MisFire, no codes, dash lights and shaking

2009 / 228k mi / V6 / TRD Sport
Misfire on cylinder 6 confirmed. NO CODES other than misfire on #6 and no codes in memory. truck shook all over the road. Pulled over, shut it off. Restart and drove fine for miles. I did a coil and 6 new plugs. Problem went away for a few weeks. I felt a subtle misfire today around mid day and it grew to horrible in 15 min again. OBD reader shows misfire on #6 again no other codes.

Engine light flashing with solid traction control light.

Funny thing that gives me a suspicion of the problem is that when it shudders bad bad, if I give it more gas it will smooth out. Basically, under load it doesn't happen. Mostly happens when i try to hold a speed and am just barely gassing the motor. giving it gas and it improving is blowing my mind for a misfire. Seems totally illogical.

 

Sure sounds like secondary ignition based on your description, did you change the correct coil? #6 is drivers side rear.

 

Yes, that's the coil I replaced. Ran great for a while but the problem came back.

 

Try moving that coil to a different cylinder and see if the miss follows it, could just be shitty parts especially if it was aftermarket.

 

I figured a bad coil would be SUPER rare

 

OEM coils don't fail very often but aftermarket ones can fail after only a few miles.
Either way it's an easy test to rule out a failed coil.

 

So I need a code reader for this. Would you suggest doing this in an autoparts parking lot? #6 requires some effort to get to and if that is hot I won't be able to.

 

Oh I was assuming you had a scan tool.

 

One thing that many mechanics don't think about when it comes to diagnosing a misfire is to also check the companion cylinder to the one indicating a misfire. There are times where a companion cylinder miss will actually trigger a code for its match. The way to find the companion cylinder in a V6 or V8 configuration is to place the first half of the firing order over the 2nd half. In this case, as noted above, the firing order is 1, 2, 3, 4, 5, 6. So you would get
1, 2, 3,
4, 5, 6.
#6 companion cylinder is #3 cylinder. What a companion cylinder is, is the cylinder that is in exact opposite of the other cylinder's stroke. So when #6 in TDC of the compression stroke about to fire, #3 is in TDC of the exhaust stroke.
Now I'm not saying that it IS the culprit, but something to consider taking a look at. As DM93 stated, having a bad coil from the aftermarket isn't unheard of. I would get a Denso coil to replace them if it were my truck.

 

You got a EGR valve on that truck? Sounds like a carbon sticking EGR valve if it is a part throttle issue.

 

Good idea on something to check. I'm curious where the air from the EGR system enters the intake manifold, and if it is close to the #6 cylinder.
Thinking about that as well, the fuel rail ends at the #6 cylinder too, right?

 

Where ever the EGR is mounted is where the exhaust air enters. But, it will lean the hell out of all the intake air.

 

There's no EGR valve on a 4.0L

 

Not all air enters the air stream at the point of installation. Many vehicles have internal passeges in the intake. That is why I was curious. I don't know for SURE where it owuld enter. But it seems that according to DM93 below, the 4.0 doesn't have an EGR.

 

Most modern engines do internal EGR by varying the cam timing although EGR valves are making a comeback on some newer engines due to stricter emissions standards.
Neither one of the 2nd gen engines has an EGR valve.

 

I’m going to guess spark plug tube gasket

 

Thanks guys. I just got done unplugging 2-4-6 while the engine was running. All made the truck shudder. Engine light is on but when I started it, she was idling smooth. I did not try #3. Funny how it is intermittent tho.

Edit: there is a "breather/vacc" line exiting just behind 6 and entering into the intake just above 6. Sorry I don't know the proper name of that thing.

 

Compression test and leak down test. After swapping coils of course.

 

Mileage? Did you change or look at the spark plugs?

 

Changed all plugs. None looked horrible. All were dark with even amount of carbon. 228k miles on truck.