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Jeep Wrangler YJ
YJ General Discussion
Head gasket/ piston rings replacement 89 2.5l
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<blockquote data-quote="Flyer58" data-source="post: 436642" data-attributes="member: 18629"><p>Yes two steps. The compression test should have the fuel pump off by pulling the fuse, not sure where that is, Disconnect all sparkplug wires and hold the throttle wide open then turn the engine over using the starter. You can try it with both a warm engine and cold but I bet a low compression will show up on both tests.</p><p></p><p>The second test of turning it by hand is not really necessary but may indicate if the leak is in the head or piston and you should notice a different feel in one cylinder compression even though you may not hear the difference.</p><p></p><p>Backfiring is usually caused by bad spark timing, valve problems, or poor mixture control. Since you have a throttle body injection it would lead me to think all plugs would be close to the same. You have one black plug so for whatever reason that cylinder has a lot of unburned fuel in it. Could be poor spark but you said you were going to change the cap, wires, and plugs. Poor compression also causes a rich condition because the fuel doesn't completely burn as it should. </p><p></p><p>You can try the Sea Foam trick of slowly pouring or spraying a can of Sea Foam into the throttle body as the engine is running, turn off the engine and let it sit for 10 minutes or so and then start it. Look for a youtube video about that. Lot's of smoke but it does clean the induction, valves, and pistons. You may just have a chunk of crud preventing the valve from seating. </p><p></p><p>I still find it strange that this started by replacing a belt. I'm not familiar with that year YJ so I can't say it's not something else.</p></blockquote><p></p>
[QUOTE="Flyer58, post: 436642, member: 18629"] Yes two steps. The compression test should have the fuel pump off by pulling the fuse, not sure where that is, Disconnect all sparkplug wires and hold the throttle wide open then turn the engine over using the starter. You can try it with both a warm engine and cold but I bet a low compression will show up on both tests. The second test of turning it by hand is not really necessary but may indicate if the leak is in the head or piston and you should notice a different feel in one cylinder compression even though you may not hear the difference. Backfiring is usually caused by bad spark timing, valve problems, or poor mixture control. Since you have a throttle body injection it would lead me to think all plugs would be close to the same. You have one black plug so for whatever reason that cylinder has a lot of unburned fuel in it. Could be poor spark but you said you were going to change the cap, wires, and plugs. Poor compression also causes a rich condition because the fuel doesn't completely burn as it should. You can try the Sea Foam trick of slowly pouring or spraying a can of Sea Foam into the throttle body as the engine is running, turn off the engine and let it sit for 10 minutes or so and then start it. Look for a youtube video about that. Lot's of smoke but it does clean the induction, valves, and pistons. You may just have a chunk of crud preventing the valve from seating. I still find it strange that this started by replacing a belt. I'm not familiar with that year YJ so I can't say it's not something else. [/QUOTE]
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Jeep Wrangler YJ
YJ General Discussion
Head gasket/ piston rings replacement 89 2.5l
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