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Old 06-25-2014, 10:12 PM   #1
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Need some help!

Sometimes when I start my jeep it will crank for a few seconds then lock up and then start and when it does this its very strange because after it starts it will have like a perfect idle that just sounds louder from the exhaust. And its solid at 900 rpm but when I try to rev it up it is slow to rev and kind of hesitant. I then shut it off and restart and its fine. Same old quiet idle. That feels bouncy but doesnt move on tach. Jeep hardly starts half the time. Is it possible for my 2.5 to temporarily sieze and then free up?

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Old 06-25-2014, 11:21 PM   #2
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Sounds like symptoms of a head gasket to me. My 4.2 was doing something similar to that a while back and it finally got to the point the motor locked up. I pulled the plugs and spun it over and blasted coolant all over my shop wall. Don't remember which cylinder it was but R&R cyl head gasket and it fixed the problem. 2weeks later I found a 4.0 head (dammit)

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Old 06-25-2014, 11:52 PM   #3
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Wouldn't that show up on a compression test?
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Old 06-26-2014, 12:20 AM   #4
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Yes a compression test would be a good start.

Smell the oil and look for signs of moisture yellow milky residue on oil cap or dipstick.

Look at coolant level has it gone down recently.

Could also be a timing issue. May have a loose timing chain.
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Old 06-26-2014, 12:23 AM   #5
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Quote:
Originally Posted by MikeyinaYJ View Post
Wouldn't that show up on a compression test?
You bet it would, too many people miss the obvious options to diagnose vehicle problems like a stethoscope, compression tester, vacuum gauge, and even pulling the codes where possible like post 90 wranglers!
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Old 06-26-2014, 01:15 AM   #6
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Compression was actually pretty good. 135-145. I have tapping/rattling coming from the bottom when cold at idle and at about 1200rpm warm. From what ive looked into it aounds like piston slap or wrist pin noise. Oil pressure 40-60 sometimes 30 at idle when im wheelin. Besides my tapping and horrible starts the little 4 banger moves quite well around town and on the trail. I wish it was showing a code lol. I need a vacuum gauge..been lagging on it. Btw coolant is nice and green and oil looks good.
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Old 06-26-2014, 01:23 AM   #7
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Vacuum gauges aren't the best choice for multiport/throttle body injection motor diagnosis, mostly carbureted motors.

Almost seems like a bad sensor is preventing your engine from running right too me, or even an exhaust leak before the O2 sensor or something silly like that or even a bad oil pump
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Old 06-26-2014, 09:15 AM   #8
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Ah I see. Guess it wouldn't hurt to make sure vacuum is in spec. I heard an exhaust leak before I removed it to do my clutch. But now its gone and sounds better. Id think an o2 would affect higher speeds and not start up. I was thinking about pulling it out of the down pipe to see if theres a difference but ive been focused on open loop. Maybe the crank sensor? Seems most likely but everything ive read on it throws me off. I did have a similar symptom yesterday, crank crank crank then it fired for a split second. I wouldn't have considered it actually being started but yeah. Do that 2 more times then by the 4th try it fired up and stayed running. But my exhaust sounded normal and it reved just fine. Seems to start differently everytime. Its very frustrating lol.
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Old 06-26-2014, 09:31 AM   #9
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I thought about the timing chain because it used to backfire from intake on some hard starts but it hasn't done that since I fixed my iac circuit. Had code 25 and replaced the stepper motor but turned out to be a shorted wire. Iac would close off throttle bypass fully and made it so I had to hold the throttle open when starting. Can a fuel pump intermittently lose pressure? Fuel pressure test was confusing and gave me some wierd results. Trying not to confuse the hell out you guys sorry haha
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Old 06-26-2014, 11:06 AM   #10
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A fuel pump can definitely work intermittently. Even a fuel pressure regulator could be causing issues. What were the fuel pressure test results?
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Old 06-26-2014, 12:00 PM   #11
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While running everything is perfect. Except 2 out of 6 tests gave me a fluctuating pressure of about 30-33. Unless I revved it up or unplugged the regulator hose. Then it would steady at 39. The other tests showed 31 at idle with no needle bounce. It did this after I reinstalled the injectors. After I drove it and tested again it was back to a steady needle. Maybe the o-rings on the injectors needed some heat to seat in and become air tight who knows. But after half an hour my pressure would sometimes be 20 and then sometimes be 11. It held at 31 the longest with the fuel line pinched before the filter. One test I had it stayed at 20 for 2 hours til I reprimed for another test. Watched it climb to 44 while cranking and was hard to start still.
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Old 06-26-2014, 12:04 PM   #12
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I only had the test kit for 48 hours. I prefer oriellys over autozone but next time ill borrow one from autozone, no time limit. That and im forgetting stuff trying to think too hard what my results were lol. Think I might try it again and make some notes/videos.

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