Misfire woes

Two weeks ago with my MS6 I suddenly had shaky acceleration and a loss of some power and the CEL came on. Misfire cylinder 4. A couple of times in the past I’ve felt misfires (although no CEL) and Techron has easily cleared it up—dirty fuel tank? But this time it was much worse. By the time I made it to the auto parts store it was mostly better. I put Techron in it anyway.

The misfire issues persisted on and off. It drove fine one day then issues the next. I tried some Lucas fuel system cleaner the next time I added fuel. Continued improvement but occasional issues.

Currently it will still sometimes misfire on cold starts and sometimes throw the CEL for it. Otherwise it drives fine.

Any thoughts would be very appreciated.

 

check your spark plug gaps

 

Sorry, meant to say that after the Techron didn’t seem to fix it I had swapped the #4 ignition coil with #3 and put in the previous spark plugs that I had taken out prematurely and which still had plenty of life. There was no change.

 

what was the gap on the newly installed plugs

 

The plugs I took out were from EdgeAutoSport and pregapped. I had checked them before I put them in and they were 0.026. They’ve run fine for maybe 6000 miles. The ones I put back in were the Ruthenium plugs that I had gapped to approx. 0.026 and maybe had 8000 miles on them. I quickly checked them before putting them in and they were all less than 0.028.

 

Just as an update, today it was misfiring while driving even after warming up. It’s very noticeable below 2000 RPMs (with light acceleration). Above 3000 seems normal even with WOT. Does this back and forth more suggest a dirty fuel system?

My tank is below 1/4 now.

 

Can you scan ignition, fuel, rpm. Both the misfiring area and normal area of running. Hopefully logs will show some insight for us to read and give advice.

 

I did get a log when it was misfiring pretty badly and I got one today when it was doing quite a bit better. However I need to find my Accessport USB cable… I’ll post once I find it.

 

I suddenly remembered that the AP doesn’t use a specialized USB cable. Not sure why I was thinking it did. Anyway, my current computer only has USBC ports and my USBA -> USBC adapter doesn’t appear work with the AP for some reason. My computer can’t find the AP.

Anyway, I’ll have to get a standalone cable.

In the next few days I’m just going to swap out the cylinder #4 injector. Hopefully that’ll take care of it. Maybe I’ll do compression tests while I’m at it.

 

Ok, I was able to replace the injector. Way dirtier than I've seen any of my injectors before.

When I started it up it misfired enough to bring up the CEL. It actually continued to misfire even while it warmed up (normally the misfires are gone after maybe a couple of minutes). After those cleared up I floored it in second up to maybe 6500-7000rpms. There was quite a bit of dark smoke out the back and then it seemed to drive better and no longer smoked when I floored it. I filled it up with some Shell V Power and drove around a while. The engine felt good.

We'll see if it misfires again in the morning when it's cold.

In the meantime, I was finally able to get the logs from the AP. It's been a while and I wasn't 100% sure which log was which, but I think I got the right ones.

 

It misfired again at start up. And the misfires were more severe than I was having previously. They cleared up after a while and then the car drove fine. But according to my scan tool there were 424 misfires in the “last/current driving cycle”, which was about 5 min/2 miles of driving before they cleared up.

Weird that this would get worse with a much newer injector. Maybe I should have cleaned it before putting it in. I had previously driven on it for maybe a couple of hundred miles at most. I’ll add some Techron again and see if that helps.

If anyone can verify in my logs that this is a fueling issue that would be helpful. Maybe I’m barking up the wrong tree.