45-55 mph stutter/missfire 4.6l v8

[MugsySiegel]

I changed plugs and discovered they were oem and rusted from coolant. I saw they had replaced the intake manifold with the dorman one that uses a rubber plug on back of it,so the older version. I suspect it may be still slow leaking from the cap as my plugs have slight rust marks on shoulders. They used a non screw type clamp so it may not be tight. I got a piece of 3/4" heater hose and a bolt to plug the hose up. I was getting a rough idle so I cleaned maf and seems better but nlw the 45-55 mph shutter/missfire feeling is still happening strong. Im not getting any check engine lights at all. Id like to check the coils but not sure since im not getting a code to pop up.

 

[Bookworm370]

Is it shuddering at a specific RPM. If at abound 2K or so, that's the range that the EGT valve will open up. If it doesn't the engine will appear to shudder in a certain range of RPM, not necessarily MPH but the two are interleaved of course based on the gear you're in.

The PCM (ECM) is designed to detect real misfires by measuring any drop in RPM (100 or more) right after a cylinder should have fired. If the engine drops after a plug is supposed to fire and then goes back up when the rest do, it will assume it was a misfire and flag it. No direct way to detect a misfire so the RPM drop method is rather reliable. When I had my problem, it was good enough to notice that 3 of my 4, bank 2 cylinders were misfiring. Turned out that I accidentally put in the wrong injectors into those three and the ECM was trying to balance out the fuel flow by cutting down the injector open times. But the problem is that this works across all injectors and not just the ones that are the problem. So those three injectors ended up being cut back to too lean.

 

[Fix4Dirt]

welcome to EF!