Spark plug Gap? Poor idle? 2003 4.0 Need HELP! - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 11-15-2012
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Spark plug Gap? Poor idle? 2003 4.0 Need HELP!

My manual says something like .052-.056 spark plug gap, and the sticker under the hood says .062 - .065. It is currently gapped at the 0.65 area. After i had changed plugs and wire to try and solve a poor idle issue. Well that didnt help the idle so tonight i replaced the coil pack and it continues to idle rough. I did notice while in park in idles pretty good, but when i turn the lights on it gets worse an with the brights on even worse. Which makes me to think my plugs are losing spark performance with other things running. Also when in drive coming to a stop at a light the idle also run poorly.

Also changed the MAF, IAC Valve, and PCV valve to help fix the issue

- Would re gapping the plugs down a bit help?
- any other ideas?
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Old 11-15-2012
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If it idles worse after the headlites are on and even worse after the brights are on, I might check the voltage at the battery while running and with the headlites on.
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Old 11-16-2012
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14.2 volts running , 14.0 volts running with lights on?
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Old 11-17-2012
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According to this article all 4.0L spark plugs are suppose to be gaped at 0.54. The Ford Ranger 4.0L Engine - The Ranger Station I would probably start by regaping them to that.
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Old 11-17-2012
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Do u think I,need new plugs. Just changed them a month ago. But will they be fouled
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Old 11-17-2012
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Ok, re gapped and no change. Fuel mileage has been steadily dropping off since it began doing this a few months ago.
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Old 11-17-2012
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Also truck is not throwing any engine codes.. I am now thinking 02 sensor, or cat?
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Old 11-21-2012
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Your O2 sensor would throw a code if its readings are outside the measuring thresholds. After driving your truck a few miles, get out and check if your catalyst is glowing....could determine if it's clogged or getting clogged and creating an exhaust blockage.

You can also pour 1/2-1 full bottle of 91% pure isopropyl alcohol in the tank and allow it to burn through. If there's any fouling or varnish in the cylinder head or valves, it should help burn it all off.
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