what happens when the distributor condenser fails?

A bad condenser will usually result in weak/no spark. The engine may run well at idle or little load but, misfire or backfire at increased rpm or load. A bad condenser can and usually does result in short point life. In the days of points ignition, it was routine to replace the points and condenser as a set. A condenser is like many electrical items that perform properly until their moment of death. I have more than once replaced a condenser with 50K or more miles on it with a new one that was bad. A bad coil can give some of the same symptoms especially if the problem gets worse as the engine warms. Low voltage because of a bad ballast resistor, resistor wire or a loose connection can also result in similar symptoms. The condenser and the other components can be tested. An oscilliscope can easily detect a bad condenser if you happen to have one in your shop.

When the old condensers started failing on a points system, you got an orange spark instead of a blue one. The more orange, the more dead the condenser.

When the condenser fails on the newer coils, it can make AM radio noise and someone tried to tell me it could allow power surges which could hurt the ignition module, but I don't know about that part...

You need special tools and know how to electrically test one. They are cheap, when in doubt change it.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

"K. Elliot" wrote:

Mike Romain wrote in rec.autos.tech

In a points system the points will become badly pitted and burned. The condensor stores a charge, so when a spike in voltage happens it is absorbed by the condensor, then when the voltage drops the condensor lets the excess voltage back out into the line. Thus a condensor helps stop static because it absorbs the spikes that cause it, and if it fails the spikes will surge on through the system. It has been awhile since I have played with them so I don't remember exactly how to test a condensor, but all I ever used was ohm meter. Charge it one way, then reverse the leads and watch it discharge. A faulty condensor will not store a charge.

K. Elliot wrote in rec.autos.tech

If you are talking about a points type of ignition system your spark will get weaker, the points and plugs will foul and you will start having an erratic miss. Or your spark will fail entirely. I had a motorcycle with

3 cylinders, each with its' own points, condensor and coil. I developed a very annoying problem with the bike. The center cylinder would start to miss, and eventually die entirely as the bike warmed up. Started on a trip, and nobody had the parts I needed. Once I got home I finally traced it to a condensor that would short out when hot. Replaced that and it ran great.

Nah... A VOM (Volt/Ohm meter) and some know-how will let you get at least a "go/no-go" reading on it. A condenser is just an electrolytic capacitor with a "fake ID and a nose job", and all capacitor-targeted tests apply to it. Electrolytics are a type of capacitor with very high (relatively speaking) capacitance, and good high voltage/current handling capability. Unfortunately, they're also notorious amongst electronics folks for drying up and dying, or shorting out and dying, in all applications they're used in - too bad there's no really good alternative to them that can handle the jobs they can do without odd side-effects like exploding into powder, or melting into little puddles of slag.

First test: Set your VOM to high ohms (A 5-10K setting should do you fine) with the negative lead to the metal "can" of the condenser, and the positive on the lead coming out of it. Flip the power switch on your VOM. You should see the indication go from low ohms to high ohms over a few seconds as the cap charges. An "open" indication, or a steady low resistance says "replace this dead pile of junk". Leave things connected that way until you can see no more meter movement.

Second test - You want to do this one as quickly as possible after doing the first one if the results are to be valid - capacitors can and do "bleed off" their charge given enough time, and this test relies on the charge you just put on the capacitor with the first test being present for this one. If you get interrupted, or get no reading at all the first time you try this one, repeat the first test, allowing the resistance reading to build to its highest point before immediately doing this test:

Disconnect the VOM's positive lead, and switch the meter over to volts (the 20-ish volt range should be adequate - much higher, and you'll get no useful indication, lower than about 10 volts *MAY* blow cheap meters), then touch the condenser lead with the positive probe while watching the meter. You should see a "spike" of voltage (exact number isn't critical for this very crude test) that drops to zero relatively quickly. No spike? The condenser is toast. Replace it.

If both tests pass, you've got at least a minimally functional condenser sitting there in front of you.

Word of warning: This test is *CRUDE* - It will give you an indication of whether or not the condenser is operational, but will give you no clue whatsoever as to whether or not it's operational *UP TO ITS DESIGNED SPECS* - IE, It won't tell you that the cap is only functioning at "half capacity", or tell you the cap's rating - Only that it *IS* or *IS NOT* functioning as a capacitor. For the intended purpose of preventing the points from burning, actual rating is pretty unimportant, as long as it's "something big". For the secondary effect of reducing AM radio noise, the value is relatively critical, since it's intended to either (depending on the exact manufacturer) "absorb" the noise before it can be radiated away and interfere with radios, or "tune" the spark noise to a band outside that which a typical car radio can "hear". Most design goals since the mid 60s have been to "soak up" the noise, rather than "detuning" it, but both variants are still on the road today.

If you want to know the actual rating of a given condenser/capacitor, you need a "for real" capacitor tester, which can be pretty pricey depending on the source. For most automotive applications though, a simple "go/no-go" indication is all that's needed, and a cheap VOM can give you all the cap-testing information you're likely to need.

One of two things will happen- if the condensor shorts out, the engine won't run. If the condensor fails open circuit, the car will run normally but the points will burn faster and fail prematurely.

The only way to test a condensor is on an impedance meter (its just a capacitor). That's why its SOP to replace it every time you replace the points.

Big sign of a bad condenser is arcing at the points. Looks like a small welder in there if the condenser is bad. Another is spark cut off at speeds higher than idle, since the condenser cannot charge fully.

On older ignition systems, you get a pattern of metal buildup on one side of the points and a cavity on the other. Used to be a rule of thumb for positive and negative side buildup indicating a too small or too large capacitor, but darned if I can recall it.

If the capacitor fails to a short, your engine stops immediately, but this is a rare failure mode. If it fails to a complete open you may get poor performance, poor idle and loss of power+misfire at high rpm...but I've had it open and not really notice it much on a rat motor.

L0nD0t.$t0we11 wrote in rec.autos.tech

As you said, it will run rough, sometimes so rough that it will die. Losing the ground or the positive connection will cause it to act the same as an open. My parents had a car die on them, turned out the screw was loose, causing them to lose the ground connection. I had a car run rough on me right after I put in new points, turned out the wire to the points had come loose.

escept the effects of points that burn out in a couple of thousand miles. :-p

?!?!?

That's contrary to everything I've ever been told about the how and why of a condenser being in the ignition system - Essentially, all of my information, however phrased, boils down to "The condenser is like a shock absorber that keeps the points from electrically 'beating themselves to pieces' as they open and close, the same way the closer on a screen door keeps the door from slamming shut or bouncing off the wall."

My understanding of Kettering (points-based) ignitions is that they couldn't care less about capacitance, except as a means of keeping the points from burning up. The "moving parts" are purely magnetic in nature, with zero meaningful contribution from the condenser, which is there only to prevent the points from being destroyed.

I can't for the life of me figure out WHY that would be the case, unless the little booger failed "intermittently shorted" on you, which isn't exactly what I'd think of as a typical capacitor failure mode. If it fails shorted, I can see the engine dying, since the primary wouldn't be interrupted by the points (cap makes things look as if the points aren't opening, electrically speaking), but if it were to fail open, I can see no reason (unless, perhaps, the points burn so quickly as to become ineffective) that there should be any short-term change in engine operation. Over time... Well, that's a different tale - Eventually, the points will be turned into junk. But immediately on condenser failure? I can't see a failure mechanism?

(Hmmm... then again, it could be that the condenser failed days/weeks/months/whatever before, but the damage to the points only got bad enough to cause "visible" engine trouble that day...)

But the spark is a result of a collapsing magnetic field, not capacitance... If it weren't for the "preservative" effect of the condenser on points-life, there would be no reason to include it that my electronics knowledge can explain.

That's nice.

Fact (points pitting/burning one way with too-small condenser, the other way with too-big condenser) beats opinion/guess (everything you've ever been told) every time.

Cute analogy, but it's not "the same way". Not even close.

And now you have correct information to improve your understanding. Science fact has a nasty habit of shooting ugly holes in beautiful theories...especially when the beautiful theories aren't understood correctly.

If capacitance is completely unimportant, why do we have what we have on pages 696-697 of the Echlin Ignition System Component Buyer's Guide? It is titled "CONDENSER SPECIFICATIONS BY PART NUMBER". No, it doesn't talk about physical size of the condenser or configuration/length of the lead wire or how the condenser is retained in the distributor. Only spec listed is capacitance value in microfarads. 288 different condensers listed. Lowest value I see is 0.16 - 0.20 =B5f. Highest value I see is 0.4 to 0.6 =B5f. Commonest value I see by far is 0.19 to 0.23 =B5f. That they bother t= o tell us this condenser has 0.19 to 0.23 while that one has 0.18 to 0.22 tells me it ain't good enough for them to say "They're all about 0.20". How 'bout you?

'cause the condenser open-circuited. No more "screen door buffer", primary current arcs across points when they open, no more sharp transition from high to low in coil primary winding, therefore shitty/no induction in secondary winding, therefore shitty/no spark.

Oh yeah, points would've burned up if I'd run it that way for long. But it's not like the engine will run happily and smoothly w/no condenser until the points burn up. Try it sometime and see for yourself. Fortunately for me, I had a setup where the condenser was mounted across coil (-) and ground (coil bracket) instead of inside distributor, so repair work was easy in the parking lot. Engine starts hard, barely runs. Disconnect condenser from coil (-) to check for short condenser, engine still starts hard and barely runs. Connect new condenser between coil (-) and ground, engine starts immediately and runs smoothly. Pretty good proof.

Nope. Pulled and inspected the points that same afternoon. They were a little worse for wear, mostly just "dirt" (residue from arcing) easily removed w/business card pulled through closed points. They were still plenty good enough -- as evidenced by the engine's return to easy starting and smooth running soon as I installed a new condenser w/same points.

DS

AHA!

OK, that makes sense - except for one minor detail: What's the maximum length arc that can be sustained in "regular air" when discussing 12 volts of DC?

But that point becomes moot the instant I find out that 12 volts can sustain an arc across a larger distance than the points typically open...

And now that the light has come on, I can see where the condenser's value could be the difference between "good", "poor" and "no" spark - It affects how "clean" the cutting of primary power is, which in turn assures a nice quick collapse of the magnetic field, and good transfer of energy to the secondary.

Damned if I know why, but I was off on a radio-related tangent, deep in the "forest" of resonant LC tank circuits (and wondering what the heck they had to do with the ignition going whacko when I know darn well it's all about the magnetic collapse in the primary) without noticing the "tree" of cleaning up the primary cutoff that I kept bumping into.

Point gap is 20 thousandths of an inch, answer is "more than that".

Ayup.

DS

Hi, Cap is there to increase the life of points. Cap can fail open or shorted. If shorted, no spark, if open, points will burn out very fast. Also car will run rough because there is no more clean spark. Tony

And somewhere around the time of 04/16/2004 09:10, the world stopped and listened as Don Bruder contributed the following to humanity:

Actually, it's both. The condenser(capacitor) is about .22uf give or take for design differences. I don't know what the mH rating of a coil is, but the coil is a electrical device known as a auto-transformer. It's like a regular transformer, but both the primary and secondary share some of the windings.

The capacitor is wired in parallel to the points and in series to the coil. The capacitor tries to maintain a constant voltage while the coil tries to maintain a constant current. The basic design of a automotive ignition circuit is basically a series resonance circuit not unlike those used in radio.

When the points are closed, the capacitor is shorted out and current flows from ground, through the points, through the coil, and out onto the positive power rail. This sets up a magnetic field around the windings of the coil. At the moment that a sparkplug is to fire, the points open which interrupts the current flowing through the coil, but the coil is charged (magentic field), and in an attempt to keep the current going, the coil discharges right into the capacitor.

At this point, when the coil is fully discharged, there is a voltage charge on the capacitor in the range of +700-1000 volts in reference to ground. Since this is much higher than the +12V rail that the other end of the coil is connected to, the current flows BACKWARDS from +12V, through the coil, and into the capacitor to even the charge. Because there is little resistance in the coil, a high amperage pulse is generated through the coil primary, and with a winding ratio of 40:1, causes a voltage spike between 28KV and 40KV on the secondary, which is more than enough to jump the gap between the rotor and distributor cap, and the gap on the plug itself.

A leaking capacitor will disapate some of the charge before it can be used to draw the current through the coil resulting in a lowered high voltage output and a weak, or no spark condition.

A shorted capacitor will cause a no-spark condition because the current will still flow through the coil.

A open capacitor will burn the points because the points will be forced to absorb the discharge from the coil causing them to arc, and you will get a weak or no spark.

Too little capacitence will cause the points to burn do to the same reason that a open capacitor will. But, it may or may not cause a weak/no spark condition depending on how much under the spec the cap is.

Too much capacitence will cause a weak or no spark condition because the voltage across the capacitor will not be high enough because of the larger value. The bigger the cap is, the bigger the charge on the coil has to be to get it to the 700-1000 volt range.

If you're condenser is bad will it stop the spark going to the spark plug

Generally the bad condenser will cause the contact points to burn

*unless* the condenser itself develops an internal short. Then it will ground the primary current from the coil *permanently* hence no interruption of the coil primary current flow resulting in no high voltage (spark) generation in the secondary circuit.