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Unread 01-21-2010, 03:11 PM   #1
myoldjeep
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timing and compression on 93 2.5L

I've replaced the timing chain and gears on a 93 yj 2.5L engine.

With an autozone comp tester I get 90, 120, 120, and 150 lbs frt to bk.

Engine runs like it has no power and misses a little in lower rpms. Smooths out at higher, but still not much power.

I took the chain cover off and looked a 2nd time and thought it was correct.

Any ideas as to why this could be? Wouldn't compression be lower for all cyl's?

Thanks.

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Unread 01-21-2010, 03:23 PM   #2
SDGBASSE
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have you played with the distributor? Even if you haven't, I would take it out and make sure it's positioned right.
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Unread 01-21-2010, 03:25 PM   #3
myoldjeep
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I think this dist. is locked in place with no adjusting possible. It ran better before I replaced the chain.
I'm wondering if the timing is off, would I see this type of compression results. I did the test twice to be sure.
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Unread 01-21-2010, 03:31 PM   #4
SDGBASSE
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No, the distributor is not locked in place, you can take it out and reposition it properly to make sure your not off. If you aligned the timing marks on the cam and crank sprockets when you put the chain on, then you should be fine, but the actual timing is done by the distributor.
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Unread 01-21-2010, 03:34 PM   #5
myoldjeep
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I wondered if someone had adjusted the dist. before I got it to make up for timing. But it is fi and the computer adjusts the timing. That doesn't mean you can't tinker.
What about the compression? I was wondering if the cam timing could cause valves to be opening incorrect and lower compression.
I'll check here for more posts on friday. Thanks.

Last edited by myoldjeep; 01-21-2010 at 03:39 PM.. Reason: going home
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Unread 01-22-2010, 02:23 AM   #6
SDGBASSE
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If you have a Chilton or a Haynes manual, it's explained quite well how to reposition correctly the dizzy, which you should do just to make sure it's fine, as for the compression numbers they look normal (#1 is a bit low, as for #4 it seems to be higher on every 4cyl jeep on this forum), if your valves weren't opening at the right moment you would get major backfires, Have you changed your timing chain guide and tensioner? Was the engine warmed-up when you checked the compression?
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Unread 01-22-2010, 06:15 AM   #7
myoldjeep
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This engine ran well before changing the timing chain. I did it as precautionary since I had just purchased it. What do you think I'd see as symptoms if it was just one gear tooth off? I took the old chain off and put the new right on without moving anything. I've read some people say the cam position sensor in the dist. wears out at around 2k rpm and that's when you feel it miss. Above that it smooths out for the most part. But theres a real lack of power up hills at all rpms.
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Unread 01-22-2010, 06:25 AM   #8
Jeeeeeeeeeeeeep
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In this thread about half way down there is a diagram of a good way to line up the timing chain. This diagram is for a 4.0, There must be 20 pins on a 2.5L. If it is a tooth off it will run like crap. http://www.jeepforum.com/forum/f12/tearing-yj-apart-rebuilding-869713/index6.html
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Unread 01-22-2010, 06:50 AM   #9
modre
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[QUOTE=myoldjeep;8736799]I've replaced the timing chain and gears on a 93 yj 2.5L engine.

With an autozone comp tester I get 90, 120, 120, and 150 lbs frt to bk.
... Wouldn't compression be lower for all cyl's?>


90 is bad 150 is good 120 is marginal...if the cam were out of time all cylinders would read low. you wouldn't see 150.

I'd pull the head and do a valve job. I just got a 2.5 head back from a valve job yesterday and replaced all the exhaust valves at 122K due to pitting beyond what could be ground down and keep the height spec. it's possible you have stuck hydraulic lifters or a loose seat in the head, but from my experience I'd look directly at the valve seat sealing surfaces. the breather piped into the intake dumps carbon. check to see if the butterfly in the throttle block (FI) or carb shows carbon buildup...if so, my bet is on the valve seats.
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Unread 01-22-2010, 07:54 AM   #10
myoldjeep
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I found a lot, and I mean a lot of oil residue in the intake. Oil was going from the valve cover to the air filter and then thru the throttle body to the intake. I've wondered if when I used seafoam on it to clear it out, could I have wound up with buildup on the intake valve of cyl 1 and get this?
The engine runs smooth at idle, and beyond 22k rpm it feels smoother but that might be too high rpm to notice it. But there's definitely not much power going down the road.
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Unread 01-22-2010, 11:35 AM   #11
SDGBASSE
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Quote:
Originally Posted by myoldjeep View Post
I found a lot, and I mean a lot of oil residue in the intake. Oil was going from the valve cover to the air filter and then thru the throttle body to the intake. I've wondered if when I used seafoam on it to clear it out, could I have wound up with buildup on the intake valve of cyl 1 and get this?
It's possible seafoam might helps you out, I would definitely try it, and try everything else that's free (or almost) before taking the head off and sending it to a shop to get a valve job done on it.
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Unread 01-22-2010, 12:06 PM   #12
myoldjeep
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I've already seafoamed it several times. The intake is still taking on small amounts of oil. Instead of drawing air in from the air filter box, I have oil (I'm assuming) blowing out of the engine into the air box and on from there to the intake. That might relate to the low compression I have on 1 cyl. I know that's how it built up in the intake before I purchased the vehicle. It was black inside the intake. I cleaned it and I'm not sure if the gunk that come off the intake the first time didn't build up on that #1 cyl. It ran smooth when I first got the jeep it was just weak. I thought I'd tune it up putting the timing chain on it and cleaning everything up. It's been missing ever since. Idles smooth and does ok at high rpm, but terrible at low rpm.
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Unread 01-22-2010, 12:30 PM   #13
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Sounds like you are getting close to new rings, especially in number 1. poor some oil down the spark plug hole and do another pressure check, see if the pressure goes up.
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Unread 01-22-2010, 12:40 PM   #14
myoldjeep
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I'll try the oil and compression check when it warms up. It ran smooth and was the same compression before I installed the timing set though. I've not put many miles on it since purchased.
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Unread 01-22-2010, 02:37 PM   #15
SDGBASSE
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If you want to be sure everything is fine, you'll need to open the timing chain cover and make sure your timing marks on the camshaft and crankshaft sprockets are aligned and check your tensioner and guide for wear, then make sure the dizzy is positioned right, then if you want do a leak down test on your cylinders, so you'll know what's worn out exactly. I had about the same numbers on my old engine and it didn't have a lot of power since it's a 4 cyl but I was still able to drive around, on highway I could reach 75 MPH , it just had awful MPG.
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[QUOTE=ZeroGravity;10681914]I didn't click the link because it says "power probe" in the url.[/QUOTE]
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