Misfire cylinder 1

That's unfortunate as it is clear you've put lots of effort into this.
Do you notice the engine missing or other driveability problems?

What is the odometer reading?

If the odometer reading is high could it be that cyl. 1 has a wear problem - which an engine compression test would reveal? (Note that the Toyota diagnostic laptop is required to run such a test since MG1 normally spins the engine at 4x the speed compared to the starter motor of a traditional gas engine.)

The wiring to the igniter and the injector is potentially suspect. The engine ECU itself is another suspect. Ideally you might use an oscilloscope to look at the cyl. 1 igniter and injector signals and compare to the other cyls. Perhaps you may need to rely upon Toyota dealer assistance?

Cyl 1 is at the "front" of the engine, closest to the passenger-side fender in LHD vehicles.

 

i had one of the wires on mine work loose on the coil plug causing a misfire code . pull plug off coil inspect to be sure that the pins are all the way in and locked in place to assure god contact

 

The engine ECU is mounted behind the glove compartment, next to the hybrid vehicle ECU.

If it gets to the point where the ECU is diagnosed as the problem, you can buy a salvage unit for ~$300 or so. There isn't much demand for used ECUs because they are generally reliable.

Then you might download repair manual info from techinfo.toyota.com and replace the ECU yourself.

 

You have to be careful replacing the engine ECU aka ECM because of the immobilizer. The service manual is not exactly clear on this but it is possible that you would need to jumper the DLC for half an hour if replacing either the HV ECU or ECM. I'd do a compression or leakdown test before replacing the ECM.

I am very suspicious of your coil packs and the wiring from them to the ECM. That is usually the source of misfire.

 

It might still be worthwhile getting the compression (or leakdown) test done as it still could be marginal compression on that cylinder. Perhaps the "new" short block was really just a salvaged part, assumed to be in good condition but in reality no quite so.

If it does turn out to be marginal compression then you could try a ring soak or few other things before going for the more expensive options (or selling).

 

Sheesh, you have dealer malfeasance combined with used car dealer malfeasance. Honestly, you may be better off pursuing the dealership that performed the repair. Such carries a 1 year, unlimited miles warranty and I believe does transfer to a subsequent owner. If they did engine mechanical work, and now there is a misfire that cannot be explained by all the usual non-mechanical suspects (plugs, coil, injector) then it can only be something with the valves, timing, or pistons/rings.

The alternative is to install a used motor. It's a fair bit of work, at least two days. But you could get a good one for fairly cheap. Car-Part.com--Used Auto Parts Market.

 

Yeah I'd say a week was just the time frame that it took her to get back to them, not necessarily how long it took for the light to come on.

"Hit a big rock" could mean that it smashed though the sump and slammed into the bottom of a rod/bearing in one mighty hit, but it also very likely could mean simply cracking the sump and losing all the oil. Whichever way, but particularly the latter, if it was still running after the impact then she probably drove it without oil until it died. (LOL sorry about the women + oil light stereotype). So after the event the heads mightn't have been in the greatest condition either.

BTW. Do you know if the "short block" was a new or a salvaged unit?

The only other thing that makes me wonder about the "hit the rock" thing, is that it might have given the car a pretty serious jolt. So while an internal engine problem is definitely looking the most likely at this point, it still might be an issue with the wiring from the ECM to the igniters as Seilerts mentioned previous. (eg wire lose due to jolt.)

 

No one in their right mind would install a salvage short block. A junkyard will sell the whole motor, and all you have to do is shove it up in there. More likely the PO paid the dealership a few thousand install a new block, crank, and pistons, because a new motor installed by a dealership at full MSRP is $10,000.

It is possible that the misfire only occurs under certain conditons. Further, it takes two OBD II trips and a misfire rate of only 2%.

I wonder if anyone checked for vacuum leaks and proper operation of the VVT actuator, as the VVT oil filter could have been clogged with debris.

 

My truck had an intermittent misfire on cylinder 1 (ford ranger, not a direct analog to this). The light would be on most of the time in the winter, off in the summer. I assume this is because of the ethanol in the gas. I put in fuel injector cleaner (two tanks full) and it went away for a year or so, then would come back the next winter. Another tank of fuel injector cleaner would cure it again. I suspected carbon build up causing per-ingnition, but never knew for sure.

 

For most of these, if you start the car 3 or 5 times (I forget the magic number) and the problem is not there, the light goes off. The code is still logged in the ECU, but the light goes away. So that would mean that over the weekend went it off and back to a couple restarts before that, the issue hadn't occurred. And it still hasn't come back if the light is still off.

 

That's a really good suggestion tdelker.

Hi Clark. If the light comes back on, then test tdelker's suggestion by running a few tanks of the high octane (premium) fuel, just to see if it makes any difference.

 

I was wondering if there had been an outcome to this story.

What would the theory be here? Pre-ignition based on a hot spot caused by a sloppy overhaul? I suppose the knock sensor would not retard timing enough if it was only happening in 1 cylinder. Some other guy claimed that he was able to make knocking in general go away with two treatments of Gumout Regane to decarbon the piston tops. Might be worth a shot to run some of that through.