Arcing coil

[wtd]

I have a 98 chevy with the 5.7L V-8. Over the last two years, I've had a reaccuring problem with the coil starting to arch on the outside of the coil body. You can see the blue arch as the truck is running. Symptoms of this are sluggish performance as RPMs rise and reduced fuel mileage.

I believe the problem was first caused by a loose ground wire that grounds most of the sensors and electronics on the engine after an intake manifold gasket replacement by the dealer.

Here is what I've done and replaced:

1. Replaced two main braided ground straps and cleaned and retightend all of the other ground wires.
2. Replaced the spark plugs, cap & rotor, plug wires, coil, and coil driver module. All of these ignition components have been replaced about four times in the last two years except for the coil driver module which has only been replaced once. The arching coil eventually causes my wires to arch and the cap to get small cracks in it. You can see where the coil have been arching from the white "burn" marks on the outside of the coil body. The coil archs to the bracket that goes all the way around the coil.

I'm using all new AC-Delco replacement parts. There are no trouble codes being stored in the ECM.

My coil has again started arching and I was wondering if anyone had an idea at what I should look at next. I'm all out of ideas and am pretty fed up with this problem. If I could afford it, I would trade this truck in. Anybody got a clue?

Wayne

[ October 08, 2003, 11:03 PM: Message edited by: Dan4510 ]

 

[Christopher R. Wise]

As far as the white coloring this is normal, you will see this on almost all GM coils that is setup this way, I have seen it on every truck, doesn't mean it is arching.

But if you are seeing the blue arch again well that is different.

Loose ground will cause a misfire but not arching, the only thing that will cause that is bad coil or open circut in the secondary ignition circut.

Are you running wider gap plugs then stock? If so this causes higher voltage in the S.I.C.

Just some thoughts.
What mods do you have????

CRW

 

[MolaKule]

Where is arcing from? I see you mention where it is arcing to.

Is the arcing from the coil tower or top, where the HV wire goes to the distributor? Or is it from the HV terminal to one of the power supply wires?


Corona discharge or "plasma" glow is normal, especially in humid areas.

 

[wtd]

The arch is from the side of the coil body to the bracket. It is not from any of the wires or the coil tower. Its almost like there is a crack in the coil body and the spark is coming out of the side. It archs in approximately the same location on each coil.

Wayne

 

[Christopher R. Wise]

quote:

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I don't know if you are familiar with the coil on the 5.7L vortec, but the coil body is surrounded by bracket which is used to bolt the coil down.

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I am very familiar with this coil, I'm was formerly a GM tech a dealership. And I can say that I don't think I have ever see what you are descibing.

quote:

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It always archs at a point right next to this bracket.

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It is trying to find the shorted path to ground, well the bracket is ground.

quote:

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How would I go about finding an open circuit in the secondary ignition circuit and what components make up the secondary ignition circuit?

---

Well the secondary circut includes the coil and everything after the coil. You can use a simple Ohm's meter to measure the wires and plugs.

Well good luck, it sounds a little strange.

Does the truck misfire at all.

CRW

 

[got boost?]

check your plug gap, it also doesn't hurt to lube the boots liberally with silicone grease. where is it arcing to?

 

[wtd]

CRW,
You can definately see the blue arch in the dark and it always archs where the the white marks are on the coil. I don't know if you are familiar with the coil on the 5.7L vortec, but the coil body is surrounded by bracket which is used to bolt the coil down. It always archs at a point right next to this bracket. Sometimes on the frontside and sometimes on the backside. Eventually if I let the problem go long enough, the plug wires will "light up" with a blue glow along different areas of the wire. Some people have told me this is normal but I don't know.

My plugs are the recommended AC-Delco platinums which I gapped to the .060 the manufacturer recommends. These stock type plugs use a platinum disc on the side electrode which sometimes falls off, thus opening the gap up slightly. I don't know if this set has lost any discs yet, but some of my past plugs had lost theirs. I used dielectric grease in the boots of all of the plug wires.

The only mod this truck has is a Borla cat-back exhaust system. Everything else is stock.

How would I go about finding an open circuit in the secondary ignition circuit and what components make up the secondary ignition circuit?

Thanks for all the replies.

Wayne

 

[wtd]

CRW,
I pulled out my sparkplugs yesterday and all of them still had their platinum discs attached and the gap was still within specs. I replaced these with AC Delco Rapidfire platinum plugs that don't have the discs so I don't have to worry about them falling off.

The SES light has never came on and there is no history of misfires or any trouble codes stored on the ECM. The only symptom of this problem is the feeling of power loss as RPMs increase. The best I can describe it as feeling as if there is a brick under the accelerator pedal and the truck has no get up and go.

I will check the resistance of the plugs I just took out and the wires. What should the resistance of the plugs be?

Is there a better brand of wires, plugs, cap, rotor and coil that I should be using? I have heard that the factory type wires are not that great. Thanks for your help.

Wayne

 

[LM]

CRW would have likely mentioned if there's a TSB on the coil or bracket, but perhaps search just in case

Is there a torque spec for the coil bracket, and the bracket is applying uniform & moderate clamping pressure (i.e., the new coils aren't being subtly cracked on installation)?

Otherwise, what you're describing sounds like excessive secondary ignition resistance. The resistance is less between the coil and bracket, vs the spark plug gap(s) and high cylinder pressure, hence the arc. Some possible causes include: open or high resistance wires, lean fuel mixture, retarded timing, worn or improperly gapped spark plugs, corrosion build up on plug wire terminals (the latter you've already got covered). I'm not up on later ignition systems - probably no longer used or is integrated into the module - but if your system uses a ballast resistor, ck that it is okay/within specs

A scientific analog oscilloscope, an automotive scope, a modern day digital storage oscilloscope (DSO) or hand-held scope unit (first two are relatively inexpensive, last two aren't - all require some experience), with the proper pick-up clamps (probes), should be able to pinpoint the problem. Good diagnostic shops/garages will have them. Can usually discern between an electrical or fuel mixture problem, by the slope of the spark line, essentially displaying the ignition process as it occurs (do a google search for "secondary ignition waveform"). Some specific tests to perform would be a "Snap-throttle" and a "Cranking KV", to stress the secondary ignition system (yours would fail or be abnormal in it's present state)

Plug wire resistance generally shouldn't exceed ~20K ohms, depending on length, and more specifically so much resistance per foot (there should be min & max specs for your wires somewhere). But doesn't seem to be the root cause, as you've been thru several wire sets (am assuming you've been also replacing the coil wire, if present). Well-regarded aftermarket wires would include Magnecor, Holley, Accel, Crane, and others (but again, may not fix the fundamental problem). There are price/quality/ model steps within some lines

Suggest using only a light amount of dielectric grease, as is a weak conductor. Also make sure that the spark plug seating areas are clean.

 

[MolaKule]

ON my '92 Suburban with the 5.7 L, the coil is bolted down at the bottom through the steel laminations of the coil, there is no real bracket surrounding the coil, per se. There are two plugs going into the coil body, one for ignition current, the other from the coil driver and the EST module. The HV connection is pointing toward the front of the engine and my Acel HV wire goes to the distributor cap at the center.

Is this the same setup?

 

[wtd]

LM,
The original coil was riveted on to the mounting bracket. To replace, you have to drill out the rivets and replace them with a bolt and nut supplied with the new coil. There are no torque specs and the way this coil is bolted down, wouldn't affect the coil body.

The coil, plugs, cap & rotor only had about 14,600 miles on them. The coil module only has about 12,100 miles on it and the wires only have about 10,000 miles on them and the coil wire is getting replaced with the rest of the wires. None of this stuff should be bad this soon. I did have Magnacor plug wires on this truck but they did not make any difference that I could tell. I put the factory wires back on because the Magnacor's did not fit in the factory holders and I had them zip tied to everything. I may end up trying Magnacor's factory replacement 7mm wires instead of the 8mm race wires I was using.

Last year when I had the truck in the shop for this problem, they put the truck on a scope and said everything checked out normal.

I didn't start having any problems untill after the intake manifold gasket replacement. I'm wondering if the distributor was somehow messed up when they took it out or when they reinstalled it. It was put in slightly off from factory since my #5 plug wire will no longer fit in the plug holder closest to the distributor but the shop said its set within specs.

Molekule,
My coil has one plug in on the top and the HV tower on top. Those are the only two things on this coil.

Wayne

 

[LM]

A few more questions, if I might

What do/did your 'old' inner distributor contacts and rotor tip look like at replacement - are they burnt black or rutted at all? Or normal grayish/chalkish tracks, with little to no depression, located somewhere approx lower 1/3 to 1/2 up distributor contacts

Do all the 'old' spark plugs have the uniform normal gray/tan/brown color appearance, w/very little variance?

Does/did your truck initially run really well - like it should - after putting in the new ignition parts (for a while, until deterioration)? Or are there any flat spots on acceleration, hesitation, vibration?

Lance

[ September 29, 2003, 01:23 AM: Message edited by: LM ]

 

[BOBISTHEOILGUY]

I like problems like these, but only on someone elses engine.

Might I suggest something here.

First clue, you've stated that it only started to happen after the manifold job.

Second clue, it always happens at the same location(spark)

Ok, current follows the least path of resistance to ground. The wires, have to have some resistance to keep rfi problems down to a min. So, the spark from the coil will always be met with resistance under normal conditions.

So, what my be connecting the spark problem to the manifold job? Well, some questions you need to answer, was the engine or has the engine performed up to specs after you got the job done or has it been lax, possibly due to incorrect distributor installation? Does it start immediatly or sometimes hard? If the distributor is incorrectly installed for timing, the gap between the rotor point and cap(wire) can be such that the arc could find ground easier after it has had some time to slightly carbon up the inside cap tip.

The design is cap tip should be matched up to the rotor tip at time of fire, but if rotor tip fires after it passes the cap tip, then now it looks for nearest ground. When cap is new, no carbon on cap, but as it gets used, it can build up higher resistance on cap. This kind of condition can exist on newer engines with the new computers as it will "learn" the engines problems and slightly adjust itself which can somewhat "mask" to problem. Also this would cause performance and fuel economy issues as well.

A distributor can be installed such that you can be a tooth off and compensate with some manual ajdusting but yet still be off. I've even installed a distibutor 180deg out, and reversed the wiring and made one run.

Second clue to look at. Always arcs out at the same place. Looking at the cap, arcing sometimes leaves a carbon trail. See where it is inside of cap. If the trail leads directly to a specific wire(cap tip), then that is where you are getting high resistance on that wire/ circuit. If it's between cap tips, then see which way the rotor turns and the tip that it had just past will be where the problem lyes as it should have been firing on that tip. Again, possibly leading to the timing issue I discussed in prev paragh.

Be interesting to see what you find.

bob

 

[wtd]

Lance,
The contact points on my last cap are like you describe, gray/chalky color and go up the post between 1/3 to 1/2". They look normal to me. The rotor tip is not pitted but does look a little black.

My original plugs and the set I just took out all looked normal except for a little carbon buildup on the flat part of the plug. They are all uniform in color. One of my original plugs was missing the platinum disc on the underside of the side electrode.

After I install all new ignition components, the truck runs like it is brand new, with plenty of power and no flat spots or surging. Before I found the loose ground wire that attaches to my thermostat housing, The coil was only lasting about 3,000 miles before it started arching and the truck started feeling sluggish and down on power. This last set of ignition components lasted quite a bit longer since I tightened the ground wire. Truck feels very sluggish right now and milage is down.

Bob,
The timing on this truck is non-adjustable. The only thing that can be set is the cam retard offset adjustment which according to my helms service manual is supposed to be set to 0 degrees. If this is not set right it could cause crossfire which is why I had the shop check this adjustment last year. They said it was set at 0 degrees like it was supposed to be. The technicion did say that the distributor might be in a tooth off but since the cam retard offset adjustment was set where it should be, that it being a tooth off would not matter.

The performance right after the gasket replacement seemed the same as before but the truck did seem to start a little harder than before. I took it back to the dealer and told them it felt like the timing might be off but they said everything checked out fine. The truck eventually started like it did before the gasket replacement and I chalked it up to the computer finally adjusting back to normal as I assumed that the dealer disconnected my battery when they did the repair. Right now, the truck starts right up with no hesitation. Once in awhile it starts a little sluggish but thats a very rare occurance.

I checked my last cap for carbon tracking but I'm not sure what I'm looking for. There are a few places on the inside and outside of the cap that look like faint lines but I'm not sure if they are carbon tracks or just part of the construction of the cap. How do I know which it is for sure?

I'm probably going to take the truck back to the dealer and have them check to see what the cam retard offset is and see if its within spec like the other shop said it was.

Thanks to the both of you for your input. Maybe we can get this figured out.

Wayne

 

[LM]

Wayne - not sure I can help, but let me give this some thought

You're now on fifth coil or so (+ other ign parts), in two years, if I understand things correctly. What specific model truck do you have

http://www.alldata.com/TSB/9811_mo.html

Do you have a wiring diagram of your ignition system (do you happen to have a Bentley or Haynes service manual)? Maybe we can find on line

Do you have a Digital MultiMeter/DMM/DVOM and are you familiar with circuit voltage-drop testing? The loose ground wire at your t-stat housing - what component(s) does it ground, exactly?

Lance

 

[LM]

What immediately stands out is, of course, the ignition control module being part of the t-stat housing grnd array

And, just to be clear with all the synonyms and acronyms in our auto tech world, the ICM is the heart of your ignition system, controlling timing advance, retardation, has various input sensor signals coming in to it, and is connected to either your ignition coil or coil module?

Also, are your blinkers part of the 'instrument cluster', or does the former have a different ground, and the latter is for the speedo, tach, dash gauges, etc.?

Grounds can actually be voltage-drop tested - I'll write up something and/or provide links on how to do it (is fairly straightforward, w/a few caveats [DMM just has to be able to measure volts, so should be okay]).

Can you get to the ICM (and possibly other) wiring harness connector (we won't be messing with any control units, per se), w/o having to rip apart half of your truck?

Do you happen to have a scanner and could PM/jpeg me the ignition system wiring diagram, with the associated component number guide? Also, if the ICM interfaces with any other control modules, would like to see those, too.

I know the others but am blocking on what is "VCM"?

Lance

[ September 30, 2003, 02:52 PM: Message edited by: LM ]

 

[wtd]

Lance,
My truck is a 98 Chevy ext-cab Z71 with the 5.7L. I do have a subscription to Alldata where I can view all of the TSB and recall information and various diagrams. I also have the factory Helm service manuals which comprises of four large manuals and it does have a diagram of the ignition system.

I do have a digital multimeter but its a pretty basic model. I'm not sure if it does everything I need it to.

I'm not familiar with circuit voltage drop testing.

The ground wire at the thermostat housing and a ground wire that bolts to the back of the right hand cylinder head, grounds these components according to the helms manual: VCM, fuel pump relay, transfer case shift control module, instrument cluster, cruise control module, EVO/passlock module, data link connector, A/C compressor low pressure cutout switch, MAF sensor, ignition control module, A/C compressor cycling switch. Both of these ground wires are tied into each other.

I also have some type of electrical problem that started around the same time, that causes my voltmeter gauge needle to move back and forth with the clicking of the blinkers. The light that illuminates the passenger side airbag shutoff switch also brightens/dims with the clicking of the blinkers. I've been told that this is a grounding problem, but I've checked every ground I've been able to find on this truck and cleaned and retightened the connections. I also replaced the two braided ground straps that ground the engine and the body.

Thanks for any help or input.

Wayne

 

[wtd]

Lance,
I emailed you some diagrams and hopefully they will help. One is the ignition control diagram and the other is the 103, 104 ground wire diagram. Ground wire 103 is the one that was loose on my truck for quite awhile before I found it.

I'm not sure where my ICM is because my service manual and Alldata seem to contridict themselves. They both say my ICM is located where my ignition coil driver module is so I don't know what to think. In my helms manual they describe my ICD(ignition coil driver module) as just a big switch with limited functions. They also reference the ICM as being in my VCM(Vehicle Control Module-Truck's main computer).

I'm going to do a little more research and try to find out exactly where the ICM is and if its the same thing as the ICD.

Wayne

 

[LM]

Hey Wayne. I think the problem is that your truck has about 3 or 4 too many "modules" on it

PCM, VCM, ECM, ICM...

Seriously, I think I got most of the data

Wrt the ICM: at the top of your coil is the plug you previously mentioned (?), which should actually be a 3-pin wiring harness connector. See if you can gently peel back the rubber protective boot on the connector - I assume there's one there - and locate the white & black wire. If you are able to trace that wire (it might get buried in a bigger wiring harness), it should take you to the ICM "D" terminal, for the tach signal. Is that the same as the "coil module" aka ICD that you replaced once (as you state, I'm not seeing an ICD, per se, on the diagrams so far)?

I'll look at the diagrams a bit. We may be limited in what we can do, but we can safely do a couple of things. I saw the V-drop info in the data: I think I can provide a simpler and clearer explanation of how that works

Also, do you recall, possibly have in your records, when the dealer scoped the ignition, did they also scope the alternator? Specifically, did they check for AC ripple current? I need to research that some more myself, anyway

Maybe we can also entice an EE or EET - there must be one or two on the board - to look at this

Lance

[ October 02, 2003, 12:44 AM: Message edited by: LM ]

 

[BOBISTHEOILGUY]

I don't think you are going to find the ICM or ground as a problem.

Since I don't know which coil system we're talking about, I'm assuming it's the 50k that installs on the top of the cap. The only other one other than old style point system is the 3pack coil with no cap.

A coil is in this case a step up transformer. It takes a 12vdc input, induces across to the secondary output causing higher stepped up vcc.

An AC Ripple from the alternator, or a icm running ttl logic signals, wouldn't/coudn't burn out a wire in a coil. The coil is burning out as it arc's to the ground, which then has no resistance, so it allows excessive current to flow through the primary/secondary.

So, The problem is, how is the coil seeing excessive resistance to the plugs via the cap/ rotor/wires/plugs. This higher resistance will force the high vcc from the secondary to find a less resistant path to ground ie, the arching thus creating a miss/slugish condition.

Because the engine runs good for about 3k, this indicates that the ICM is good. It also indicates that your ICM is compensating enough to keep it running smooth while there is no direct short to ground. All the while, the coil is starting to build up some slight or higher resistance to the bad area, once, it has started to create higher resistance under normal use, then it now starts seeing ground with less resistance.

I have a suggestion and maybe you've done this already but have you tried this. It is very simple.

Have you tried to replace one thing at a time. Rotor cap first, try it, and see if it clears the arch?, cap second, try again, see if that clears the arch. Wire, and then plugs, each one at a time? Also, if it is running with a miss, you can shut off the engine. pull one wire at a time, put a used plug on the wire leaving the existing one in the engine. Ground the used plug on the engine, thus giving you a path for the vcc to ground while the plug in the engine isn't doing anything. Start, see if miss stays the same or if engine is running with harder miss. This will help show what cyl/wire circuit you are having problems with when you start an no change occurs.

Just some simple steps to try to localize the area you're looking for. From there, maybe you'll find something in that area to cause problems.

Also, what I find interesting and not out of the picture is that you shouldn't be having lights dim while the engine is running. You may have a weak battery or in that case a bad/loose ground on that cucuit. I'd have battery and alternator checked for charging issues before tearing into cicuit for ground issues.