Hi Scotty,
I have always loved your information and loved your videos!
I am beside myself currently on my truck, as it only has 118k miles but I cannot get rid of the misfire under load. Code says misfire "H" which i think means cyl 8 from what I have read.
I have replaced all coils, plugs (iridium NGK gapped to .042), mass air flow sensor, cyl 8 fuel injector, and wires. I have used my noid lights and even rang out the harness wires to pcm for shorts or opens. None found so I replaced the pcm (reprogramming the imobilizer with forscan software, etc). Same issue so I put origional pcm back in.
I just went through pulling both valve covers to check for a broken spring or rocker arm, As I was at my wits end and need my truck so bad, even though the compression was 160 cold on all cylinders. Nothing was broken and seemed to function normally when I had Trina crank it with valve covers off.
I have pulled the connectors off of coils and injectors while running and #8 is the only one that made no difference. (thats why I thought I had a broken rocker arm)
Is there anything else you would like me to check before reassembling? I was thinking that the cam sensors or O2 may cause no power and miss under load?
I am going to check fuel pressure and mass air flow circuit readings next but, it seems like I have went down the rabbit hole on this one. Im 52 year old electrician, and have always worked on Model A's and English roadsters. A lot easier pastime, lol. I will try to look at live data on my ALLTECH scanner, or should I try the forscan software again?
Thank you for any information you will provide me. Im sure you are chuckeling at some of the steps that I have taken, and that is ok,lol. Please do not hesitate to tell me how badly I screwed up diagnosing this modern truck.
Your Friend,
Bill Gaul
Batavia, Ohio 45103
Now here's the problem. It can look okay but if you get valve float it will misfire only under heavy load. What you should do when you're analyzing that is before taking anything apart. Erase the codes. Drive it around slowly. The code doesn't come back, but then when you go in the highway and drive it faster and harder, the code comes in. It's under load and that often would be weak valve springs
I did not realize that could happen with only 118k miles, that is exactly how it is driving, thank you so much. So without fixing it the proper way (changing all springs) could I just change the cylinder 8 springs (p0358 code) until I have time to tear everything back down this summer? Or is that code not specific to cylinder 8 and could be multiple springs? Most likely should go back to dealer and get a second spring and seal, or is it the intake spring only causing the misfire? Not wanting to half ass it totally, just need to get it back on road until I can replace everything in a few months.