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Old 11-01-2013, 04:32 PM   #1
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Rough starting, but good running, new motor

Looking for some diagnostic tips: just replaced the 2.5 with a reman 2.5 on my '00 TJ. It doesn't like starting, but once started it runs like a top. Not sure what might be the cause, since it is so smooth once it's going. On starting it will hesitate, stumble, act like timing is WAY off, but then run quiet once it's started. I have to stand on the gas to get it to start. Stumbles a bit when letting off the gas when it's running, but then will settle back down to a smooth idle.
Still burning off some oil I spilled on the manifold, so I haven't even really let it get warm yet. Seems like a clocked distributor or wires out of order would result in rough running, not just rough starting, right?
I'm sure there's some wisdom out here, would love any ideas.

thanks!

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Old 11-01-2013, 05:04 PM   #2
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Check the crank position sensor to make sure it is good and tight.

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Old 11-02-2013, 01:17 PM   #3
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Hmm. Replaced the CPS (thanks for the tip - another person said the same thing, and after looking at it I can see how I may have damaged it when I was putting in the motor.)

Now it starts like a champ and idles fairly rough (not dying, but shaking pretty good.) So looking for rough idle tips.

AND now that I got it warmed up I'm getting water (?) boiling out of the front most exhaust manifold stud (!?!?) not at all sure what's up with that, about to search.
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Old 11-02-2013, 02:18 PM   #4
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Crack in the block maybe? Water where it shouldn't be is bad news bears.
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Old 11-02-2013, 02:24 PM   #5
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Looks like there are a few freeze plugs under the manifolds, going to pull it back apart and see - not this weekend though.
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Old 11-02-2013, 03:59 PM   #6
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I don't know for sure but this is just a guess.

That stud is going into the water jacket in the head. The way to fix it would be to pull that stud and make sure the threads in the head are dry and put silicone on the stud and put it back in. let it sit overnight and put the coolant back in. Good luck!
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Old 11-02-2013, 04:46 PM   #7
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Quote:
Originally Posted by harley jones View Post
I don't know for sure but this is just a guess.

That stud is going into the water jacket in the head. The way to fix it would be to pull that stud and make sure the threads in the head are dry and put silicone on the stud and put it back in. let it sit overnight and put the coolant back in. Good luck!
Google turned up a few other people making that connection, though not as many as talking about the freeze plugs under the manifold gasket. Either way I'll dig in and see.

What I haven't found so far is a very detailed diagram of the head water jacket to see which theory makes more sense on paper. Anyone here know where to find such a graphic?
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Old 11-02-2013, 05:01 PM   #8
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I am assuming that you just had the motor rebuilt. If it acts like that I wonder if you are off by a tooth between the crank and the cam?
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Old 11-02-2013, 10:32 PM   #9
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I am assuming that you just had the motor rebuilt. If it acts like that I wonder if you are off by a tooth between the crank and the cam?
Reman not rebuild, but yeah. Have a link to proper procedure to get them matched up?
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Old 11-02-2013, 11:02 PM   #10
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Yes. Go to http://www.jeepslimited.com and become a member for free. Then you can download a Factory Service Manual, FSM, and it will tell you exactly how to check if it was lined up correctly. I had a situation like that on a car many years ago. I was surprised what one tooth off could do. Keep us posted.
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Old 11-03-2013, 10:28 PM   #11
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You threw an "un" in that link, got me for a minute I was a JU rat back when JUOT was part of the board, since '03. Logged in to look for the FSM and based on unread PMs I hadn't been there since '07!

Then I realized you meant the other site, got the FSM, definitely wasn't followed when I slapped the new motor in, and the behavior would make sense for a tooth off. Will disassemble this week/end, and press the harmonic balancer back on, and then tackle the exhaust stud - from my reading there I really suspect a freeze plug in the head.

thanks!
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Old 11-04-2013, 07:11 AM   #12
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Also, the title of this thread isn't accurate. Still starts rough (in an earlier post I said it started smooth, I just caught it right a couple times - luck of timing!) and also idles rough (seemed smoother when I wasn't watching it wobble). But it's a quiet rough, no stumbling.
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Old 11-08-2013, 08:30 PM   #13
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Gah. OK, so I re-installed the distributor according to the factory service manual, and now I got no start at all.
BUT - following the directions appeared to put my rotor squarely between 1 and 3, not solid on 1. After I got the no-start I went back and re-read and noticed that. Instructions say that re-assembly should have the rotor on the firing 1 spot, but it was well past. So I'm probably 45 deg off. Gotta go back and figure out which piece was not lined up right.

Rotated motor to TDC (used finger to confirm compression stroke)
Turned oil pump drive to 10 oclock (block is noon, front is 3, etc)
Put pin in distributor on the right alignment hole per the FSM (the one ahead of the start of the crank sensor, not the one right on it for the 4.0)
Placed distributor in with the fork at ~1 oclock, rotated as it slid to the ~3 oclock position of the hold-down
Removed pin, installed cap and rotor (again - rotor only goes on one way but it was past #1)
Fastened it down, re-installed plugs, re-tensioned belt, spin no start.

So, if I used the right alignment hole (almost certain I did per the FSM) why was the rotor so far ahead of where the manual said it should be?
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Old 11-08-2013, 08:36 PM   #14
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And just to confirm firing order (certain this is right, but to be complete)

Cylinder, counting from front of motor (front is 3oclock)
1 in the ~3oclock position
3 in the ~6oclock position
4 in the ~9oclock position
2 in the ~12oclock position
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Old 11-08-2013, 10:09 PM   #15
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ok, lesson of the night:

don't try to feel for compression and turn the motor over at the same time by yourself. took it apart again and I was 180 off. fixed and now it starts smooth every time. still a good bit of vibration at idle, it's not super smooth. but it's a lot closer to right than it was.

tomorrow, i'll tackle the head freeze plugs.
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Old 11-09-2013, 01:32 PM   #16
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Took off the manifolds, and the freeze plugs were looking fine. So I rented a pressure tester and I am getting coolant from the front exhaust stud hole. Hopefully by design

Now my delima is which RTV to use on that stud? Blue, black, red? Leaning toward blue. same temp range as black (up to 500f) and recommended for water.
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Old 11-10-2013, 09:25 PM   #17
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Used blue, let it cure for ~20hrs over a cold night in the garage. Knock on wood no leaks yet after a short drive around the 'hood.

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