OEM Ignition Coil Resistance/Voltage Specs for 1.8L 1ZZ-FE Engine?

[schwartzy18510]

Background & Context
I have a 2003 Vibe base model equipped with the 1.8L 1ZZ-FE engine, FWD, and the automatic tranny. Odometer currently reads a little over 190,000 miles. My wife and I purchased the Vibe with 91,394 miles back in 2013, and it's been the best vehicle we've ever owned.

For the better part of the last two years, I have been trying to track down the cause of a maddening rough idle that is most notable when the vehicle is stationary and in gear. I'm cursed with a DIY addiction and as a result am pretty comfortable under the hood, so I have been methodically working through an exhaustive list of possible causes as time allows — which I'm afraid is a separate thread for another day.

I had initially considered the ignition coils as a potential cause, but had given them a green light after considering the following:

1) There were/are no pending or confirmed check engine lights or misfire codes visible via my various OBD-II scan tools.
2) Multiple cylinder balance tests performed by disconnecting one injector connector at a time bogged the engine equally across all four cylinders.
3) A visual inspection of each ignition coil for cracks, burn marks, or oil down the spark plug tube wells came up empty.
4) Testing ignition coil resistance with a multimeter revealed no major outliers, with resistance roughly the same across all four coils.
5) Fuel economy was/is still the same as it always has — 30-32 MPG at 55-60 MPG (winter gas), 34-36 MPG at 55-60 MPG (summer gas).
6) Fuel trims were/are somewhat lean, with net STFT + LTFT which climbs to +3-7% at idle but drops to 0% at 2,500 RPM. If one or more coils were weak and causing incomplete combustion, I would expect the ECM to be compensating with a negative fuel trim.

The above body of evidence was enough to initially convince me the coils were not an issue. However, after having since ruled out many other potential causes of a rough idle (dirty air filter, throttle body, IAC valve, PCV valve, or MAF; leaking intake manifold, throttle body, and valve cover gaskets or vacuum lines; worn spark plugs, clogged fuel injectors or clogged VVT-i oil filter; failing VVT-i solenoid, motor mounts, harmonic balancer, or torque converter; low compression, incorrect idle speed, etc.) I am returning my attention to the ignition coils themselves.

Specs Needed for Definitive Ignition Coil Performance Test
This brings me full circle to the reason for this post. Having already performed all basic tests of ignition coil function, I'm now looking to test them definitively to identify any coils which may be failing intermittently, but infrequently enough to avoid setting a misfire code. I believe the two parameters which would enable me to perform such a test would be the following:

— The resistance value between the two outside pins of the 4-pin male connector
— The voltage output of the coil, expressed in kV

Denso's product catalog doesn't specify either of these values for the OEM coil, Denso P/N 673-1300. I did reach out to Denso via email, but have not yet received a response. The Factory Service Manual for the Vibe and its sister Toyota Matrix don't specify these two values either — the coil troubleshooting workflow simply calls for checking resistance between the ECM and coil connectors to rule out an open or short in the wiring loom.

I did check the resistance of all four of my current coils between the two outer pins of each 4-pin connector in search of an outlier. At an ambient temperature of 65° F. (resistance varies with temperature), I obtained the below results by cylinder:

#1 — 22.1K Ohms (22,100 Ohms)
#2 — 24.3K Ohms (24,300 Ohms)
#3 — 22.7K Ohms (22,700 Ohms)
#4 — 23.6K Ohms (23,600 Ohms)

I just purchased the Lisle 20700 COP Spark Tester from Amazon, which should enable me to not only test and view the spark produced from each coil, but also check the voltage output by adjusting the spark plug tester's gap to determine the relative spark strength in each coil. The spark plug tester has a scale marked in kV for exactly this purpose.

While I may be able to use this to compare the spark strength across all four coils, I don't currently know what the spark strength is supposed to be on a new coil for sake of comparison. If anybody has new or new-ish OEM Denso coils and would be willing to test the resistance of the two outer pins of all four coils with a multimeter or the kV voltage output of the coil with an adjustable spark tester, I would be indebted!

Why Not Just Buy New Coils?
I'm not usually a fan of just throwing parts at a problem, and even though my current coils are likely original and now have 190K miles on them, I'm reticent to simply replace all four due to the cost ($200+) as well as the supply chain issues of the last year or two which seem to have reduced the quality of even OEM parts and given rise to many hard-to-spot counterfeits.

I'm pretty fed up with buying replacement parts (even authentic OEM from authorized dealers) and installing them only to find that they work less well than the old, supposedly worn out parts that they replaced. I've had really bad luck with replacement parts the last 2-3 years.

I've considered purchasing a single OEM Denso coil and swapping it into each cylinder one at a time and monitoring the rough idle condition to see if it improves. This would work if my problem is only a single coil, but likely wouldn't if the rough idle is a result of slow degradation across all four existing coils. I could also purchase a single coil and test it for primary resistance as well as kV output to use as a baseline against my existing coils, but thought I'd consult the collective hive mind first to see if anybody has previously tested specs on a new Denso 673-1300 ignition coil.

[Caretaker]

My initial thought is: ignoring the spark plugs and ignition coils is like ignoring to feed a malnourished baby because its belly is getting larger. Kids need feeding; cars need feeding. If you have never replaced either in the now 100,000 miles since you've owned the car, I'd bet good money that you are due. Secondly, given the car is now 20 years old, with your rough idle at rest and in gear, I'd surmise that your engine mounts could need replacing.

[schwartzy18510]

My initial thought is: ignoring the spark plugs and ignition coils is like ignoring to feed a malnourished baby because its belly is getting larger. Kids need feeding; cars need feeding. If you have never replaced either in the now 100,000 miles since you've owned the car, I'd bet good money that you are due. Secondly, given the car is now 20 years old, with your rough idle at rest and in gear, I'd surmise that your engine mounts could need replacing.

I replaced the spark plugs 1.5 years and 16,000 miles ago as part of routine maintenance with the NGK IFR5A11 (P/N 4996) laser iridium's recommended in the Factory Service Manual. I sourced them from Rock Auto, and they came gapped to the factory spec of .043". I torqued the replacements to the factory spec of 18 ft. lbs.

The old plugs that I removed still looked fantastic with no signs of fouling, and the worst of the bunch was only worn to .047" after having at least 80K known miles on them. I also bore-scoped all four cylinders at that time and could still see cross-hatching on the cylinder walls with no evidence of carbon build-up or oil burning.

I've replaced all four motor mounts twice now — once with aftermarket replacements which made the vibrations far worse, then again with the originals, which returned the problem to its original severity. All mounting bolts torqued to spec on both occasions (I triple-checked). I comprehensively examined and tested my existing mounts by hitting the throttle while in gear with the brake depressed and my engine doesn't have excessive movement forward or reverse, so I've ruled out motor mounts as the issue.

I plan another thread detailing my pursuit of the cause of the rough idle, so I'm trying to keep this one focused on the ignition coil element. I'm simply hoping to find a way to definitively test my current coils against known good coil specs as a baseline so I can rule them out as a cause before potentially throwing $200+ away for replacements with no observable difference in the idle issue.

[Caretaker]

Good. You certainly seem to be doing all the right things to rule out what it is not. It can't be the plugs unless like mine, one (or more) is getting constantly fouled by oil. I don't blame you for not wanting to throw parts at it. Mine is 6 years younger than yours and has been informed that it won't be signed to another contract. It is running fantastically right now and hopefully will get me to see all five of the hybrids I'm waiting for come years end (to include today's announcement that the new HRV should be out and about next month).

[jolt]

Coils are very heat sensitive. Your tester can not allow for the heat factor that the coils see when in an engine. Also be careful when testing the coils as a cracked or leakage (as in spark/voltage) from a coil can jump out and have a shocking result for you. A cracked spark plug will produce the same spark leak as the voltage gets higher. Your lightest voltage load at the spark plugs is at idle. The highest voltage is needed at heavy engine loads. This is were the coils and/or spark plugs will start to misfire. A tighter spark plug gap will reduce the energy load required from the coil. That is why spark plugs with a wider gap that factory spec will put more load on a coil and may cause the coil to have a short life span and misfire.

Is engine vacuum steady at idle? Have you checked the valve clearance? Does the idle vibration change from cold engine to hot engine?

Four cylinder engines are not smooth at idle by nature of their design, unless it is an opposed 4 cylinder like a Subaru. Larger four cylinders, like the Vibe 2.4L, have counter balance shafts to help smooth the engine at idle. The 1.8L does not have counter balance shafts.

[schwartzy18510]

Coils are very heat sensitive. Your tester can not allow for the heat factor that the coils see when in an engine. Also be careful when testing the coils as a cracked or leakage (as in spark/voltage) from a coil can jump out and have a shocking result for you. A cracked spark plug will produce the same spark leak as the voltage gets higher. Your lightest voltage load at the spark plugs is at idle. The highest voltage is needed at heavy engine loads. This is were the coils and/or spark plugs will start to misfire. A tighter spark plug gap will reduce the energy load required from the coil. That is why spark plugs with a wider gap that factory spec will put more load on a coil and may cause the coil to have a short life span and misfire.

Appreciate the details regarding the coil-and-plug relationship. The odd thing in my scenario is that the roughness I experience at idle disappears as RPM's increase — there is no discernible roughness to engine operation at 1,800-2,000 RPM's or anywhere above. This, combined with the lack of misfire codes makes me think plugs and/or coils can't be the culprit, but I'd like to rule them out if I can all the same as I have exhausted an incredibly lengthy list of other possibilities which I plan to detail here in a separate thread for sake of reference.

Is engine vacuum steady at idle? Have you checked the valve clearance? Does the idle vibration change from cold engine to hot engine?

Haven't found a really good way to monitor engine vacuum as of yet. I have inspected valve clearances, with results posted in the below thread:

viewtopic.php?p=530754#p530754

The idle vibration doesn't seem to change based on when the engine is hot/cold or in open/closed loop. However, it is MUCH worse in the cold winter months than it is in summer. Right now it is barely noticeable, but in winter it shakes the entire frame of the car. I would say it is temperature-dependent, but I think I also noted that when temps are cold but humidity is high (say, after a rain in spring/fall) it's not nearly as bad. Since humidity is usually much higher in summer in my area (Michigan) than winter, it could be moisture-dependent more so than temperature-dependent.

Four cylinder engines are not smooth at idle by nature of their design, unless it is an opposed 4 cylinder like a Subaru. Larger four cylinders, like the Vibe 2.4L, have counter balance shafts to help smooth the engine at idle. The 1.8L does not have counter balance shafts.

I know the 1ZZ-FE isn't known for being a super-smooth engine, but I've owned the car for nearly 10 years and 100K miles, so am familiar with its normal behavior. Something definitely changed about 10K miles ago and I can't figure out what. In the winter months, the car is virtually non-drivable due to the severe vibration.

[schwartzy18510]

It's been a busy spring and summer that has seen my family grow to a total of (5), which necessitated the purchase of a larger family hauler. We managed to pick up an '07 Toyota Sienna with only 95K miles on it that is in good shape for the year, so I've been fixing up odds and ends on it the last few months and am just now returning my attention to the Vibe.

By way of an update, I tested my ignition coils last night with the Lisle 20700 Coil-on-Plug Tester I linked to in my original post. Outdoor temp was 66° F., humidity was about 85%, testing was done with the engine cold and after dark in order to be able to get the best possible view of the spark output of each coil.

Before testing for spark, I double-checked the resistance between the two outer pins of each ignition coil. The results were virtually identical to my original resistance test results since the outdoor temps only differed by 1° F. between the two tests (resistance varies by temperature):

#1 — 22.1K Ohms (22,100 Ohms)
#2 — 24.3K Ohms (24,300 Ohms)
#3 — 22.8K Ohms (22,800 Ohms)
#4 — 23.6K Ohms (23,600 Ohms)

To avoid flooding the cylinders with fuel while cranking during the spark testing, I wanted to disable the fuel injectors, However, I found that pulling both the 15A EFI fuse in the fuse block under the hood as well as the EFI relay disabled spark to the ignition coils as well. I ended up simply disconnecting all (4) fuel injector wiring connectors. I also disconnected all coil connectors other than the coil being tested during the test.

I grounded my Lisle 20700 tester to the long valve cover stud sticking up on the front edge of the valve cover. My multimeter showed continuity between it and the negative terminal on the battery, with only 1.4 Ohms of resistance. For sake of comparison, this was less than the resistance between several body grounds that I checked and the battery, so I believed it a decent ground choice.

Ignition Coil Spark Strength Test Results:
#1 — Intermittent, yellow spark at 30kV; only 1/10 sparks at 40kV
#2 — Consistent, yellow spark at 20kV; intermittent, yellow spark at 30kV; no spark at 40kV
#3 — Consistent, white spark at 20kV; consistent, yellow spark at 30kV; consistent, but faint spark at 40kV
#4 — Intermittent, yellow spark at 20 kV; consistent, white spark at 30kV; intermittent, faint spark at 40kV

Based on these results, it looks like coil #3 is the strongest of the bunch with coils #4 and #2 the worst. There was no obviously "dead" or bad coil that I could discern. However, I may repeat this test tonight and seek to identify the exact cutoff point for consistent spark from each coil, rather than simply testing at the pre-marked 10kV intervals on my spark tester. This should give me a better picture of the relative health of each coil.

That said, I have only comparative results to go off of here as I cannot find any specs for resistance or kV output for the OEM coils. I even emailed Denso Technical Services and heard back that even they do not have access to this information. Is there anyone else with access to a coil-on-plug tester and OEM coils willing to chime in with resistance values and/or empirical spark strength test results expressed in kV?

[jolt]

Am not a lot of help here because I did not find any info about the coil resistance in the information I have for the Vibe. I do have info listed for coil resistance on KIA's. All KIA coils are:

Primary Coil Resistance (Ω) is 0.62 ±10% [20°C (68°F)]
Secondary Coil Resistance (Ω) is 7.0 ±15% [20°C (68°F)}

The coil resistance is going to vary for any given make because the control input voltage can vary from car manufacturer to car manufacture. There is info from Toyota about the supply voltage to the coils, and this may be another thing to check. Attached is the section about the ECM signal to the coils. If you look at section 5, marked as page 5-119 in the attachment, it sates "During cranking or idling, check the waveform between terminals IGT1 – IGT4 and E1 of the ECM connector.". You will need a scope to check this pattern to make sure that the signal from the ECM is consistent to the coils and not breaking down. The coils can only do what they are told to do, and if the signal is not getting to the coils from the ECM consistently, you will have issues. This should also cause a fault code too, but may be another thing to look into.