How do I tell which of my spark plugs/plug wires is bad? - Mustang Evolution

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Old 12-14-2011, 04:00 PM   #1
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How do I tell which of my spark plugs/plug wires is bad?

I have a 1998 mustang. I think one of the spark plugs or plug wires is bad. I am not getting a warning light or anything like that. I had a drastic drop in milage, even after replacing fuel and air filters. I also have a shaking that starts at high speeds, but not in a way that makes me think my tires are unbalanced.
Any ideas?
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Old 12-14-2011, 04:43 PM   #2
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How do I tell which of my spark plugs/plug wires is bad?

If those are the factory wires, they should last the lifetime of your car. For testing purposes, POWER WASH your engine with GUNK orange at a DIY car wash AT DUSK with engine running. A bad wire will light up and sparks will dance around. If you were unlucky enough to have replaced the factory wires with cheap after market ones, that's another issue. On the top of your intake manifold there is a gizmo called an IDLE AIR CONTROL VALVE. If you have been using wax based oils in your engine, this critter will be ALL fouled up. A good cleaning here is in order. Ford designed this engine so that the IAC valve is easily renmoved for cleaning. This thing affects low engine speed mileage and starting. CLean it out with SeaFoama nd Gum-out, and the THROTTLE BODY and PCV, too. Run both chemicals through the intake system to clean off the muck on your piston tops. rings, and valve heads. Switch to Mobil 0W30 engine oil. Change your spark plugs if you are NOT using platinum or iridium plugs. The Bosch and Denso plugs designs work the best. Eiother Fusion or Denso Iridium or Twin Tip plugs will gev you extra power and ileage. GOOD LUCK!!
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Old 12-14-2011, 05:27 PM   #3
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How do I tell which of my spark plugs/plug wires is bad?

Old school is to unplug the wires and reconnect the till you find the miss.
The thing is that if one plug is bad, more then likely all of them are bad.
The reality on the plug wires is that most places only sell them in sets.
So just go down to a parts place, buy a new set of plugs and wires- then do them all. Read the plugs and see if any indicate a rich condition. Check for exhaust leaks (bad gaskets, cracked welds or headers).
To tell you the truth, I suspect an exhaust leak.
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Old 12-14-2011, 05:52 PM   #4
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How do I tell which of my spark plugs/plug wires is bad?

it is called a continuity check test do this to them with and ohm reader or a high cost test engine machine you will see spikes in the screen and you read the spike series just like it was a heart beat. the shortest one is bad with the ohm reader i believe what your look for is that it be reading infinity .
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Old 12-14-2011, 06:12 PM   #5
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How do I tell which of my spark plugs/plug wires is bad?

Unless there is physical damage that you can see all the wires are going to be in the same condition so if one is bad the rest are going to be in about the same condition. If you really think the wires are the issue or they are original you should just replace the complete set.
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Old 12-14-2011, 06:46 PM   #6
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How do I tell which of my spark plugs/plug wires is bad?

Try disconnecting one by one spark plug while engine working. When you notice that there is no change in idling though you have unplugged spark plug, you have found it. Replace spark plug and if it doesn't help, replace wire too.
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Old 12-14-2011, 06:54 PM   #7
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How do I tell which of my spark plugs/plug wires is bad?

By replacing them all!
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