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Hi guys, help me out here. i've got a Volvo v70 2001 non-turbo 2.4L with 320,000kms and original coils that is eating COP coils (3/5 within weeks),by killing secondary. I can't find an underlying cause and i have new Bosch plugs as per spec. The head breaking curiosity I have is that I get pretty good, normal secondary ignition waveforms, but suddenly on same cylinder my Pico spits out a Firing line that goes to 100kV with an apparent misfire and waveform nose that is also crazy high ... sometime this waveform persists even I check for secure connections (i'm using a good secondary lead to tap into the COP with an inductive pick up). Then i stop and restart everything and it's all back to normal.
i don't think a real secondary waveform at 100kV plus is even possible -- even on an open circuit coil. If this was real it would definitely kill a coil; but I don't think it's a real waveform.
Can anyone give me a steer on what is happening here with the waveform.
This happens on cyls that have eaten and others (maybe it's getting ready to eat them too)
I've posted a normal and a crazy pattern here for reference.
Only thing that will cause that is break a open between the coil and the gap of the spark plug.
A high energy coil can create a massive voltage only really limited by the the quality of the coil insulation if the spark energy is blocked and has no route to the spark plug gap.
Once this happens a often enough the coil secondary insulation is damaged by tracking and you get a recurring misfire.
To me as your captures were taken using an extension lead downstream from the coils to me it points to a spark plug problem as the initial cause.
I would try a different spark plug, I like NGK and know the recommended grade work well in Volvos, check the spark gap before fitting it is listed as 0.028" or 0.7mm and make sure the conductor in the end of the coil pack is making good contact
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Wow. So you believe it's a real spike! I just couldn't get me head around it. Never seen one so high and it means the new bosch plugs are rubbish ... I'm really amazed and disappointed in equal parts
Thanks, I wish I could confirm the plugs are fake. I replaced Volvo OEM plugs and three new coils and it's now running like milk and honey. No secondary spikes.
For the record, the highest spike I captured was nudging 200kV!!! I thought my scope was losing the plote. I just didn't think this was posssible.
Learning 1: Open after the coils can cause monster V spikes
Learning 2: Trust your tools
I'm in doubt a secondary spike would reach 100 or even 200 kV.....
It would be interesting to see the coil's current ramp and the primary waveforms.An extremely swift current cut off would affect/rise the self-induced primary voltage level. An open in the 2dary will also show oscillations as the current doesn't have a place to go.
A semi-brutal test is to force the secondary intentionally open and see what voltage spike is being produced. I would love to know.
Thank for your feed back.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
I think this has to be a tooling glitch? Or, it is in Primary. Even, the beginning of dwell/point of turn-on is extreme. I am curious what the current ramp looks like, too. Have you tested on another vehicle, to rule out a tooling glitch?
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
Hi Chad and Juergon, attached is a pdf (only file type i could upload) of a typical primary capture I got of this Volvo ... never saw evidence of a spike on the primary side ... Maybe it doesn't exist, maybe it just didnt have during the capture.
I am very puzzled by the 100kV on the secondary and I'd like to believe it's not real, but I'm not sure.
Fact is, I've now changed out all coils and replaced OEM Volvo plugs and i see not spikes on any cylinder so far.
What eating me is to answer what was eating the coils ... still possible they were just old - 320,000kms - but to all start dying in the space of weeks????
Very interested to know what you all this.
The equipment I've been using is a baby Pico 2205A (only 2 channel), Hantek plug extension leads for secondary captures, Hantek 1008 for Primary multi channel capture ...
Would channel 3 (purple trace) show the ground leg/voltage of the coil you´re synced to? If so, the first rise in voltage there shows what looks like a shorted coil, look at the instant surge.
In general the resolution of this capture does not allow to see enough detail to analyze. You could try a shorter time base and two channels only. If you had captured the secondary kV spike with the hantek too I would have said: know the limitations of your tool....
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Good point. True Eric, but the current doesn't reflect that. Agree the Hantek is not ideal, but I use if for a 'first look' ...In any case, was synced off a new OEM coil.
Important update: I now believe the mega spikes were a fault in the capacitive pickup. I two on different cylinders and picked up a high spike again and swapped them around, and the spike moved with the pick up...
Nevertheless, there's still the issue of what is cooking coils ... I can't detect a lean condition, let alone an extreme lean condition ...
On that point, this Volvo is in a substituted value default fuel trim because of a faulty AFR sensor ... I'm waiting on customer to approve replacing sensor, but I don't believe a default running mode is going to put in engine into an extreme lean state.
Rear O2 is respond to added fuel and vacuum, and going rich on accel and full lean on decel.
Spark voltage is dictated the by the voltage it needs to get to ground by jumping the spark gap.
The max the KV the coil will produce only limited by the quality coils secondary insulation.
A couple of years back I calculated the energy stored in a wasted spark coil on a Rover it worked out as 0.178 Joules
I x V x t = 5a x14v x 2.45ms= 0.178 Joules
The only exit route for this energy is current via the spark gap.
If it is blocked and can't jump the spark gap the KV will climb verticaly untill it finds another escape route.
If excessively high KV is demanded downstream of the coil the coil the KV at the coil will eventually destroy the coil secondary insulation.
Looking at the dwell period the dwell time is fine not excessive so any fault on the primary cannot increase the secondary's peak spark voltage.
That the dwell period looks a bit odd is probably down to a combination of the vertical scale required to fit the high the high KV on screen and the hardware limmitations of the model of scope used.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Andy, what you describe as spark voltage otherwise is also called the firing kV, isn't it? The kV requirements to jump the spark in an ignition system will be dictated by the greatest gap within the secondary. In an ignition system working properly this happens to be the spark plug gap. A faulty secondary may cause higher kV demands than the plug gap does, depending on the fault.
So, an unauthorized open in the secondary -other than the spark gap - will make rise the firing kV until this open gets ionized and current starts to flow. This still could be across the plug's electrodes. Or it could be sideways, arcing out of the cylinder.
If the insulation was strong enough to not break down under this fault condition (quality coils will hold quite a while before they get damaged in my experience) then the voltage would climb indefinitely without establishing current flow wouldn't it? But it does not. It does not do so because it gets to a point where the secondary voltage , which keeps in movement/change at this time, is induced 'backwards' into the primary side of the coil which now acts as a step down transformer. Without any breakdown present this will cause a kind of flip-flop between the two coil circuits and finally the energy will be dissipated in this process. This also can be observed within the current trace as oscillations. In the long run these high voltage levels will destroy the coil.
There are (not only) two factors impacting the potential voltage and the energy of the secondary:
If the magnetic field (primary) was to collapse excessively fast than the induced voltage in the secondary potentially will rise, as well as with a higher than normal current flow due failing current limiting. Though, the captures in this thread do not reveal these problems.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
This really is fascinating me because of the pactical issue I have of getting down to the bottom of what was eating the coils.
As I say, I can't detect an extreme lean condition that would cause this (unfortunately I don't have a 5 gas analyzer).
On the spike, I understand the theory of voltage rising until it finds a path to ground, and/oscillating .... However, if I were asked (outside of this issue of I have) I would say once you are above 50kV and heading for 100+ or 200kV the V is going to find a path across the boot or track down plug if not flow out the coil insulation and' the waveform shape would be odd ...? Also, I'd expect oscillations like the end of a sec waveform?? ... I'm not sure if this is correctly called "inductance" because the field is not collapsing when V has nowhere to go? I think it may be capacitance? (side point as this stage)
Overall, I've been seeing a pretty typical looking waveform shape. Just ridiculous voltages ... (see attached)
I need to do some further comparative testing of my 2 pick up leads ... I think one is faulty and causinge both scopes I have to output incorrectly.
However, that aside, I think the issue of how high kV can go is worth trying to get to the bottom of ...
Really interested to hear further, particularly if anyone has actually seen such high V anomalies?? Thanks for staying with the topic guys.
It’s an interesting thought. I think Given coil secondary current is so low mA and V so high, i think it would have to be a hell of a resistance that wld prob affect all kinds of circuits??
Coils discharge through the engine block. Could high resistance in the engine ground cable cause this?
No a coil won't even notice it, If the engine block ground is bad even by less than 0.1ohm the starter motor will soon complain in contrast spark leads have a resistance of around 12,000 ohms per foot (300mm)
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Coils discharge through the engine block. Could high resistance in the engine ground cable cause this?
No a coil won't even notice it, If the engine block ground is bad even by less than 0.1ohm the starter motor will soon complain in contrast spark leads have a resistance of around 12,000 ohms per foot (300mm)
+1
High resistance won't affect the firing kV as long as there's no complete open. Once current flow is established this same high resistance will show as a higher than normal burn kV, the voltage level required to keep the spark going.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
