LARS are you out there?
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Joined: Dec 2005
Posts: 76
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From: St Louis MO
LARS are you out there?
Ignition help needed.
My 73 350 is running like a V-6. Troubleshooting has confirmed cylinders # 2 and #7 are not firing. Consecutive cylinders in firing order. I tried a different plug, different wire and have replaced the cap and rotor with new. No change in operation.
This is an original GM ignition points style distributor, I have no idea of it's history, came with the car when I bought it in 2003.
Visual inspection of the cap after running the engine shows no evidence of fire between the rotor and the cap on these two cylinders. All others have evidence of fire having occurred. Also noteworthy, the removed rotor looked as if it had come into contact with the cap. Is the distributor at fault? Worn bushings allowing shaft to "float around?"
Suggestions?
Thanks,
knbwag
PS:I sure would like to resolve this and start leaving black marks again!
My 73 350 is running like a V-6. Troubleshooting has confirmed cylinders # 2 and #7 are not firing. Consecutive cylinders in firing order. I tried a different plug, different wire and have replaced the cap and rotor with new. No change in operation.
This is an original GM ignition points style distributor, I have no idea of it's history, came with the car when I bought it in 2003.
Visual inspection of the cap after running the engine shows no evidence of fire between the rotor and the cap on these two cylinders. All others have evidence of fire having occurred. Also noteworthy, the removed rotor looked as if it had come into contact with the cap. Is the distributor at fault? Worn bushings allowing shaft to "float around?"
Suggestions?
Thanks,
knbwag
PS:I sure would like to resolve this and start leaving black marks again!
Tech Contributor
Joined: Aug 1999
Posts: 14,380
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From: At my Bar drinking and wrenching in Lafayette Colorado
Some basic troubleshooting is in order. I'd start with a cylinder leakdown test to verify the health of the cylinders and cylinder sealing. Do a leakdown rather than a compression test, as the leakdown will give you much more usable info.
If the cylinders check out below 10% leakdown, they should fire and run with all else being as it should. You can pop the valve covers off and just verify that the valves on those cylinders appear to be functioning while turning the engine over on the starter.
If valves are opening and closing, and the cylinder is sealing, you have verified that it is mechanically good.
That being the case, you can start the engine and pull the plug wires out of the cap just far enough to see the spark jumping from the cap to the end of the wire. If the spark is jumping to the end of the wire, put the wire back in the cap and pull the wire off at the spark plug and see if it jumps from the wire to the plug. This will narrow down where the problem is. If there is no spark jumping from the cap to the wire, take a new/different plug wire, ground the plug-end of the wire, and see if you can get a spark to jump from the cap to the grounded wire. If not, you have something going on inside the distributor. If you can get a spark, you have a problem with the wire or the plug.
If the cylinders check out below 10% leakdown, they should fire and run with all else being as it should. You can pop the valve covers off and just verify that the valves on those cylinders appear to be functioning while turning the engine over on the starter.
If valves are opening and closing, and the cylinder is sealing, you have verified that it is mechanically good.
That being the case, you can start the engine and pull the plug wires out of the cap just far enough to see the spark jumping from the cap to the end of the wire. If the spark is jumping to the end of the wire, put the wire back in the cap and pull the wire off at the spark plug and see if it jumps from the wire to the plug. This will narrow down where the problem is. If there is no spark jumping from the cap to the wire, take a new/different plug wire, ground the plug-end of the wire, and see if you can get a spark to jump from the cap to the grounded wire. If not, you have something going on inside the distributor. If you can get a spark, you have a problem with the wire or the plug.
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Joined: Dec 2005
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From: St Louis MO
Lars, thanks. I did all that. Good compression, rockers all moving equally.
I used a trouble light at the cap towers, number 2 and 7 do not light the light, all other cylinders will light the light. Also, as you described, with the engine running, (barely) and I pull the number 2 and 7 plug wires from the distributor cap, no spark and no change in the engine operation. When pulling other wires, there is spark and you can hear the loss of that cylinder.
What could be causing this inside the distributor?
I used a trouble light at the cap towers, number 2 and 7 do not light the light, all other cylinders will light the light. Also, as you described, with the engine running, (barely) and I pull the number 2 and 7 plug wires from the distributor cap, no spark and no change in the engine operation. When pulling other wires, there is spark and you can hear the loss of that cylinder.
What could be causing this inside the distributor?
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Joined: Dec 2005
Posts: 76
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From: St Louis MO
Dwell was a solid 30 degrees. I have the dist. out on the bench, I have checked each lobe, opening the points and measuring with a feeler gauge, fairly equal, points open eight times for each complete rotation of the dist. shaft.
Also does not seem to have any wobble.
When disassembling, I noticed that the advance springs are not the same. One has more tension than the other. Advance flyweights seemed a little stiff, but understanding the force applied by centrifigal force, I don't think they are failing to move.
Thoughts anyone?
Also does not seem to have any wobble.
When disassembling, I noticed that the advance springs are not the same. One has more tension than the other. Advance flyweights seemed a little stiff, but understanding the force applied by centrifigal force, I don't think they are failing to move.
Thoughts anyone?
