If you swap #4 with say #2 will the code follow?
What brand and source of coils?
Check all your grounds.

 

I have swapped coils and fuel injectors and the codes did not follow. Still the p304. The coils I bought are: DENSO # 6731309 and I ended up replacing all six as they were the originals. I did label my original coils so I know where each one went. I am taking the car back to the dealer and running a full diagnostic as my handheld scanner just does not tell me enough. So another $198. All I can do is laugh now, otherwise I would go crazy lol. I am hoping it is just a ground but I don't see any loose connections or broken wires. The car in park sounds like a new engine, under load it sputters and throws the P304.

 

What really is stumping me is why I am able to disconnect the coil and injector at the 4 cylinder and no sputter. I do the same on any other cylinder and it stutters. Just wild.

 

That makes me wonder if #4 is firing at all?

 

Well will keep you updated. Took it to local Toyota dealer this morning for full diagnostic. I have had a buddy help me who is a retired Toyota mechanic and he is stumped as well. We took the engine apart and everything inside looked clean with no burn marks. We are hoping it is something electrical. Don't think it is a dead cylinder as all the cylinders compression wise are within specs and we did a leak test and could not find any leaks. We had the computer tested last week and it checked out fine. This all started because my serpentine belt tensioner went bad. My buddy accidently took out the bolt that held the oil cooler line in and we saw it had a heli-coil installed. I know the part was a factory recall and the dealer must have stripped the bolt out when doing the recall repair. I know I did not do it as getting to it required removing the alternator, dropping the A/C and disconnecting the radiator. But the repair was done so long ago I can not prove the dealer did it so I was stuck. I was not mad at the time as the car has had a small oil leak that I never could figure out and was glad that I finally found it. We initially tried just JB weld to fix the leak but no luck. Oil was now gushing out. Well when we took it apart again we saw the head had a crack in it at the inlet for the oil cooler line where the banjo bolt went in. So I had no choice but to do a top end job and replace the heads with used ones. They were redone at a local machine shop. The car prior to all this had no issues and no check engine lights. So thus far I have put in new used heads, timing chain (chain, guides and tensioner), new water pump, new coils, new plugs, new fuel pump.

 

Also, I am the original owner of the car and it has only 170k miles on it. I don't think it is that bad for a 15 year old car. I have always done the routine maintenance at the scheduled intervals. The car has been a great car with only minor issues up until this.

 

Dealer stumped. They stated that it may be a faulty ECM or poor grounds. They did compression, fuel and leak test. Just seems I am throwing money away at this point.

 

There's 3 ECM p/n's with the info you mentioned based on production date. You can check for yours below.
They're inexpensive either via ebay or a local salvage yard. Car-part.com shows a decent selection of used ones at yards near you. Odd that in the 1st post the dealer said it was good but now since they don't have an answer it could be bad? Still doesn't explain why it seems to run smoothly when you intentionally take that cylinder out of action.

ToyoDIY.com

 

I fully agree. To me none of this make sense. One dealer said ECM checked out and now a dealer closer to home says bad ECM. But a bad ECM kind of makes sense as at rest car runs like new. Under load, P304 code. But what no one can figure out is why it runs smoothly when the 4th cylinder is manually taken out. All other cylinders, engine bogs down. I just want to figure this out so I can have my car back LOL.

 

Do you have access to a scanner that shows live data?
A used ECM that even has a 30 day warranty is well under an hour of labor and shouldn't be to hard to swap in and out.

 

Yeah I am just looking for a used ecm now. I do have a scanner with live data.
Figured what the heck, what's another 100 grrr.

 

FWIW, there small and light enough to be easily shipped so you can locate exactly what you need and one with a guarantee. What is crazy, if it clears the code does that mean it would sputter if you take that cylinder offline intentionally with a different ECM?

 

Ill keep you updated. This is just totally weird and it is baffling my friend who is a master mechanic and also the dealership.

 

You need 3 things for a proper combustion event. Air. Fuel. Spark. Assuming leak down and compression are ok which you mention are. When you disable fuel/spark to that cylinder and the engine doesn’t “stumble” this indicates to me that #4 isn’t even firing. Has anyone pulled the front valve cover and spun the engine by hand to ensure all 4 valves are operating properly on #4? You can have all the compression in the world but if the valves aren’t opening, it won’t fire. Has anyone verified if the fuel injector is actually firing on number 4? Has anyone physically checked spark on #4 coil? Considering you had This thing torn down to the short block you could very well have a broken wire somewhere in the ignition coil or fuel injector circuit. Crack open a schematic and start testing. Disconnect #4 coil and the PCM connector. Find out what pin locations are in the pcm connector for #4 coil and ohm each wire out to check for continuity. Do the same for #4 injector. If everything is ok mechanically (compression, leakdown, valve operation) and wiring tests OK, start looking at the PCM.


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You need 3 things for a proper combustion event. Air. Fuel. Spark. Assuming leak down and compression are ok which you mention are. When you disable fuel/spark to that cylinder and the engine doesn’t “stumble” this indicates to me that #4 isn’t even firing. Has anyone pulled the front valve cover and spun the engine by hand to ensure all 4 valves are operating properly on #4? You can have all the compression in the world but if the valves aren’t opening, it won’t fire. Has anyone verified if the fuel injector is actually firing on number 4? Has anyone physically checked spark on #4 coil? Considering you had This thing torn down to the short block you could very well have a broken wire somewhere in the ignition coil or fuel injector circuit. Crack open a schematic and start testing. Disconnect #4 coil and the PCM connector. Find out what pin locations are in the pcm connector for #4 coil and ohm each wire out to check for continuity. Do the same for #4 injector. If everything is ok mechanically (compression, leakdown, valve operation) and wiring tests OK, start looking at the PCM.


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I actually showed my buddy who is working on the car this thread. He stated that he did everything mentioned. He actually took it back to Toyota today to have them re-look at the car. They still have no idea why it is throwing the P304. Every suggestion that they made, we have done. I just wasted another $180 on a full diagnostic but I was told that my ECM is running fine and that my grounds are good. They said I have spark at the 4 cylinder, I have good fuel pressure and my injectors are firing. Compression is all within the top range of specs. We have done a diode check before on the injectors. We have checked all grounds and manually checked the engine wiring with an Ohmmeter. My last ditch effort before I get rid of the car is we are going to pull everything out and we are going to inspect the lifters on the effected bank. Maybe they are too soft as my buddy is saying. No idea what that means. He feels that maybe the machine shop did a shoddy job in the rebuild. So another day of tearing it down tomorrow. This is tear down number 3 so at least we can do it fast now and just take a few hours. All I can do is laugh, well I could cry as this is frustrating the heck out of me LOL.

 

We are also looking at the O2 sensors for Bank 2 as that is where the #4 cylinder is. I saw on some other posts online (on Tacomas, range rovers and various other cars) that a faulty sensor could throw a misfire code. At this point nothing would surprise me. The downstream sensor is cheap, the upstream sensor is pricey. I also know that they are the original sensors.

 

Woo hoo finally fixed. A lifter was stuck throwing the p304 code. Ended up changing all of em, figured why not as I had the head off and just changed the other side so they matched. So this job went from a serpentine belt squeeking, taking off the tensioner, taking off the oil cooler line by mistake, finding reason for an old oil leak, seeing dealer during recall over tightening banjo bolt and cracking head and cheated a fix by installing a heli coil. Can't prove it as recall done in 2010. Having to replace heads as a result and then chase a p304 code. A total nightmare.

 

Oh yeah, used a voltmeter and tested the oxygen sensors, they are good.

 

Good job for hangin in there. I did not see that one coming.

 

Yeah buddy stated that the lifters were soft (sticking maybe?). Got them at Rock auto and they were $11.00 each. This entire job has been a nightmare. Had the car scanned twice at the dealer and they had no idea what was wrong with it. I guess it just took some old fashioned know how to do this fix. My buddy laughed and stated that the dealer mechanics rely on the computers too much and do not know how to to actually fix cars. He is a retired master tech. He called them "part swappers" LOL. On this one I have to agree with him. They did a scan, made suggestions and ended with a maybe you need to do a full overhaul after he told them what he had done to the engine.

 

I know a lot of those "part swappers", being paid flat rate doesn't provide any incentive to diagnose anything based on experience anymore.