Help with misfire, not so simple

Hey everyone,

so I searched around quite a bit couldn’t really find an answer aside from the typical issues that would cause a misfire.

so a little bit of background I bought this 2010 Toyota tundra with 178K miles and a misfire. Codes P0300 P0305 p0304 and p0306.

The previous owner wasn’t really too knowledgeable on anything only thing he described to me was that his cats were cut off and stolen so he took the truck to the dealer and they had it for a couple months while they ordered a brand new OEM exhaust from the headers back including the cats from Japan. So I have a brand new OEM $6000 exhaust and a misfire

Misfire is primarily on cylinder five with 1056 misfires in 2 minutes of idling. Cylinder 4 has 220 and cylinder six has 74 and 140 on cylinder 7.

being at these are misfiring on both banks with the most happening on cylinder five I swapped spark plugs five and one no change (so not plugs). Them I swapped coil packs five and one also no change (not coil packs) and moved onto swapping injectors five and one and again no change, cylinder five was still misfiring.

I then cleared the codes and fired it up again to see how the other cylinders were comparing to cylinder five. The misfire on cylinder fire was evident within 30 seconds or so and the rest of the cylinders didn’t show much of a misfire, sometimes cylinder forward pop-up sometimes cylinder six would pop up sometimes cylinder seven would pop up and I would check the misfire counts and there was no pattern. When cylinder forward pop up along with cylinder five misfire accounts were dwarfed by the counts on cylinder five and seven and three had almost no misfires.
Clear the codes again and run it again to see what I get and again cylinder five is misfiring and cylinder seven would pop up as misfiring with cylinders three and six having almost no misfires.

next logical thing was to test compression and I got
180 on cylinder one
180 on cylinder three
165 on cylinder five
180 on cylinder seven

pressure on cylinder five is slightly lower but only 8% lower and I know the rule of thumb is 10% difference and less is okay. Still something to note though.

so with nothing really to point the finger out so far confidently I proceeded to doing some top and disassembly removing the valve covers to check for any cracked or broken springs as well as gaskets and the intake manifold to check for any cracks in the intake or bad gaskets/seals.

The only thing that stands out to me is an oil residue in the intake runners in the manifold, and cylinder five has much more than the rest of the cylinders, cylinder one for comparison looks great without any oil residue.

Aside from that everything looks good except for some varnish from oil but that’s about it.

anyone have any pointers or direction to help tackle this?

what is something all cylinders share that primarily affect cylinder five that would cause it to misfire mostly on the middle cylinders?
I’m pretty stumped, and don’t wanna pay Toyota $580 just to diagnose it

 

I don't know much technical expertise, but any chance the valve is bent?? I mean if you can probe the cylinder from the top with a borescope to inspect for any water damage or other type damage.. I got one from Amazon like 2 years ago for like $30...

 

Valves could be issue but you likely would hear something odd. Have you looked inside the cylinders? Did the plugs look OK?
Have you checked all your wiring? Months sitting in the dealer lot means alot of time for rodents to feast on your wiring. You know the dealer just parks it and doesn't even look at it until they have to.

Have you monitored fuel trims at all?

 

There is a chance of that, I checked the intake valves when I took the intake off and they look fine, I used my horoscope as well and everything inside the cylinders looked fine, carbon buildup but that’s it

 

Did you use oem plugs Toyota likes densos

 

I checked all my wiring nothing loose cut or broken, it all looks good.

i have monitored fuel trims but I’ll be honest i don’t know much about them or how to interpret them.

 

Generally anything under 10 correction for short and long trim should be perfect. You could probably go a little higher but I'd be worried if your approaching 15.

 

Yeah I moved the oem plugs around to try and chase the misfire instead of replacing plugs needlessly

 

so that’s for short term under 10 up to 15. Ok so my freeze frame For misfire on 5 is 0% short term on both banks
Long term is 15.62% bank 1 and 7.81 bank 2

 

Bank 1 is were most of your misfires are right?
What spark plugs were in the truck and what did you put in?

 

Also did you check O2 sensor function? Since cats were stolen maybe they messed up the sensors or they got fouled somehow

 

Bank 1 cylinder 5 has the most with additional misfires on 4,6,7 occasionally.

so bank 2 has more culminates misfiring but bank 1 has the most misfires with cylinder 5.

spark plugs from the truck stayed in the truck. I didn’t replace any with new parts I just moved them around. So spark plug 1 went into cylinder 5 and vise versa. Yet issue remains at cylinder 5

 

I did check them The o2s downstream are brand new oem as part of the new exhaust.
The sensors upstream were untouched and still a bit old.

 

This really is a tough one

 

Yeah I’m hoping someone who knows the 4.6s well can chime in and point the finger somewhere. I can’t think of much else aside from head gasket starting to potentially fail.

It’s gotta be something that all cylinders shares and cylinder 5 just happens to be most susceptible to

 

Maybe timing? You did state the cam tower leak was resealed... What are the chances that timing chain jumped a tooth, or timing wasn't set correctly... I would assume a borescope inspection would show signs of a head gasket issue.

 

Cam tower leak? I don’t recall anything about a cam tower.

 

my bad, was reading another thread and must have clicked on the wrong one.. sorry.

 

Could it possibly be a voltage issue related to the battery going bad after sitting on the dealer lot for so long awaiting repairs and/or an aging alternator?

 

Intake gasket leak

 

Did you toss a dab of oil in 5 and test compression again? If it increased, points to rings. If it's the same look at top end via leak down test.

 

I would think this would affect compression if it was bad enough to cause a misfire?

 

Something is “ leaking” compression just a bit.

intake gasket, warped gasket surface,slightly bent valve, slight compression ring leakage, slight sealing issue with valve seat, slight head gasket leak at combustion chamber.

could even be a slightly flat cam not opening up all the way.

like you said up thread— this would be real fun to diagnose.

in reality I’d be doing leak down testing

 

At this point it might be the only thing left to try

 

I'm a little surprised we got to rippin-n-tearin before doing a leakdown (to be perfectly honest), but good for the OP gettin after it.

 

Just another update. I took the valve covers off and inspected the exhaust valves. I noticed that the exhaust valve for cylinder five one of them has a broken spring and missing rocker arm.
So lucky me I have a truck that fell victim to spring failure.

 

I have a leakdown tester but haven’t used it yet. My compressor is hot garbage and I don’t wanna drop some good change on one to use my leakdown tester. Had I maybe I would have heard the leak out of the exhaust and saved time.

 

Nice work. Broken valve spring is likely keeping valve from not sealing perfectly and this the low-ish compression.

 

Yeah I am. I considered it but I need this thing up and running quickly and can replace this spring without touching the cams or timing.
So I’m going to replace just this one and see if that solves all my problems and then order the rest for a full tear down. No use in buying the whole set if other things could still potentially be a problem.

 

Got the new spring in using a method I found in here involving zip ties and a heat gun (worked great after keepers were lined up).

gotta wait on a valve stem cap now as I found the rocker next to the spring but the valve stem cap is nowhere to be found. I scoped the oil drains and no sight of it. I already drained the oil a week ago and didn’t notice any metal in it or the cap.

I may drain the fresh unrun oil and pull off the pan to see if it’s in there and remove it. I’ll report back after I have it all together if this solves my misfire. I hope it does. Im eager to fill the tank at $6.40 a gallon….