Engine Miss While Accelerating
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Engine Miss While Accelerating
I have a 1990 f-150 with a 4.9l. The engine has an intermittent miss while accelerating after the transmission shifts up a gear (second and third only). KOEO and KOER both read a passing code 11. Engine compression is good, around 155-160 psi measured in each cylinder. TPS and MAP both tested ok. The plug wires, distributor cap, spark plugs, injectors, fuel filter, both vacuum reservoirs, and upper intake manifold seals were replaced within the last 2,000 miles. Also, switching between fuel tanks didn't change anything. I don't currently have a fuel pressure gauge and none of the local parts stores have rentals available, so that is about the best I have been able to do. At this point I have no idea what could be causing it besides a darn gremlin 
! Any help would be greatly appreciated.
! Any help would be greatly appreciated.
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Thanks! I tested the ignition coil's secondary coil resistance. It was about 600 ohms low of spec. It was replaced. I also went through all the ground cables I could find in the engine bay and cleaned them. Took it for a drive and the miss seems to be gone! If I had to guess it was a combination of a bad ecm ground and the coil pack.
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Well, after driving it around for a week the miss is back. I tried cleaning all the grounds again and adding dielectric grease to prevent possible corrosion from forming. I disconnected the power while doing this. After taking the truck for a drive, the miss was gone but showed up after the computer worked itself in. Could this be a computer issue? The grounds seem solid now and it doesn't feel like a broken wire.
Mountain Pass
Joined: Mar 2019
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From: MO
This may not be your problem, because I experienced a misfire only at idle. But, my ignition control module suddenly died in December and after I replaced the ICM, my idle misfire went away. The local AutoZone has a machine to test an ICM, but not sure if it'll test as faulty if it's not completely kaput.
Mountain Pass
Joined: Mar 2019
Posts: 183
Likes: 7
From: MO
Well, after driving it around for a week the miss is back. I tried cleaning all the grounds again and adding dielectric grease to prevent possible corrosion from forming. I disconnected the power while doing this. After taking the truck for a drive, the miss was gone but showed up after the computer worked itself in. Could this be a computer issue? The grounds seem solid now and it doesn't feel like a broken wire.
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