When to replace Ignition coils. (5 Viewers)

[Hapyhour]

333,333 miles and 2 coils just went bad. CEL and VSC trac / VSC off lit up on dash. low speed ran rough with misfire.
replaced just the 2 and running great again. Think I will carry a spare.

 

[white_lx]

Ever since OP started this thread, I have been thinking about building a coil tester. But not having access to a 'bad coil' makes it difficult to set the criteria for a good/bad coil. Well finally it happened, I had to replace a coil. No more excuses not to build a tester.

Here is what I came up with:

It is a very simple circuit that pulses the coils as normally the ECM would. To test the output of the coil, I'm using a Lisle ignition tester that can be set to a wide variety of gaps. The connector + wiring came from Ebay in a 6-pack.

Here are my first observations of the marginally failed coil at 214kmiles / 17 year (from a 3UZ-FE with slightly higher compression ratio, but it shouldn't really matter too much).

The failed coil pulses fine at 10 Hz (1200 rpm) up to around 7.7mm gap. If I set the gap any wider the pulsing becomes erratic / unstable. Per FSM, the max spark plug gap is 1.3mm. But under compression the actual gap that can be bridged is smaller because of the higher pressures inside the cylinder. So for the coil work in an engine, it needs to be able to arc across at least 7.7mm at 10 Hz on the test bench. At 12mm gap, I can hear this coil short internally and there is no arc visible.

I verified another working original coil with 214kmiles from the same engine and it has no problem firing at 12mm. I will try to do some more testing to see how much more I can increase the gap before it starts failing (edit: coil arcing fine at 20mm as well). Ultimately, I also want to test a brand new OEM coil. Maybe even compare it to a Denso, to see if those are less powerful than OEM Toyota.

Other things to test are effect of pulse rate, temperature, etc etc. The list goes on.

Assuming the deterioration is gradual, this could be a simple test during a tune-up as PM.

A good coil at 12mm, 10 Hz (camera does not capture all sparks, note the consistent sound):




The failed coil at 7.7mm, 10 Hz (note the inconsistent sound):

 

[2001LC]

I'll see if I've some of my bad and misfiring coils marked as such. If so I'll ship to you. I also have some that just didn't run as smooth. But in those cases I swapped out all 8 and have no idea of which are good or weak.

PM me your address.

 

[white_lx]

One more. Good coil at 20mm, 30 Hz (again not all arcs are captured):

 

[white_lx]

I see if I've some of my bad and misfiring coils marked as such. If so I'll ship to you. I also have some that just didn't run as smooth. But in those cases I swapped out all 8 and have no idea of which are good or weak.

PM sent. It would be very interesting to look at your coils. This will help establish proper criteria for a 'good' v.s. 'bad' coil.

Once we define what a good coil is, it would be rather easy to use a low-cost coil on plug tester (such as the Lisle 20700) to test coils in the vehicle. Just set the gap of the tester, insert in the coil and crank the engine (EFI fuse removed).

Edit: Found this little table in the instructions of (obscure) COP tester. Maybe that can also provide some guidelines to minimum gap required for reliable engine operation. Note that the first column lists 'pressure', but they mean 'compression ratio' - which is 9.6 for the 2UZ-FE. So 2cm/20mm would be a good start. As per the previous posting a 'good coil' will arc across 20mm.

 

[2001LC]

I've your address and will search my shop and see what I can find. Hope I didn't toss out the bad ones. I toss a lot while putting ceiling, heat and electrical in shop last winter, so just not sure what's remaining. I'm very busy getting "Merlot" ready for deliver and HIH, and then have AC line repair Tuesday for HIH bound 99LC also. So will be later this week at best.

 

[Dannyboy lx470]

When checking for misfire in tech stream. I find it helpful to put engine under load. This can be done by holding brake on with left foot. Put transmission into gear (i.e. "D"). Then raise RPM with right foot on gas, to 1,500 RPM or so.

Just because a coil looks new doesn't mean it's firing properly. But ones that are crack will not last, nor likely be firing at peak performance.

The really tough part is finding coils that aren't operating peak performance, like as when new. Without the specialize equipment shown in OP.

I've found that if engine is well tuned (i.e no vacuum leaks, tested and rebuilt fuel injectors, new spark plugs, new air filter, clean properly MAF sensor, properly operating OAT & water temp sensor, clean throttle body, de- carboned pistons & valves, proper voltage, coolant system to spec, etc.). I'll smell gas from exhaust after warm up, and when giving full throttle to enter HWY or pass. I'll feel ever so slight hesitation in acceleration. Swap in a new set of coils and gas smell goes away, and acceleration is flawless.

Whereas split coils may still operate and not show misfire. The split is sign of running excessively hot. Heat is the enemy of coils. Two main reason for excessive heat being created in coils IMHO is:
1) Gap of spark plug is out of spec (new is 1.1mm, at 1.3mm they must be replaced). The larger the gap the more current delivered from the coil. The more current produced by coil the hot it gets internally.
2) Spare plugs walking out. The hot gasses escape from combustion camber passed the spark plugs (SP) thread into the SP tube. This heat coils from outside. Additionally as plugs walk out (loosen) they seal (expand from heat) as engine reaches op temp. But once plugs become to loose it no longer seals. Then hot gasses escape even at op temp. As SP electrode (tip) moves further away form optimally firing point and enters thread area of head, the coil keeps delivery more power. This not only overheats coil. But it will blow the spark plug out of the head. A search in mud, will produce pictures/accounts of Spark Plugs blown out of the head.

Spark Plugs that have a brown halo are "typically" slightly loose SP, that expand and seal at OP TEMP. The boots of coils brown and harden.

Spark plugs and coils boots that are blackening, are those that "typically" are so loose they don't seal be expansion at OP TEMP.

#3 coil was the loosest. Notice the blackening of plug and coil boot. This one was very close to blowing out of the head.

Coils and spark plugs (junk Bosch platinum, I'd never use them) are in order. With #1 in upper LH corner and #2 in RH upper corner. The tube oil seal where not leaking:
View attachment 2007444

Thanks for that. My car runs fine and all tuned up well and no codes,but as you say sometimes entering the Hwy and need to give it gas a bit sluggish and revs a bit before get going maybe a sign the coils a not the best.

 

[Wilsil]

I couldn't bear the misfiring anymore and dropped it off at my mechanic (not my local).
He rang me and said they found it was a bad coil.
One if the 4 I didn't replace.........

 

[2001LC]

@white_lx I found my old coils and have some in a box, that I'll be shipping to you. 1 is marked misfire, 1 overheated (engine) plus a hand fully of IDK's.

It will interesting to see how the misfire reacts in your test. It only misfired under a load. When it first acted up, it felt like a bad torque convert while siting a red light in "D". Looking in tech stream it did not misfire, until under load. That is, I put shiftier in"D", foot on brake peddle and raised RPMs. Then it started misfiring.

The one from overheated engine, was just 1 of 8 that where replaced. Replacing the 8 coils gave back smooth acceleration during HWY passing. That is I could feel the slightest hesitation throughout the power cure as I floored it, keeping it floored. Replaced all 8 coils, and smooth as silk acceleration. I can't say if this one I'm shipping you or which coil(s) where weak. I can say; none showed a misfire.

Next I hope to see you develop equipment to test coils while in the engine... that cost pennies to build..

 

[2001LC]

Thanks for that. My car runs fine and all tuned up well and no codes,but as you say sometimes entering the Hwy and need to give it gas a bit sluggish and revs a bit before get going maybe a sign the coils a not the best.

Could be coils. Remember engine needs a good tuning first. Then look to coils.

But your statement "revs a bit" if I understand you. Sounds like transmission slipping! Is transmission fluid level low or set correctly, does fluid smell burnt or anything feel off in shifting of transmission.

 

[white_lx]

I found my old coils and have some in a box, that I'll be shipping to you. 1 is marked misfire, 1 overheated (engine) plus a hand fully of IDK's.

Thanks. I'll be looking out for those.

Next I hope to see you develop equipment to test coils while in the engine... that cost pennies to build..

The Lisle COP tester listed in post #205 might work, we just need to establish the parameters to which to test too. I hope that the spark gap at ambient is sufficient, but we may have to look at more.

The other important parameter is coil aging. If there is no gradual aging but just a sudden failure, then testing COP's for performance would not make sense as aged coils would look like new coils till the moment of first failure.

As an example, I tested 3 more coils from the same vehicle (all 17 years, 214 k miles). All three fired perfectly across a 20mm gap. So so far it is either a pass or a no-pass. No advance warning in deterioration based on arc distance. This is where your 'marginal' coils will come in handy. I'm hoping to find some that are in between good and bad coils and find a way how to detect that.

Also found this attached document. It is a pretty interesting background about coils, albeit from a different manufacturer than Denso.

 

[2001LC]

Look at OP the 2nd video.

 

[udubfl]

In the spirit of sharing!...Been in the other thread fixing my rough idle/RPM jumps/jerking and acceleration hesitations. I believe it was 2 cracked coils. Here's the stats:

Year: 2001 LC
Miles: 177,000
Previous Coils: Original Toyota (never replaced)
Previous Park Plugs: Denso SK20R11 replaced in 2014 @ 137k miles
Areas of Issues: #4 and #5 coils cracked
Symptoms: It all started one day...it didn't get progressively worse. In standing "D" or "R", it RPM was jumping up and down. "Park" seemed more stable. Starting to accelerate (pressing gas pedal), not always but sometimes, it was jerking/shuttering initially and smooth out at higher speed. So, I thought initially, it was only when idle. But then, when pushing the acceleration harder (going uphill), it would jerk/shutter little more like it was starving for gas or air.

Resolution to Fix: Replaced with 8 new Denso SK20R11 plugs and 8 new Denso coils. I figured if 2 is cracked now, its envitable that others might crack right behind it. Besides, I was going through a checklist and been spending days on this so I wanted to just end it for awhile and call it a PM for the next 150K miles if I need to justify it.

PS - this forum is always helpful as I'm continuously learning and not really savvy under the hood, so kudos to all. I even learned that there are fake (knockoff) Denso coils so I was careful where I was ordering from, inspecting it after delivery, etc. Thanks to all.

2 cracked coils:

 

[LateOnTheBrakes]

I noticed a cracked coil when I changed my spark plugs this weekend. I have not received any CEL and the truck seems to be running fine. Is everyone else replacing only based on symptoms? Is a cracked insulator cause for concern?

 

[2001LC]

I would replace with Denso or Toyota (pricier Denso). You'll likely get misfire under load. I'd not grease the boots, may retain more heat.

If any boots on coils or top seal are dry and crack (seen when end squeezed), I'd replace. Use dense coils kits (boot, spring and seal)

I would replace all spark plugs with factory Denso or NKG, even if plugs aren't that old. If pulled the crush washer is not as good a seal when re torqued.

 

[udubfl]

Its been about 3 weeks since I replaced all the coils (2 were cracked and rest didn't have cracks) and plugs and went on a 1000 mile trip last week and its running really smooth and probably better than it before. My symptoms were rough idle at "D" and jerking affect when accelerating under heavy load.

 

[LateOnTheBrakes]

I would replace with Denso or Toyota (pricier Denso). You'll likely get misfire under load. I'd not grease the boots, may retain more heat.

If any boots on coils or top seal are dry and crack (seen when end squeezed), I'd replace. Use dense coils kits (boot, spring and seal)

I would replace all spark plugs with factory Denso or NKG, even if plugs aren't that old. If pulled the crush washer is not as good a seal when re torqued.

It had the (dielectric?) grease when I removed them. Already replaced with Denso plugs. I only noticed the one coil that was cracked. I am at 149k miles. I have never noticed a rough idle and there are no pending codes with my generic OBDII reader or TechStream.

 

[Vision]

As always, this community is a wealth of knowledge.

I had the typical misfire under acceleration, and went to the same shop I always to do to see what cylinder was misfiring. New mechanic not only didnt know where to read the code, he got into an argument with me and bet me lunch that is was a driveshaft. The other place I went did read the cylinders in the parking lot, but then wanted to charge $90 for reading it and then wanted to do a full electrical diagnostic. I spent the better part of a week trying to troubleshoot it myself by switching coils around, but ended up more frustrated.

I finally just broke down and ordered a $20 WiFi scanner from Amazon and got the OBD Fusion app for $10. You do need to pay the extra $10 for the Toyota specific Mode 06 reader, so I spent $40 total. I have a 1998 and a 1999 LX470, so I will hopefully get some future use out of it all.

After setting up the display, I took it out for a spin and found that the #1 and #4 cylinders were the culprit. I had my last two spares ready to go, and now it works like a champ. I ordered a set of 8 NDK Spark plugs and will be changing them all out at once in the next day or two. Bottom line, change the spark plugs at regular intervals to prevent the coils from going out, and spend the $$ on a scanner app.

 

[nitteo]

As always, this community is a wealth of knowledge.

I had the typical misfire under acceleration, and went to the same shop I always to do to see what cylinder was misfiring. New mechanic not only didnt know where to read the code, he got into an argument with me and bet me lunch that is was a driveshaft. The other place I went did read the cylinders in the parking lot, but then wanted to charge $90 for reading it and then wanted to do a full electrical diagnostic. I spent the better part of a week trying to troubleshoot it myself by switching coils around, but ended up more frustrated.

I finally just broke down and ordered a $20 WiFi scanner from Amazon and got the OBD Fusion app for $10. You do need to pay the extra $10 for the Toyota specific Mode 06 reader, so I spent $40 total. I have a 1998 and a 1999 LX470, so I will hopefully get some future use out of it all.

After setting up the display, I took it out for a spin and found that the #1 and #4 cylinders were the culprit. I had my last two spares ready to go, and now it works like a champ. I ordered a set of 8 NDK Spark plugs and will be changing them all out at once in the next day or two. Bottom line, change the spark plugs at regular intervals to prevent the coils from going out, and spend the $$ on a scanner app.

link to everything you bought?

 

[2001LC]

Good spark plugs, nice tight gap and properly torque in. Is the key to health of coils.

I'm now trying the TT Denso spark plugs with my new Denso coils. They start at 1mm gap and boast greater efficiency (low power consumption yield a greater spark).

Ticking time bomb TICK TICK TICK: Spark plugs Alert Alert Alert!

TICK TICK TICK POP POP POP is a ticking time bomb, often mistaken as exhaust manifold crack or gasket leak leak. ALERT, ALERT, ALERT: Spark plugs are working themselves loose. "Walking Out" Then blowing out of head, taking their female threads of head with them! Very damaging! You think TICK...

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