1973 Ford F-100 Two Cylinders Not Firing

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COWBOYCREE63
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I have a 1973 Ford F-100 pickup, with a 302 V8. The engine runs, but not very well, and I'm not sure why. I think it's because I have 2 cylinders not firing. I can pull one plug wire from the distributor at a time, but 2 of the plugs make no difference in enging RPM. I pulled the plugs out, and ran the engine without the plugs in, and watched for spark, had spark, and the plugs were wet with gas when I pulled them out...any ideas? Your help is much appreciated.
Nov 24, 2006 at 2:49 PM
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BACKYARDMECHANIC
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have you done a compresson test on the motor. If not do one and see if the 2 cylinders you are having problems have good pressure. Remove all the plugs and check each cylinder with a compression tester. I suspected that the 2 cylinders that are not working properly have bad values. You can confirm this if the compression results for the 2 cylinders are bad by doingh a wet test on them. Take 2 to 3 table spoon of motor oil and pour it into the cylinder through the spark plug hole. Then repeat the test for the two bad cylinders. If the compression results go up then the rings are bad. (This is usually accompanied by oil fouled plugs) If the 2 cylinders are next to each other I would then suspect the head gasket is bad. A compression test is probably a good gauge to tell the condition of the internal parts of the motor. (RINGS, VALUES and HEAD GASKETS) Good luck Backyardmechanic :roll:
Nov 29, 2006 at 12:17 AM
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COWBOYCREE63
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I did a compression test, and all cylinders are within 10 PSI of each other, with the average being 125PSI, which is normal as far as I know. I've taken the plugs out, and put the wires back on them, and run the engine with the Plugs grounded, and they are sparkin, and when I pull them out after running the engine, they have fuel on them...
Nov 29, 2006 at 9:06 AM
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BACKYARDMECHANIC
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It may be something as simply as a basic tune up.Try changing the points cap and rotor while you are at it. Also check the dwell and make sure it is correct. I'am assuming you still have the original distrubutor in the car. Can't remember the last time I adjusted or change a set of points LOL. Hope this helps :)
Nov 30, 2006 at 12:43 AM
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BRUCE HUNT
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You could have very simple problems. I would suspect wires, distributor cap and/or plugs themselves but start at the distributor cap then the wires and down to the plugs.
Nov 30, 2006 at 1:27 AM
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COWBOYCREE63
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I just put in new points about 3 weeks before the problems started, and the dwell is correct, the Cap and rotor are new as well (replaced them with the points) The wires are old, so I'll start checking those, and the plugs aren't new, but they've been cleaned and regaped, so they should be fine. Thank you all for your help.
Nov 30, 2006 at 2:17 PM
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1BIGG1
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if they constanly get wet with fuel i would assume you need a valve job.
Dec 3, 2006 at 12:32 PM

Suggested Repair

Compression is even, so rings, valves, and the head gasket are less likely. Recheck the ignition system, especially the old spark plug wires and plugs, then recheck the distributor cap, rotor, points, and dwell.

Conversation Summary

A 1973 Ford F-100 with a 302 V8 runs poorly, and disconnecting two plug wires does not change RPM. Those plugs have spark and are wet with fuel, and all cylinders tested within about 10 PSI of a 125 PSI average. Experts recommended a compression test, then a basic tune-up including points, cap, rotor, dwell, wires, and plugs. The owner reported that the points, cap, rotor, and dwell were already addressed and planned to check the old wires.

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