Misfire Cylinder 6

Hi all,

I know this has been posted about a million times over, and trust me- I've read through so much and done everything I could to test my truck before coming here to post. This misfire has been so elusive and don't know where else to turn.

Truck started misfiring in cylinder 6, but not steady at all, just randomly stumbling. Didn't matter if it was cold/hot, if I was idling or driving at high speed. Last year I had a misfire problem that ended up being a bad coil on cylinders 3/6 so my first thought was that that coil was cheap and failed already or I installed something loose. So I swapped it with the coil next to it and cleared code to see if the misfire would change cylinders. It stayed on cyl 6. After about a week the random misfire turned to a steady misfire, so I parked the truck for good in my garage until I could figure this out.

Both plugs and wires are a year old- changed them when I changed the coil last year. Did a spark test anyways and definitely am getting spark at cylinder 6. Did a compression test to see if I'm losing compression. This is where things get weird to me. All cylinders 1-5 were at about 175-180 psi, but cylinder 6 was actually the highest compression at 190. I then thought maybe it had high compression from being wet from head gasket leak. Did a leak down compression test on all cylinders. Cylinders 1-5 had 5-7% loss and Cylinder 6 only had 3% loss. Listened to throttle body, exhaust, radiator and oil cap just for the heck of it and the only place I could hear anything was the oil filler cap, which I'm assuming is just normal loss around piston rings?

Any thoughts on this? I don't understand how the cylinder I am misfiring in has the best compression. Also forgot to mention I replaced the fuel injector for cylinder 6 just for the heck of it, and no change.

Any thoughts/ help would be appreciated, thanks in advance.
Aaron

 

Carbon buildup or valve is out of adjustment? I've heard of people doing the Sea-Foam treatment to blow out carbon out of a cylinder/valves.

 

I thought about carbon buildup and ran a can of sea foam through it with no results...I guess if it’s really bad then the sea foam may not be enough.

I thought about valve being out of alignment but wouldn’t that show in the leak down compression test? If I set piston at TDC compression stroke both valves should be closed, if it was out of alignment I would assume it wouldn’t be closed and I would notice air pressure escaping at bad valve...

Also had a thought that a valve may be stuck in closed position so compression test checks out but isn’t opening properly when engine is running...but I don’t know what the odds are of a valve being stuck exactly in closed position.

 

Did you put Sea Foam in the intake or in the gas? Never heard many people having luck with it in the gas.

Typical high compression is Carbon Build up.

I imagine the plug looked ok?

You only used Toyota plugs?

Is the misfire consistent? (you said no). I did see a youtube vid with a misfire and the guy was showing off his scangauge. It showed some odd misfire behavior. Turned out to be the sprocket on the crank was missing teeth. Prior mechanic put the sprocket on backwards and it got caught on the t-belt. (very easy to do)

But I'd still suspect the combustion chamber since you have a bit of high compression there.

Just spit-balling here.

 

Good thoughts. I put it in the gas and not the intake, I’ll have to try that. Misfire started off not consistent, but now is completely steady, not a second that it won’t miss.

I have wondered about the plugs...like I said before they are only a year old, but def some off-brand things I got at oreilly. Plug looks pretty normal, no oil or carbon or coolant...just a normal light brown. I swapped plugs from 2 other cylinders that were firing fine and it didn’t move the misfire. Might be worth a shot to buy a legit plug just for that cylinder to see if I can get it to fire.

Thanks for tossing ideas around with me!

 

I may be blowing smoke here...but usually a plug will misfire under load like going up a hill...or possibly the higher compression in that cylinder...I know you put a new plug in but I would put another one in just for fun...it's cheap, we've all had bad plugs before. Also with the higher compression plugs get weird with high compression...like under load and don't like to fire 100%...in the old days we would use a hotter plug to solve some of these issues but maybe just a new plug...it's probably the hardest one to get to isn't it???

 

Yeah gonna have to try it- you’re right it’s cheap and simple. Still doesn’t change my high compression question regardless but fixing misfire is my first priority.
And #6 may technically be the hardest to get to, but none of them are that hard to be honest. Plus at this point I’ve had them all in and out so many times I could do it with my eyes closed

 

A 10% higher compression on one cylinder is not considered too much...a leaky valve seal or worn valve guide can cause a little more oil in that cylinder. When you take the old plug out see what color it is it may help some of the mystery even though it's not that old. I've taken engines apart and many times different cylinders the staggering on the rings had moved too which can cause that bit of discrepancy in compression...the typical 120 degree staggering for each ring can change a lot...oil and blow by which you said was normal. Worn valve guides can sound like an out of adjustment lifter...try the plug...take a picture of it and post it if you don't mind...now I'm really fascinated!!!

 

Will do! Just gotta get home from work.

 

So here’s my plugs, at least from that side. After thinking about the plugs and going to buy a new one to stick in cyl 6, I realized I never should have bought these single ground plugs. Actually had never heard of the waste spark system. I all of the sudden became convinced this could be my issue, that I burnt these plugs out in a year of driving on them. I bought all 6 OEM NGK plugs with the double ground and put them in to see what it would do. Still misfiring in 6. Cleared my codes and ran it again, just the p0306. The only thing different is that it isn’t as steady of a misfire anymore, but still way more misfiring than not.

Any thoughts after seeing color of plugs?

 

They all seem to be firing pretty good in my opinion...#6 is a little more rusty like a poor firing but not bad...the gap looks excessive and that could be from the picture angle? My 22REC is about a .034 gap and I think yours should be around .043...in any case the three shown look worn but good. Maybe use some "dielectric" grease on the boots before reseating. I'll keep looking for some other ideas...I know how frustrating a consistent problem can be.

 

No expert, but they all look gunky to me. I'm thinking the other cylinders aren't far behind.

https://www.championautoparts.com/P...-and-maintenance/how-to-read-spark-plugs.html

When I pulled mine, at 200k, they all looked like the "Normal one" in the link above.

Also, mine were original to the car when I changed them. They made it 200k miles. I won't put anything else but Toyota back in.

 

That was a good link to send Negusm...it should help everyone!!!

 

Yep, I’m thinking they look a little gunky too, especially only at a year old. But still no major indications of what problem could be...and like I said, I put new Toyota plugs in but still didn’t fix misfire.

With good compression and no major pressure loss after leak down, is gunkiness most likely from carbon? Is it possible my valves are just clogged up bad with carbon and #6 is the worst?

 

I also have read about timing belts slipping teeth and causing misfires. I just don’t know if it would cause a steady misfire in only one cylinder or if it would cause a random misfire. If it comes down to taking this thing all apart to do timing belt water pump and gasket rebuild, I don’t mind at all- just wanna properly diagnose problem before doing all that

 

Maybe...doesn't seem like a valve problem to me. I know this is a "snake oil" thing but I have used in both my main tank and auxiliary tank in my 85 4 Runner for 8 years now and in my 64 Chevelle Marvel Mystery oil on every fill up...which is suppose to clean pretty much valves, combustion chamber and any where fuel goes...I also use Lucas Ethanol fuel conditioner with stabilizer and have for ever too!!! These older engines really don't like the ethanol on the "O" rings, seals and rubber components...I may be nuts for adding both but my engines have ran great! Put both in and get out on a road trip and run a couple of tanks through on the highway at a comfortable speed and let us know what happens. I'll still keep doing some research on the 2000 4 Runner V 6 and see if anything pops up and post it

 

I don't think it's a timing belt...that's a pretty decisive effect that would be universal on all cylinders. I know this is a last resort but I had a consistent vibration at 2500 rpm and for the life of me couldn't find it...I started thinking tail shaft bearings, transmission bearings and so on and so on...I took it to the guy who installed my 2 inch exhaust after I put on the LCE header and he found a loose starter bolt...WTF...he tightened it and the vibration was gone. Sometimes having another pair of eyes makes you see things more clearly...have you got a trusted mechanic to take a peek for a second opinion?

 

Wish it was just a starter bolt, but it’s clearly a misfire. Computer says it too.

 

Yep...I knew that it wasn't a starter bolt, I was hoping you had a trusted mechanical friend that could take a look for a second opinion and who could hear what you have. Sorry if it sounded like I suggested a starter bolt would fix your miss firing issue.

 

Haha no worries, I’m glad you weren’t suggesting that unfortunately I don’t have many mechanic friends around me here in Seattle to come take a look- a couple places I have called that we’re nice enough to listen to my problem just told me to buy a new engine...I’m just not that type of guy. Would rather fix something unless for certain it is toast, but good compression numbers are giving me hope that it’s not a lost cause yet. Thankful for online communities where we can all get our heads together!

 

Get the right plugs, dual electrode Densos or NGKs..
and swap the wires with NGK too. Everything else seems good. Its the simple stuff a lot of times...hope you get it figured out

 

I have both NGK wires and plugs installed, brand new.

 

Dual electrode?

..and are the coils oem? All these if not, can cause random misfires due to quality control. Just an idea for you.

 

Yep, dual electrode. Coils oem, even swapped to see if misfire would move and doesn’t. Did resistance readings on them anyways and they are in spec.

Misfire is steady, not random.

 

Also, bad coil would misfire the paired #3 cylinder, which has never thrown a misfire code.

 

Aaron...your doing your due diligence for sure and your right with an engine with that kind of compression your pretty solid...your going to find that one little thing (in my case the starter bolt) that you'll go...Oh Shit...and it will be fixed!!! Please let me know when that happens...I'm really curious...Amos

 

Thanks for the encouragement! Can’t wait for that Oh Shit moment haha. I’ll definitely keep you updated if I figure anything out.

 

If it's now steady, wouldn't that point to something like timing now?

 

You mean valve timing or ignition timing? My experience with valve timing is it never changes once it's off it stays off and doesn't improve until you take the timing gear off and re-align to the marks. Ignition timing if really advanced or retarded can cause funny firing issues but that too...it never changes until you re-adjust. OK...crazy thought...plug off your EGR valve and let me know what happens...

 

Head gasket