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Misfire

Tiny
CHASPAT
  • MEMBER
  • 1999 FORD F-150
  • 4.6L
  • V8
  • 4WD
  • AUTOMATIC
  • 195,000 MILES
Replaced two coil packs. Truck idles okay, drives okay at thirty five mph. At forty five mph will misfire. Up small hills will sput, back fire, on flat ground at fifty mph seams to ride okay.
Sunday, March 25th, 2018 AT 9:23 AM

10 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

The fact that it back fires tell me spark is being delivered at the wrong time or a valve may not be closing.

Are there any codes in the system?

Roy
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Sunday, March 25th, 2018 AT 3:32 PM
Tiny
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  • 4 POSTS
No engine light. No code.
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Sunday, March 25th, 2018 AT 4:16 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, thanks.

This sounds like a mechanical issue. It could be a weak valve spring not allowing the valve to close all the way and that would result in the back fire.

The other thing is you just replace two coils. What about the plugs? What coils did you replace and how did you know they were bad?

Roy
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Sunday, March 25th, 2018 AT 4:22 PM
Tiny
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Is this the engine with two coils in the front with wires going to the plugs? There were two systems for this in 1999.

Roy
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Sunday, March 25th, 2018 AT 4:23 PM
Tiny
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  • MEMBER
  • 4 POSTS
Yes, two coil packs front of engine.
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Sunday, March 25th, 2018 AT 5:03 PM
Tiny
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  • MECHANIC
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What about the plugs and wires?

Roy
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Sunday, March 25th, 2018 AT 5:07 PM
Tiny
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  • MEMBER
  • 4 POSTS
Have not changed them. I have thinking the plugs and or wires might be the problem but not sure.
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Sunday, March 25th, 2018 AT 7:04 PM
Tiny
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  • MECHANIC
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I would do those basics first before going into anything else.

Roy
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Monday, March 26th, 2018 AT 12:01 AM
Tiny
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  • MEMBER
  • 4 POSTS
Yes I will. Thank you.
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Monday, March 26th, 2018 AT 8:06 AM
Tiny
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  • MECHANIC
  • 52,797 POSTS
You are welcome.
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Monday, March 26th, 2018 AT 9:19 AM

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