P0304 Cylinder 4 Misfire - Headgasket Replacement

Howdy all! Hoping to get thoughts from you guys and maybe get pointed in the right direction... Earlier this past week my '05 Tacoma, V6, 6 speed manual, SR5/TRD Offroad w/ 139k miles had a rough/shaky start-up for a few seconds and turned on the check engine light. My heart sank. Popped the hood and checked fluid levels. Although my truck previously wouldn't drink a drop of oil between changes, when I checked it this time it was 1.25 quarts low . My heart sank further. Got my handy OBD2 reader out and pulled the P0304 Cylinder 4 misfire code. Quick search of this forum made me start thinking head gasket problem.

I cleared the codes, topped off oil. 1 day went by with no rough starts or codes, then the following day I had a few rough starts and when leaving an auto parts store where my truck had only sat for a few minutes, it had another rough start and threw the same code again. Next day no codes or rough starts. I have been monitoring oil/coolant levels since, coolant levels seem to be all over the place, but I can say I've added coolant like once or twice over the course of the 3 years I've owned the truck. Oil level appears to be holding thus far. It's cold and rainy so I've done limited testing thus far, but no visible oil leaks, spark plug looked fine.

Questions: Am I looking at a head gasket problem? Is there still a decent chance my problem is coil, plug, or injector related? Am I safe to continue driving the truck until I get a break in the rain? I know there are a lot of various head gasket tests, which one should I do? If this is a head gasket problem, I'd rather not spend too much time/money testing it to confirm- better to buy the parts and dive in for the fix.

 

if there is water/coolant in your oil it's a head gasket. sounds to be a bad coil pack though

 

Thanks for your thoughts. I hope you are right, I opted to pop in a new coil pack last night. Perhaps I'll do an oil change today to look at the oil. If its only a small amount of coolant, would I really be able to see the difference, or would I need to send a sample in?

 

water is heavier then oil so it would sit at the bottom of your pan. when you pull the plug look at what comes out. if it milky you have problems. if not your good

 

Makes sense. I'll give it a check when the rain lightens up a bit

 

Looking like I'm hosed more and more. I went out and started my truck, seemed a little rough at start-up, checked with OBD2 reader, no codes. Started it twice more and although it didn't turn on the CEL, a pending P0304 code appeared again on the reader. So that basically rules out the coil. Safe to drive to work tomorrow or get a rental and start tearing into it?

 

did you change your plugs?

 

I have done a lot of maintenance since I bought the truck, including plug replacement around 1.5 yr. ago. You thinking a bad coil would ruin the plug? There doesn't seem to be a change after replacing the coil, and when I pulled the plug it looked like normal wear, although I didn't have a gap tool handy to verify.

 

the porcelain on the plug could have a small fracture in it. try pulling another plug and shaping the two. if the misfire moves it's a bad plug

 

Honestly the misfire is not consistent enough to get quick confirmation when switching. Looked closely at the plug, didn't see anything. #4 plug is a chore to get out, so I'll put in a new one over swapping. Since my truck is an '05, is at 139k miles, and I believe I have seen water dripping from exhaust, I still thinking HG. Could a bad coil/plug eat engine oil?

 

water dripping is pretty normal this time of year. doesn't really sound like a HG but you never know. run a compression test first.

 

bad piston rings would eat oit

 

I popped in a new spark plug at cylinder 4, I'm not very hopeful but will see if that helps. I picked up a gap gauge while I was getting the plug, the old plug measured about 0.060.

 

That is a pretty big gap. You may want to replace them all... Normal is what 0.040.

 

Probably will after I solve my misfire issue. Previous plugs installed around 50k miles ago, so I thought I'd still be good. Chilton book says 0.043.
You think 0.060 is bad enough to cause issues like a misfire code?

 

yeah that's a big gap. I would change them all. I do mine every 30k. and set gap at .040

 

The maintenance schedules says every 30K miles on the V6 with standard plugs. A huge gap could cause an intermittent miss fire.

 

Have you done a compression test?

 

I like the advice in here. Am curious about a compression test being performed as well.

 

No compression test yet. Sounds like that should be my next move. I'll pick up a full set of plugs and run the compression tests as soon as I can. Query: Does the FSM say 0.040 gap? The store's computer said the matching NGK LFR6C–11 plugs for the truck are pre-gapped 0.044, but when I checked with my gap tool it looked looked about 0.040. Chilton says 0.043. Which is it? Also, when I run the compression tests, should I expect to see much variance even if the leak is a super small one? (Which if there is a leak, i suspect it's tiny)