Multiple misfires after rebuild

I have a vacuum test gauge coming and I plan on testing it when it gets here.

 

Those fuel trims keep jumping out at me. It’s pulling fuel from bank 1, so it thinks the mixture is too rich on that side. A vacuum leak ought to make it go the other way, right, and add fuel? So probably not an air leak into the engine. Are the plugs on that side turning black again?

 

That's kinda where I was back on the 1st page, reply 21: https://www.tundras.com/threads/multiple-misfires-after-rebuild.110071/page-9#post-2857274

Then again ~200 replies later. Granted, this one's felt like a game of whack-a-mole with nearly every possible suspicion tossed at it. I'm thinking vacuum may be one of the only easily-measurable things not fully sussed yet.

I've found it really weird the issue seems to gravitate to the left/DS bank of the engine, and remember looking at your plugs: https://www.tundras.com/threads/multiple-misfires-after-rebuild.110071/page-14#post-2875780

Supposedly #3 is the only one misfiring now, per the last page. The spark plugs shown had #3 as the cleanest, with #7 most fouled, and #1/#5 equally moderately fouled. I would've expected #3 plug to look the worst, not the best?

I wouldn't think it's electrical because, IIRC, the coil pack wiring has 2,3,5,8 together and 1,4,6,7 together. Symptom of IGN wiring or ECU problem would have one of those sets misfiring.

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Actually, is it misfiring on all 4 bank 1 cylinders, just like before. Sorry for the confusion.

 

Nah, I probably just scrolled back too far. I remember after the last time you were in it, you said 3 only.

Just to be clear, right now, all four bank 1 cylinders misfire, but only at idle/no load?

 

That is correct. But only not under load. At idle under load it does not misfire.

 

Where I am right now with my thought process is that the -18 fuel trim on bank 1 is the ECU saying that bank is much too rich. It has to be saying that because of information from the bank 1 upstream oxygen sensor. That oxygen sensor is the component put there just for the purpose of adjusting fuel mixture for the cylinder bank, and it only has that one purpose. So we have to ask the question, "Is the mixture in bank 1 really too rich?" If it is, the plugs will be turning black again and OP can focus on something jacked up in the fuel injection system. If the plugs are white, then we know that the oxygen sensor is lying and something is jacked up in either the oxygen sensor information or in the ECU's interpretation of that information. I think he's swapped all of those parts already, but I'm thinking the gremlin is still hiding in one of those two areas. I'm saying the misfire is really just a symptom, so where in the fuel map it shows up isn't the main thing.

 

Couldnt agree more. That O2 sensor has been my suspicion since the beginning.

 

I did replace the o2 sensor and I didn’t even have to extend the wire. So it is plugged straight into the harness. I think I have another o2 sensor that I can throw in.

The odd part to me is that the misfires happen before the o2 sensor even warms up and starts giving readings.

 

I thought this was weird too, but still, I swear I suggested on the 1st or 2nd page to flip-flop the pre-cat O2 between left and right bank if possible to see if the problem switched banks with it. I haven't had to do my pre-cat O2 yet so not sure if the part number is the same, but I feel like you said you'd tried it. Maybe I misread or I'm making things up.

 

Should be two of these denso 02 sensors.
https://www.rockauto.com/en/moreinfo.php?pk=991966&cc=1357938&pt=5132

 

Use a little bit of anti-sieze on them to help with replacing next time. I can't remember if you've already changed yours or not, but if you haven't... you may have to walk it out. Tighten, and loosen to help get all the crunchies out of the threads.



Also a thread chaser may be wise...
https://www.rockauto.com/en/moreinfo.php?pk=8760712&pt=1001068

 

The upstream O2 sensors are now mounted in the new long tube headers, right? Make darn sure that the bung welded into the header tube puts the sensor “probe” out into the exhaust stream with no obstructions of any sort. Even an obstruction upstream causing turbulence past the sensor could be an issue.

 

Here's a theory:

The stored fuel trim information is telling the ECU to seriously lean out the mixture in bank 1, which the ECU does while the engine is in open loop warming up. When the engine warms up and goes closed loop, the sensor information just keeps reinforcing the message to keep bank 1 lean. That bank of cylinders is so lean that its borderline whether the cylinders fire or not, pretty much regardless of whether the engine is hot or cold. At idle, misfires show up occasionally. Under load, the fuel map adds enough fuel that the thing will at least sustain combustion most of the time.

The flip side of the argument is that the mixture really is too rich. In this case, I would expect it to run better cold and have more problems when it warms up. Other than that, if the mixture is rich enough, the engine is still going to struggle to keep the fire going.

I'm advocating for another look at the spark plugs and to hard reset the ECU to wipe out the long term fuel trim settings every time some corrective measure is tried.

I also really like the idea of taking a hard look at the O2 sensor bung area and upstream as @landphil mentioned.

 

Yes, they are in the JBA long tube header bungs. I can check the depth when I check the back pressure.

 

I think your logic is sound. I did put the other ECU that I bought in. I can switch it back for my stock ECU, which should cause it to relearn everything.

 

I did replace them both with actual denso spark plugs. They were like $80 a piece.

 

Where did you order them from? Amazon, ebay?

Spark plugs won't work in your oxygen sensor bungs .

I know what you mean. Not trying to be a butt, just thought it was funny.

 

Oops, my bad. Late night typing. Yes, I bought them from Amazon: $43.68 each

Denso 234-4169 Oxygen Sensor

 

These:

 

When @shifty` pops on the forum he'll tell you, and most likely link you to threads where people have gotten "fake" parts that look real, and plug in like the real deal, but simply don't operate as long as they should.

Here's some links I could cobble up without having enough coffee in my system

https://www.tundras.com/threads/fake-oem-oil-filters.84013/

https://www.tundras.com/threads/real-vs-fake-denso-plugs-w-pics.60880/

Good info in each. @Brynden29, personally... I would order two new 02 sensors from Rockauto, and replace with known good parts.

@shifty` will get into this more as he understands it better, but rockauto doesn't source from a third party or whatever that eBay or Amazon do. Much less likely to get a fake part.

 

I'm good I think you covered it

Basically, for any order scAmazon fulfills, scAmazon warehouses lump all their inventory together for ease, for all vendors. They don't scan incoming inventory to look for fakes. Doesn't matter who on scAmazon you buy through, if a load of fake or grey market merch hits the warehouse, it gets tossed in the bin for that part number, and any vendor you order from that's fulfilled at that warehouse is shipping you counterfeit or grey market product, not authentic OEM.

 

See what I mean? That's why you're the man.

 

Actually, I bought this o2 sensor from advanced auto. The extra one I have is an Amazon one.

 

Who did the jba install? Is everything torqued proper? No exhaust leaks on that side?

 

I did the install. I took that header off to remove the head and it torqued it down as hard as I could so I am pretty sure there isn’t a leak.

 

What gaskets did you use?

 

The ones that came with the headers.

 

This is what I bought for the coil packs and plugs:



They seem legit, but reading the fake parts threads have me concerned. The plugs are the u groove conventional plugs. Are those correct?

 

Brand: "Newparts". Image: Totally generic.

Yup. That shit is fake as hell. Classic scAmazon.

Never buy auto parts on scAmazon.