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1990 Jeep Wrangler 4.2L With Timing Mark Issues


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Moses a few days ago you asked about the engine in our 1990 Wrangler I always thought it was a 4.2 liter I6 but took the time to find the engine code stamped on the distributor side of the engine.  I guess the L is for long? and it is definitely a 4.2 with a mountain of emission equipment!  Most of which came on the Jeep when new.

 

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This Jeep has been used sparingly over the past few years by our college interns sometime it is all we can do around here to just keep oil in it and air in the tires.  I drove it for the first time in years and it felt "tight" like you had to force it to run, for the most part it ran fine on dirt, only occasionally sputtering and lurching.  When the ignition switch was shut off it can't wait to shut down like a force against the motor could finally overtake it once the key was off.

 

I'm waiting on parts for the CJ and decided to investigate what ever was causing the Wrangler's problems.

 

I grabbed the timing light and soon discovered that the timing at idle was very advanced... almost 90 degrees by my estimate.  When I moved the distributor it would run very rough before I got close to the gauge on the timing cover.  I shut the engine down and wrenched the crankshaft to where the timing mark was aligned with 0 TDC.  I removed the distributor cap and noticed that the rotor was pointing at the post that leads to the #5 cylinder ( if I remember correctly),  I took out the #1 spark plug and turned the motor over until I thought it was at TDC on the compression stroke, then I made a mark on the vibration damper which is about 70 degrees from the manufacture mark.  See photo... and the pulley is turned opposite its normal direction.

 

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I put everything back together and started the engine back up and began the timing check using the mark I made as a reference instead if the original groove.  The distributor movements were more inline with the way a normal timing adjustment would go.  I didn't move the distributor very much at all before locking it down.  Really I didn't change the timing much at all compared to when I started.

 

I noticed that the damper pulley was damaged and I wondered if the key that holds the damper in place on the crank was damaged so I took it off but everything was intact.  

 

Three things come to mind.  Did someone change the vibration damper with one that is not compatible with my Jeep?  Would the mechanical advance, if hung advance the timing this far? Did it jump timing when the damage was done to the damper pulley.

 

I think that pulling the timing cover is my next step.  What do you think?

 

 

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Forman...Of course valve timing could be involved, as the distributor turns from the camshaft.  A loose timing chain cannot be ruled out, either, even a chain that has jumped teeth.  At the forums, I offer a very simple test for chain wear, and the chain and sprockets would have to be extremely loose to "jump" sprocket teeth.  This does not rule out a timing chain installed incorrectly, with valve timing way out of sync from the crankshaft position.

 

Before borrowing that kind of trouble, be aware that a vibration damper ring can creep on the harmonic balancer.  This could very well be the case here.  If the engine runs well after you referenced TDC for #1 cylinder and piston, then the damper could be creeping.  Use my test method for checking the timing chain wear:  http://forums.4wdmechanix.com/topic/174-quick-test-for-engine-timing-chain-wear/?hl=%2Btiming+%2Bchain

 

If the chain is not excessively loose, use a timing light to confirm the distributor's centrifugal advance function.  Stay away from the engine's fan when raising the engine speed!  The advance mechanism will not account for the degrees of crankshaft rotation involved here.  Full advance would never exceed 30- to 35-crankshaft degrees.

 

Update after the timing chain wear test.  I like your initiative around finding TDC on #1 cylinder and moving the crankshaft TDC mark.  If you suspect a valve timing error, I can share some ways to test that...Also, this engine could stand a good old fashioned compression check.  Test the manifold vacuum at idle, too.  This can help pinpoint valve timing errors.  Let me know the compression and idle vacuum at the intake manifold, including the steadiness of the vacuum gauge's needle.

 

Moses

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Just thinking back, the dent the pulley sustained was potentially enough to contribute to the damper creep. The kids that drive our Jeeps drive like they are in a Jeep commercial. They are indestructible you know! I will do the tests tomorrow.

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I was able to do the timing chain slack test this morning and there was virtually no play.  Thanks for telling me about that Moses you saved me some trouble.  

 

I had removed the radiator to clean it and replace the hoses which also made it easier to get my puller on the vibration damper.  Upon inspection of the radiator I found some hard water deposits that i'll probably find in my engine cooling jacket as well.  I will buy a new radiator is there anything else I can do to prevent further scale build up?

 

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I will get things buttoned up tomorrow and complete the compression and vacuum tests you spoke about .

 

 

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The vacuum test with the spark timing set normally will be revealing, Forman.  Low vacuum would be telling, indicating low compression, you've ruled out late valve timing with the timing chain test.  (The only exception would be the timing chain having been replaced and set off a tooth or so, highly doubtful if the engine is running okay now.)  A waving vacuum needle, with wide swings, means valve leakage.

 

This radiator and engine castings need a good flush.  The buildup is from non-ionized, non-distilled water.  When you flush the cooling system completely, evacuate all tap or garden water.  Make your coolant either 50/50 antifreeze premix or a 50/50 mix of pure ethylene glycol antifreeze with distilled water.

 

I just did a unique reverse flush of the Cherokee's heater core.  The heater was losing heat output with no symptoms other than a cold return line from the heater core.  I picked up a Lisle $40 heater core flushing tool for a reverse flush.  Disconnected both heater hoses from the engine.  Ran water through the back way, from the return hose to the pressure side of the heater core.  Blew through with compressed air after each fill/flush of the core. 

 

The compressed air, in brief controlled spurts, created a blast with turbulence.  (Do not use high PSI compressed air by itself to unclog a heater core, you can blow a hole in the core!)  After five flushing intervals, I used the compressed air to completely evacuate the remaining tap water from the heater hoses and heater core.  The engine remained unaffected this whole time.

 

I reattached the heater hoses and filled the coolant recovery tank above the top line with a 50/50 mix of pure anti-freeze and distilled water.  Ran the engine to complete warm-up to circulate coolant.  Shut down and cooled the engine completely.  Topped off the radiator with 50/50 mix and watched the recovery tank for normal fill.

 

The result is phenomenal.  At 152K miles, the heater has never been this effective—we bought the vehicle at 94K miles...Reverse flushing the heater core does wonders!  I'll be testing an OTC 6043 Blast-Vac tool soon, it combines compressed air with household or garden water pressure.

 

Moses

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Compression test results. 40,000 miles on original motor

Cylinder #1. 132

2. 135

3. 140

4. 145

5. 135

6. 132

Vacuum at manifold. I took this to be the place under the carb with the highest amount of vacuum. 20 inches and a steady needle.

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Yes, Jeff!  This one's a keeper...Some tuning and you're good.  You want 10% maximum variance between highest and lowest cylinder compression.  This will work.  A cylinder leakdown test would be ideal, but don't bother.  Concentrate on tuning and restorative measures.  You're in business on this '90 YJ Wrangler 4.2L!

 

Manifold vacuum is excellent and suggests that the ignition base timing is correct.  Good job on that damper issue...The firing order on all of these AMC sixes is 1-5-3-6-2-4.  Simple, easy to tune and master.  At 40K miles the BBD Carter should be okay, too.  This may be the blueprint for your earlier CJ emissions if the Wrangler has everything intact.

 

Moses

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I'm going to set this project aside for now, the Weber carb should be here and I can install that carb on my CJ.

I do plan on following your BBD carburetor instructions when I come back to this project. After reading your chapter on rebuilding the carb in your book Jeep CJ rebuilders manual, I feel confident that I can follow your steps to a successful rebuild. I will need some instruction on how to test the emission components. I'm ok with the WOT switch and the choke pull off, a little shaky on the electric choke and the stepper motor, as well as the components associated with the air cleaner.

There is also an old MJ 2.5 near my home that has peaked my interest lately, I may have to pick your brain about what to look out for when buying a non running vehicle... But that is probably another book in itself.

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When evaluation that 2.5L MJ Comanche, we'll do the CliffsNotes version here at the forums, forman! 

 

Ask away about the BBD on the YJ, you'll likely get that stock 1990 YJ Wrangler running as new with some basic tuning measures...Too few miles for major issues.

 

Moses

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