P0304 Misfire Code - Need to replace Ignition Coil - How do I get to it?

[StevoDevo]

Ok so like the topic says, I need to replace cylinder 4's ignition coil on my 2002 Pathfinder. I have replaced 2 other ignition coils over the past year or so when they threw error codes so I know what I'm doing - the problem is is that I can't work out how to physically get to the ignition coil to replace the thing. There are so many things blocking access (to both cylinder 4 and 6).

Would love some help / advice here!

I'm removed the big air tube (technical term) but now I have the black circular thing (arrowed in the image) in the way! I'm not sure I can even get a screwdriver in there to remove it, but if I can would that be safe to do? I've already pulled the blue power connector!

[VStar650CL]

That's the Idle Air Control stepper motor. It's safe to remove but be careful not to bung-up the seals. You'll need to run an IAVL (Idle Air Volume Learn) after repair if you pull it, so you're better off loosening the whole throttle body and setting it aside without removing the hoses (4 allen screws, one is right where the top arrow starts in your pic). Just an aside, if you're replacing coils routinely then there's almost certainly a problem with your engine ground. COP's with built-in transistors are extremely sensitive to resistance on the low side of the circuit, it makes them heat up and eventually produces the familiar "warts" in the epoxy. Once she's back together, do a ground integrity test. Put your voltmeter on millivolts and with the engine running, measure from the block to the negative battery post. Anything north of 50mV (0.05V) will explain why your truck is eating coils. You can locate the bad contact by repeating the test back along the length of the ground cable at all the attachment points. If you find a spot where voltage falls suddenly (like between a bolt head and an attachment lug), clean it. If you see a gradual rise all the way from terminal to block, then the cable is shot.

[mdmellott]

#6 is in a cramped space but it can be removed easy enough with a bit of patient effort. #4 on the other hand is impossible to remove without first removing the entire throttle body/IACV assembly. There are two coolant hoses that have to be removed and plug as well. The hoses are coming into the IACV housing from opposing directions and too short to be left on the housing and successfully move the entire assembly away from the intake plenum in order to access and remove the #4 coil. Place a big wad of paper towels or cotton rags under the hose connections before removing them and be ready to plug the ends of the hoses immediately after they are removed. There is no easier way to accomplish this task and no short cuts. I recommend purchasing a new throttle body gasket as well since the gasket is a thin metal crushable type. It is not designed to be reused once removed. There is a risk of creating a vacuum leak if you reuse the old gasket.

[StevoDevo]

You guys are awesome - thanks so much! I removed the 4 Allen screws and popped off that throttle body and was able to get to the 4th cylinder (with a bit of work and choice words!!)

I did reuse the gasket which I just read from mdmellot’s reply that I should replace - it wasn’t broken or torn so I’m hoping I won’t create an issue with that!!

I’ll check the engine ground, but what has been happening is that different cylinder coils have been failing (so far it’s been 1 and 3 in the last 12 months and now 4). Could that just be that they are failing rather than it being a ground issue?

I really appreciate your guys responses too - as a YouTube mechanic it really helps having this type of advice when I get stuck and I’m sure I speak for a lot of us that we do appreciate the knowledge you guys share!!

[mdmellott]

Odds are in your favor that they are just old tired coils. It's not uncommon to see coils fail, one at a time, as you replace them, one at a time, over a relatively short year or two. You haven't replaced the same one twice so you're probably in good shape and don't have a ground issue.

If you do find that the old throttle body gasket leaks, it is easy to replace it without actually removing anything except those four hex head cap screws. The thin metal gasket will just slide out if you part the throttle body away from the intake plenum by just a pinch. It might just fall out on its own when you remove the last of the four screws and a new one can be slid right into place.

[VStar650CL]

I'll defer to mdm on this, his ride is identical to yours and it's been awhile since I worked on one this old. If the TB coolant lines on the '02 are too short then he's right, at least one of them will need to come off. He's right about the gasket also, but that kind of goes without saying. Vacuum leaks are a bear, never re-use that stuff.

[StevoDevo]

How would I determine if I had a vacuum leak?

[VStar650CL]

PS - Takes 10 seconds to check the block ground, and Nissan coils rarely get tired without a reason. There's a popular myth among techs that COP's "fail in bunches", but it's worse than mythological, it's complete BS. Virtually every ride I ever inspected that had multiple coil failures had some sort of ground issue. Not always the main cable, the wires to the individual coils can be faulty too, and the ground contacts inside the connectors can get crummy with age. But if it's suddenly eating coils, guaranteed there's an underlying cause.

[VStar650CL]

Since it's only one gasket you need to check, just spray some Brakleen around it. If there's a leak the idle speed will surge when the Brakleen gets sucked in.

[mdmellott]

A smoke test (requires specialized equipment) is the correct answer. However, there are a few shade tree mechanic tricks that work also. My favorite is a propane gas torch (not lit) pointed at various areas looking for a suspected vacuum leak while also looking at fuel trim readings on a scan tool. When the readings go rich while pointing the torch head at a particular area, you found your leak. Otherwise, you can wait and see if your ECM throws a DTC.

[VStar650CL]

If your scanner can stream A/F alpha or short-term fuel trim, that's even quicker. If it idles lean but normalizes above 1.5~2K, you have a small leak. No need to wait for a DTC.