Shudder/Skip
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Tuned
Joined: Oct 2021
Posts: 297
Likes: 42
Shudder/Skip
Hey all, I’m back. 1990 F-250 5.8L manual trans.
I had an issue where I lost spark, found the ignition coil was faulty and replaced it. Then set timing and the weirdest thing happened… I watched the mark I made at 10BTDC, which is where I set the timing and watched it with a light, as the truck was idling, the timing mark went up, and up, and up. The truck was changing timing on its own. Spout still unplugged. It worked its way from 10BTDC, to about 10ATDC and the truck shut off. Well I had a warranty on the distributor FD14 WAI-GLOBAL, so I replaced it. Set timing again and this time all was well, timing marks on the HB did not move. So naturally I went for a drive, The truck is shuttering/skipping on me really bad. It goes away at WOT or close to WOT. It also does it with no load on the engine while pressing the throttle on and off. I do not have an Illuminated CEL, but I have yet to check KOEO, CM, and KOER codes. I’m thinking it is a Throttle Position Sensor, I have never replaced it and have no idea how old it is. Any ideas?
I had an issue where I lost spark, found the ignition coil was faulty and replaced it. Then set timing and the weirdest thing happened… I watched the mark I made at 10BTDC, which is where I set the timing and watched it with a light, as the truck was idling, the timing mark went up, and up, and up. The truck was changing timing on its own. Spout still unplugged. It worked its way from 10BTDC, to about 10ATDC and the truck shut off. Well I had a warranty on the distributor FD14 WAI-GLOBAL, so I replaced it. Set timing again and this time all was well, timing marks on the HB did not move. So naturally I went for a drive, The truck is shuttering/skipping on me really bad. It goes away at WOT or close to WOT. It also does it with no load on the engine while pressing the throttle on and off. I do not have an Illuminated CEL, but I have yet to check KOEO, CM, and KOER codes. I’m thinking it is a Throttle Position Sensor, I have never replaced it and have no idea how old it is. Any ideas?
Logistics Pro
Joined: Nov 2013
Posts: 3,921
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From: Mojave, Ca
With the SPOUT disconnected, the computer doesn't control the timing. The pip sends a signal to the ICM...the ICM amplifies the signal and sends it to the coil. And the coil send the spark to the distributor and sparkplug.
Did your timing move with the new distributor?
Did your timing move with the new distributor?
Thread Starter
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Tuned
Joined: Oct 2021
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Likes: 42
With the SPOUT disconnected, the computer doesn't control the timing. The pip sends a signal to the ICM...the ICM amplifies the signal and sends it to the coil. And the coil send the spark to the distributor and sparkplug.
Did your timing move with the new distributor?
Did your timing move with the new distributor?
Thread Starter
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Tuned
Joined: Oct 2021
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Logistics Pro
Joined: Nov 2013
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Likes: 1,191
From: Mojave, Ca
How about trying a cylinder drop test. Allow the engine to idle and remove 1 sparkplug lead at a time. As you remove each plug lead, listen to the rpm drop. The cylinders that aren't working won't cause a rpm drop.
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Logistics Pro
Joined: Aug 2014
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the #1 and #3, or #5 and #6 spark plug wires must be separated
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Tuned
Joined: Oct 2021
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Can’t do anymore tests tonight, it’s raining, will pull some data for you tomorrow. It’s hard to separate #1-4 spark plug wires because they are routed through the tunnels between the upper intake manifold. Will see what I can do.
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Tuned
Joined: Oct 2021
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Or maybe wiring? Is there no chance it’s a TPS?
Logistics Pro
Joined: Nov 2013
Posts: 3,921
Likes: 1,191
From: Mojave, Ca
TPS has nothing to do with your ignition system. The only thing that'll make your tach bounce like that is bad PIP, ICM, or ignition switch. And since none of your other gauges are dropping out, it's not your ignition switch.
It could be a loose connector on your distributor, but you said it clears up near WOT, so probably not a loose connector.
It could be a loose connector on your distributor, but you said it clears up near WOT, so probably not a loose connector.