Sudden Misfire Condition

2006 4.0 with 285,000 miles and never had any issues until sudden condition on Highway today. Noticed a vibration and then noticed some power loss. Looked down and saw CEL continuously flashing. Pulled over and noticed idle was a little rough. Drove home about 5 miles and noticed that truck would only rev to 4000 ish RPM under a load. At lower RPM or initial load, engine bogs, but then seems to spin up freely to around 4K and then hits a wall. Maybe limp mode???

Connected code reader when I got home and it came back with "No Codes" but CEL was still flashing.

Cycle ignition power a couple times and after a few power cycles, it finally pulled 3 codes, 0305 (cylinder 5 misfire) and 0420/0430 (both banks catalytic operating below efficiency). Strange if only cylinder 5 has misfire. So I cleared the codes and went for a quick drive. This time, as soon as I put it in gear, the idle became seriously rough but would smooth out at light throttle. Flashing CEL came back immediately but not pulling any codes.

Pulled air filter and found a literal rats nest on the dirty side of filter. Hopeful, I started with no filter but same condition.

Pulled Cyl 5 plug and it was well worn with large gap. Replaced all 6 plugs, but now when I start, it goes to immediate super rough idle. In neutral, I'm able to rev up and engine smooths out until returning to idle. Also very rough when I put it in gear and only able to limp the truck to drive. Flashing CEL hasn't returned and no codes avail.

At this point, I don't know if I can trust the original cyl 5 misfire code because no codes are generating.

The fact that it came on so suddenly, makes me think it might be one of the coil packs, or injector that stopped working.

Tomorrow after work, I plan to do some searching for possible vacuum leak(s), but other than that I'm a little lost other than randomly replacing parts.

Any suggestions on proceeding with troubleshooting. Struggling since codes don't seem to be repeating and I'm a little paranoid to keep running it to produce codes if I'm dumping raw fuel into the Cats. That said, I'm not smelling strong fuel in the exhaust...

Every time I start the engine, the initial idle is becoming rougher and closer to sounding like it will die, but in neutral will rev up super smooth and then rough at idle or under any load.

Thanks for any suggestions or guidance. I understand the flashing CEL indicates misfire condition but even my code reader is not registering misfire detection while monitoring PIDs

 

How is your coolant level?
What does the under side of your oil filler cap look like?
What does the dipstick look like?

this is sounding like a potential head gasket.

what MM/YYYY code is on your sticker on the driver door frame?

 

https://www.tacomaworld.com/threads/05-06-tacoma-head-gasket-failure-poll.595994/

 

Swap coils on #5

 

Did you check the coil boots for carbon tracking or burned spots while you had them out?
You can swap the coil to a different cylinder and see if the misfire follows it.
A scan tool that can read live misfires would be very useful here instead of relying on codes to set.

 

No signs of coolant in the oil or oil in the coolant. Coolant level is a little low because I've never replaced it or added. It is still bright clear pink.

Oil is clear on dipstick, under filler cap and when I look down the filler spout, the timing chain is super clean.

Production date is 02/06.

 

Ill try swapping the coil. At the end of my thread I did say I was monitoring PIDs while it was running and the misfire count read 0. I did notice that 1 of the O2 sensors was reading ~3 volts while all the others were 0-1 volt.

 

Coming back to close this out. Thanks for the suggestions feedback. I found a function in my scanner that allowed monitoring misfires by cylinder, rather than just all misfires.

Cylinder 3 had 300+ misfires so I moved that coil pack to cylinder 1. Restarted and saw high number of misfires on cyl 1. Replaces coil pack with a Denso unit and driveability issue has been resolved.

One strange thing is that now Cyl 1(where I installed the new coil) is reporting 15-20 misfires. Much less than the 300, but should I be concerned about a repeating low count? I had already done plugs before the coil pack.

Maybe injector is dirty/weak? Truck has 285,000 miles and I've never used any fuel system cleaner during its life???

Also, where can I find data showing expected/normal values for PIDs? Things like MAF and O2 Sensor values for this vehicle. I'm

 

Swap coil to another cylinder. Rescan

 

A low count can be normal. If it's running smooth and the cel isn't flashing don't worry

Sounds like you fixed it

You could also consider replacing the other 5 coils simply due to age

 

Been monitoring the Scanner and it looks like no misfires anymore but a new/old problem has come back to surface....

About 6 months ago, I got a P0420 code for Bank 1 Cat Efficiency. I cleared it and it eventually came back a few months later. After the recent issues with coil, it has shown up again, but now it's throwing it every 20-30 miles. I have been monitoring O2 Sensor voltages and it looks like both banks are reading almost exactly the same, so why am I not getting a code for both banks???? I'm assuming at almost 300K that my cats are plugged up, but not sure why only one bank is reporting an error. The only thing I can think of is a short in the O2 or wiring on that side that is intermittent...

When monitoring O2 temps, it does look like the inlet side O2 is reporting hotter than exit O2, but it's identical on both sides. This is also assuming that I'm reading the sensor descriptions correctly... I don't just want to blindly start replacing O2's or Cats. Can someone share typical temp and voltage reading I should be seeing on each specific O2?

Thanks,

 

Converters don't like raw fuel. The misfire condition may have been feeding raw fuel down the exhaust pipe resulting in converter damage.


You can watch O2 voltages and take temp readings but you're never going to be able to monitor the cats the way the pcm software does.



Check for any exhaust leaks at/near the oxygen sensors or the ex pipe connections. If there's no air leaks then it probably needs new cats

 

So, just replace both cats on that bank if no evidence of leaks...

 

Pretty much

Are the fuel trims stable while driving around?

 

They move when I accelerate and then stabilize at constant RPM.

But, I've been doing some reading and studying about monitoring engine data and I keep seeing this reference to open vs. closed loop. To my understanding from recent reading, the fuel system should only be in open loop while the engine is cold/start up condition. I have seen on my truck, while driving, it toggle back and forth between open and closed loop. Is this a concern?

 

Sorry, by stable I mean they're under 10% for the most part

 

I'll log some data and take a look at it.

Unfortunately converter replacement means big dollar for as I'm in California. But to be honest, I'd be surprised if the smog techs are looking for evidence that my Cats are California approved.

 

Usually as long as the CEL isn't on you should be fine

 

CEL keeps coming back every 30-40 miles.

 

I mean if you put in good converters that will work properly and don't code then you should be fine