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Thanks for the engine information.

Ok .... update for today.  I'm really not finding a vacuum leak and before I build a smoke machine there's been this gnawing in the back of my mind to check the valve timing.  I found this pdf manual http://oljeep.com/JeepEngines.pdf  and on page 63 it tell how to check valve timing.  So I removed all the plug, it was easier to rotate by removing all the rocker bridges, set up a dial indicator on the #1 intake push rod and checked .... Hmmm the dial moved .010 but I don't see the index mark anywhere (????) ... oh, there it is 3 inches to the left, or 3 inches BTDC  ... really????  Guess I'll pull the timing cover and check it out.

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Oh, boy, Lowell!  Timing chain and/or tension is shot.  Very delayed (retarded) valve timing.  That would drop manifold vacuum dramatically and retard the ignition base timing.  Let us know what you find, sounds like you're ready for a timing chain, sprockets and a tensioner assembly.

I would run a cylinder leakdown test on all four cylinders, each cylinder with its valves closed and piston at TDC despite your chain play...Confirm that the cylinders are sealing before doing a timing chain set.  Could be just the timing chain, sprockets and tensioner, or it could be the rings, valves and cylinder taper as well.  Separate issues before making the repairs.

Moses

I did the rings and rod bearing a few years ago.  Out of 8 compression rings 6 were broken.  I few years earlier I had a valve keeper shear so while I had the head off I lapped all the valves.  When I did the rings there was NO ridge at the top, not even a carbon ring.  I de-glazed and re-assembled.

Timing chain is going back in.  The adjuster was completely worn out and the chain had some slop.  I still don't quite understand the pdf manual page 63 because the timing gear marks were right on the money.  They had not slipped a gear tooth.  Could that later model engine time completely different than the 84/85/86 engines?

Lowell, the chain adjuster wear is common, it's very likely this is all that's going on...Think of the tensioner as pulling slack out of the backside of the chain.  So, in the normal pull direction, you can have minimal timing variance without the engine running.  This is unloaded and with the crankshaft simply pulling the chain taut between the two sprockets.  Now envision the slack on the backside becoming play as the crankshaft rotates with force and momentum.  The slack  may influence valve timing variation or "play".

You're changing the sprockets and chain to be sure.  Measure the old chain for space between pins, you may discover that the valve and distributor timing error is partially from the tensioner wear.  It's generally, however, the chain stretch or space between the chain pins that creates valve timing error.  Make sure the ignition timing is correct after starting the engine.  

If you need any pointers on aligning the 2.5L valve timing marks, let me know.  Otherwise, share how much of a difference this renewal of parts makes...

Moses

Edited  by Moses Ludel

There was a wear mark on the timing cover.  Turns out the harmonic balancer rubber is old, hard, and coming out so I have a new one on order for Monday.  It was also a great time to install a new seal.  I never would park in people's driveway because of the constant oil drip from the front seal.  I did the rear seal when I replaced the clutch 6 years ago.

Lowell...Cover off, yes, time for the new seal!  You mentioned timing marks on an AMC/Jeep 2.5L inline four.  I have the July 1985 revised, the 1989 and the 1994 official/factory shop manuals.  There is often confusion about aligning marks on the 2.5L (actually the 2.46L/150 AMC four) engine.  

First off, you align the two stamped timing marks on the camshaft and crankshaft sprockets by facing them toward each other (inside the chain, the camshaft stamped dot at 6 o'clock, crankshaft dot at 12 o'clock).  With the stamped dots inside, between the sprockets, confirm their alignment with a straight edge placed through the center line of the camshaft and the crankshaft snout.  This establishes an accurate angle of view or reference point.  Make sure there is no chain slack at the "pull" side of the chain.  Rotate the crankshaft in its normal direction of rotation to bring these marks into alignment without putting slack in the timing chain.  

Notes and cautions: Do not rotate the crankshaft backward (counterclockwise when looking at the front of the engine), or this will put slack in the chain and throw off the mark alignment check. It is assumed that a technician/mechanic is not rotating the crankshaft and camshaft much at all, since the valves, lifters and rocker arms are still in place; if the rocker arms and bridges are not removed, you don't want to ram a piston into an open valve by rotating the crankshaft with the sprockets and chain loose!  (In your case, since you removed the rocker arms and bridges, the valves are all closed, and there is no risk of pistons interfering with the valves.)  This is just a sprocket and chain replacement, and the best method is to align the marks on the old chain and sprockets before removing them.  Then carefully remove the two sprockets and chain as an assembly; install the new chain and sprockets the same way, without disturbing the crankshaft and camshaft positions.

Then there is the "verification" timing check, which is explained using different clock positions over the years.  Roughly, the crankshaft sprocket mark is placed at 3 o'clock with the dot-marked tooth engaging the chain.  There should be 20 chain pins between this sprocket tooth and the tooth on the camshaft where the camshaft's marked tooth engages the chain.  This is a 20 pin count at the right side of the chain when looking at the front of the engine.  The 20 pin count is between these two marked sprocket teeth.

So, why the verification check on the 2.5L and not the 4.0L or 4.2L inline sixes?  Because the 2.5L uses a chain tensioner and the 4.0L or 4.2L engines do not.  The concern here is true valve timing.  The most accurate verification is the actual number of chain pins between the two marked sprocket teeth.  With the tensioner, there could be confusion if there is any slack in the chain when aligning the two dots face-to-face.  By measuring with the sprocket teeth engaged in the chain, you get a double check verification, which makes sense.  

Moses  

Edited  by Moses Ludel

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Lowell...Here is how the timing sprockets are aligned and how to verify valve timing on your 1986 Jeep 2.5L TBI engine.  The information is from the 1989 Jeep® FSM.  The procedure is similar for all years of the AMC/Jeep® 2.5L/150 four that use a chain tensioner:

Jeep 2.5L Valve Timing Check.pdf

Note that the 20-pin check is proof that the timing marks and teeth are set properly...

Moses

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Monday ... all back together.  New timing chain.  Engine vacuum at idle doubled :). .. but :-( the engine still misses, I think only on 1 cylinder, but when you only have 4 it's quite pronounced.  I didn't do the 20 pin check but I check and re-checked several times the dot alignment with a straight edge, both before and after the tensioner was installed.  Before, I took up the slack with my hand.  With 22-24 "hg at idle should I still make a smoke machine to check for vacuum?  I'm really at a loose to what the real problem is.

All sensors checked and rechecked, Replaced intake air sensor, crankshaft position sensor, throttle position sensor (even though both checked good) EGR valve, fuel pressure regulator, timing sprockets & chain /w tensioner, Harmonic balancer (probably not contributing to the problem, but worn out).

Do I go more complex in my diagnosis or am I thinking this too deeply and I need to go shallow and look for the obvious ?????  .... Hmmmmmmmm

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