2004 Tacoma misfire on cylinder #1, replaced cracked exhaust valves ,misfire continues ...

Hey,
my 2004 Tacoma ( 350,000 km, 6 cylinder, 3.4 5VZ-FE) truck was sitting this spring for a bit while I had some work done on the frame.
Noticed a bit of a rough idle when I got it up and running again and engine light on.
Misfire on cylinder #1 engine code P0301.

-I took the advice from this forum (which was great and detailed) and replaced my sparkplugs and the high tension leads with OE manufactured parts from toyota.
-still getting the misfire, I switched the coils 1+3 and the error is still misfire on cylinder #1.
My guess is to inspect the fuel injectors next ?
Any advice or suggestions on how to go about that and any other things to check in addition ?

 

I am here for the same situation on cylinder 6 of my 2nd Gen. New coil, new plugs. Lets bump this up

 

I forgot to add that my misfire is very odd and I wonder if you noticed the same. When it is under load (gas pedal heavy acceleration) the shuddering and mis is far less if not gone. Is yours doing that? This more than anything pointed to fuel. Under load, it would seem that the pressure in the fuel system is greater and getting fuel into the cylinder. I have not proof this is right.... but seem legit.

 

Sounds like it might be the wiring harness.

 

My misfire on cylinder #1 seems to only be noticeable when at idle. The RPM's drop down to about 750 after about a minute and it gets a bit rough. At highway speeds it runs smoothly and without issue, there could be a loss of power but hard to tell. I put a bottle of fuel injector cleaner into a near empty tank and then cleared the codes. The engine light stayed off for about 50 miles but is now back on. I'm past due for a new timing belt which I'm getting replaced next week.... I'm not sure if that could be having an effect ?

 

Currently have the same exact problem on my 2001 v6 Tacoma with under 150k miles, except on cylinders #3 and #4. First thing I did was check the ignition coils as well as swap all the spark plugs. Cleared the codes, but they didn't go away, after some research I think it might be the fuel injectors, so i bought some and I'm going to replace them this Friday. Before I do that though I plan on swapping the fuel and air filter, running a can of seafoam through the gas tank next time I fill up, and cleaning the throttle body. If none of those work, then fuel injectors or maybe even the fuel pump need replaced !

 

I think realistically at 20 + years all that stuff just needs to be cleaned or replaced.

 

Yeah, probably didn’t help that the truck sat for 10 years before I got it

 

Hi again.
to follow up on where I'm at with the misfire on cylinder #1, having had no success with replacing the plugs, high tension leads, swapping the coils between #1 and #3. Also replaced the timing belt (water pump, etc.) as it was well over due (I think it was the original belt 350,000km).
I borrowed a cylinder compression tester and tested the cylinders.
Moment of truth....
Cylinders:
#1: 57
#2: 180
#3: 121
#4: 183
#5: 180
#6: 185
clearly there is a significant issue with #1 and also # 3 (its neighbour on the passengers side.
I then preformed a "wet" compression test by adding about a spoonful of oil to the #1 and #3 cylinders.
both cylinders tested basically the same ( maybe an increase of 1 or 2 lbs ? ). I gather that this rules out an issue with the pistons and rings.
I have ordered a cylinder leakdown compression tester kit to try and isolate the problem as what's left to consider my understanding is that it's the either the head gasket, cracked head or the valves.
Will update my results once I get this done !

 

I had the same issue and replacing the coil pack fixed it for me. The coil pack igniter could be suspect as well.

You are correct about the compression test - 1-2 lbs difference with the oil added is within the margin of error.

the 1 & 3 cylinders are troublesome - head gasket would be my guess. If you do pull the heads, have them serviced at a machine shop so you don't have to worry about it in the future.

Good luck!

 

Thanks Lost in GA !
Preformed a leak down test of cylinders #1 and #3, cylinder leakage was about 85% and 60% respectively. First I checked the radiator for bubbles or fluid rising and there was no sign of either ( preformed the test 3 times). Nothing at the oil cap or dip stick (wet down had already ruled out cylinders but checked anyway). Couldn't hear anything at the intake manifold ( hard to tell as there was hissing from the air going into the engine ? Next checked the tail pipe and I could definitely hear a hollow sounding air leak coming down to the end of the exhaust pipe.
I assume this means the loss of compression and misfire is due to a leak in the exhaust valve ?
Any thoughts ?
thanks again for all the input so far, it is much appreciated !!!

 

High odds of a burnt or valve not closing fully (carboned up?). Doesn't this model engine have a valve adjustment procedure?

 

I'm not sure, this was the last thing that I thought it might be and so far I haven't found much in the way of videos or info on this problem!
At present the truck seems to be running well other than a bit rough at idle.
At the moment the task of pulling the head and servicing it and the valves seems rather daunting ...

 

UPDATE !
So finally after many months I managed to get my truck in to a mechanic to remove the head and check if the leak-down test was correct in it’s indicating a leak in the exhaust valve.
Turns out it was correct. A good sized crack in the #1 cylinder ( the one with the misfire error code, po301 and only 57lbs compression). Cylinder #3 has a smaller crack ( 125lbs compression) all other four cylinders recorded 180lbs.
My recommendation to anyone with this situation, do a compression test before you start replacing plugs, high tension leads, etc. Then a leak-down if the compression test indicates an issue. I’m of course replacing all seals and gaskets in the process. Hopefully it will run another 350,000 k before I have To go back in there ( will try to attach a few photos of the head and valves to show how they looked)

 

Update: Misfire on cylinder #1 continues and engine is actually now running much worse....???

Took the Head to a machinist who honed the head and replaced all six exhaust valves ( #1 and #3 were cracked causing low compression and misfire in cylinder #1. Everything looked great.
My mechanic then reinstalled the head and now the engine is running very rough, engine light is flashing and still getting a misfire on cylinder#1. Plugs, high-tension leads were replaced (Toyota parts) just a few months ago, mechanic says he tried swapping the coil but with no change in symptoms. Mechanic says the timing is correct and is looking to replace the plugs on cylinder #1 and #3 and also the coil.... He seems to be scratching his head on this one
I had been driving with a 301 error code (misfire on cylinder #1) for several months but other than a decrease in power and the engine light on you probably wouldn't have noticed it, now it's running very rough, I assume I now have full compression on #1 and#3 but still a misfire.... any thoughts on what it might be would be greatly appreciated...

 

Maybe @Dm93 or @TnShooter has an idea

 

I think the first thing I would do is verify compression again, just because work was performed or a part was replaced doesn't mean it's good.

 

I agree with this.
Check this first.

 

Right, I had not thought of this and was assuming it was no longer the issue.... will get that done and report back, thanks very much for the advice !!!