Low idle, missing
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So, as far as my weak spark goes, I have already replacedone the distributor, plugs, plug wires, and module.... so all that is left is the coil, cap & rotor, and wiring. All of the connections in the engine compartment have been cleaned with contact cleaner. I am getting proper voltage on the green wire (6-7 volts) at the coil but I'm not totally sure what voltage I'm supposed to get at the red wire.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
The voltage at the coil when the engine is running is hard to measure since it is a ringing wave, and different meters handle the ringing differently. But when the engine isn't running it is easier to measure as it is steady state, and should be around 7 volts on the red wire.
However, of what you have left l think the coil is the only one that will change the spark's voltage. The cap and rotor may change where the spark goes, like to which plug wire or to ground, but the coil determines how strong the spark is. So, if you are troubleshooting I'd swap in another coil and see what happens.
However, of what you have left l think the coil is the only one that will change the spark's voltage. The cap and rotor may change where the spark goes, like to which plug wire or to ground, but the coil determines how strong the spark is. So, if you are troubleshooting I'd swap in another coil and see what happens.
Lead Driver
Joined: Nov 2013
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Careful with this one. If tested in bright sunlight, a decent spark can look orange. This can lead to lots of frustration and the replacement of perfectly good parts. I do not care to discuss how I know this...
You may still be on to something. It wouldn't hurt to reconfirm your diagnosis under different lighting conditions, that's all.
Have you checked for a loose timing chain? That's a fault that can appear suddenly if the chain jumped. If the valve timing is now way off, could that cause incomplete combustion? That might give the same appearance on the plugs as an overly rich condition. Just thinking out loud, and only takes about two minutes to check.
You may still be on to something. It wouldn't hurt to reconfirm your diagnosis under different lighting conditions, that's all.
Have you checked for a loose timing chain? That's a fault that can appear suddenly if the chain jumped. If the valve timing is now way off, could that cause incomplete combustion? That might give the same appearance on the plugs as an overly rich condition. Just thinking out loud, and only takes about two minutes to check.
Lead Driver
Joined: Nov 2013
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However, of what you have left l think the coil is the only one that will change the spark's voltage. The cap and rotor may change where the spark goes, like to which plug wire or to ground, but the coil determines how strong the spark is. So, if you are troubleshooting I'd swap in another coil and see what happens.
Not all damage to a cap and rotor is so obvious. I've had instances of essentially invisible carbon tracking that weakened a spark. Seems like once carbon tracking starts, cleaning is no good and replacement is the only fix.
I've even had a bad cap right out of the box. Replaced it with another new one from the same bad batch. Talk about a troubleshooting nightmare!
Distributor caps and rotors are normal wear and tear items with a finite life. Those are almost always the first things I'll change during initial troubleshooting of rough running. I didn't see this before that you hadn't changed them yet. They are cheap and even if it's not the fix now, you'd have a spare set you are 100% guaranteed to need in the future.
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I will swap out the coil today.... it tests good, but I have seen a coil in the past test good but arc thru a small imperfection in the seam. Maybe I will swap out the cap n rotor too, years ago I had a no start condition on a Chevy astro that was from a bad cap that looked totally good- I almost gave up and took it to a mechanic! I agree about the orange spark and sunlight, however it was very shaded when I tested it and the arc was very orange. I will keep you updated, hopefully I don't have to spend countless hours of troubleshooting wiring!
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Putting on my orthopedic diplomat's hat, I'm not sure I fully agree with this one. I've fixed many a rough running vehicle by replacing the cap and rotor. I've even done roadside repairs of chipping off scale at each terminal inside the cap. That was good enough to get me safely home.
Not all damage to a cap and rotor is so obvious. I've had instances of essentially invisible carbon tracking that weakened a spark. Seems like once carbon tracking starts, cleaning is no good and replacement is the only fix.
I've even had a bad cap right out of the box. Replaced it with another new one from the same bad batch. Talk about a troubleshooting nightmare!
Distributor caps and rotors are normal wear and tear items with a finite life. Those are almost always the first things I'll change during initial troubleshooting of rough running. I didn't see this before that you hadn't changed them yet. They are cheap and even if it's not the fix now, you'd have a spare set you are 100% guaranteed to need in the future.
Not all damage to a cap and rotor is so obvious. I've had instances of essentially invisible carbon tracking that weakened a spark. Seems like once carbon tracking starts, cleaning is no good and replacement is the only fix.
I've even had a bad cap right out of the box. Replaced it with another new one from the same bad batch. Talk about a troubleshooting nightmare!
Distributor caps and rotors are normal wear and tear items with a finite life. Those are almost always the first things I'll change during initial troubleshooting of rough running. I didn't see this before that you hadn't changed them yet. They are cheap and even if it's not the fix now, you'd have a spare set you are 100% guaranteed to need in the future.
But, and assuming he's correct, in this case the spark is getting to where it is supposed to go, but looks weak. To me that means the spark generator, meaning the coil, has shorted windings and isn't producing full spark voltage.
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Today I swapped the coil and the cap n rotor. No change. Checked the spark this evening after the sun went down and it is weak and orange still. Voltage at the coil is 6-7 at the green wire and a little over 10 at the red wire. Voltage on the red power wire to the module while running is a little over 14 (same as battery). From my reading it seems as power to the coil and module are good. So what next... I suppose ground wire cleaning. I read that it is a good idea to splice in another ground wire to the distributor ground wire.
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Does the coil wire itself give a good healthy blueish spark to ground? It should jump maybe a half inch or so easy. This test sort of divides the ignition in half or at least eliminates the distributor from the equation.
Lead Driver
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Also, how are you testing for a spark? If using a screwdriver inside a plug boot, your gap to ground may be way too big. That may account for the orange color.
Get a spark tester and try again. The one I have looks like a spark plug with a big alligator clip on the side to connect to ground. Whatever you get, make sure it's the HEI version, with the proper gap for an electronic ignition system.
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Here's a question... the three wires that power the ignition system (white "start" wire going to module, red module supply wire, and red coil wire) all are grounded while the ignition switch is off. Is this correct? Seems as they should not be going to ground at any time, but maybe the ignition switch does this in the off position. I thought that the ignition switch just shut off the power not routed it to ground.
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From: Northeast, OK
Here's a question... the three wires that power the ignition system (white "start" wire going to module, red module supply wire, and red coil wire) all are grounded while the ignition switch is off. Is this correct? Seems as they should not be going to ground at any time, but maybe the ignition switch does this in the off position. I thought that the ignition switch just shut off the power not routed it to ground.
So the red/light blue wire has probably something like a 12 ohm resistance to ground through the starter relay. But I can't guess the load on the other wires.
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Yeah, I don't know, I had the harnesses unplugged when I tested them so the module was out of the equation. I understand the starter relay aspect of it, but that dosent explain the other 2 wires. It may be nothing at all, but I'm just exploring potential problems with the supplied power to the ignition system. I have never had so much trouble diagnosing a vehicle before!
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