SOLVED/REPAIRED - Misfire Mayhem - P0301, P0302, P0300

RPM is blue line, range roughly 1200 to 4600
Like Dm93 said, LAMBDA is my reference for AFR. Perfect LAMBDA of 1.00 is perfect 14.7:1 AFR. LAMBDA range in picture is roughly 0.80 to 1.25, so he's right in saying the LAMBDA is dropping to 0.80 (fuel increasing) when I gun it


LAMBDA drops = absolute AFR number drops = actual fuel in mixture increases
LAMBDA rises = absolute AFR number rises = actual fuel in mixture decreases

 

Yes, lambda drops to .80, but not before climbing to 1.25 in the heart of the acceleration load. Accell encrichment is there to throw extra fuel in the mix to avoid that lean spike during heavy acceleration. FYI, 14.7:1 is not a perfect mixture. It is great for cruising along with no load. However, when you floor it going uphill, you need 12.5:1 or richer. The .8 is fine, but you are not getting there until 10 seconds into the run. It should go there the instant you floor it when things are operating as they should.

 

I’m just gonna throw this out there. Change your valve cover and more importantly, spark plug tube gaskets immediately if they haven’t already been done

 

Thanks for the tip. Given the low miles (93k), is this a serious problem possibility? Anything in specific I should be looking for if it's a leaking valve cover gasket? Is it possible further troubleshoot and diagnose to make sure I'm not just tilting at windmills and messing up something else in the process?

 

Pop a coil out and make sure the tip is dry and not coated in oil, I guess.

 

I mean the 2.7 isn't known for being a powerhouse, typically effects of low compression show up more at idle so that could explain a rough idle. If your compression results are correct your about 30 psi below the minimum recommended compression of 128 for the 2.7L

When I say secondary ignition I'm referring to the high voltage side so coil, coil boot, and spark plug. As cylinder pressure increases the voltage required for the spark to jump the plug gap also increases so if it can find an easier path than the plug gap it will take that. This is why ignition misfires most often occur at higher engine loads because that's when cylinder pressure is the highest. Usually you can feel ignition misfires especially on a 4cyl.

I don't think any of that would have anything to do with it, you would have other signs and codes if that was the case.

Being your compression test showed it was low you could get a second opinion on it, this is definitely not gona be an easy one to diagnose over the internet. If compression is indeed that low that is a problem but I can't say for sure that it is the problem or I should say the only problem.

It would be really unusual for a 2.7L to be that tired with only 93k on it unless it was just totally abused.

 

I think I read you used an AutoZone rental compression tester.
Was the O-ring on the plug side that screws into the head?

95 is low. The odd part is they were all low. And at basically the same 95 psi.

 

Have you checked vacuum at idle with a gauge? Should be steady at 18-21 inches. Less than that could indicate a mechanical problem

 

Most 4 bangers require around 150 for compression to be pretty good 130 is starting to show signs of a tired- ish engine. The fact you are losing power and your compression numbers tells me your valves are most likely not sealing as well as they used to.

Believe it or not, this issue is fairly common amongst 2.7L 4 banger Tacoma engines. In my time as a tech I had at least 4 if not 5 roll in all with low compression numbers and all of them ended up needing to have the head removed to check the valves. If I remember right the fix usually wound up being replacing the valves entirely. I definitely remember one having the EXACT same issue you have and the fix ultimately resulted in head removal and mechanical work being performed. It's been years since I hung up the wrench set professionally though so I can't say for sure. I will tell you right now for sure though, 2.7L 4 bangers are notorious for compression and valve issues for sure. As are the 2.4L as well if I remember correctly.

 

Yes it was.

So I'm going to give the compression test another go, going to try a kit from O'Reily's this time. How do you guys tighten down the compression kit plug adapter with the hose attached? Line sockets? I don't have one so last time I fixed me up a 3/4" copper pipe with slots cut in at the end to act as the socket and seriously hand-tightened. Should that be enough?

So you think it still could be a coil problem even though early on coil 3 and coil 4 have been tried in cyl 1 and the problem remained? What can cause the volts to find as easier path than coil, to coil boot tip, to spark plug? (plugs are essentially new)

I'm going to have the coils out to try the compression again, so if there's anything I can do at that point I'm all ears.

Going to test each coil with a multimeter like the video below. Anybody have any specifications on what the 2.7 4-cyl coil packs voltages and resistance should be?

http://www.youtube.com/watch?v=UsrhulWa3e0

 

I'd be happy to pick up the vacuum tester when I'm at O'Reily's and run the test. So it's possible to have a weak vacuum pointing to a mechanical problem without showing any codes for a vacuum issue?

 

Still bothered by the second cylinder misfire showing up after diagnostics began for the first cylinder.. A thing happened. Something changed. Wish I had our truck handy for reference

 

That's interesting, I've seen several people with oil burning issues on the 2.7L but I haven't seen where too many had compression issues especially not at under 100k.

It doesn't need to be super tight, just snug it by hand.

Well you said you swapped them so not likely but I can't be certain.

Alot of things can cause spark to "leak", cracked plug, excessive plug gap, carbon tracking on the plug and/or coil boot, a crack or pinhole in the coil boot, oil on the coil boot from a leaky valve cover causing it to swell, or a crack/internal problem in the coil.

That really won't tell you alot, best way to stress test a coil is with an air-gap spark tester (not one of those neon bulb ones) set to around a 3/4 - 1 in gap and see if it sparks consistently with the engine cranking or running.

 

Could be a mechanical problem spreading, like a leaking head gasket, no? Either way, if the codes didn't spread I'd still have this mysterious misfire with cyl 1 with no other codes popping up. So I'm thinking if this original cyl 1 misfire is solved, it might (or will) shed light (or a solution) on cyl 2.

 

I'm out of my depth here. The 2.7 has thoroughly baffled me. But whatever answer comes from this has to also explain the fault's extension to the second cylinder after diagnostics began. It may be coincidence, but.. work was performed. Next time you're messing with coils or injectors, draw or etch numbers onto them. I press little dots in with a scratch awl on connector tabs: • •• ••• ••••

gah. I need to get a freakin real scanner..

 

You're referring to oil burning more than what regular operation oil consumption is right? Because TBH, when I first cracked the manual open last year I was seriously surprised how high the manual said normal expected oil consumption was...

I did swap coils and carefully:
4 to 1: 4,2,3,1
then 1 to 3: 3,2,4,1
then 1 to 4 and 2 to 3: 1,3,2,4
Code never left cyl 1 before popping up with cyl 1 & 2 at the same time

Plugs are basically new and have been two complete sets since summer 2023. This last time I made sure to check the gap before install even though they are pre-gapped "Denso Iridium Spark Plug 3421" from autozone.
Can I clean the outside of the coils and the boots with a rag sprayed with some engine degreaser when I have them out? Idea here is to clean them as much as possible and see if I notice any engine performance improvement once I put them back in AND BEFORE and oil/carbon builds up on the coils.


And for a gap tester, would this work?

$10 OriGlam Spark Plug Tester, Adjustable Ignition System Coil Tester, Coil-on Plug Ignition Spark Circuit Tester, Autos Diagnostic Test Tool

https://www.amazon.com/Deal】OriGlam-Adjustable-Ignition-Circuit-Diagnostic/dp/B06X9RC3PF?crid=302BIPIJTVO1Y&dib=eyJ2IjoiMSJ9.NtWe4qU4hS_J4pvQU_JXgQF-blbjsVDWzvTbxYBQZGDz2OfHDQnt_-rUAr6GveFiCBDJD7acgJnF_g4JG8T4wKbsFFCbkDJ86vwYaY9VmfjUW3Emk6ZP-2AJd6LkwVfgpKTCLr87dlwbnwATuQSgr5SQaedpiuTUbQbPnAhJ-I4X5QSZgLh3aKagwSQRbOgAh7CwYYMIc0dDfFrxvW9LuntW_9wu1T6p3aJMX_AGi9d_Vz1MzZS2fa9WZCUoQpcWrRzfPWJZnQcJjs_RVERLU8a_e7jb2EfneMnBenDisfk.pz6dHiJzfTCNMHwu-Dlj2cxLQZJ5drPeBhdz8hDWvqc&dib_tag=se&keywords=air+gap+coil+tester&qid=1715484318&sprefix=air+gap+coil+teste%2Caps%2C164&sr=8-1

 

There really shouldn't be much of any oil conumption on a good engine with no leaks, I would say a quart or less between oil changes. The reality is alot of newer engines burn oil, wheather it's design/manufacturing flaws or the low tension rings they use who knows but more and more it seems it's not uncommon for many modern vehicles to use alot ot oil.


The reason the guidlines for "normal" oil consumption are so high is so manufactueres can get out of warantying engines for oil burning.

They shouldn't really be dirty, if they are getting oil on them then the valve cover gasket is leaking. If the boots are cracked or swolen from oil they should be replaced.

That will probably work.

 

My spidey-sense keeps telling me it's this. But trying to rule out everything else and pinpoint on the valve cover gasket before tackling that issue...

 

Not really a fan, IMO there's much better options out there at that price point. Autel, Launch, and TopDon are my top 3 aftermarket scan tool manufacturers.

Vehicles have graduated far beyond just needing a basic OBD tool that can read codes and basic data if you wana do any kind of in depth diagnostics. The good thing is scan tool prices have dropped substantially in the past few years, features that you used to have to get a $1500+ tool for can now be had for as little as $60 + $50/year subscription for a smartphone based tool or around $500 for a standalone tool.

 

Yeah, I somewhat got that feeling once I got the tool. That's one thing I failed to research before putting down money for it. I'll delete the post lol.