87 f 150 l6 300 missing while driving
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Joined: Sep 2024
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87 f 150 l6 300 missing while driving
my 87 F-150 has recently started acting up by "missing" while its driving as if the engine stops for only a fraction of a second. it causes the cab to shake and the RPM's to bounce around. this issue started by it only happening maybe once a month but recently as the weather got cold it happens every time I drive it and it happens constantly. (see video)
I've recently replaced my whole distributor with a new ignition module and the majority of the fuel system for a separate issue i was having a few weeks ago. but the issue i was having ended up being my distributor drive gear broke loose. the truck drove fine for about a month then this started. I've read the codes from the trucks computer and i got
-33 (EGR valve fault)
-25 (knock not sensed during dynamic response test) ill add more about this later
-44 (thermactor air system fault)
i unplugged my knock sensor as i read if its faulty it could be telling my ignition to retard timing momentarily. this did not fix the issue.
maybe im getting a bad ground somewhere?
maybe a vacuum leak?
ive also tried cleaning the MAP and replacing all plug wires, cap, rotor ext. that as well didn't solve the issue.
i read somewhere that someone found corrosion in some connection for there coils. so i cleaned about every electrical plug i could which also didnt help.
does anyone know what might be causing this???
i dont know if its important but it seemed as if it does it more often when its cold... i also haven't seen any evidence of it happening at idle just while under load (accelerating and in cruise)
I've recently replaced my whole distributor with a new ignition module and the majority of the fuel system for a separate issue i was having a few weeks ago. but the issue i was having ended up being my distributor drive gear broke loose. the truck drove fine for about a month then this started. I've read the codes from the trucks computer and i got
-33 (EGR valve fault)
-25 (knock not sensed during dynamic response test) ill add more about this later
-44 (thermactor air system fault)
i unplugged my knock sensor as i read if its faulty it could be telling my ignition to retard timing momentarily. this did not fix the issue.
maybe im getting a bad ground somewhere?
maybe a vacuum leak?
ive also tried cleaning the MAP and replacing all plug wires, cap, rotor ext. that as well didn't solve the issue.
i read somewhere that someone found corrosion in some connection for there coils. so i cleaned about every electrical plug i could which also didnt help.
does anyone know what might be causing this???
i dont know if its important but it seemed as if it does it more often when its cold... i also haven't seen any evidence of it happening at idle just while under load (accelerating and in cruise)
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Joined: Oct 2016
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From: Parts Unknown
My 87 4.9 had a lean miss with occassional bucking while driving. I had 33 and 44 codes.I found multiple breaks in the vacuum lines at the solenoid packs above the # 6 spark plug.It appeared at some time I disturbed the already fragile plastic lines and broke a vacuum fitting on a solenoid while attempting to change plugs. I also changed the EVP sensor on top of the EGR valve which had very erratic resistance readings.
Last edited by raski; Nov 4, 2024 at 12:11 AM.
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Joined: Sep 2025
Posts: 1
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Fluid is low then probably trans is slipping. Fill it to spec then try. Also, since it's been sitting, did you verify your brakes aren't rusted up? If your trans isn't slipping and all wheels are free then sounds like you engine isn't running right.