I installed some pacesetter it headers on my 97 Dodge Ram and discovered a misfire. Has brand new o2 and was fine before the install. Later found out the o2 was plugged in all the way. Smoothed our just s little bit. Put plugs and wires on as well as a cap and rotor. Misfire got a little bit better. Almost non existent until under heavy load in over drive.no misfire code had been stored after all of that. I put a free flowing dual muffler exhaust on my truck and now the misfire is at idle and at cruising speeds. I found a vacuum leak and sealed it up as well as putting the exhaust on. When it started misfiring i can hear an after-fire (unburned fuel in the exhaust igniting) as if a cylinder isn’t firing like it’s supposed to. (#7) I’ve spent lots of $$$ tracking this down and it its a roller coaster. I know my plenum gasket is going bad but burns less than 1/4 per oil change as it sits right now. I was thinking maybe coil but I was told it will either work or it won’t. Then I thought maybe crank sensor. Was told that’s very rarely an issue and doesn’t usually cause a misfire. Later informed it could be a knock sensor. I’m doubting fuel relation simply because the misfire was bad then better then bad again as i fixed issues. I disconnected the battery to let everything reset. Any help is appreciated. I attempted to put as much info as I can so people have an understanding of what’s going on. Thanks I’m advance!

 

It's not the knock sensor, as your truck doesn't have one. May be a clogged injector, cracked heads, failing crank sensor, or a selection of other causes. You have done the most obvious fixes already, but, may want to look at the plug wire routing TSB in the FAQ section here. Beyond that, think I would consider a compression/leakdown test. Wanna fix the plenum too......

 

I didn’t think I had one. But wasn’t positive. The guy I was talking to didn’t seem super knowledge. I’m gonna look at the spark plugs and see if the are fouled out tho I doubt it. Read the color on them and go from there. I think it might be crank sensor though. I’m going to inspect some the wires and stuff. I plan to do a leak down test and inspect the p0307 code on that cylinder. I have to replace my fuel rail in order to do any pressure testing because all I have is the plastic rails.

 

I was driving home last night while it was colder than usual and the misfire was not nearly as bad as it was earlier that day. Was colder out about 67 instead of 82

 

How old are your O2 sensors?? Not that I think that would give you a cylinder specific miss...... That *might* be the plenum..... leaning out one cylinder....

 

Replaced brand new a month or so again when the pacesetter headers went in. It may be the plenum gasket leaking right by the #7 cylinder causing it to lean out with a much less restrictive exhaust system.

 

What brand O2 sensors?

 

Denso

 

So the brand isn't the issue

 

No. I did my research. I’m not sure what it might be. Otherwise. Only
o2 code is the lack of s down stream. My only concern is I have a true dual so if the driver side bank is not being read.