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Why Do I Keep Killing Coil Packs


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#1
kyepan

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So brain boxes... 

 

I was going to post this on the DTA forum, but there is probably more expertise here, so here goes. Also before you ask i've checked the dwell setting with Sandy and it's fine. We think it's running about 10.6:1 compression, on a 270 inlet and 260 exhaust cam, makes about 200ish BHP and 150 ft lbs of torque. 

 

I've been through about four/five coil packs in the past two years. The first one was high quality, the next two were s*ite, then last couple were good quality. The failures have all been identical. I use the standard Mi-16 champion (i think BCP7ET) plugs always. 

 

 

Over the course of a few months the following symptoms gradually surface. 

 

  • Car takes ages to turn over and fire from cold.
  • It struggles to pull itself off idle for at least 10 seconds after initially firing.
  • The car audibly looses all its deep bark, and sounds hollow and tinny.
  • It looses about fifty horsepower, it's massively down on power. (it wheel-spins in the dry in second with and LSD when it's on form) 

What I really need to know, is what exactly is failing within the coilpack (106 wasted spark) to cause these symptoms.. is it the windings breaking down, or the ignitor integrated circuit. As then i can take remedial action to resolve.

 

As i understand it, both heat and vibration kill coil packs. Heat because the integrated circuit is silicone and doesn't like heat. Vibration because the resin used to hold the thing together has a habit of coming apart allowing the windings to not be as insulated as they would normally be. The third cause i understand is a misfire, the car runs pretty sweetly 

 

Change the plugs, change the coil pack, and boom, it's back to it's monstrous old self.... then after a very short time it begins to imperceptibly degrade... the first start is the best. From then on it's a gradual decline. I have not given it a set of leads for perhaps a year, but this pattern doesn't seem to be affected by them. 

 

The coil is currently mounted reasonably solidly to the right hand of my MI-16 engine via a little bracket, there is plenty of air around it, and it's over the gear box. So there is metal - metal contact from the head, to the bracket, to the bolts through and metal inserts in the pack. There is currently no vibration damping from the engine. 

 

Initally the pack was mounted on some l brackets hovering to the side of the same location, and i didn't really have any issues. I may be answering my own question here. But.. I still need to understand what's failing in the coilpack or how to test it using the multimeter to find out. 

 

Secondly, when the car is cold it's tidy to drive, when it warms up, it's not quite as nice, very light throttle loads are a bit kangeroo.. this is both in traffic and at cruising speeds around town. Now i was in the car when sandy ironed this out at the original mapping. He pulled a bit of ignition for very light loads. It seems when the car (or something electrical) is cold it's pretty happy, warm, not so happy. 

 

The car spends... quite a bit of time sitting in london traffic whenever I escape from the big smoke to give it it's monthly spanking, so it does sit there heat soaking regularly. However the car doesn't overheat, doesn't even have the soundproofing on the underside of the bonnet. And standard cars run these for years without problems. 

 

Cheers

Justin. 


Edited by kyepan, 03 November 2015 - 05:18 PM.


#2
dcc

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My engine runs over 12:1 cr, i use bcp8es, a coil i stole from a scrap yard 6 years ago, leads which were new in 2009, engine bolted solid to the shell, the coil mounted to the side of the head, and being honest the engine spends most of its time near the 7.7k rev limit (because racecar?). I do change my plugs ever 6 months or so, at £1.48 each it is no problem. To say my engine gets hot and abused is an understatement. I've been trying to kill it for 2-3 years.

The point of the above? I've never had a failed coilpack. I can't tell you whats wrong, but I can hekp you by telling you whats not with mine (same style wasted spark coil). Maybe you should be looking elsewhere to whats happened!

#3
kyepan

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I'm quite happy to swap plugs out more regularly if that's the answer. 

What do your plugs look like when they come out? are the electrodes noticeably eroded. 

 

also why do you use the 8 temp plugs rather than the 7? 8 is cooler isn't it?

 

Ps, changing the plugs out will get it to fire immediately from cold.. perhaps the plugs are dying, taking the coil packs with them, as misfires kill coils too.

 



#4
welshpug

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100% sure its the coil?

given you change the plugs at the same time, I'd say the cold start map needs a tinker is all, nothing wrong with the coils, just fouled up plugs, it is the hardest part of a map to perfect.

I had issues as you may recall, fresh plugs fixed it, I have tried the ropiest looking coil in all my piles of tat and it works fine.

dan is on 8's as he has a 300 degree cam in an 8v on a decent bit of compression

Edited by welshpug, 03 November 2015 - 05:44 PM.


#5
Tom Fenton

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I've used the same type coilpack on a few cars, no issues with it for me. Mi16 on bodies and my 1600 8v turbo. Both bolted to the engine.

#6
Simes

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Same coilpack, same leads, new plugs only because one broke when I was checking them. No cold sfart map.
6 years about 9k miles.

#7
petert

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 Also before you ask i've checked the dwell setting with Sandy and it's fine. 

 

You really need to verify with an oscilloscope to verify the correct dwell time.



#8
kyepan

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You really need to verify with an oscilloscope to verify the correct dwell time.

the dwell is set in the software by sandy when he did the mapping, so i would assume with the number of engines he's mapped it would be correct. 



#9
wicked

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Dwell settings can differ per coilpack.... if the the dwell time is too long, you'll run too much current in the coil. 

Did you change wiring when you changed the mounting? Is the capacitor still used? Ignition module properly grounded (if used)?

If the switching signal needs to provide sharp edges on the coil input. (slow edges will generate more heat inside and less energy in the spark).

So check with a scope and make sure your wiring is ok.



#10
RossD

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So what do you have your dwell time set too? About 2.5 - 3.5 ms is about the right ballpark for these coilpacks. You say its been checked, but what is the actual number?!

 

Also are you running a lambda? I'm wondering if you are if its playing with the fuelling?


Edited by RossD, 04 November 2015 - 11:24 AM.


#11
petert

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http://www.dtec.net....Calibration.htm



#12
kyepan

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So what do you have your dwell time set too? About 2.5 - 3.5 ms is about the right ballpark for these coilpacks. You say its been checked, but what is the actual number?!

 

Also are you running a lambda? I'm wondering if you are if its playing with the fuelling?

no lambda, and yes it's about that, i think 3. something from memory, we checked it ages ago. 



#13
kyepan

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that is the link i've been searching for, thank you peter. 



#14
kyepan

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My dwell is set to 3000 microseconds

 

 

 

Another thermal consideration is for example, the mounting location; this may increase the components temperature as in when mounted directly on the engine above each cylinder. Temperatures can easily reach 80ºC under the bonnet.

 

Temperature will increase the resistance of the coil and wiring, ‘0.393 % per ºC’ is copper’s temperature characteristics so at 100 ºC its 39% higher, drivers actually have lower losses at higher temperature (semi-conductor materials used) and so help cancel out some of the temperature effect on losses.

A cooler coil pack is better, as it's internal resistance is lower, if it's struggling to charge up in time at higher rpm, the heat won't be helping. 

If the strength of the spark in amps is low, it's going to struggle to last any decent duration and help the ignition.. so that means it's going to be rich because of the slow incomplete burn and the plugs are going to get coked up. Which is not going to help anywhere else. 

 

 

 

 You could reduce the dwell at high temperature, sustained load and high RPM

So reducing dwell takes the load off the coil pack, if it's already struggling, and also if it's set too high, that will reduce the likelyhood of coil damage

 

Standard ignition modules, such as the bosch ones monitor and manage dwell.. but ECU's generally don't, they use dwell mapping, so they monitor rpm and voltage. 

 

In brief, these actually monitor the coil current and adjust the dwell to ensure the target level is always reached (about 7 amps is usual), this allows for RPM, temperature, voltage, coil tolerances etc.

 

longer dwell = stronger spark, up to the point where the coil gets too hot and then it kills the drivers in the ECU. 

 

NEVER have your dwell set long enough so that the driver is clamping the current, seen as a ‘flat’ section on the top of the current trace when viewing. Drivers (not modules) are generally not designed to limit current in normal continuous operation and they will fail very quickly.

 

 

DTA doesn't have a dwell RPM map, just one setting and a voltage compensation table, which I will have a look at.  I'm still not completely clear why it's having trouble starting in the cold, except that it has a weak spark. A strong strong spark at sparce intervals is required when at cranking rpm, because everything is cold, the petrol is less inclined to ignite. The period between ignitions is long at cranking, so this should give it ample time to built ampage. So i need to check that at cranking voltages (see graph and table below) it's increasing the dwell times, and then reducing it at higher voltages. 

 

 

Have a good look at coil current during cranking also; ensure it’s still acceptable as the battery voltage plummets under cranking. Dwell requirements are often so long that we need to compromise with what’s achievable.

image050.gif

 

Some voltage compensation tables including dwell time for different coils at different currents. 

image044.gif​

 

 

 

Power dissipation in the coil exceeds design limits, the plastic bobbin melts and the epoxy filler brakes down. Expanding material and gasses rupture the casing.

Clearly a duff or dying coilpack is really going to struggle further up the rev range if the following is beginning to happen. 

 

 

So it sounds like:

 

  • Checking the battery compensation table in the DTA software to make sure it's filled in, as i've not checked that. 
  • Making sure the Coil is in a slightly cooler place, if mounted to the side of the head, make sure its not bolted directly to it, just to a plate that is in turn bolted to the head. 
  • Reducing the dwell slightly would be a sensible safe step to see if the coils are getting overworked.
  • Running hotter plugs will keep them clean if sitting in traffic. 
  • Check that the alternator is outputting within a normal range, and not pumping too much voltage into the system. 

 

I don't have access to an oscilloscope to actually see how long the coil is taking to charge at idle. 

 

Cheers

J


Edited by kyepan, 04 November 2015 - 05:13 PM.


#15
Rippthrough

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Sensible list to check, I'd add to that, do you still have the capacitor in line on the power side by the coil in your loom? Line ripple from noise can kill coils over time as your dwell doesn't stay constant.



#16
petert

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A good check list, however I'd still find a friend with cro and ask them to check. Even if you pay them for their time, it's cheaper than buying new coils and you'll be able to set the dwell time precisely.



#17
wicked

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Did you change wiring when you changed the mounting?

Is the capacitor still used?

Ignition module properly grounded (if used)?

 

?

 

If you have to pay for someone to measure it with a scope, you might consider buying a USB scope from ebay; search for Hantek 6022E for instance. About 40 quid...

It's not a high end scope but good enough for these kind of measurements. (It comes with 1:10 probes so it can go up to 50V.) 



#18
wicked

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To complete the new toy, you could order this one as well, to measure the current profile on secondary side:

http://www.ebay.co.u...=item4180082be2



#19
Anthony

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Did you change wiring when you changed the mounting?
Is the capacitor still used?
Ignition module properly grounded (if used)?


On J's behalf since I know the car reasonably well:

1. The coilpack wiring wasn't changed because there was enough length in the wiring - the coil only moved about 3 inches.
2. There's no capacitor used, although this doesn't seem to cause issues on other cars running a similar setup with a DTA and TU/XU 8v wasted spark coil.
3. It's using the drivers built into the DTA itself rather than an external ignition module

#20
kyepan

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?

 

If you have to pay for someone to measure it with a scope, you might consider buying a USB scope from ebay; search for Hantek 6022E for instance. About 40 quid...

It's not a high end scope but good enough for these kind of measurements. (It comes with 1:10 probes so it can go up to 50V.) 

sorry i missed the first message wicked, the ecu is grounded, as is the coilpack. 

Thanks for the hantek link, i'll look into that.