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Old 04-16-2014, 11:37 AM
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P0304

2005 JGC w/ 112,000 miles

Started it this morning and was surprised with a check engine light! Scanned for codes, P0304. - My 22 mile drive into work was fine, no rough idle or harsh driving on the hwy.

Brief History of latest maintenance;

-Tune up @ 95k (new plugs, fuel induction, trans flush)
-New Control Mod and Ignition switch @ 105k (Thanks, remote starter for frying my wires and system)
-Water pump @ 107k

The jeep is running fine, no noticeable loss of power.

Any ideas?
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Old 04-16-2014, 03:47 PM
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Re: P0304

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Originally Posted by klong31 View Post
2005 JGC w/ 112,000 miles

Started it this morning and was surprised with a check engine light! Scanned for codes, P0304. - My 22 mile drive into work was fine, no rough idle or harsh driving on the hwy.

Brief History of latest maintenance;

-Tune up @ 95k (new plugs, fuel induction, trans flush)
-New Control Mod and Ignition switch @ 105k (Thanks, remote starter for frying my wires and system)
-Water pump @ 107k

The jeep is running fine, no noticeable loss of power.

Any ideas?
Did you/they check the ignition wires when the tune up was performed? I would check the resistance in those first.

A P0304 is a misfire in cylinder 4, so the usual culprits (coil, plug, etc.) would be the next thing to check. What type of plugs were put in during the tune-up?

On the more rare, but still possible side you're looking at EGR valve (which are known to go around your mileage), vacuum leak, crankshaft/camshaft position sensors. Usually all of these would be accompanied by stalling or nearly stalling behavior.
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Old 04-17-2014, 01:44 PM
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Re: P0304

My moneys on a coil or a sticking valve. Try seafoaming again.
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Old 04-28-2014, 07:13 AM
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Re: P0304

I disconnected the battery to clear the code. I've put about 400 miles on it since the reset and the check engine light has yet to come back on. - Still no apparent loss of power or MPG. It had to be a coil or wire that was disconnected for whatever reason but I checked them all out and none were loose.

I will have to keep an eye on it.
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Old 04-28-2014, 03:47 PM
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Re: P0304

Quote:
Originally Posted by klong31 View Post
I disconnected the battery to clear the code. I've put about 400 miles on it since the reset and the check engine light has yet to come back on. - Still no apparent loss of power or MPG. It had to be a coil or wire that was disconnected for whatever reason but I checked them all out and none were loose.

I will have to keep an eye on it.
Just as info: many times a single or multiple misfire code without feeling the misfire (rough running or power loss) is caused by the TPS sensor. It can, after time, produce an electrical noise signal on the wires, which the PCM interprets as a misfire.
But if it had a real misfire, then it could have been a bad contact in one of the connectors. Vibration induced fretting corrosion is a common problem in connectors, which increases the resistance of the connection and can cause partly or full failure of an electrical system. Removing the connector can wipe away the high resistance residue, whereafter the normal electrical operation is re-estabilized. Some di-electrical grease in connectors can prevent this problem.
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