Progress on my truck problems

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Feb 20, 2019 | 07:01 AM

#31

1981 F100

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While I was under the hood yesterday tinkering with it, I observed a red wire with yellow hash marks, with a grey female plug on one end, is part of the Duraspark harness, this wire is part of the 4 wire plug that goes into the Duraspark module( No clue what it's for) The Duraspark harness I have came out of an '83 F150 with a 300. With my glasses I cannot make out wire diagrams, I'm grasping at straws here I know

Feb 20, 2019 | 08:22 AM

#32

Franklin2

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From: Virginia

If you want to check to see if the timing gear is correct and in time, you can do a compression check. You can set the distributor to #1, but that is the ignition timing. If the gear was stripped that would mess up the valve timing. The valve timing being messed up will affect the compression in various cylinders. That is what will cause the engine to crank funny with a wavering speed. It's a shot in the dark, grasping at straws like you said.

Feb 20, 2019 | 02:19 PM

#33

1981 F100

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Quote:

Originally Posted by Franklin2

Only problem with doing a compression check is, it has to be at normal operating temperature, and I can't get it to run long enough for it to get to operating temp. Could I, as an alternative, pull the valve cover, and then crank it, to observe the valves?

Feb 20, 2019 | 03:23 PM

#34

Franklin2

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You don't really need to be at operating temperature. The only reason they tell you this is so the general numbers you get during your tests will be in the same ballpark as their numbers in the book. They also tell you to make sure the battery is fully charged to make sure the cranking rpms are high, and they tell you to open the throttle wide open so it sucks in the max amount of air into the cylinders. All so the numbers you get are relevant to theirs.

You are just troubleshooting. What you are looking for are numbers that are generally the same from cylinder to cylinder. They may be low compared to the book, but you do not care about that. If you have some cylinders that are radically lower than others, that is a sign the valve timing may be off.

Feb 20, 2019 | 03:50 PM

#35

1981 F100

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I took the valve cover off, just so I could inspect things, inside of the head and valve cover looked remarkably good. I then jumped across the starter relay to observe the valve motion, they moved as they should, no bent pushrods or anything else broken. So not sure if that's a good sign or not

Feb 21, 2019 | 01:53 PM

#36

1981 F100

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I unwrapped some suspicious looking electrical tape work on the Duraspark harness, and look at what I found: Not sure if this would be a cause of all my problems, or not