Experts, teach us about misfires

Over the last couple of months I have made tremendous progress with my truck and aside from the normal complaints of low end torque, etc., the only thing that's still bothering me are misfires. It seems many people experience the "slight miss" feeling in the 3rd gens but no one has been able to get to a root cause. Logging data, I generally see 1-3 misfires on any given trip even though my truck runs generally pretty well otherwise (after CKP replacement, MAF cleaning, tranny fill, TSB, u-joint grease, torquing a bunch of stuff that wasn't assembled properly, etc.,). The misfires are not cylinder-specific and appear at random.

In review of the service manual, what I can't understand is why Toyota would consider a misfire count of 0-35 "normal." I've learned a lot on here, but for the life of me can't understand how/why/if this truck would have been designed with the expectation of minor misfires. Is it an expected function of the faux-Atkinson Cycle and occasionally it can't fire properly due to the vapor its supposedly re-igniting? I'm grasping, but I'd be willing to wager that most folks that do experience the "slight miss" feeling are indeed recording misfires, but unless it does it hundreds of cycles it would appear the truck is not programmed to throw any codes.

Help me understand the logic behind potential, intentional misfires in a modern truck? Should we be concerned about long-term effects of this behavior on the engine even if it only happens 1-3 times per trip?

Facts from experts welcomed and requested, not for this to become a 3rd gen hater thread. Trying to learn. That is all

 

Am I moron? Misfire, maybe I have yet to pay close attention, but I don't recall ever having a misfire

 

I log random misfires on pretty much any engine. You have to understand a bit more about how the engineers program the vehicles. Not just for power but for emissions.

Under normal situations the engine is trying to advance the timing well over 30 degrees trying to get the most energy from the fuel. This alone means the engine is monitoring what it can get away with, sometimes may tickle the misfire counter.

Poor fuel quality, a shift that retarded timing too much etc can cause a "misfire" but it takes a lot for P0300 to set.

I believe the 0-35 normal rate is actually determined by the standards in OBD2 vehicles, not Toyota specifically.

 

Once upon a time, misfire meant a serious problem - you could feel it, you'd be severely down on power, and you'd get a CEL. Ignition timing was relatively static, valve timing was static, AFR was a relatively broad estimate, compensation for knock was very rudimentary. If you used the wrong octane or forced the ECU to suddenly adapt to a drastic change in air density, you might have serious problems.

Modern ECUs and knock sensors are extremely sensitive and are getting more-so with every revision. Because of the newfound sensitivity and adjustability, modern engines can adapt to a broad range of environments and are constantly adjusting, looking for the ideal parameters. It will happily adapt to changes in octane, ethanol content, air density, and do so very quickly before any damage is done. Meanwhile the basic process of combustion is relatively archaic and uncontrolled. So, combustion is often not absolutely ideal. By the ECU's standards, anything less than an ideal combustion is considered a misfire and is cause for an adjustment in ignition or valve timing and/or AFR.

In short, nothing to be concerned about. If it was a misfire by the old definition - bad enough for you to feel it and for it to potentially cause damage - you'd be seeing a CEL.

 

This makes a lot of sense to me. I for some time was concerned my misfires I record in the OBD data were a symptom of all of the other issues I was having but once I got those knocked out and the truck feels like it's running well, the misfires (which perhaps a bit less common) are still there. But when I do have a misfire or 3 recorded, it does indeed seem to correct and they go away. I tend to see it more on acceleration after it's been sitting for a few hours than any other time. Definitely not a fuel quality issue - I've gone through lots of tests and I now exclusively use a very busy, new BP station (top tier) station that my truck seems to "like" subjectively anyway.

This is what I was hoping to hear though and it makes sense - it's testing the boundaries and then course correcting, most likely. I don't like (as many others have noted) the "feeling" of a slight miss when you accelerate but it's not as bad as it used to be.

 

Indeed the 0-35 was in the Toyota manual itself but I could see how that would be a standard in OBD2 vehicles. And yes - it only seems to tickle the misfire counter. was more concerned that I'm doing long-term damage if this happens consistently and from your assessment that seems unlikely.

 

In my case, it doesn't feel like a misfire in my old Datsun used to have. The loud banging misfire shudder, its not audible at all, just feels like a momentary lapse in power delivery that quickly returns. And in some cases I will log a misfire and not feel anything at all. most times I can feel at least a little shudder. reminds me somewhat of the shudders in some of the original (and maybe even current) CVTs

 

Likely it's your AC compressor kicking on you are feeling. Try turning your climate control stuff to off and see if you get it.

 

Getting my truck properly inspected has, unfortunately led me to teach myself how to do it with the help of this forum and the inter webs after many failed trips to my dealership. I would be a very unhappy owner if I had to rely on Toyota's inspection but I still may have another mechanic take a look. I do wonder about the driveshaft for sure. For example, my transfer case had a cable (not sure which, honestly) that was rattling against it and I found this to be the primary source of my gas pedal vibes. I didn't do anything to diagnose the transfer case itself honestly, but I did secure the cable to the cab and my vibes reduced. Thanks for the input - greatly appreciated.

 

I believe I've recorded this both ways, but it's summer in the south as you know... so no A/C is a rarity. I'll do a test run and see if it happens w/o A/C on and confirm though.

 

My truck does this, normal.

 

Funny this thread popped up today as I noticed this misfire counter in my scan tool yesterday. I reviewed the log and nothing was recorded, but if it happens under 35 times in the 1k revolutions/ cyl, it just clears itself? I haven't looked into the manual about this area of "normal" operation at all.

 

I notice the A/C compressor cycle only at idle. Never do I ever feel it cycle off at speed.

 

I can feel mine engage when the truck is moving.

 

Slipping, stumbling, stuttering... All great adjectives to describe it. This truck needs a helmet and a pass for the short bus.

I feel it. It feels like a tranny slipping to me. I wouldn't be surprised if that's it. This tranny was run low on fluid for a while.

But it also feels like my old boxster did when it was misfiring because it needed new coil packs.

Could a differential cause this?

 

Detecting a misfire is an imperfect thing. They have to allow a tolerance for false positives. If you are feeling it, and it's not logging a misfire at that time, it's not a misfire.

 

What part(s) does the ecu use to monitor misfires? Just sayin'

 

Hmm, thanks for the info. I am not mechanic by any stretch, so I guess misfires happen in all engines?

 

No, if you are capturing logs you would still SEE it if its recording a misfire, but a few lines of data later it would then reset to zero