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ok, so I have a lot of shacking or rumbling going on, and it gets worse when I put the truck into gear. Also once every couple of days my number 3 cylinder just stops working. So I pull over, turn the truck off then on again and then its back to the rumble as I described before. My code reader is reading P0303 (misfire #3 ). I have changed spark plugs, fuel injectors, switched coils, cleaned MAF sensor, and nothing has changed. I can't figure out what I'm doing that makes the number 3 to stop firing. Any ideas?

2007 Fj
86,000 miles
 

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If the tune up was done because of misfire on cyl 3 and changing coil didn't change miss location it may be a wiring problem. If the miss began after the tune up maybe you have a bad spark plug. Did you try moving the plug?
 

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Discussion Starter #3
I did switch the sparks around and nothing changed. I recently checked the plug and it looks good to me.
 

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There are only a limited number of potential causes for a consistent problem with cylinder #3 . You didn't mention any loss of coolant that could indicate a head gasket problem, right?

So, the primary suspects are:

1. Intermittent electrical problem with the #3 ignition coil. However, you indicate that you swapped ignition coils, and the problem did not follow the coil from cylinder #3 , so it's unlikely its the ignition coil.

2. Intermittent problem (electrical or mechanical) with the #3 fuel injector. However, you indicate that you swapped fuel injectors, and the problem did not follow the injector from cylinder #3 , so it's unlikely its the fuel injector.

3. Wiring harness or connector problem with the wiring for either the ignition coil or fuel injector for cylinder #3 . You're going to have to very carefully inspect the pins in the ignition coil and fuel injector connectors for corrosion or physical damage, as well as every inch of the wiring harness in the engine bay for any insulation damage, etc.

4. The driver transistors for both the ignition coils and the fuel injectors are integral with the engine ECM. Mate and de-mate all the electrical connectors at the ECM, looking for corrosion, physically damaged pins, wiring damage at the connector pins, etc. There is a remote chance that there is an intermittent electrical fault in the ECM.

5. Equally unlikely is a sticking valve in cylinder #3 . Next time it's "missing", as quickly as possible pull the #3 spark plug and take a compression reading on cylinder #3 . Then, take compression readings in at least two other cylinders to see what a "normal" compression pressure is for your particular engine. If cylinder #3 is significantly lower, you've got a more serious problem.
 

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great info FJtest as always, OP have you changed the plug wires out and got new ones?
Like most modern Toyota engines, the FJ's 1GR-FE uses a "coil-on-plug" ignition system, so there is no distributor or HV spark plug wires.

Each cylinder has its own dedicated ignition coil, mounted directly on the valve cover over each spark plug. Being an overhead cam engine, there is a long "reach" from the valve cover down to where the spark plug is, so Toyota makes these ignition coils long and skinny to fit down in the spark plug access hole.

The low-voltage wiring to each ignition coil can still get insulation damage from rodents, getting pinched during service, etc. but is nowhere as vulnerable as the old HV ignition wiring was.
 

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did u ever find the cause of your misfire? i ask because i have a similar issue but too add a bit if mystery to it.. my misfire is random. the code comes up relatively regularly now.. but the rough idle an actual misfire is random.. I've also put new plugs, new coils, swapped injectors, even swapped new coil & plug location. still shows misfire on cylinder 1 (P0301) but here's the twist.. if i cycle the ignition off/on.. the misfire goes away.. (most of the time) i just drove to Dallas for Thanksgiving ( i live in Orlando) an i noticed that the rough idle/ misfiring persisted until the engine warmed up to operating temp.. then if i cycled the ignition it would go away... spoken to 3 techs they all think its electrical.. I'll be checking compression soon.. as we'll have cooler temps soon.. (obviously i couldn't before as if i cycled the ign it would go away.. but now knowing the colder temp would make it persist i now can plan accordingly) any other ideas I'm at my whits end with this.. i love my fj so its a keeper..
 

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did u ever find the cause of your misfire? i ask because i have a similar issue but too add a bit if mystery to it.. my misfire is random. the code comes up relatively regularly now.. but the rough idle an actual misfire is random.. I've also put new plugs, new coils, swapped injectors, even swapped new coil & plug location. still shows misfire on cylinder 1 (P0301) but here's the twist.. if i cycle the ignition off/on.. the misfire goes away.. (most of the time) i just drove to Dallas for Thanksgiving ( i live in Orlando) an i noticed that the rough idle/ misfiring persisted until the engine warmed up to operating temp.. then if i cycled the ignition it would go away... spoken to 3 techs they all think its electrical.. I'll be checking compression soon.. as we'll have cooler temps soon.. (obviously i couldn't before as if i cycled the ign it would go away.. but now knowing the colder temp would make it persist i now can plan accordingly) any other ideas I'm at my whits end with this.. i love my fj so its a keeper..
Check each wire for damage.... rodents, etc.
 

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Check each wire for damage.... rodents, etc.[/QUOTE]


I've done a quick glance.. but so far all seems ok... put on a test light... injector is seeing power... will check ign coil too. compression test set for sat. that will tell the tale (hopefully)
 

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so we did a "warm engine" compression test.. with no results cyls 1,3,5 all measured about 150.. now i have to wait until i get the p0301 code & the actual misfire/ rumble to check it again..an its completely random.. the only time it consistently occurred was during the colder temps in dallas...
 

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so cold compression test yielded no results (other than to ease my mind about compression/valve issues) all cylinders are the same.. so back to square 1.. since we're having a cold spell the misfires are more frequent.. but as of yet no solutions in site... pcm swap may be in my future. we've also slightly adjusted idle to no avail..
 

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update.. my buddy suggested buying a camera to scope out the cylinder area. low an behold i found oil on the bottom of the spark plug well. on the spark plug threads not too mention the piston head looked damp & pitted. I'm dropping it off on the 25th to see where the problem lies. the upside is i still have a yr on my warranty.. but FINALLY a solution seems to be close at hand...
 

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FINALLY FOUND the problem.. there was a leak on the intake valve of cylinder 1.. (which has since migrated to cylinder 5). I've spoken to the warranty company. They asked for pics inside the cylinders (found damage in cyl 1) . So they have since sent me a new long block.. Which we swapped out yesterday, truck idles & runs even better than b4... I'll post an update after the break in period...
 
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