42 DeSoto runs VERY rough, help needed

Did you check the point gap ? Also, when you say you have spark, is it a snapping, crackling spark ? If those check out OK, it sounds like a vacuum leak. Hook up a tachometer. Then take carb cleaner and spray it at the likely areas for a leak, especially where carb meets intake. If the rpm jumps noticeably, you've found your problem.

Ron

Thanks Ron! Yes, I checked the gap several times. Can the symptoms I described come from a weak ignition coil? Can a "weak" spark cause this? Good idea on the carb cleaner except I can't get the car to run long enough to even check it. I think my options at this point are to replace the coil and then replace the intake gaskets. Any other ideas are welcome!

Just thinking out loud....

How 'bout confirming your plug wires are in the right order on the distributor cap and plugs...?

Thanks Tim. When I changed the wires I changed one at a time so I didn't confuse them. I don't see a diagram in my service manual to double check it. Where can I find that info? Also, why is my intake manifold "connected" to the exhaust manifold? What happens between them?

If I was standing next to the car trying to figure it out, the first thing I would do is pop the forward most plug out and stick my finger in the hole and have you crank the engine until I began to feel the compression whistle past my finger. Then paying attention to the timing mark, I'd carefully bring the rotation around to the "0" on the timing marks. That puts you at TDC on the #1 cylinder.

Then I'd pop the distributor cap and make sure the rotor is pointing at the #1 plug wire.

Then, with the distributor clamp loose and the key "on", I'd rotate the distributor until the points sparked, and then set the distributor at the point RIGHT BEFORE they sparked. This will set your static timing close enough to allow the car to run.

Then, knowing the direction of rotation of the distributor, I'd start at #1 and make sure the order of the plug wires was 153624.

If you have fuel and strong spark, the car should run....

The intake and exhaust is bolted together to allow the intake air to be pre-warmed by the exhaust heat.

Thanks Tim. I'll try this tomorrow night.

You might wiggle your distributor shaft and see if the bushings are excessively worn. We had a car that ran very poorly, and it turned out that the shaft bushings were worn so badly that it was impossible to maintain a point gap/dwell setting.

I did the checks you suggested and here's what I found. When the #1 cylinder is at TDC, the rotor is pointing at the 3 o'clock position, #2 cylinder. When the #3 cylinder is at TDC, the rotor is pointing at the 7 o'clock position, #1 cylinder and the timing 0° mark is very near the timing pointer. When the #6 cylinder is at TDC, the rotor is pointing at the 8 o'clock position, #5 cylinder. Does this sound right? It's not what you said I'd find.
Also, how would I check resistance on the ignition coil? It has just one terminal post and the high tension of course. While I was in there I also checked the point gap, right at .020". I've had the distributor out and the bushings seemed ok, very little play.
I read that the #1 and #6 cylinders should be at TDC at the same time? My engine definitely is not. When I do get it running, what plug wire should my timing light be getting a signal from? I'm figuring #1, but maybe 3?

Unless your timing has jumped on the sprockets, anytime your timing pointer is located at the "0", both 1and 6 are at TDC. Depending on the rotation, one is at TDC compression, and the other just finished its exhaust stroke.

Here's what I would do for a quick elimination of everything else, because somehow I think your firing order got all messed up.

Find TDC #1 again. Locate where the rotor is pointing, and put the #1 plug wire at that terminal on the cap. Re-route the wires on the cap in the correct firing order. Set the points with #1 at TDC to just before they fire. Button everything up and give it a try.

Thanks again Tim. I'll try this tomorrow night. How can I check the ignition coil?

When #1 was at TDC, was the "0" at the pointer on the timing cover?

I'm not real confident when I have a meter in my hands, but I'd start by setting my ohm meter on the terminals of the coil and see what it reads.

Your timing light will read the firing of #1 cylinder.

Have you cranked the engine and watched the rotor spin nice and evenly?

No, when the #1 cylinder is at TDC, the rotor is pointing at the 3 o'clock position #2 cylinder wire on cap.

Only when the #3 cylinder is at TDC is the rotor is pointing at the 7 o'clock position #1 cylinder wire on cap, and the timing 0° mark is very near the timing pointer.

The rotor seems to spin fine and evenly when the engine is cranked.

Sorry to ask a potentially insulting question, but you are counting the forward most cylinder as number one, right?

It's weird and concerns me that the timing mark is not at zero when number one is at TDC.

Have you pulled all the plugs and checked for compression on all six cylinders? You might do that to make sure that your cylinders are coming up on a compression stroke. If you're timing has jumped it might show by not having compression on the cylinders