Multiple misfires after rebuild ** FIXED **

@Brynden29 I'd say roll with the coil packs but get the proper denso sparkplugs from rockauto or a local parts store.

 

Which plugs should I get?

 

Denso K20R-U is what I got for my 01
Link

 

And only for reference sake to confirm what Nick is saying, this is taken directly from the '02 owner's manual that's here on the forum. You've got two options. Gapping is below the recommended plugs.

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Here are the drivers side plugs (misfire side):


Here are the passenger side plugs (working side):


They all look good to me.

 

I just did a cold compression test:

1 - 210
2 - 210
3 - 204
4 - 195
5 - 198
6 - 215
7 - 215
8 - 210

 

I swapped the ECU back to my stock one. When it first started I was only getting misfires on 1 & 3. Once the STFT went negative it started missing on all the cylinders. I hooked a vacuum gauge to the intake manifold:



I don’t know how much vacuum I should have at idle. Here is a video of the gauge:

https://youtube.com/shorts/1zkrxs6OrFU?feature=share

Thoughts?

 

I also hooked up the exhaust back pressure tester to the drivers side upstream o2 port. It was right about 0 but when I reved it up and let off it actually went negative. So I assume it is very free flowing? Should there be some back pressure at idle? If there isn’t could that mean and exhaust leak at the manifold? I know that I tightened the nuts down but they were the original nuts and I don’t know if I should have replaced them. Thoughts on that too? Thanks guys.

 

One other thing, I just took it for a drive and the STFT were very low:



I hadn’t driven it enough to calculate a LTFT when I took this picture.

what could be causing the ECU to pull so much fuel?

 

Vacuum is definitely one thing I'd brought up - mostly because the 'happens at idle, not at load' is a typical sign of vacuum leak.

Other members have mentioned potential for exhaust leak causing this, and it makes logical sense it could be the cause.

IIRC, you mentioned using the gaskets that JBA supplied with the headers, right? If it were me, I'd have gone with new hardware, but usually it's because exhaust hardware ends up being rusty as hell/degraded by the time I'm swapping headers, and I just want fresh bolts.

Either it believes it's burning lean (i.e. O2 is reading lean on that bank when actually not, or pulling outside oxygen after combustion, but before pre-cat O2?) or it believes it's pulling in way more air than it actually is (bad MAF, bad TPS?) would be the two big ones I can think of.

 

Thanks for the replies. I am sure you are tired of this, as am I.

I used the JBA gaskets, but the nuts and bolts are stock that I reused. The bolts all stayed in when I took the stock exhaust manifolds off. I reused the nuts, but I am thinking maybe I need to get new ones.

I did replace the maf sensor (I bought a hitachi one from Amazon for $71.66) and I assume the TPS sensor lives in the throttle body, which is brand new also.

If there was a maf issues why would only one bank be affected? The intake manifold feeds both banks equally. That doesn’t make a lot of sense to me.

 

At this point, I'd just like to see some success, wouldn't you? (that's rhetorical)

I assume you'd want to stick with the JBA because they're made for their LT headers and don't necessarily match stock. But I really don't know. Bolts are easy enough to swap. Pop out and swap one at a time, torque to spec, then (I like to) go back over with two random passes, usually in a 1-3-2-4 style pattern to confirm torque. FSM may say something different, this is just how I've always done it since I was a teenager and never had issues.

Exactly. Neither would TPS. I was just tossing out the two cases I could figure OTOH that would explain it.

 

The plugs definitely don't look like the mixture is too rich on bank 1, so to me that puts the spotlight firmly on something being jacked up in the O2 sensor system on that side. It could be something like a bad ground connection, not just a bad sensor itself.

 

This makes me think!!! Do you have any reputable shops that do harness testing?

I had a ground issue on my truck that I simply couldn't find... I was missing a ground on one of the upstream 02 sensors that kept making my trucks fuel system go into Open Loop. I took it to a shop that tested the entirety of the wiring harness, and found that there was a ground disconnected somewhere in the circuit of that oxygen sensor. I swapped ECUs, changed sensors, and just about everything before I broke down, and plopped the truck off at the shop. They had it fixed in a few days.

Just a thought for you. Might be worth pursuing.

Heres a link.
https://www.tundras.com/threads/crackhead-resurrection.94083/page-57#post-2641393

 

I will say, the wiring harness I am using is the one I bought from an online junk yard. I assume that it is good, all the connectors look way better than my old broken ones.

 

Any progress?

 

I haven’t had a chance to mess with it. I am waiting on new exhaust manifold nuts from Toyota. Then I will be putting them on.

 

Copy. Hoping that is the trick for you bud.

 

Regular old NGK V powers

BKR6EYA

 

I finally got the exhaust manifold nuts. They say they are locking. They appear to be able to lock against the threads. I know that my current ones don’t lock anymore. Maybe they are coming loose and causing the leak. I’m hoping to swap them out this weekend.

 

If this whole issue ends up being nuts ... that'll be seriously nuts.

But will also be a very potent lesson for others, down the road, and a learning experience for a LOT of us.

Fingers crossed ....

 

Thinking more….. it thinks it’s too rich so the ECU pulls fuel. It’s not, so it starts to misfire. Bring rich drives the O2 sensor voltage high, so the voltage on the sensor output wire is either too high or the ground reference is messed up. If the new exhaust nuts don’t fix it, recommend OP back probe the o2 sensor wires and see what they are really saying.

 

Welp, the nuts didn’t fix it. I guess I will be calling around next week to find who can back probe my o2.

 

Here is some fresh o2 data. It appears that I can see the voltage of the o2 sensors. I don’t know what it means.

https://youtu.be/1EWRYR9aPeA

 

That’s good that you have the voltages there, so no need to probe anything. The voltages range from 0 (lean) to 1 volt (rich). They both seemed to be oscillating back and forth, but with that huge long term fuel trim subtraction on bank 1. Could you swap the sensors again, reset the ECU and see see where the trims settle out after that?

 

Swap the sensors from the left to the right? The problem is, I had to extend the passenger side o2 to make it reach. So I can’t just swap them over.

 

Well, crud. O2 sensors are expensive, so its tough to just say to make a blind replacement. If you're open to lengthening the cable on the drivers side one (which is the one giving the questionable readings anyway), you could swap them.

From the video you posted, it looked like both sensors were oscillating from low to high, but the drivers side fuel trim was pegged out lean. That sensor should have been staying low all the time I would think. My theory is the misfires are due to the lean condition caused by the fuel trim.

I'm wanting to see if a known good sensor (the one on your passenger side) would generate that same fuel trim number if you swapped them over, reset the computer and drove for a few days. If the good sensor acts the same as the other one, the next move is probably to check the ground wires. Best of luck brother. If there's any justice in the world, you'll get it picked apart. You've definitely earned it!

 

I totally get your thinking on this. It would be a good test. My struggle is, the truck misfires right after resetting the ECU and before the o2 sensor starts sending info. The more I think about it, it might be something mechanical. I probably need to pull the valve cover and check the cam positions.

when I reset the ECU all the fuel trims are set to 0.4 (I think). And the truck still misfires at those fuel trims. It’s not as bad and it is just a couple cylinders. Maybe I’ll reset it and film the first start up on the scanner.

 

Considering the O2 sensor has lengthened wiring, and it's not in the factory position, would the added resistance or changed sensor location have any bearing on this conundrum? I know this was previously mentioned, but I just had to ask...