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Old 08-13-2012, 04:36 PM   #1
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Need Help - Some Sort Of Tap/Knock

I bought this jeep with quite a few problems on the side of the road. That in itself was a mistake but I have soldiered through fixing everything possible. We have done many sensors (Crank, O2,etc) and we did a starter because the fuel pump died and we kept trying to start it on a slow cranking starter as it was. BUT the largest problem by a mile is that this is the small 2.5L 4cyl and it sounds like a DIESEL, when its cold it just pulses and runs somewhat normal, but once it warms up the RPMs start pulsing and dropping and it sounds like a god damn Mack truck. It goes away at high RPM but at low it is ridiculous. Does anyone have any ideas on what it could be? My friends say it could be valves not opening or something out of alignment. We had to up the idle to stop it from dying coming up to stops or just flat out stalling.

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Old 08-13-2012, 05:45 PM   #2
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Bad wrist pin,piston slap or broken piston skirt. Is this going to be a toy or DD?

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Old 08-13-2012, 10:40 PM   #3
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Quote:
Originally Posted by Redrider94
Bad wrist pin,piston slap or broken piston skirt. Is this going to be a toy or DD?
+1
I vote piston slap.
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Old 08-14-2012, 02:00 PM   #4
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It was going to be a mix between the DDing and toying around but the thing is actually up for sale now im getting too deep into this thing its an old motor as it is.
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Old 08-14-2012, 02:05 PM   #5
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Check compression. If the numbers are good, even a loud engine will last a while.

Do a search for jeep diesel engine noise or similar. Usually it is lifters, which on the four banger is an extremely easy replacement. Can also be a pinhole header leak. Go for the easy before going for the rebuild.
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Old 08-14-2012, 02:22 PM   #6
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Alright ill look into it. Thanks.
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Old 08-14-2012, 04:08 PM   #7
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Get the engine up to normal temp, while it is idling pull the plug wires off one at a time ( use some high voltage pliers or a plug wire puller). Listen to your engine, if still making the noise put that wire back on and pull the next one. If the noise goes away this is the cylinder that has the problem.

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