Old school misfire diagnosis?

[eolson]

Hi all,

After reading through a lot of misfire threads, I wonder if mine won't be a little easier to diagnose than I thought. These things are never simple, so I'm hoping my thought process is at least a simple way of ruling something out.

I scanned for codes and found misfire in cylinder #6 and decided I'd start with spark plugs since they were due anyway and often give a hint of what might be happening. It's been running rough consistently starting this week, almost like it has a vacuum leak, or running on 5 cylinders.

In replacing the apart plugs I found that they all looked exactly the same, worn, but not fouled and all with the correct gap even. They were proper Denso plugs, no sign of coolant, none of the fouled, etc. if I'm taking the traditional route of plugs, wires, could packs, and fuel injectors (before moving the head gaskets and beyond) wouldn't it seem like this points more towards a fuel injector? In my mind, the plug from #6 is perfectly dry just like the others, which to me point to a cylinder that's been firing but not had any fuel delivery.

Curious what you guys think, I'll swap coils around next, but I think I'm looking at an injector replacement?

Erik


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[Troybylt]

I'm going through this right now, will it start just fine cold, but after it's warmed up and started it will missfire l. Apparently one of my injectors is leaking and throughs off the fuel map until everything is burned off or evaporated.

Mine ended up being the #6 injector.

If it was a coil pack you would have 2 cylinders missing due to our wasted spark setup. You just changed the plugs so thats out.

Engines are simple, suck squeeze bang blow, take an element out of that system and you have problems, suck, squeeze, blow are nearly a given so there's something wrong with your bang, either too much or not enough fuel it seems like here.

You can check the injector resistance, it's not uncomon for our injectors to increase in resistance until they no longer work. With it being #6 though it's going to be a ***** to get in there, might as well plan on replacing them all so it's all balanced.

Can't recommend Witch Hunter Performance's injector service enough.

 

[eolson]

I'm assuming there's a cold start injector that makes up the difference when its first starting up. I have the same problem, runs ok when cold, then settled into the misfire. All plugs look the same so my guess is injector or injectors. I'll have to look for that test next.


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[eolson]

For what it's worth, I do think this type of issue can be solved much easier than most of the threads I found that have you switching coil packs around and such. Not that that's time consuming, but here's what I did:

I put new spark plugs in first since that needed to be done anyway, and also because it's inexpensive. I hoped to find some evidence when removing the plugs of what might be wrong, but they all looked the same. My code was for a misfire on #6 so next I pulled that spark plug wire out, stuck one of the old plugs in it, and let it rest on the exhaust manifold (cold engine). I started the engine and looked quick to see if there was spark, which there was (and obviously I quickly shut it off).

At this point I figure I mostly have my answer on whether it's a coil pack or injector as I'd have no spark if it was the coil and the plug was clean so it likely hasn't been getting fuel. Being that it's cylinder #6 and access is horrible, I bit the bullet on 6 rebuilt and flow-matched injectors on eBay. That's a gamble, I know, but the company is local so I figured it was worth the risk for $130. That can be the cost of one injector depending on your source.

All installed tonight and it's noticeably smoother with maybe a little more power. The injector in question gave no reading at all on an ohm-meter, so something's up with it since the others all read about 19.5.

Maybe this won't be of any help to anyone, it's certainly a lengthy write-up without any exciting pictures, but I think it's cool that basic mechanics can still apply to modern fuel injection.

Good luck!


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