One of my cylinders are misfiring.

Tiny
CODYWASMER
  • MEMBER
  • 2002 FORD FOCUS
  • 2.0L
  • 4 CYL
  • FWD
  • MANUAL
  • 45,000 MILES
I bought the car from someone that melted the number 2 piston. I replaced the piston, piston rings, rod, rod bearings, and had the cylinder honed. I put it back together and it seems like that cylinder isn't working correctly but it isn't throwing any codes. It is acting like a misfire because if you unplug the spark plug wire while running, it doesn't effect it. I ran with that and changed the coil pack, spark plug wires, spark plugs, I ran a compression test, leak down test and everything is in specs. If I drive it at a higher speed it seems that the cylinder is fine but it idles rough and smokes a bit. The smoke might be from the previous guy melting the piston. It dumped a lot of oil and gas in the exhaust system. My question is, could the computer just need reflashed since it passed all the tests?
Monday, June 30th, 2014 AT 6:54 PM

7 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
Try swapping the injector with one of the other ones, then see if the same cylinder still has no change when you remove the spark plug wire.
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Monday, June 30th, 2014 AT 8:05 PM
Tiny
CODYWASMER
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  • 4 POSTS
I tryed that and ther is no change. It still acks up on the same cylinder.
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Monday, June 30th, 2014 AT 8:48 PM
Tiny
CARADIODOC
  • MECHANIC
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Keep in mind that when you remove a spark plug wire, you're actually killing two cylinders. If the Engine Computer failed to fire one of the coils, the misfire would be so bad you wouldn't be able to drive the car, so I don't think you have a computer problem.

We know you have compression, and if we assume you have spark and fuel, what about a collapsed lifter / lash adjuster or rocker arm problem?
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Monday, June 30th, 2014 AT 9:10 PM
Tiny
CODYWASMER
  • MEMBER
  • 4 POSTS
What would be the best way to check those options?
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Tuesday, July 1st, 2014 AT 2:08 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
Pop the valve cover off, then look at those parts to see if both valves are opening fully.
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Tuesday, July 1st, 2014 AT 2:30 PM
Tiny
CODYWASMER
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  • 4 POSTS
I pulled the valve cover and everything is operating correctly.
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Wednesday, July 2nd, 2014 AT 10:42 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
You need fuel, spark, compression, and timing. One of those has to be missing, and it isn't timing because the other cylinders are working. A 2002 model should set a diagnostic fault code for a misfire and tell you which cylinder is responsible. It should turn on the Check Engine light too. Have you checked for fault codes? Some of them will stop other self-tests from running, then other problems won't be detected until the first problem is fixed and the code is erased.
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Thursday, July 3rd, 2014 AT 10:28 PM

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