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Misfires in cylinders 6 and 7

8K views 17 replies 7 participants last post by  2010TundraVA 
#1 ·
Hi all,

On the commute this morning, truck started running rough at cruise and worse at idle. I had it towed home, and the CEL codes were P0300, P0306, P0307. I swapped plugs and coil packs on both, and no luck. It does seem to start and run fine for about 10-15 seconds, but then it starts running like crap. Any ideas on what to check next? It's 2008 5.7L Crewmax with 170k miles.
 
#3 ·
Start with the simple stuff, clean your MAF sensor, pull the spark plugs and inspect them, how do the plugs look on the affected cylinders compared to the ones not throwing a code?, engine air filter, etc... I have seen some people on here have issues with the wiring to the knock sensors from years of heat degradation. Being that all this has come up all of a sudden, I would tend to lean towards something all the cylinders have in common.
 
#7 ·
Misfire detection on this engine is done indirectly by measuring the speed of the crankshaft after each firing pulse to see if it speeds up or slows down.
This method is often prone to setting codes on cylinders that don't actually have a problem.
I have seen it where there is a problem with only one cylinder, but it will show misfire on all 8 or a random number of cylinders etc.
 
#11 ·
What caused the issue? Dropped a couple of valves, timing chain jump or what?
 
#15 ·
well she is finally back on the road. I ended up buying a reman long block from Fraser Engines for 5900 shipped. 2kish to swap it in, and my 10 year old tundra should be good for another 10. I definitely wasnt keen on spending that much, but it sure beats buying a new one for 50k.
 
#18 ·
I brought my truck in for a maintenance lights. Changed the O2 sensors, but while I was there, I did a tune up on my 2010 Toyota Tundra 5.7 liter V8 with a generic mechanic. I only had 100,000 miles, but figured it would help my truck continue to run smooth for the next 100,000 miles. The tune up included replacing all the spark plugs and all 8 coils. Within 3 weeks my truck started to misfire. I brought it back to the mechanic 2 times and they said the computer was not reading anything wrong. I brought it to the toyota dealership and had their mechanics look at it, and they said their computer could not find anything. I told them I did not have a problem until the tune up was done. The toyota dealership hooked it up to another computer. I guess this other computer is more in depth on its tests and it found 2 cracked coils. Replaced the 2 coils and the misfiring was gone. My truck was running good again. Fast forward 2 months and my truck is misfiring again. Bring it back to Toyota Dealership and they found another 2 broken coils. This time I replaced the other 6 coils that the non Toyota mechanic put in and my truck is running strong and smooth again.

The diagnosis according to my Toyota Service Rep.: The brand new coils that my generic mechanic put in were most likely not up to Toyota Specs. The coil specs from Toyota had changed from the time the original coils were made. He said that the original coil specs had a tendency to overheat and crack. The new coil specs are built with a heat shield to keep them from getting too hot and cracking. I have had my truck for 2 weeks now after all the coils have been changed out and all seems to be good. Be sure that if you change your coils that you make sure they are from Toyota and that they have the heat shield built in. I think my generic mechanic used Non Toyota Over the Counter Parts that met the original coil specs but not the updated specs with the heat shield.

Hopefully this is the end of my misfires, but so far, so good!
 
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