2000 Mercury Cougar 2000 Mercury Cougar #1 Cylinder Misfire

Tiny
SIMSR004
  • MEMBER
  • 2000 MERCURY COUGAR
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 160,000 MILES
I have a P0301 error code. I had the car taken to a repair shop and they said it was a valve train issue. I tested the spark plugs, all 6 have a spark. I swapped the #1 and #2 spark plugs and received a P0301 and a P0302 error (expected). I erased the error codes and swapped the #1 and #4 spark plugs and no errors came back (not expected). The firing order is 1, 4, 2, 3, 6, 5. After closing up for the night, I realized that antifreeze is leaking, I have not found the leak yet, I suspect the thermostat area. My question is, could the thermostat or some part of the cooling system cause a misfire or the same indication as a misfire (engine bucking) or is it a seperate issue all together. The car did not overheat, but the low antifreeze light came on around the same time the check engine soon light came on.
Thursday, May 6th, 2010 AT 7:21 PM

9 Replies

Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Low coolant will only cause a misfire if the engine is overheating, or if the leak can somehow contaminate the coil/wire/plug, besides a blown head gasket, but if your leak is external that probably isnt the case. Does this vehicle have COP (Coil over plug) or one coil per spark plug?> If so try swappping the coils around to see if you can get the miss to come back. If it has wires they should be repalced considering the mileage, same goes for the plugs. Just to be sure the basic electrical part of the ignition system is good
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Friday, May 7th, 2010 AT 8:05 AM
Tiny
SIMSR004
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The spark plugs and wire are brand new, the electric coil has all 6 wires attached in same unit, it is not like, say a buick regal where 2 wires are attached to each coil. I cleared the P0301 error code, and as soon as the coolant starting leaking the error code has not come back. If I swap # 1 and #2 wires, I get both codes back. But with #1 and #4 wires swapped, I do not receive an error code, and same with all wires on correct connectors. I plan to replace the thermostat, upper and lower hose and then test again. But I don't understand where the #1 cylinder misfire comes from (because the car does not look like it is over heating) or why my indications changed once the coolant starting leaking. Also, a compression check would have proved that the head gasket is good correct? Thanks for your help.
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Friday, May 7th, 2010 AT 8:36 AM
Tiny
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Not sure why swapping wires would do that either unless one is bad or has aquestionable ontact issue that was cured when it was swapped.A compression test doesnt rule out a head gasket problem.A chemical test for exhaust gasses in the cooling system is the best way to find that.
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Saturday, May 8th, 2010 AT 9:00 AM
Tiny
SIMSR004
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I changed the radiater hoses and the thermostat, the low coolant light went away. The Car still has a P0301 Code, Engine idles rough at first and then is fine, misses going up hills. The lights are also fading in and out (Dims a little then back to normal). I verified a spark on all 6 cylinders, I checked one at a time, brand new spark plugs and wires. Any suggestions on what I can do next for the misfire?
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Monday, May 10th, 2010 AT 6:58 PM
Tiny
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Possibly a bad injector, but usually a miss under load (Uphill) is an ignition issue.
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Tuesday, May 11th, 2010 AT 7:54 AM
Tiny
SIMSR004
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I replaced the fuel injector, electric coil, spark plugs and wires, I still have a misfire, what else can I check?

I also replaced the radiator (found a hole), went driving today and car misfires, also smelt electrical burning, found the fan is also bad on the radiator. I figured that this was shorting and causing the lights to blink in the car, not sure if it would cause a misfire also? Don't think so, but you never know.
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Friday, May 21st, 2010 AT 6:46 PM
Tiny
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What exactly did the original shop say was wrong with the valvetrain? Does it have a broken valve spring? Bad valve?
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Saturday, May 22nd, 2010 AT 8:15 AM
Tiny
SIMSR004
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All they said was that they would have to take it to the Ford dealer to diagnos a possible valve train problem. They said the compression check passed. But that the #1 cylinder continues to misfire. I replaced the coil, wires and plugs and found that #1 cylinder is burning more oil than the other valves. IE. The #1 spark plug end looks very black with obvious extra oil in that cylinder.
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Tuesday, May 25th, 2010 AT 10:00 AM
Tiny
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Then it may need further diagnosis. It could be a bad valve guide or possibly a bad intake manifold gasket if the intake ports are subject to oil (not sealed off from engine). A cylinder leak down test will identify where the leakage is that is causing the plug to oil up.
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Wednesday, May 26th, 2010 AT 7:58 AM

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