P0305 on a 2007 5.7

Hi everyone I'm at a total loss here. Truck has 330,000 miles on it but has ran fine.... even perfect.

I did the secondary air bypass kit when that came up about 10,000 miles ago. Was running great. Then I get the #5 misfire. No biggie. Replaced all my plugs and coils. Another 2,000 miles and I get P0305 again.

Took it to a reputable shop here in Jacksonville and asked them to do a compression check. Came back better than factory tolerances.

I had heard the early 5.7's had issues with weak valve springs so I figured a compression test would rule that out.

I love the truck, so much so I'd probably put a new engine in it if I have to. But I really want to hit the 500,000 club and am hoping someone can tell me why I keep misfiring this one particular cylinder and what it's going to take to fix it. Thanks guys.

 

Who are the mods now? My phone is being dumb. I can't get it to load.

Can we get this thread moved to 2nd gen to.get this individual some help?

 

I tagged a mod to relocate to 2nd Gen...

@richancock, if you have good compression, chances are the motor is fine. There's likely something electrical or air/fuel (a/f) going on. In the future, never swap all coils. Instead, swap the misfiring coil with the one adjacent, and confirm whether or not the misfire code jumps with it. If the issue stays on cylinder 5, note that misfires can be caused by bad plugs, failing injectors and/or improperly installed injectors, manifold leaks, bad grounds, broken electrical connectors at the coil pack, and even ECU/ECM failures. This is why you don't just want to see a "misfire #5 code" and throw hundreds of dollars on new coil packs (I know, I know, hindsight is 20/20!)

It's worth noting also, never buy car parts on scAmazon or fleaBay (if it applies here), since counterfeits/knockoffs are rampant from both vendors. It's true for auto parts, appliance parts, small engine parts ... I can't tell you how many damn BS fake parts I've gotten from both.

Hope you get it figured out sooner or later. But don't give up. That truck has at least another 100k in it.

 

Swap that coil to the otherside of the engine. Also check your ground cable, may be damaged. I think I had a weird misfire in cyl 5 too, if I remember correctly, but it was the ground cable on the battery had broken.