03 LeSabre P0300 and/or P0304

[Dave85]

Hey all, I’m new here and am looking forward to hearing from everyone.
I have been chasing a P0300 and P0304 code for weeks now and I can’t figure it out.
After I troubleshoot one thing and plug it all back in for a drive, I initially get the random misfire code. I’ll stop, remove the code then drive a little more and the cylinder 4 misfire code will pop and stay consistent. I’ve swapped coils to see if it travels and it doesn’t. I swapped a couple plug wires with the same result. Today I removed the fuel rail and checked the injectors. They all looked fine so I swapped the cylinder 4 injector with the cylinder 6 injector and still got P0304 misfire code. The car idles great and if I give it gas and hold at 3,000 rpm, it runs fine. It starts the misfire while under a load at higher rpm. When it’s actively misfiring, I can hear a noise that sounds something like an intermittent sucking or intermittent blowing. All plugs, wires, coils and ICM have been done. Replaced the cam and crank position sensors. Checked extensively for vacuum leaks. Also replaced the fuel quick connect and fuel pressure regulator. I just don’t know where to go from here.

 

[02LTD2.0]

Check the inside of your spark plug boot on #4. If you see white marks inside that is a sign of arcing.You may have a crack in the porcelain of that plug.
I once had a misfire after doing plugs. One of my plugs had a hairline crack in the porcelain that caused a misfire but not immediately...only under a heavy load. Try replacing #4 spark plug.

 

[Dave85]

Check the inside of your spark plug boot on #4. If you see white marks inside that is a sign of arcing.You may have a crack in the porcelain of that plug.
I once had a misfire after doing plugs. One of my plugs had a hairline crack in the porcelain that caused a misfire but not immediately...only under a heavy load. Try replacing #4 spark plug.

Thank you. I’ll check again. I just put new plugs in today because when it first told me cylinder 4 I checked the plug and it came out shattered. I’ll update how it goes.

 

[02LTD2.0]

When I ordered my AC Delco 41-101s from Amazon they came in two packs of 4 plugs so I had 2 extra which came in handy.

 

[Dave85]

When I ordered my AC Delco 41-101s from Amazon they came in two packs of 4 plugs so I had 2 extra which came in handy.

I checked the inside of the spark plug boot and plug for #4 and it all looked perfect. I think next I’m going to check the compression on cylinder 4.

 

[Dave85]

I checked all fuses and grounds today to no avail. Except that it didn’t throw the cylinder 4 misfire. It threw the random misfire instead. Still at a loss.

 

[ulycyc]

Doing a compression test is a good idea. Also make sure your maf sensor is good. If you have a good scantool you can better trouble shooting.

 

[Dave85]

I am replacing the MAP sensor tonight. Finger crossed it works. If it doesn’t, could this be a timing issue or would that be a lot easier to diagnose?

 

[02LTD2.0]

MAP or MAF? Please clarify.

 

[Dave85]

MAP or MAF? Please clarify.

Manifold Absolute Pressure sensor. I did the MAF already. I swapped it and it didn’t work. Picking up a better scan tool tomorrow. Maybe it will help me pinpoint the issue.

 

[02LTD2.0]

Doubtful that it will make any difference. If the MAP was not working it would have thrown a code.