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Keith Vicker's Guide to Fixing the MMC 3.0 V6

Also see the main 3.0 page and the 3.0 general repairs and rebuilding guide

The Mitsubishi 3.0 liter engine in many Chrysler vehicles, from the Shadow to the Caravan, is prone to oil burning in later years. An otherwise reliable engine, the early 3.0s almost invariably went to burn oil. Keith Vicker's guide is posted here with his permission to help you to save tons of money in repairing this defect. - contributed by [email protected]

A little 3.0 liter history

Drew wrote that Chrysler went to a sequential multi-point fuel injection system (SMPI) on the Mitsubishi engine for the 1992 model year (from a standard multi-point fuel injection system). The horsepower ratings stayed the same (141 @ 5000 RPM for cars and 142 @ 5000 RPM for vans), but the torque rating was reduced to 167 lbs/ft for the Daytona and LeBaron coupe and convertible. Other cars were rated at 171 lbs/ft of torque in 1992, while the minivans stayed at 173 lbs/ft. For 1993, the ratings returned to 171 lbs/ft of torque for all cars. Using sequential injection may have been done to increase fuel economy or cut emissions.

The 1989 3.0L was rated at 142 HP and 173 lbs/ft of torque, while the 1988 was 136 HP and 168 lbs/ft of torque.

3.0 V6 oil consumption: issues other than valve guide seals

Carl Vann wrote:

After my 1989 Grand Caravan was several years old, I started noticing a smell of scorched oil, and found a big cake of hardened, burnt oil on the exhaust manifold which had dripped from a valve cover. I tightened the four valve cover bolts [warning: the torque specification on these is extremely small] and the smell stopped shortly thereafter. I later changed the valve cover gaskets and the oil consumption was further reduced.

I also noticed that, while checking the oil level with the dipstick, it always seemed full. Looking closer at the backside of the dipstick, I saw a lower level. Something in the tube holds a small amount of oil which coats the front of the dipstick. If you do not notice this, you could easily run low. My recommendation is to read both sides of the dipstick and to use the lower of the two readings.
Roger Lister wrote:

A common problem with the 3.0 is that when you drain the oil down low and leave it low, the valve lash adjusters (hydraulic) also drain out. Sometimes they take a while to refill, sometimes they never do completely. I had a severe oil leak last year; the motor was dry for several days while I did the work. The motor almost never ticked before the repair. Now it does "when cold and when it hasn't been run for a few days." But it goes away. It isn't bad now, almost a year later.
Keith's Guide

Brian Martin wrote: "I had poor acceleration and backfiring in gear under a load. It revved fine in neutral/park.

I had done a top end rebuild, using chrysler heads/cams, with Mitsubishi cam gears and distributor. Eventually I noticed that Mitsubishi has the firing order of 123456 and Chrysler uses 126453. I swapped 3 and 6 and it runs well now. This was on a 1992 Mitsubishi Montero."

1.0: This is a pretty serious job and if you don't have a lot of experience working on cars, I'd leave it to another mechanic. Most of the procedures are covered in the Haynes manual, and I highly recommend you purchase that manual and read the related sections under 3.0 Liter Engine. I'm not going to cover all of the gritty details, only the parts that none of the manuals cover. READ THIS ENTIRE PROCEDURE AND THE RELATED SECTIONS IN THE HAYNES MANUAL BEFORE YOU BEGIN.

1.1 There are a few tools that you MUST have to do this job, in addition to the standard stuff.

1.2 You have to have an "on the car" valve spring compressor that requires very little clearance (about 2 inches above the spring). I am told that such a tool is available from Snap On, although I haven't tried them. I made my own tool, which basically looks similar to an itty-bitty strut spring compressor. If you can get the one from Snap On, do it, because it would save you much time. You will have a clearance problem between the intake plenium and the intake valves. Frankly, the job would be a lot easier if you remove the intake plenium, but that removal is not easy or trivial, so I skipped it.

1.3 To get to the valve seals, you must remove the valve springs and the "keepers" that are on top of the valves. Now, STOP AND THINK WHAT CAN HAPPEN - THE VALVE CAN AND WILL DROP INTO THE CYLINDER IF YOU DON'T TAKE THE NECESSARY STEPS TO KEEP IT FROM FALLING IN!!!!!!

1.4 For this, you should have an air compressor and the necessary hose/fittings to put compressed air into the cylinder and this will hold the valve up. Use at least 100 psi. As an added precaution, I recommend putting the cylinder at top dead center prior to working on the valves for that cylinder.

1.5 Don't forget, you will need to purchase a new set of valve guide seals and I recommend replacing the valve cover gaskets and cam end-caps while you are there. You should get some of the silicone-gasket maker material for the sharp corners on the valve cover (I use the orange stuff - be sure the stuff you buy is O2 sensor safe!) Also, one of those little mirrors on a telescoping handle is very handy for inspecting hard to get to places.

2.0 Start this job with the engine cool, lots of time, and a spare vehicle. The front bank of cylinders is very easy to work on, but the rear is a pain in the butt, so start with the front. I don't remember exactly, but I think that these are the 2, 4, and 6 cylinders. Remove all 6 spark plugs from the engine to make it easier to rotate by hand. Remove the front valve cover (you'll have to get the plug wires out of the way, and be careful to note the cylinder that they go to-the factory wires have the number on them).

2.1 Before going any further, I would use that mirror to inspect the seal and guides through the springs. There is a "side-view" picture of a valve guide/valve seal assembly in the Haynes manual. Your valve guide should extend out of the head the same relative distance. In some cases, the guides will slip in so far that the seal cannot be attached to the guide, and this is when the really bad oil burning takes place. If it looks as though your seal is no longer attached to the guide and the guide has slipped into the head, you are SOL. The heads will have to come off to really fix the problem. If the guides on this bank are OK, I recommend you inspect the rear bank before proceeding. There are general guidelines for removing the rear valve cover in Para. 2.6 below.

2.2 Assuming that you don't have this problem, you can procede. Prior to removing the rocker arm assembly, you must first do something to keep the hydraulic tappets in place in the rocker arms. I used twist ties - they worked very well. With these in place, remove the rocker assembly, following the guidelines in your shop manual. Remove the cam bearing/cap that is located on the end away from the timing belt and put it back on the head in its original position This MUST be done to hold the cam in place and keep the timing belt from coming off its gear on the cam. If you let the timing belt get out of position, you are into another 3 or so hour job to re-establish the proper timing.

2.3 Now its time to get your cylinder of choice on top dead center (TDC). I started with number 2 (the one on the left). Put a No. 2 phillips screwdriver into the spark plug hole and SLOWLY rotate the engine clockwise (in the same direction that the wheels turn when going forward) with a ratchet/socket on the crankshaft pulley bolt. You should feel the top of the piston with the screwdriver. Continue to turn the engine until you begin to barely feel the piston start to move down. This is just past TDC (at this point I positioned the ratched on a floor jack so that the engine could not turn any more when I pressurized the cylinder). Then put pressure in that cylinder. You may now remove the valve springs for that cylinder.

2.4 Follow the instructions that came with your new valve seals for installing the new seals. There should be a little "slip cover" that allows installation of the new seals over the "keeper cutouts" on the valves - use this cover to prevent damage to the new seals. Put the springs back on, being careful to get the keepers in properly. Depressurize the cylinder, and go to the next cylinder. Don't forget - TDC on this cylinder and air pressure! If you do forget and drop a valve, don't blame me!

2.5 When you finish those 3 cylinders, take the cam bearing off and reinstall it on the rocker assembly. Follow the Haynes directions for re-installing the rocker arm assembly, being careful to tighten the cam bearing bolts slowly and evenly! And don't forget to remove those twisties from the tappets! Replace the cam bearing end-caps and the valve cover gasket, put the valve cover back on and go have a beer.

2.6 The rear bank is similar, except that you have to remove the alternator and the air filter assembly First the battery should be disconnected. I always remove the negative cable so that I don't get sparks in case my wrench hits the vehicle body or any grounded metal.

2.7 The procedure for this cylinder bank is the same as the front, but this one is more difficult due to having to get around the intake plenium.

2.8 Before you try to start it, don't forget to put the spark plugs back in and the wires back on the plug. And be sure to get that ratchet or pull bar off the crankshaft pulley!

3.0 General Discussion

3.1 I've heard that even if the valve guides haven't slipped into the head and the seals are replaced, the problem may return within 20,000 miles. I can only assume that the guide/valve interface is wearing out, allowing the valve to 'wobble' and wear out the new seals prematurely. You might want to consider this prior to embarking on this mechanical journey.

3.2 When I did this job, my little valve spring compressor worked only so-so. On some springs it kept popping off. One spring would take 5 minutes to remove/reinstall, and the next would take 45 due to the tool not staying in place. If you can find that mystery tool at Snap On, buy it, because it will save you much grief. As a result, the entire job on all 6 cylinders took me over 8 hours. This time would have been cut in half by the proper tool.

3.3 It's not absolutely necessary to replace the valve cover gaskets and the end caps, but I recommend it because these get hard and brittle about the same time the valve seals go bad.

4.0 GOOD LUCK!!!!

Notes from David J. Allen

I was able to buy the on engine valve compressor and the hose (air compressor to spark plug hole) at the local Pep Boys. The valve compressor worked okay. It did the job but I wasn't overly impressed. The one I bought included a bolt that replaced the handle if there wasn't enough clearance. I had to remove the handle and use the bolt for all the valves.

I didn't bother with setting each piston at TDC. The air pressure pushes the piston all the way down. I replaced all the spark plugs, the valve cover gaskets and the valve cover end caps. I did the forward bank of valves (1-3-5) on Friday night and it took me 4-5 hours. I worked at a leisurely pace and I'm a novice. A real mechanic would take an hour or two.

I did the rear bank (2-4-6) on Saturday. It took me all day. Again, I went slow and took lots of breaks. I highly recommend removing the alternator and the mounting bracket for more clearance. I was happy to find no valve guides sunken down into the head. Also, my back screamed at me for a couple of weeks after due to leaning over that engine for so long.

Good luck!

-- Dave (David J. Allen)

Addition by Lee McKusick of El Granada, California

I add some details for mechanics replacing the valve stem seals. As
mentioned above, this inner engine work is fussy and has some big risks.
Interesting but fussy!

I just finished the valve stem seal project on my 178,000 mile synthetic
oil Dodge Caravan. I had engine smoke when pulling out from stoplights
after a 30 mile mountain and freeway drive.

Here is what I have learned, presented as a shopping list with some

  1. It took me 3 solid weekends to do this job. If you need a rental car, line up your best price in advance. I wasted 2 days looking for a dropped valve spring keeper. I wasted another day when I
    dropped a valve. More days passed due to family demands.
  2. I used 4 restaurant plastic "bus trays" from Smart And Final,
    rubber bands and 12 plastic sandwich bags to "keep related
    engine components together" in order of disassembly.
  3. Not having bag ties mentioned above, I used 6 pieces of 22 gage
    copper wire 3" long to hold the hydraulic lifters during
    assembly. All my lifters fell out on disassembly.
  4. Use the Lisle #16750 "On the Car" valve spring compressor tool
    (or similar tool) with the handle removed and the 1/2" bolt
    installed, as mentioned above.
  5. Arrange your air hold with an shutoff air valve. I used a quick
    disconnect fitting on the air hold. Next to the air coupler, I
    put a ball valve. The same place I bought my air compressor
    carried valve. I have done the rope trick with 1/4" plastic
    tubing too.
  6. Use a floor jack and wood block to gently prevent the crank from
    turning when applying air pressure, as mentioned above. 50 psi
    was OK for me. If the piston stays at the top of the cylinder,
    you have much less trouble if you drop a valve. If the engine
    turns and you drop a valve, you are in trouble.
  7. A major risk is dropping a valve spring keeper wedge into the
    engine. Prevent this by plugging openings and laying down paper
    towels to catch the slipped or popped keeper.
  8. I suggest you take 24 half sheets of paper towel and number the
    sheets #1 to #24 with big felt tip pen letters. Use those sheets
    to plug the 22 holes in the cylinder heads. Uncrumple and stack
    the sheets in order when you reassemble the engine. Just like
    surgeons count sponges when they finish their surgery!
  9. Plug all the holes in the cylinder heads before removing the
    rocker shafts. Eleven plugs needed per cylinder head.
    1. Three oil drain holes in the dark below the three exhaust valve springs on each head.
    2. Two square water ports on each head.
    3. Three intake ports on each head
    4. Three spark plug holes on each head.
  10. Lay down a double layer of paper towels as follows:
    1. In the vally of the engine.
    2. Cover the gap above the rear exhaust manifold.
    3. Cover the gap above the front exhaust manifold.
  11. A second major risk is damaging bearings or cam lobes with a dropped wrench. Prevent dings to cam and bearing surfaces by covering everything except the valve spring you are working on
    with a double layer of clean shop rags.
  12. If you drop a valve stem into the engine, get a General Tool
    magnetic retriever with a neodymium magnet or similar. The 1/4"
    neodymium magnet in this tool is extraordinary. I used the
    magnet and a 5" piece of polished 1/4" drill rod to pull a
    dropped valve back out. I also guided the valve stem with a
    General Tool brand grabber that I inserted through an intake
    valve passage.
  13. Double check that you remove all those paper towel plugs
    mentioned earlier.

by "slbrass," a service manager: Added: July 15, 1997. Slightly edited for space. Valve seals can be replaced, but that will not correct the problem: oil is drawn into the EXHAUST by the EXHAUST GUIDES. It never enters the cylinder/combustion chamber. It's getting drawn into the exhaust as it's leaving the engine from around the OUTSIDE of the guide. The friction/press fit of the guide to the head casting becomes loose. (Some guides get loose enough to actually become disloged and fall downward into the port. THAT'S when they REALLY start smoking!) Acual fix is to cut a retaining ridge to the outside of the guide to which a special "snap ring" attaches which prevents guide movement/displacement.job is finished off by new revised valve seal which is "umbrella-ed" to cover the whole top of the area and prevent oil to seep down into the area. A special tool is required. Easier to see dealer part man and buy a set of Mopar remanufactured heads. All valves reworked and gaskets and all related is in box. 1991 and newer V-6 has the revision already.

Gene (sblvro): The valve spring compressor tool to use to replace the valve stem seals is available in NAPA parts for $30 or $40. It is compact, and can compress the valve manually with a few turns, will even fit the rear bank of the 3.0 liter Mitsubishi V6 with no problems. I am not a mechanic but was able to replace the valve stem seals and now the engine is working fine with no oil burning 40,000 miles later. my car has now 145,000 miles and running good, passed the threadmill emission test without any oil additives whatsoever. It is a 1988 Mitsubishi Sigma.

Jack from Austin, Texas (2007): I did this job on my LeBaron the other day. But only one side - the front three cylinders of the "V". And the smoke has pretty well completely gone. 95% gone, in fact, so I'm not going to bother to do the rear three cylinders. It doesn't take much to put the whole car back together before starting the rear three cylinders, so you might as well give it a try. It's also a way to test the car before carrying on with the job.

Also see the main 3.0 page and the 3.0 general repairs and rebuilding guide


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