misfire is occurring at high speeds (I know, I know: drive slow, then), but I don't have a scantool that is good enough to really diagnose this. I will say that I was getting an intermittent _flashing_ CEL at high speeds before I replaced the distributor [it would come on for about 15 flashes, and then it would go off. It would only come on under load, and dropping the rpms seemed to kill it]. I have not seen that in the month or so since I replaced that.

Formerly, the code was thrown at low fuel (and often went away when I filled the tank). This behavior stopped some time ago.

I have done a few fuel treatments and have replaced the fuel filter a few times in the last 6 months as well. It's probably time for a new one.

So I've read the "p030x explained" and the "dreaded p0300" thread. And I've had this car to two mechanics, both of whom are stumped (one doesn't want to look at the car anymore, the other wants to re-replace the fuel rail, and I said no).

I have a friend with a good scantool, and I can go see him, but he's an hour away, so if I go, I'd like to go with a purpose.

Any help? Thanks in advance.

 

What brand were the parts you used for the ignition?

 

Delco platinum plugs for sure. Delco fuel rail. [I know, since I bought these myself.]

Not sure about the dist, rotor, cap, or wires, since I had my mechanic do them.

 

Definitely:
Either identify as or install Ac D cap and rotor. Might's well change it anyway if it has more than a few thousand on it.

Then:
Make sure #1 wire is not contacting any other wire or metal part. Suggest you buy enough of that split plastic 'wire loom' for the length, remove #1 wire from keepers and encase in that. Tie off with plastic ties.

But here's what I think will fix it - install one stage colder plug in #1. I believe the heat range goes 'hotter' with higher number in second digit. If you use 45 now, buy the same plug in 44. All other identifiers being the same.
Here's how to tell by sight:
The center electrode ceramic inside the metal barrel is 'longer' for hotter, shorter for colder.
Spark plug - Wikipedia, the free encyclopedia
Does not mean it extends further past the metal barrel. Though that can have the same effect.

I'm ticked that I cannot find an AC D heat range chart anywhere. They used to be common as hell.

You might also try reducing the plug gap from .060 to .050 but if it's really detonating under high load like I think it is, that probably wont help.

And yes.. I know about the knock sensor. Do it anyway. It's not the absolute arbiter and indicator.

 

Update: Ignition parts are all AC Delco

I thought about pre-ignition and regapping the plug and installing a colder plug. I think that the distributor solved the "under load" problem, as I no longer get the flashing CEL at highway speeds.

Mechanic cleaned out my fuel injector with "some really powerful ****." And he recommended that I add some Marvel Mystery Oil to the oil.

I've only driven it 80 miles, but wow it feels like new. I will be happy but upset if all it took was cleaning a dirty fuel injector.