miss in engine

[SFK830]

Front plugs wired left to right : 2,4,6
Rear plugs wired left to right : 1,3,5

My plugs should all have less than 10k miles on them
Does anyone know how i can test my coil packs? I plan to pull y plugs later and see if one of them is causing a miss. I am also runnign only a downpipe currently could that be the caue of a miss?

[bszopi]

When did you start getting the miss? Was it after maintenance, when you might have messed with the plug wires? Do you have any codes set?

[SFK830]

Yeah my CEL blinks, however like i said my rear o2 isnt currently in place and have only the downpipe on the engine but yes the miss developed after matnence. There was a slight miss in the engine befor we took it apart however it was nowhere near as bad and i assumed was just from the bad intake gaskets and leaking headgasket.

[SFK830]

A code reader came up with "random Miss" so if anyone knows what would cause a thro code like that please lmk. Cylenders should all be wired correct and plugs look fine, i am gonna replace the plugs but assume something like a random miss is more along lines of cas or iavc or somthing.

[SFK830]

I really need help with this. Do none of you pros on the 3x00 have any idea what my problem could be?

[bszopi]

Well, if its not a miss on a specific cylinder, that makes it harder to troubleshoot. You might want to inspect the CPS wire to make sure there are no burns or nicks in it.

[pocket-rocket]

What sort of maintenance was it?

[SFK830]

Well it started as just replaceing intake gaskets but by the end of it we had the heads planed and installed new headgaskets.

[pocket-rocket]

Are you 100% positive you kept the pushrods in the right order? Intake and exhaust pushrods on 3x00 engines are different sizes. Also, you can't go by the cylinder numbers on the lower intake because the ports cross over from one side to the other, so port labeled 1 would actually go to 2 and 2 to 1, ect. These are two common mistakes people make on these engines. Hopefully one of them is it, but hopefully it's not the pushrod one because that can cause bent valves.

[SFK830]

Well i cant be 100% on the push rods see my father did most of the work he just had me torquing things down so i will ask him. as for the lower intake manifold im not sure i understand what you mean

[pocket-rocket]

If you look at the intake from the top, the rear ports actually lead to the front head and the front ports actually lead to the rear head. Each one of the ports has a cylinder number on them and because of the way the intake ports cross sides like that, if you run the wires according to those crossed over port numbers you are hooking the wires up to the wrong cylinders.

[SFK830]

Is 135, in the back and 246 in the front from left to right not the correct order?

[Schmieder]

Random mis ehh..... How random? Is it something that comes and goes or is it a constant issue?

Check your spark plug cables. Often they can break when removing them. When they are put back on, the connection is weak and resistance jumps up. Occasionally the spark energy will jump from the spark cable to the block instead of the spark plug. Because the break in the cable creates resistance and it may be easier for the current to arc to the block. Test the cables by measuring the resistance. Look up the resistance value per foot and do the math.

If you flipped your fuel injector wire harness upside down your injectors may be off. Which would still fire fuel into the intake, but at the wrong time.

Or your Crank Position (3xCKP) wire is damaged. Make sure the purple and yellow twisted wire is not resting on or very near a spark plug wire. Any interference could cause a random miss.

The camshaft sensor is also sensitive to interference. Check and make sure your 24xCKP sensor is plugged in (by the crank pulley), the other 3xCKP (aka 7xCKP) is on the back side of the block.

To test the coils, get a multimeter and test the resistance across the two towers and across the two plugs. Primary is 0.5-0.9 Ohms and Secondary is 7k-10k Ohms. But if the coil was bad, it would be a lot worse running, if at all cause you will loose 2 cylinders.

Check all vacuum lines for leaks. A can of starting fluid, spray around the vac lines (not a lot). If there is a leak it will increase the engines RPM.

[Schmieder]

Is 135, in the back and 246 in the front from left to right not the correct order?

That is correct.

1 3 5
2 4 6