O2 sensor odb code plus cylinder 7 misfire

(4.7 v8 4wd) Noticed truck running rough when I went to take it for a trip. Obvious misfire, truck losing power and shuddering and" big cam sound". Hooked up odb scanner, p0136 and cylinder 7 misfire code. Removed the sensor throwing a code, sensor code went away. Misfire remains on 7.

Looked over all 02 sensors, they look brand new. Checked coils and plugs, new as well. Changed oil+ air filter as soon as I got it. Coolant looks normal no milky color, no smoke out of exhaust. The exhaust has been leaking from manifold area

Bought this truck a month and a half ago ran great until today. Misfire isn't noticeable at all until truck warms up a bit. It still has power just shakes like hell at lower rpm especially uphill. This is my first v8 apologies for lack of info. Any suggestions at what I should look at next?

 

Always look first at what the other guy did last. Maybe have a close look at all the new parts and see if they're OEM or some Amazon shit. The plugs especially are frequently counterfeited.

 

Swap cylinder 7 and 5 coil packs. Recheck and see if the misfire has moved to cylinder 5. [Cylinders go 1-3-5-7 on the driver side/front(1) to back(7) ] Easiest way to check the coil pack itself.

coilpacks can look perfectly fine but be trash.

while you're at it. Get some new NGK iridium plugs. Misfires usually make plugs unhappy/dirty af.

 

Swap coils and see if misfire tracks. If it does, change coil. Also, our trucks are finicky if not using Denso (OEM) sensors. Watch out for counterfeit ones from Amazon.

 

Easiest diagnostic step.

unrelated, but I want this shirt

 

Neglected to mention I did this already, plugs are NGK and misfire stayed on 7 after swapping plugs and coil with 5

 

If the plugs are good (check the gap for sure) and the coils are swapped, next you'll need to trace the harness to see if you have a break in it. Rodent damage is common, unfortunately. Also, if you do find damage, this is one of those harnesses that SHOULD NOT be repaired (unless the issue is at the connecter and you're able to re-pin and or replace the connecter), only replaced.

 

Ok, so let's stop and think on this for a minute.

First of all: I appreciate the gusto, but would recommend to stick to one thing at a time. Swap the coil pack. Test. If no luck, swap the plug. Why? Say you swap both and the misfire jumped to 5. What did it, the coil or the plug? Now you're doing extra work to figure it out. I would've swapped coil pack 5 to 7, and if that failed, swap plugs between 7 and 8. But anyway...

Second of all: When was the last time the timing belt and water pump were done? It MUST be done at least every 10yr/100k miles, Toyota recommends 9yr/90k, but... if that timing belt snaps, the 4.7L is a low interference engine, and you can boat anchor it if the belt snaps. It's easy enough to loosen up one of the timing belt covers to check the belt condition. Timing being off by a tooth could cause these symptoms so it's worth checking the belt.

Third, let's think about the bigger things at play here.

You understand the purpose of the upstream air/fuel ratio ("O2") sensor and the downstream O2 sensor, right? Your ECU knows how much air volume is coming into the top-end because you have a MAF that's hopefully working correctly and it knows the position of the throttle plate. To dumb it down a bit, it also knows roughly how long to spray the injectors to create an ideal air/fuel ratio for combustion, and uses other sensors to figure out spark timing etc.

Once combustion happens, gasses get pushed out of the exhaust manifold, which we hope isn't leaking. The upstream O2, aka "air/fuel ratio" sensor, sniffs the combustion mixture to see the byproduct of combustion. Is it rich? Is it lean? And it adjusts air/fuel based ratios based on that input. Then, the combustion passes thru the catalytic converter to filter/burn off hydrocarbons, and upon exist from the cat, the downstream O2 sensor sniffs the output, sends that info to the ECU, and the ECU calculates the difference in mixture before/after passing thru the cat (delta) to understand: Is the cat working correctly/efficiently? And if not, you'll pop a P0420 / P0430 code.

Say your upstream sensor isn't functioning correctly. If it's feeding invalid data to the ECU because it's skewing numbers on combustion, what will happen? A couple things:

1. The ECU may inject too much/too little gas into the cylinder, causing misfires and/or lean/rich operation
2. The ECU won't get a good delta when comparing upstream/downstream values and may think the cat is bad inefficient

Say your downsream sensor isn't functioning correctly. If it's feeing invalid data to the ECU because it's skewing numbers on what came thru the cat, it may throw cat inffency codes. Aftermarket (non-Denso) and counterfit (scAmazon/fleaBay-bought) sensors can also cause problems, as can cutting the O2 wires to install universal sensors. Also, FWIW, I always recommend replacing sensors in upstream/downstream pairs, because of their inextricable relationship to one another. It's also possible to see if your O2 sensors may be responsible with a scanner that supports live-data logging to see things, but before I get too far off-tangent....

What causes a misfire?

• Timing is off, either due to the belt jumping and/or belt stretch.
• Too much or too little air/fuel into the cylinder:
  • Intake manifold gasket is breached at the cylinder(s) having issues
  • Fuel injector shit the bed and isn't spraying enough fuel and/or isn't seated properly, i.e. bad o-ring, poorly seated injector, bad boot, etc.
  • Spark plug isn't seated properly (not your issue, but loose plugs will cause this, worth noting you can seriously fuck your engine over-tightening plugs)
  • MAF and/or throttle position and/or throttle assembly is not working as intended, either due to improper adjustment, bad sensor, or gunk buildup on the throttle body/plate
• Bad spark:
  • Bad and/or aftermarket coil packs are pretty notorious for this, only buy Denso brand from reputable sources.
  • Bad and/or poorly gapped and/or incorrect spark plugs for your specific engine
  • Wiring fault/issue, like bad ground, eaten wires, but this is a can of worms to diagnose and not typically the problem

What would I do?

1. Check timing belt condition if status is unknown, share pics if you don't know what to look for (This is the kit to buy to overhaul)
2. Swap injector #7 with #3 and see if the misfire jumps to another cylinder
3. Obviously, get new authentic Denso downstream sensor, look up the "DIRECT FIT" part for your specific truck (4WD vs. RWD) at www.densoautoparts.com (See the part number in pic below), best pricing for authentic parts will be at www.rockauto.com
4. Report back on what you find.

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PS - as a new owner, our community-built megathread is perfect for you @ https://www.tundras.com/threads/so-you-wanna-buy-just-bought-a-1st-gen-tundra-eh.115928/

 

Popped the fuel rail, injector gaskets were crumbling apart. Replaced all 8. Checked all coils with test light good there. Tried all new plugs. Tried swapping o2 sensors with the opposite bank, no change whatsoever. Did a compression test on 7 its still there. Checked with obd diagnostic, multiple cylinder misfire, 5 and 7. Cleared it, let it idle a minute, code for cylinder 7 misfire pops up. Is it possible it could be timing? belt was replaced 50k ago. I ran it locally for about a week like this as i have no other vehicle at the moment. Would it be worth replacing the belt still or should i look into a new engine

 

Yes, as noted above in my wall-of-text, "What causes a misfire?" you'll see timing at the top of the bulleted list.

Note: Toyota's service numbers ONLY APPLY if you use OEM parts, not aftermarket. They cannot guarantee the quality of aftermarket, and aftermarket parts are shit these days, the last 10-20 years they've degraded to garbage. They also cannot guarantee anything you buy outside of authorized Toyota dealers is authentic, and scAmazon + fleaBay are notorious for selling counterfeits, we've had people on here get burned. We often ask on here, "What'd you buy, where'd you buy it" when it comes to parts.

If you didn't buy a kit, and you didn't change the tensioner with the timing belt, as you should've, it could be the tensioner is dying and this was your wake-up call. It could be a pulley is going out. Looking behind the timing cover(s) is worthwhile, to look for things like nesting materials, in case a squirrel is storing acorns in there (don't ask) and caused timing to jump. Also to verify the belt, look for fraying of the belt or proof of slippage.

It's worth checking the timing. That can be done easily, DO NOT be intimidated! Read this: https://www.toyoheadquarters.com/threads/toyota-2uz-fe-timing-belt-marks-4-7l.335/

If/when you take the timing cover(s) off, be aware, there's a metal tube (bushing/insert) in each hole, and they get loose with time and can fall out. You don't want to lose them, and they must go back in if/when they fall out.

 

Got it back from mechanic, new coil pack fixed the issue. Definitely going to get the timing replaced asap regardless. O2 sensor stays unplugged now truck runs smooth. Will get exhaust work done after timing

 

If your O2 sensor issue is upstream (I didn't see your code), you'll want to repair it sooner than later. Three reasons:

• Your ECU uses that sensor (as explained above) to know whether it's air/fuel ratio is correct, and if it can't, it's going to cost you at the fuel pump
• Besides that, if you're running out of spec (too rich/too lean) you'll clog your cat(s), and while an O2 sensor is in the $75-140 range (per sensor) normally, an OEM cat will run you $800-1,000+ per side, a compatible aftermarket cat that won't constantly (maybe only periodically) throw codes will cost you $450-600+ per side.
• Failure to fix will result in your check engine light always being on, making it impossible to know if you have another major issue - you can't pop another check engine light if the light is already on.

Short version: Anytime you pop an O2 code, you should seek to fix it sooner than later. A lot of people unwisely chalk those things up to "EPA tree hugger bullshit", but the engine actually uses the upstream, failure to address can/will fuck up other stuff.

 

It's a downstream, the entire assembly where the sensor screws into the exhaust is rotting away. Can't afford to replace it just yet

 

Got pics? I may have a cheap, inexpensive solution for you.

 

Won't let me upload pictures for some reason, the gasket is gone and the metal is crumbling at the base of where the sensor screws into.

 

You can find a sleeve for that spot, depending on how bad it is. If really bad, a competent exhaust shop can cut out the rot, and weld a patch of sleeve in place, then pop a bung on it. Should cost about 80-90% less than getting that section of exhaust (or whole cat).

To upload from a smartphone, the 'Upload a file' button in the reply box makes it easy. On a computer, you can also just drag/drop a pic into the reply box and it'll auto-upload. Or use the button.

 

I've got the same problem on my downstream O2 sensors, where they're just completely rusted on. Luckily I don't have issues with them right now, but want to plan ahead. Do you a link to a quality sleeve for that spot that has a bung for the sensor?

 

In no way am I saying this is the correct part for you (pic below). I'm only showing you an example of whats out there, this bung may not have the correct threading for our Denso/Toyota sensors. The inner diameter (ID) of this pipe may not fit over and/or inline with your existing cat tube. But it's one example.

Any respectable exhaust shop* should have something like this available, on-hand, and they can even potentially cout a patch, drill a hole in it, and weld a new bung/fastener onto it for you to install your OEM sensor. There are a few ways to handle the situation, but if it's a mid-pipe thing OR if you have enough space between the cat can and the flange, something like this is easy enough to slide in and weld or fasten once you cut the rotted section out. Given this is a $20 part, it's half hour labor, if you can find a shop that'll charge half hour of time, you should be able to easily get out the door spending less than $100. Potentially less than $75.

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Thanks @shifty` super appreciative of that.