Chasing multiple cylinder misfire. 3,4 and 6. This 04 4.6 was towed to my house with massive oil leak and no reverse. Have sorted those now Chasing these misfires. I have changed plugs inspected for coolant and checked for combustion gasses in reservoir. It has cheap import direct plug wires. I'm not into throwing parts at this at least until I get it on the road. I can see total misfire count with my autel ap200 but not the count on individual cylinders. My question would be what are the chance 3 plug wires are bad at once? Open to insight. I don't see any glaring anomalies when watching live data but I'm not very versed in that. Vacuum is around 24 at idle. Misfire count is way more at idle. Seems to go away when on the throttle or under load. Appreciate any ideas on what to look at.

 

New gas? Techron additive to clean injectors? Compression check?

 

yes new gas and additive. Have not done compression I could go that route. It wasn't my first thought as I thought it unlikely 3 would be down. But I'm learning here. It had no codes prior to sitting at my place for probably a couple months. Fixing oil leak( front cover) , xyz switch as well as dropping the tank and cleaning up the rear chassis. Chassis work was last and took the longest. After that is when the codes came up.

 

I've always noticed coil pack miss fires more at idle vs at speed. If you pay close attention to your rig you can feel them before they are bad enough to cause a cel. 2 of those 3 cylinders share the same coil pack. My little lady will let me know when a miss cel is about to start well before I can get it to read.

Faulty O2 sensors can also cause miss fires although mine usually read random missfire on multiple cylinders for O2 sensors vs when the coil packs would go shed give specific cylinders.

If wires are the suspected culprit move the plug wire from a non miss fire cylinder to the miss fire cylinder then clear cels, see where the cel for a miss reappears.

 

Thanks for the insight. Yeah I initially also had a random misfire code along with up stream o2 sensor. Replaced those then still getting these 3 specific cylinders. i have secondary air, so getting to coils is a bit tough.

 

So I changed 6 wire and 1 wire cleared codes. Misfires return 3,4 and six still. Ugh.

 

Can you test fuel pressure? Thinking pump screen may have gotten gunked up during work on the tank. Maybe that would be more random? Just trying to rule out the simple things.

So now we know wire 1 and 6 are good. That's progress.

 

Some advice I took from Extinct: Why not swap the plug wires around and see if the misfires follow or not? Cheap way to see if the wires are the problem.

 

Yeah, use basic process of elimination. Swap known good for questionable. Do easy stuff first. Plugs, plug wires, then coils, then injectors. Do them one at a time. the ECU is really sensitive so once you find it the code will not return.

 

So finally got around to fuel pressure test. Keep in mind I've never done either test. Have never had an issue with my mechanical fuel pump on the 2a's! Fuel pressure was consistent 49 psi