P0301 - Stumped as to cause 5VZ-FE

Thanks for the info! I'll have to check that out.

 

Just got this same code. Strange thing is I lost my tunes for about a second and my Ultragauge alarm went off w/ a P0301 code. My truck purrs like a kitten. No CEL just the Ultragauge alarm (not sure if my Ultragauge is clearing the CEL?) I did put in some stuff in my coolant reservoir that helps loosen up any extra gunk because I'm getting ready for a flush. I hope that didn't eat away any gaskets!

Update: now CEL is showing.

 

I've switched out coil packs and spark plugs but still throwing the p0301 code. if I want to check if it's the wire do I just switch it out with another wire as long as it corresponds to the other cylinder it supposed to be plugged into ? Green to green red to red...



Update-switched out wires...no Bueno... Still threw the code. on to switching fuel injectors

 

Damn, that sucks brother. Keep us posted. Check the plus itself as well
Edit: nevermind just saw you checked the plugs

 

I'm thinking that it may end up an electrical issue. I was driving and lost my tunes for a full second and then three seconds later my Ultragauge detected the code. Hoping it's not the harness or ecm because I'm at a loss w/electrical.

My apologies for jacking thread.

 

I only got a p0303 due to a vacuum leak. Hasn't come back. Good luck OP.

 

So this misfire is still occuring, and now I'm also getting a misfire code for cylinder 1 and cylinder 2, with a random misfire code too. Thought it was weird that both front cylinders are now throwing codes (V6). Does this help with diagnosis? Been going on two years.

 

Mine is still throwing the P0301 code too, for a couple years now. I've changed the plugs, wires and coils....even checked the compression in cylinder 1. I'm taking it to the stealership tomorrow because I can't pass smog test with the CEL on. I used to be able to clear the code and get enough data on the computer to pass smog, but now the CEL pops before i can get enough data.

I have a feeling it's a clogged fuel injector.

 

Wow man it seems like you covered all the bases. On high mileage 3.4s a single cylinder misfire, I usually like to point to fuel injectors. They fail. But I see you've swapped them around. Cylinder 1 and 2 both share a coil pack, what would it hurt to swap those around again?? Other than that, man I don't know. Are you LTFTs in check?

Random misfire would indicate a loose ground, maybe. Check your ground at the upper plenum. That's the main ECU ground. Check the ground on the back of the firewall (firewall to block). The ignitors rarely if ever fail, and it grounds through the upper plenum ground mount.

ECUs rarely if ever fail, but you're running out of tests.

 

You know what just occured to me... with your engine running, look down at your crank balancer and see if there's any movement other than perfectly smooth. If you did a timing belt, and didn't get the bolt torqued down properly the crank pulley can walk and get your crank position sensor reading funny. It's a vital ecu feedback. Even if you don't notice any wobbling of the crank pulley, go ahead and torque it again to make sure it's not come out.

 

Curious what the outcome was for both OP and Camps. I'm having a similar issue - Recurring PO301 as well as random/multiple misfire code, but never feel any misfire.

 

I havent found out how Toyota actually calculates a misfire. Different manufacturers use different methods and sometimes they use 2 different methods on the same motor. It has been a number of years since I reserached this so I might be off on the theory... In general, the PCM is looking for signals from the tone ring on the crankshaft, the camshaft and the knock sensors on when to fire the coil. As the crank and cam rotate a sine wave is generated and if the peak of the sine waves are not where the PCM are expected to be withing a few milliseconds and this happens say 500 times, the CEL is illuminated. Again, I want to stress that I do not know if the P0301 on this year Tacomas fault is generated via a combination of cam/crank other sensors so I dont want to send you down a rabbit hole. My gut is telling me that the tone ring on the crank might have some crap on it... I came to this diagnosis because you have done everything else. The other WAG, (wild ass guess) is that there is too much play in the cam belt/cam gears IF the cam sensor is used as part of the misfire protocol. I have even seen where an aftermarket cam gears protrusion for the cam sensor is off enough to trip a code...

I will think about this off and on and post any addional thoughts.

if your scanner shows freeze frame data I would look at and record what was happening at that moment, clear the codes and run it until it pops again and do a comparison, there might be nothing there different or ?

I remembered this... http://alflash.com.ua/OBDII/PIDs.pdf. It explains some things but never enough.

The only 2 other things that I can think of at this time are to run a leak down test, yeah, pain in the ass and the second is to check if there is a weak or broken valve spring