I recently bought a 1966 Chevy c-10 with an inline 292 engine. The truck was driving then my dad and I tuned it up…big mistake. Apparently the truck liked the abused state it was in better. We replaced the points, distributor cap, condenser, rotor and spark plugs. The truck ran but was running really rough. We thought one of my cylinders wasn’t firing but no matter what spark plug wire we pulled it was the same. The amount of spark I was getting kept getting worse and worse until finally it wouldn’t start at all. I replaced all the parts again (this time better quality) and the coil, battery, and spark plug wires. I have checked and rechecked the points. The gap is fine. The truck will crank but I still get intermittent spark. Please help.
I like those old C-10 pick-ups. Classics. Good on your for preserving the old beast! Well, some kind of problem remains in the ignition system I suppose. Is it possible the spark plug wires were mixed up, and now connected to the wrong plugs? That will cause this symptom. Maybe double check that before investing more time and money. I expect you’ll get this fixed in short order in any event if you proceed in a scientific fashion. Hopefully you saved all the old parts, so you could try just re-installing them. That should bring the truck back to its prior state. Another option anyway.
The points must be set to a specific dwell angle (30 degrees). This is done with a dwell meter and is done by using the little door on the distributor cap. You must set a gap to get the engine running then set the dwell. When you replaced the coil…did you make sure to properly connect the coil wires? If you reverse them you will get very little spark.
I would go back and check all the wires inside the distributor for the points/condenser.
These components sit on the vacuum advance plate. And over time when plate moves back and forth it flexes the wires where the strands inside the wire start to break. Then when you replace the points/condenser you flex the wires to the point where the strands inside the wires do break and you get a poor connection.
Afterall, everything you replaced new. Except those wires.
Tester
Thanks for your responses. I double checked the spark plug wires and the wires connecting the coil. Everything looks good there. I’ve put the old parts in and I still had the same issue. I haven’t tried the dwell angle. Neither the new or the old distributor cap have the little door. I’ll visit the parts store again tomorrow. Thanks.
Time to check the timing, note vacuum advance I believe should be disconnected.
No. I mean the wire inside the distributor for the points.
That wire might have broken strands inside.
Tester
Sorry Tester, I think you and I posted at the same time, I didn’t see your response until later. I’ll check that out tomorrow. Thanks
There is either a coil resistor or a resistance wire leading to the distributor. The coil resistor could be open or if there is a resistance wire, it could be bad. When the points are closed, the coil should be getting about 6 volts.
New points have a habit of not working unless you file them a little. A file for points was invented because of this; not for filing old points. Usually the engine won’t start at all if you have chromed points. A points file, jeweler’s file, nail file will all do fine. For those who just don’t care, sandpaper will do but it isn’t very popular for obvious reasons.
Sometimes unfiled points will work initially and quit the first time it rains. Sometimes a set of points never fails. Old car, old mechanic, same old success.
Since the spark deteriorated and then died immediately after your tuneup, I suspect you fried the points (or even physically damaged them) due to improper adjustment. As they fried, they moved the ignition timing out of operating range. They two ARE directly related. The coil primary charges while the points are engaged, shoots the spike through the secondary to the spatkplugs when the points open, and the timing of the plugs is determined by that opening and closing operation of the points.
Start again with new points. Initially set the point gap using feeler gages, then adjust them using a dwell meter (dwell/tach). I know from experience that it’s a pain without a window, but it is important for the dwell to be right. The points need to be in contact long enough for the coil primary to build a good magnetic field to discharge into the secondary (the “core”). Set the ignition timing only after the dwell is properly set.
A tip to prevent crossing ignition wires: replace them one by one. Don’t pull them all off at once.
From your description of the trouble and reading the posts here it sounds like the first basic step in trouble shooting an ignition system problem hasn’t been performed yet. You should always, always, always, (did I say “always” yet?) make sure proper power is getting to the ignition system as a first step when looking into this kind of problem, along with a lot of other type of electrical problems. Your description of the trouble makes it sound like there is a bad power connection somewhere that is changing resistance and thus causing less spark to occur while the voltage drop across the bad wire connection goes higher as the connection heats up due to the current flow needed by the circuit.
If you have a old style coil you can verify power on the ‘plus’ side of the coil. To check the operation of the points you can place a test light probe on the ‘minus’ side of the coil and check for ignition pulses while cranking the engine. If the light stays on steady it means the points aren’t making connection to ground and completing the ignition circuit.
All good advice. If you sill cant get it going I would pull the distributor and check the gear at the bottom. I have seen the pin shear off and the gear move and cause this. You said it was running ruff. A backfire will shear the pin. Also check the bushings in the distributor. If shaft is moving side to side in the bushings the point gap will never be right. The vac advance should be checked to see if moves with out sticking.
To clarify, I am getting spark but intermittently. I have put three sets of correctly placed, adjusted and filed points into the truck. I’ve set the gap using feeler gauges and the dwell angle in all three points. I have 6 volts at the coil when the points are closed. My spark plug wires are set properly and so are my coil wires (I’ve triple checked). The wires in my distributor are in good shape. The truck will crank but not start I’m getting spark but only intermittently.
6 volts? Have you checked your battery?
new battery (please see original description)
TSM, this vintage of car used 6 volts at the coil, stepped down from 12V with a ballast resistor. At start, the ballast resistor is by-passed, sending 12V to the coil, then, at run, drops to 6V through the resistor.
@kristeneve7, how do the points cam on the distributor look? Do each of the 6 lobes give you the exact same point gap? Does the cam feel loose? Does the distributor shaft have any side-to-side play? With everything else having been replaced, I think that old distributor may be the problem.
Did you change the condenser ( capacitor ). these were known to dry out over time. I had a 67 chevy with the 327 and became difficult to start…While cranking it would backfire out the exhaust.The condenser holds the charge across the points for milliseconds after they break. Try running an engine with this capacitor removed, when they dry out the same effect.
You need to make sure that the voltage is getting to the coil while the problem is happening. The ballast resistor may have a problem. Another suspect could be the coil wire if you haven’t replaced it already.
Did you try reinstalling all the old parts to return it to the original config? You know that config worked. So it should work again. Once you get it running again, then you can install the new parts piece by piece to determine which part is causing the problem.
Edit: The intermittent spark makes me think the spark plug wires might be damaged. It is easy to damage them during a change-over like this. Even new ones can get damaged in the process of installing them as they “wires” are usually not simple copper wires, but made of a carbon filament material. Maybe ohm each spark plug wire out, end to end. They will probably read something like 1 K to 10 K ohms, and all should be about the same ohms. Do the same with the HV wire from the coil to the center of the distributor.