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Heavy Miss When Warm

 
  #1  
Old 01-25-2016, 03:19 PM
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Heavy Miss When Warm

92 F150, 5.0 automatic. When the truck is cold first thing in the morning it runs fine. Once it gets up to temp it gets a really bad miss no matter what the temp is outside. It has yet to die though, just runs super rough and doesnt smooth out when accelerating. I dont find any vac leaks and no CEL. Recently got new plugs, wires, cap, coil and the EGR was recently cleaned. Ran fine after parts replacement and then one day it started running rough out of the blue. Any ideas?
 
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Old 01-25-2016, 06:55 PM
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I'd check what your fuel pressure is doing when it's warmed up. Smooth cold starts, but rough when warm make me think coolant temperature sensor, however. Oxygen sensor is another possibility too.
 
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Old 01-25-2016, 07:14 PM
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Like Lead Head said, change your O2 sensor. My 88 with 5.0 had the exact symptoms of your truck. I found a Denso O2 sensor on EBay for $19 with free shipping. Removed, replaced, and truck is running good again.
 
  #4  
Old 01-25-2016, 09:55 PM
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Was your truck missing with the bad o2 sensor? Im smelling raw fuel out the pipe so I know all cylinders arent firing
 
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Old 01-25-2016, 11:53 PM
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Yes, more of a surge. Faulty O2 sensor can cause truck to run too lean or too rich.
 
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Old 01-26-2016, 09:19 AM
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Mine doesnt surge, it is a definite miss. I can watch the tach jumping up and down when sitting at idle
 
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Old 01-26-2016, 05:10 PM
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You might check the PIP sensor (stator) in the distributor for faults or the ECM for leaking capacitors. What brand name cap did you install?
 
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Old 01-26-2016, 06:13 PM
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TPS sensor.

Failing Injector, my '92 was driving me nuts. It was a handful of things. TPS, manifold temp sensor, and two bad injectors.
 
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Old 01-26-2016, 06:38 PM
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Good call. TPS & IAC would be a good place to start. Easy to test or replace.
 
 
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