SOLVED: V6 code P0301 caused by rodent eaten injector wires

Hi. In the last couple of weeks, I had several instances of code P0301 (cylinder 1 misfire). I temporarily resolved each instance, each temporarily resolved by disconnecting and reconnecting the wires clip into the coil assembly for that cylinder. I am about to replace the coil assembly and the spark plug, and wanted to ask for comments regarding issues which you might see in the 'old' versus 'new' parts.

The old plug (DENSO original OEM from 2007) shows a bit of dry carbon on the end of the outer ring, but the curved electrode seems pretty good. The plug tip is no longer flat, but that's (maybe) a question of age, around 15 years as I write this. As a permanent replacement, I chose NGK Iridium LFR6AIX-11, which has a sharply pointed tip and can't be gapped - but the gap is just about perfect from the factory already.

The old plug threads are a bit dirty, with dry black residue (maybe more carbon), nearly all the way up. Toyota did not install the plug with any anti-seize. I'm inclined to add a bit of anti-seize, starting above the 3rd thread from the plug tip and running for about 1/4", to keep muck from clogging up upper threads. Because ant-seize reduces thread resistance, I'll put it in with a slight reduction in spark plug torque (maybe 13 ft lbs, rather than 14-15).
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I see a more interesting difference in the old versus new coil assembly. The OEM DENSO contact appears to be a spring-loaded wire, which has perhaps become too weak to make good contact over time. My replacement 'TRQ' assembly adds a wrapping along the of the inside, with stripes of conducting material for the sides of the plug. 'TRQ' says not to add dialectric grease, and Toyota never used any within the original DENSO unit. I'm inclined to follow TRQ instructions, installing the unit 'dry'.

If this doesn't solve the problem, I'll look at an injector replacement. Should I replace the other plugs as as well? Thanks in Advance

 

Not sure what exactly you are looking for but

I'd replace them all

 

Yes definitely replace all the plugs

 

The 4th gen V6 uses basic copper plugs (Denso & NGK) and the change interval is 30k. Unless the vehicle sat in a barn for the past 15 years, you're probably past due for plug change.

 

Thanks to everyone! The old plugs were "basic copper" at almost 60K, far past their rated replacement internal (as you had anticipated ).

Yesterday, I replaced cylinder 1 coil assembly and plug as I described in post #1. Engine runs smoothly, no issues. Today I'll replace the other 5 plugs, again with NGK Iridium (I bought a pack of six). I'll be re-using the original DENSO coil assemblies, but I will be adding some dialetric grease into the plug end of those coil units, to hopefully imporve conductance if the spring loaded contacts are getting "weak". On the plugs, I used 14 ft-lbs of torque after applying anti-seize as I described. 12-13 ft-lbs was probably sufficient with anti-seize reducing thread contact forces, but I went to the full spec value anyway). I applied only 10 ft-lbs on the coil assembly clamp-down.

 

You shouldn't apply dielectric grease to an electrical connection contact points, it is non-conductive and could cause the connection to be weaker electrically, dielectric grease is designed to protect electrical connections from water, corrosion and more importantly it being non-conductive it help stops arching from one connection to another adjacent connection.

 

You don't grease the contact point but around it is fine.

 

Thanks for advice concerning "dialectric grease". Although I added some into the original coil boots , I'll either replace those coils with new ones, or remove that added grease from those original coil assemblies (cylinders 2-6), using q-tips, if those cylinders develop any issues.

The Engine ran smooth for a while, but again became rough after dropping to idle following a hard "fake acceleration" to about 3500 RPMs (gas pedal only, still in 'park', sitting in the driveway.) The error lights and code didn't come up immediately, but I got another instance of cod P0301 (cylinder 1 mis-fire) after about 30 seconds of delay. I did not add any "dialectric grease" into the new coil assembly on that cylinder (cylinder 1, passenger side rear), and I'm not sure where to look next.

The coil wire set into cylinder 1 has no visible damage, but I can only see it for only about 3 inches before it is joined with a big "bundle" of other stuff. Are there ways to verify that those wires are OK, using voltage or resistance? Another alternative source of the problem might be the the fuel injector, right?

 

^Don't get too caught up with the dielectric grease. Most professionals just squeeze a pea-sized amount from the tube into the coil boot opening, then stick the coil onto the spark plug. It keeps moisture out (important for off-road rigs) and discourages carbon tracking.

Misfires can have three general causes: spark, fuel, or compression.

To verify the ignition wires are OK, back-probe the wiring connector going to the ignition coil, then look at the waveform on a graphing multimeter or lab scope.

The #1 injector could be bad, or the wiring to it might be bad (from mice or corrosion). To verify the injector wires are OK, you'd unplug the wiring connector to the #1 injector and connect it to a noid light, then check if the noid light illuminates while the engine is running. I don't know if this is easy to get to, so you may want to check compression first.

Compression is best verified with a DC current clamp on the starter wire. The current clamp is connected to a graphing multimeter or lab scope. You'll want to get the engine warmed up and misfiring, shut it off and immediately pull the EFI fuse, then crank the engine over. There will be a current peak as each cylinder goes through its compression stroke. If there's one low peak every 6th peak, then you know one cylinder has low compression. You may be at the early stages of a head gasket leak.

There are multimeters with built-in DC current clamp that can communicate by bluetooth and graph through a phone app, e.g. https://www.amazon.com/BTMETER-BT-7200APP-Multimeter-Resistance-Temperature/dp/B08PBFJR5G/

 

This was a wonderful reply, thank you!

I did use only a "pea-sized amount" into the ends of the older coil assemblies, so my "error" probably wasn't serious. (And the problem recurred with cylinder 1, where I installed the new coil "dry".)

Following my post yesterday, I cleared codes and idled OK for a while. I then decided to try "limping down to the auto parts store", a distance of about 3 miles, to buy a Noid light set. The trip had no issues! Each direction included 3 stop lights, with long queues - idling in drive at low PMs with no issues. On the return, I chose to push it a bit hard during 1/2 mile uphill grade (about 6-7%). Halfway up the hill, I accelerated from 50 MPH to 65 MPH "aggressively". In that acceleration, the auto tranny downshifted itself from 4 to 3 (as expected, with increased RPMs).

I had no issues doing that, or following my "ease off the gas" with the tranny shifting back to 4th. The top of the hill has a stop light, the problem did not re-develop there either. I took another longer trip in the evening (following a friend to a wine bar downtown, 12 miles round trip and including the same hill) - again with no issues.
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In buying a 'handheld scope / multimeter" quickly- do I need two channels? I can get this single-channel combo device cheaper on Saturday ("ZOTEK ZT-702S 2 in 1 Handheld Digital Automotive Oscilloscope Multimeter", $66, https://www.amazon.com/ZOTEK-Automotive-Oscilloscope-Multimeter-Tester、Voltage/dp/B0C3D1KVPB/

There's also a "Bside", at the same price and same specs, but powered by a 18650 battery (I like those, and already have spares and a charger). https://www.amazon.com/BSIDE-Oscilloscope-Multimeter-Capacitance-Temperature/dp/B0C7R2PF4F/

If I need two channels, then I probably need to spend about 2x as much, maybe this one: https://www.amazon.com/Oscilloscope-Bandwidth-Generator-Backlight-Waveforms/dp/B0B497T6HR?th=1

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With respect to Noid light on the injector: my el-cheap kit includes 8 lights, labeled as follows: "GEO TBI", "FORD TBI", "GM TBI", "GM PFI", GM SCPI", GM MULTEC2", "GM MULTEC2", "BOSCH PFI", and "BOSCH2". Is one of these applicable, or will I need to obtain different version to assess the Toyota V6?

 

^Personally I'd spend more on dual channel. More useful in cases where you want a second signal as reference (like having the #1 ignition coil wire voltage on ch 1 while having the starter current on ch 2, so you know which cylinder the waveform peak belongs to).

Beware if you get an oscilloscope, you'll need to get a separate DC current clamp, and be sure to pick one with compatible leads (BNC vs. "banana" plugs), e.g. https://www.amazon.com/dp/B07Z7TXY8J/

 

Thanks, I created a shopping list with your recommended current clamp, my previous 2-channel oscilloscope, and pair of BNC-to Coax adapters. I'll wait for the problem (rough idle with P0301) to come back before buying those parts and investigating further.

 

^To be clear I'm not "recommending" that clamp. It's just an example I found on Amazon. I just have a bluetooth graphing multimeter with the built-in clamp.

 

P0301 came back, so I ordered the electric diagnostic meter/scope (2 chnnel with current clamp and BNC adapters. arriving Thursday, I rented a small Kia EV (for a week) to run errands while the 4R remains disabled.

Step 1, replace worn spark plugs is done (all 6 plugs).
Step 2: replaced coil assembly #1 (It was maybe OK, but I didn't know how to test it).

Step 3: verify 4 wires driving the coil at the connector: I don't know what should be be seen on the four wires in testing - I expect that one will be "ground", another to be 13v (or so) providing power to charge capacitors used by the spark circuit, a 3rd might provide the timing to cause the spark. No idea about the 4th wire, please advise about that one (or if bguesses about the others are wrong). I assume this is to be done with the clamp on meter, holding the already separated leads into the connector WHILE running the engine for a very short time.

Step 4: Remove passenger side plenum cover to access the #1 fuel injector wires (just 2 wires, I think). Visual inspection only? This might be the problem area, due to to mouse chewing. But this might have thrown an additional OBD-II code?

Step 5: Remove the #1 injector for testing. (Probably requires removal of driver side plenum/intake cover as well, please advise). What should the resistance value be, and is there a way to test the spray pattern outside the engine?

Step 6: Could there a be a fuel pressure issues, only in reaching back to cylinder 1?

Step 7: With no EGR or MAF codes, it's probably time for a compression test - although the time to replace is blow head gasket would be upsetting, and not pleasant (outdoors in January).

Am I missing any other diagnostic or fix steps in this plan?

Thanks in advance!

 

I would of honestly gotten the compression test done first before going in with the meter.

You did a lot by changing plugs and trying to swap around injectors.

Does your injector clip in or is it broken? I'm going to assume it broke already since its older. I'd try the zip tie fix to see if it just maybe vibrating around causing the misfire as well.

 

https://www.youtube.com/watch?v=lVCs5gWLUyI

Any of these match the #1 plug?

 

You didn't mention you had damaged fuel injector wires due to mouse chewing? If that's the case you'd want to repair the wires before proceeding with any other diagnosis.

 

I totally agree with your advice on this: I have not yet done any of steps "3" through "7" in that list, and I agree with you- the compression test should be next. That test kit just arrived by snail-mail.

As in my first steps, I can compression-test all cylinders without removing either half of the upper intake assembly, although removal of the coil assembly for #4 is slightly awkward. I'll take an initial look at just #1 versus #3 and #5, before messing with intake assembly and measuring 2-4-6. I will not be "warming up" the engine while running with fuel, because un-burned fuel mixture into the exhaust (from cyliner #1) might wreck the catalytic converter on thqat exhaust path.

Outdoor temp is only abut 45F, and my altitude is 5100 feet: we will need to "correct" for those factors before interpreting my values.

I have not yet swapped any injectors , or inspected their wirse and clips. Maybe tomorrow, if compression doesn't show a major disaster already.

 

Thanks. All the plugs are now new, The inner contact on the old ones was worn down a bit to far, due to excess age, but they were otherwise just used/old (without oil, and without significant carbon fouling.) #1 looked no different than 2-6. I'll look for issues with #1 when I remove it in a few minutes (during the compression test), but I don't expect to see anything.

 

Good news/Bad news:

compression test on #1 versus #3 (both passenger side). showed no difference in in maximum pressure #1 versus #3. The meter recorded 173 PSI maximum on #1 (failed cylinder), and 170 maximum PSI on #2 (2-6 have never had a missed). Those values are se are nearly identical, and possibly also "like new" when adjusted for altitude and cold temperatures (ambient and engine).

The two removed plugs looked nearly identical as well. with a tiny bit of carbon along the flat and round "rim" (underneath the bottom of the threads, inside the cylinders). Carbon on #1 may have come from earlier, when it was still running most of the time (with only sporadic failures.

So there's no need for a new head gasket, it's more likely electrical (and specifically busted wiring). There's still a small chance of a valve-related issues as well. (The scope and other electric test tools arrive late tomorrow, I probably can't begin further work until Saturday).

 

If you can make it misfire in the mean time try pushing one the wiring clips once it does. Maybe get lucky while waiting and its just a bad connection.

 

The engine now misfires consistently on cylinder #1 only. The coil connector "wiring clip" looks good with no burns, and it goes on very tight. I'll definitely feel for "tightness" of the injector clip, and condition of its visible wire-in side, before removing it to for comparison testing of the 2-wire wire injector leads set ("bad" versus "good" cylinders). I'll be doing the same with the 4-wire coil sets, after the meter arrives.

To do a visual inspection of the injector wires, I'll be taking off the passenger intake assembly later today, after it warms up enough to avoid new development of frost on the inside. (Outdoor car.) Visual inspection only: the meter-oscilliscope probably arrives around 8pm, when falling temps bring back the issue of frost until tomorrow afternoon. I'll probably need to put the upper air intake passenger-side cover assembly and related intake parts back on overnight.

 

SOLVED - MOUSE-CHEWED CHEWED INJECTOR WIRES.

After removing air filter assembly and upper intake passenger side air intake assembly, the problem was obvious: Mice had been nesting in the area, bringing in a lot of leaves (to make it comfortable and provide food for winter). The insulation of the black wire into the clip for injector #1 was chewed away, the red-insulated "hot" wire was chewed all the way through, completely broken. chewed the insulation off the grounding wire into the clip of injector #1, and completely chewed through the "hot" wire into the same clip.

After removing the leaves and scraping away other "living residue" from the area, I looked for my solder iron to insert a repair jumper (but I didn't find it). I don't know if everyday wire nuts can handle possible heat build-up there , but I used them anyway. .They're easy to in later spring anyway.) They're up against the upper air intake and there's lots of free air flow around there.

At the front and back of the covers (in open air), there are huge gaps for mice to re-enter in the future, so I tossed in a bunch of moth balls to discourage future "nesting" and chewing.