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Old 09-17-2010, 08:33 PM   #1
Join Date: Sep 2010
Location: Wisconsin
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Question Odd Misfire Question - 4cyl 97 Wrangler

I have a 97 Wrangler with a 4cyl manual tranny. Has about 87000 on her. I have an odd issue with the engine. When I restart the engine after it has been recently started, (usually within 5 to 10 minutes) the engine will misfire and sputter until I rev it enough and it evens itself out. It does this particularly when the weather is warm (70 degrees +). It has been going on for about a year and I am getting tired of it. I replaced the plugs a couple of times but it doesn't seem to help much. Any thoughts????????????

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Old 09-17-2010, 08:39 PM   #2
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I hear misfire, I start thinking plugs/wires/distributor cap. Have you done all of those?

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Old 09-17-2010, 08:40 PM   #3
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That was happening to me and I changed he O2 sensor and fixed the problem..
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Old 09-18-2010, 10:46 AM   #4
Join Date: Sep 2010
Location: Wisconsin
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Which O2 Sensor

Which 02 sensor did you change? There appears to be several according to Autozone??? Thanks for your help.
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Old 09-18-2010, 11:07 AM   #5
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Location: NW, NJ
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My 04 had a miss under load whenever I started out. I replaced the plugs, wires, and coil. I really feel it was the coil breaking down under a load.
Retired my 94 YJ 4cyl 5spd @ 200K
Now in a 04 TJ 4cyl 5spd CV @120K+
Both as a commuter vehicle in NW, NJ
April 2012.downsized and now a 99er.
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Old 09-18-2010, 11:25 AM   #6
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O2 sensors don't do anything until it's fully warmed up, when you are experiencing the trouble it's before the O2 sensors are doing anything. Not an O2 trouble.

Put a fuel pressure gauge on the rail. Run it for a moment, shut it off. I'll bet the pressure drops down to nothing in a moment or so.

I suspect a fuel injector is leaking, gas is puddling on the piston top, when you crank it, it splashes onto the plug, fouling it. Running a moment eventually clears the fouling.
After a longer sitting that fuel drains down into the crankcase (smell the oil) and doesn't foul the plug when you start it - no more puddle.

Before panicking, try running a strong dose of Techron in the gas tank (parts house - better stuff than all the others combined,) - it may dissolve what's holding the injector open. Pouring it down the throat will not do the trick, it has to go through the fuel system. Normally I'm against adding cleaners since the fuel has enough in it already (unless it's old and stale,) but in this case you need extra cleaning. Cleaner may not work if it's something that won't dissolve, dirt, metal fragment, sand etc. But it's worth a try.

To find out WHICH injector is leaking, run it, shut it off, start it so it misfires, shut it off while it's still misfiring, then quick - remove each plug looking for one being too wet.

You may have to remove the injector to clean it - or replace it. (Do not poke things in the injector's hole!)

After you solve it, change the oil.
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Old 10-12-2010, 04:50 AM   #7
Join Date: Sep 2010
Location: Wisconsin
Posts: 3
Problem corrected

Changed the O2 upstream sensor - problem fixed.........run great! Thanks for the help!

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