Cylinder Misfire 2002 Mecury Sable

  • 2002 FORD
113K Mileage

I felt some misfires and jerking about 2 months ago.

1. I replaced wires and plugs. Did not resolve the issue.

2. I purchased and OBD II Reader and detected codes 303, 316, 401.

3. I then did the next less expensive thing and pulled the intake manifold and cleaned injectors,
throttle body, fuel rail, intake, and tested the EGR valve manually by engaging it and feeling for suction.
After replacing all gaskets, the problem still persisted.

4. Next I replaced the EGR Position Sensor $74.00 and the 401 code is now gone.

5. I still received a 303 code (Cylinder 3 misfire)

6. I replaced the wires once again with an upgraded set of wires at $46.00 instead of the $20.00 set.

Current symptoms:
1. Misfire still persists but no code detection now.
2. Idles fine and smooth.
3. Missing only upon take-off.
4. Once on the open road, no misfire felt, no code given.

Things that I haven't replaced:
1. EGR Valve
2. PCV Valve
3. Fuel Filter

Things I have replaced:
1. Plugs (probably 6K mileage in two months)(Autolite)
2. Plug wires (twice in two months)(Autolite)
3. Injector "O" rings (Purchased from Ford)
4. Throttle body gasket. (Felpro)
5. Intake manifold gaskets (Felpro)
6. EGR valve gasket (Felpro)
7. EGR Position Sensor (Purchased from Ford)

Any advice or assistance would be greatly appreciated.


Do you
have the same problem?
Friday, April 20th, 2007 AT 7:38 AM

1 Reply

You have done alot so far and this has eliminated alot of things, and change the parts that are most likely cause for a misfire. I have to admit you are persistent and hope it pays off. Here are the things that can cause a misfire.
1) ignition problem- I think you have cover this. You may want to test the coil for # 3 cylinder with a ohm meter, see if within specs
2) fuel problem- You have done some things here. Dirty/faulty/leaking injectors and Low fuel pressure can cause misfires. You may want to check the fuel pressure and test the #3 injector and with a ohm meter and see if within specs.
3) Compression problem- Do a compression test. Pay particular attention to #3 cylinder.
4) A vacuum leak. Take a reading with a vacuum gauge. A normal heathly motor should have 17-22 hg with a steady needle. This can also help diagnosis internal engine problems like leaking head gasket, sticking valves, weak valve springs, etc. If you don't have one and plan on buying one make sure you save the chart that comes with it for future reference. This is a great tool and not expensive
The hard to find misfires are the ones that don't show any codes. The cause is still fuel, ignition, vacuum leak or compression. Good luck
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Friday, April 20th, 2007 AT 9:57 AM

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