Misfire Trouble

Hey everyone! I picked up a 2005 sequoia as a little project car. It’s in really nice condition but has misfire. Here’s what I’m working with.

I have the p0300 and other codes that just say I’m having misfires in all cylinders. The main codes I’m concerned with are p2195 and p2197. When I picked up the vehicle I knew they had replaced the fuel pump, CAT’s and all O2 sensors. I checked the coil packs and they are all OEM and working. The spark plugs are a little black, but that’s just because it’s running like sh*t.
Here’s just some data I got. LTFT for both banks is 44%. My output voltage for my bank 1 and 2 sensor 1 (above the cats) O2 sensors were at a steady 4.5 V. And the 2 below the CAT’s stayed in the normal range between 0.1 and 1 V. I also tested the harness side of the O2’s. With the key on I tested the signal and signal ground. With the plugs above the CAT I got 0.4 V. And the plugs on the CAT, I got 0 V. Something else I saw as well was the MAF was reading 19.5 g/s.

Can someone help me understand what step I should take next? The O2 sensors are brand new, so I think it’s something else. Maybe the MAF? Or ECM. I’m not sure. Thanks In advance for the help!

 

Defective upstream O2 sensors can cause misfiring. So that's my #1 culprit, given the system is bitching about both upstream sensors (p2195/p2197).

A lot of times 'cat efficiency low" error will cause an owner to replace the cats when it's not necessary. A lot of times, shitty non-OEM (non-Denso) O2 sensors *OR* or knockoff O2 sensors unfortunately acquired via shady sellers on scAmazon or fleaBay will cause all kinds of issues (don't buy parts from them, they're just as cheap @ RockAuto and Summit Racing, who have a verified supply chain, and sometimes are cheaper). That's what I suspect is happening, given the p2195/p2197 throwing for upstream sensors on both banks, i.e. the driver and passenger side - owner used shit sensors, got bogus parts, or spliced in non-OEM parts, the O2 sensor circuit is pretty sensitive to splicing in most vehicles I've owned.

I mean, I want to also warn you about the timing and timing belt. When was it last done? Have you taken a 10mm socket, loosened the bolts holding one cover on, and looked at the belt condition? Or do you have some concrete proof/evidence it was changed? This is the #1 killer of these Trucks/SUVs.

Next thing I'd do is check all my grounds, just to be 100% sure. Also, check the O2 sensor wiring to make sure the previous owner didn't splice it to use aftermarket sensors.

Look up the 'exact-fit' sensors for your vehicle at the Denso (Denso is OEM) website's part finder: www.densoautoparts.com and I would highly consider starting by replacing the upstream sensors.

 

Thank you. They owner said they had replaced the belt about 50000 miles ago. I’ll still double check it on my own as well. I’ll get some real OEM O2 sensors, and check for any splicing. And check for grounds. I’ll let you guys know how it goes. Thanks for the reply

 

Yeah, just don't bother buying the upstream O2 from the dealer. They'll charge you way more $$

 

Oh and here are your parts.

After looking up the price on the upstream (link) I'll bet you the previous owner went non-OEM because $115/side is pretty hard to swallow. Downstream are much less (link).

Interesting they went with a wideband O2 sensor on the front! I haven't seen that yet.

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Based on the experience of the other guy, I recommend a compression test before spending money on anything.

 

Right?

 

Yeah. That poor guy bought plugs and whatever, and then found out a piston had become detached. There’s a lesson in there somewhere…

 

To be fair though, cheap coils from LAPS which can undoubtedly be returned, and the plugs can be pulled/reused also. So not a total waste.

 

Just a waste of time.

 

https://www.youtube.com/watch?v=_oSRvcdlgSI​

 

Alright. I got those exact 02 sensors. And some new spark plugs for the hell of it. I installed everything and it’s worse…it’s reving super high intermediately, and giving me weird O2 readings. My down stream 02s sit at 0 V. While my upstream one’s are fluctuating between 0 and 5 V super quickly. No clue on what this means.

 

Unplug negative batt cable for 10-15 minutes to reset everything.

Reattach. Run.

 

Runs like a dream. Appreciate it!

 

Just to explain why, and warn you in case it comes back:

Your ECU basically learned how to run with shitty aftermarket O2 sensors. It stored that information.

You then swapped out good O2 sensors, but you didn't do anything to make the ECU re-learn how to run, so it was trying to run things with skew favoring the shitty aftermarket O2 sensors.

You unplugged the negative battery cable for 10-15 minutes. This forced the ECU to forget everything it learned. Now you've plugged the cable in and re-started, you've forced the ECU to initate a re-learn.

It may take hours of driving, if not a few days worth of varied driving, for the ECU to go through everything and reach "readiness" state, where it has found its prime operational state, and verified everything is cool.

If it gets through readiness without throwing codes, you're golden! If it starts running rough within an hour or ten, pull the codes, let's reassess. If it's still running solid within a week - seriously - come back and let us know this one is solved.