I’ve been getting P0300 & P0301 for little over a year now. It all started after I did a complete tune up (spark plugs/wires, distributor, cap/rotor) and changed the fuel pump(which was going out). The codes at first started as pending after a thousand miles then changed to 500 miles which eventually led to confirmed codes that come up after mins of idling. Weird thing is that after I sometimes mess around the distributor the confirmed codes come up on dash after 20 miles then I mess around the distributor a few more times sometimes it changes where it comes up after few minutes of idling. This also happened after just changing the cap & rotor out.

Over the past year I’ve done a lot to get rid of this phantom code and here is a list.
-changed fuel pump to Delphi and cleaned tank with solution
-changed spider injector to mfi and replaced all gaskets for the job
-changed out wires, cap, and rotor to acdelco
-spark plugs are R44LTS6
-cylinder 1 misses the most and compression is 150
-cam retard is at 0.2 or around at 2000rpm
-changed out passenger side precat 02 sensor and post cat sensor (driver side pre cat was changed a few years ago after code)
-changed distributor again (replaced with duralast gold) (cap/rotor still acdelco)
-MAP sensor gasket was damaged and after replacing it a lot of my rough idle went away but codes still are coming on as usual.

If anyone can help it would be greatly appreciated. I’d be willing to start diagnostics from scratch and follow each step to get whatever information you need.

 

1. Can you feel the miss?
2. Have you done a fuel pressure/leak down test?
3. Did you do a full compression test or just cylinder 1?
4. What does the #1 plug look like?
5. Has there been any carbon traces under the distr cap?
6. Try misting the ignition system in the dark at idle and look for spark
7. Let’s look at your fuel trims at idle and 2500 in park

George

 

I know it sounds stupid, but are the plug wires installed correctly? It's very common for people to mix up #1 and #3 because they're in the "wrong" order on the cap.

 

What Tom said. Good one.


George

 

1. Can you feel the miss?



Yes I can feel miss at idle, but while driving the blazer feels fine.



2. Have you done a fuel pressure/leak down test?



Yes but only at the service port a few months ago. Honestly don’t remember the numbers so I’ll perform another one later today. I did replace the fuel filter also if I didn’t mention that.



3. Did you do a full compression test or just cylinder 1?



Only tested cylinder 1 since 95% of misfire was coming from that cylinder. I will perform a full cylinder test later today and report back.



4. What does the #1 plug look like?


Spark plug #1

All plugs look the same



5. Has there been any carbon traces under the distr cap?



Yes about 2 weeks ago I replaced the duralast cap and rotor with the acdelco that I warrantied out and there was a lot.





6. Try misting the ignition system in the dark at idle and look for spark



I replaced the spark plug wires again a month ago and I found some cracks on them so i warranty them out and I got 16mpg instead of 10mpg but didn’t change the misfiring at all. I will do this later tonight when it’s dark.



7. Let’s look at your fuel trims at idle and 2500 in park



I’ve provided a screenshot at idle and at 2500rpm


-0.3 cam retard around 2000 rpm

Idle fuel trim

Idle cam retard

Around 2500 rpm fuel trim, couldn’t really reach 200 degrees

 

I rechecked that side and 1 on the cap is going to the driver side front, 3 on the cap is going to the middle and 5 on the cap is going to rear.

 

Some softwares can report misfires, but on the wrong cylinder. Seems a couple of cylinders can get switched. Pull #1 plug wire from the cap and make sure it doesn't start reporting misfire on a different cylinder. Car Diagnostic Pro has alternate PIDs for the two troublesome cylinders. Looks like you're using Dash Command - I don't know if it has this issue or not. It's easy to test by pulling plug wires.

 

See posts #5 and #6 here. https://blazerforum.com/forum/2nd-ge...-retard-90496/
was same issue for both Car Gauge (Diagnostic) Pro and Torque Pro. Never tested Dash Command. No need to change softwares - just test before believing.

 

I’m not going based off the misfire counter on the app, really going based off the confirmed code. I used a shops snap on counter and it was missing on 1 only and some early on others.

 

In addition to the other things we are looking at please follow Les' direction and pull some plug wires while running to confirm proper misfire cylinder reporting before we get too carried away. The usual starting point is to get CMPR within sped to help with this but you already have that taken care of,

George