The Chilton manual has a very good write-up on the 4.3L engine, and one of the things GM did was to redesign the seals on the pan, intake manifold and rocker covers to eliminate the possibility of leaks. Also, the engines have roller cam lifters, and starting in 1992 they have a balance shaft for smooth running. The Vortec engines have variable computer controlled tuned intake port runners - they actually change the length of the runners depending on engine rpm! The first engines were carbureted, but they went to TBI injection in 1987 or so, and in 1992 or 93 went to port injection, then in 1996 went to sequential port injection. Each change increased the efficiency of operation and power, and the newest engines get over 30% more mileage than the original engines with almost 30% more power from the same displacement and compression ratio. The 1992 engine I got is the last of the TBI engines, and is pretty efficient, but the newer ones have more power and even better mileage. Beginning in 1996 the vehicles use the OBD-II ECM systems, which are much more sophisticated, and can even tell you if a plug is misfiring and which one it is! The earlier OBD-I systems are much simpler and easy to understand. One neat feature on all of them is a knock sensor, which automatically adjusts the engine timing for the best timing for the fuel used. (Sorry, I got away from the subject at hand, didn't I?)

It was now time to test fit the engine and transmission! I put the assembly on the engine hoist and gave it a try, only to find that it didn't fit well at all! The left exhaust header hit the steering gear, and the transmission wouldn't even begin to fit in the tunnel! Oh well, it came right out again. I took off the left exhaust header and, after measuring the transmission and tunnel, decided that the tunnel would have to be widened at least 2 inches. So I first tried hammering at it, but that was unsuccessful. I decided it was time to get serious and tried a 1 1/2 ton hydraulic jack, only to find that it wouldn't budge the metal! I had an 8-ton jack also, so I tried it, and Voila, success at last! I knew that most of the width would have to come from the passenger side of the tunnel, and I only needed to widen it for about 12 inches back because that's as far as the pan on the transmission went, so I very carefully jacked and measured until I had about 2 1/2 " more width. What happened with the metal? Well, on the passenger side it started to buckle, so I "helped" it fold into a nice Z fold, which I hammered flat, thus neatening up the job and regaining some strength in the area. There were no holes produced and no metal was cut! The widened part starts just ahead of the seats when in the most forward position, and the carpet trim panels fit back in just fine, as did the heater ducts. ( I did have to trim the duct on the driver's side, which wasn't moved very much, but the duct went through two cutouts and had to be trimmed a bit both on the plastic and the cutout holes.)

Now on my test fit, the engine went in and looked pretty nice - in fact it looked REAL GOOD - the transmission fit up into the tunnel with the bottom of the transmission rear mount even with the bottom of the car's floor pan, and the V6's engine mount hangers sat right in the middle of the Mercedes rubber motor mounts! It looked like it was made for the car! I checked the clearance on the tie rod, and there was about an inch of clearance minimum, and the bottom of the pan had an inch or so also. The starter front cleared the crossmember by about a half inch. The block cleared the steering gear by about 3/4". The rear of the engine cleared the rod that goes across the front of the firewall by over an inch. The right exhaust manifold was aimed just right down the hole the exhaust pipe went on the original engine. So, it looked like things were just right! But what about the hood clearance? I installed the air cleaner and measured by closing the hood - or trying to. It wouldn't close, but by taking the air cleaner off and removing the hold down threaded rod, it would close easily, with an inch or so of clearance at the air conditioner and alternator closest points. I cut down the spacer between the TBI body and air cleaner to provide proper clearance and shortened the rod, and the hood now closed like it was supposed to! I decided it was time to make some permanent motor mounts, which I did by making up some pieces of 1/4" plywood that just fit between the engine brackets and placing them on the Mercedes rubber mounts. Then I marked the brackets and welded some 1/4" flat plate in place of the plywood. Another trial fit revealed a nice fit, and the engine sat on the Mercedes mounts. I then marked the location of the boltholes and drilled the mounts, welding nuts on the top of the plates for the stock Merc mount bolts to screw into. For the rear/transmission mount, I purchased a 6-foot piece of 1/4" x 2" flat stock, and cut it so I had a piece that just went across the tunnel area. Then I welded the other piece to it to make a plate that is 1/2" thick in the area where it spans the tunnel, but 1/4" thick in the area of the floor pan. I did this so it wouldn't flex, and to provide the maximum clearance for exhaust, etc. under the floor pan area.

What I didn't say in the previous paragraph is that so far the engine and tranny had been in and out at least a dozen times. I wanted to be sure everything fit as well as possible, and it was easier to pull the engine and tranny to work on than to leave it in. Also, the starter clearance wasn't real rosy on the side of it between it and the idler shaft mounting post - only about 1/4" there. I cut the post off and moved the location over by 1/4" to give the starter 1/2" of clearance. I welded in an additional pipe inside of the existing one to make it stronger than it was originally. All this could have been avoided if I had sprung for a gear reduction starter, which would have cleared by at least an inch or more. If I were to do it again, I would definitely get one. I decided to make up an exhaust manifold that goes up and then down at the rear - I found several of the stainless exhaust manifolds for the engine and was originally going to just put one on upside down, but the port holes are unequally spaced, so that wouldn't work. I ended up cutting several apart and making what I needed - it's not too beautiful, but it too passed the water test and doesn't leak at all. I bolted all the components onto the engine to weld them in place, then finished the welds after pulling the manifold off - Mig welding is nice to do this work with, as it doesn't distort things enough to cause problems. (I did use .024 wire, though - the manifold metal has a high percentage of stainless in it, but the standard wire worked real nice on it, making good bonds.) I also made up a crossover pipe while the engine was on the engine hoist. I bolted the joints together before welding the pipes so the joints fit properly! I tried to angle the exhaust pipe outlet towards the Mercedes catalytic converter location that's molded into the floor pan, even though the car was a diesel. I also had to weld in an 18mm threaded hole for the O2 sensor. (I used an 18mm spark plug antifoul extender, which I cut the bottom off of.) I also made up a new oil dipstick and housing and a new transmission dipstick and housing to fit the car - the van had them going way out to the front of the engine. My engine didn't have the A/C compressor on it when I got it, so I went shopping and found a bracket that had the A/C compressor and the power steering pump on the driver's side of the engine and mounted low - I think it's from a 1995 or 96 pickup. I mounted the Mercedes crankshaft pickup on the front of the engine and made a stud on the front hub for the pickup to sense. (It feeds a signal to the tachometer in the dash, through the diagnostic plug, which has a circuit in the top of the plug.) I also decided to use the Mercedes cruise control actuator, which I mounted on the engine. I measured the "throw" of the Mercedes transmission selector arm (3 5/8), and made up an arm for the T700R4 that had the same throw. I had to extend the rod 6". After getting it all together, I discovered that the front U-joint hit the shift arm in reverse, so I had to modify the shift arm a bit - I made the arm go forward from where it was originally by about an inch, which cleared the U-joint, but now I had to thread in the adjustment on the rod almost all the way to get the selector in the right position.

My engine has Throttle Body Injection - it uses a fairly low pressure (around 12 psi) fuel feed, and has a computer and several sensors to manage the engine's fuel and other requirements. I retained all of the original harness, and was able to run the computer, or ECM cable through a 1" "Half-moon" hole I made with a chassis punch right at the bottom of the hole that the A/C hoses go through on the passenger's side. I added some plastic insulation to the cable for chafe resistance. The ECM fit behind the passenger side kickplate, which is where it's installed in the van. My cable had a small plug close to the ECM connectors that the wiring for the ALDL connector plugs into, so I made up a cable to go between it and the ALDL connector. I also installed a small LED indicator next to the ALDL connector to show the "service engine soon" lamp so I can just look at it to read out the engine codes. The computer requires a VSS signal, two pulses per revolution of the speedometer cable, and I purchased a sender unit from JTR (Jags That Run) that goes in the cable - I actually located it very close to the relay box in the engine compartment, and ran a 36" speedo cable between it and the transmission. I had to use a 90-degree speedo cable adapter (1-1 ratio) at the transmission for clearance. I purchased the 90 degree adapter and cable, plus an end to put on the Mercedes cable at Speedometer Service and Instrument Company in Portland, OR. I was going to have them calibrate the speedometer when I was done, but as it turned out, the speedometer reads accurately to within 1/10th a mile over 8 miles, so it's close enough for me! I took the connector off the body cable on the engine harness, and wired the signal wires I needed through a six-position connector plug. I wired all the +12 and +12 start and crank wiring to a terminal post I installed on the passenger side inner fender. I wired a relay between the two posts and wired the +12 to the Mercedes +12 terminal post through a 20-amp fuse. (I also fused the fuel pump relay circuit and the injector and egr circuits per the wiring diagram in the Haynes manual, using the GM fuse mounts that have the blade style fuses and a cover that screws to the fender well). I ran a small cable harness around from one fender well to the other via the firewall to operate the "On" relay from the wiring that used to go to the glow plug preheat connector. It also carries +12 from a relay mounted in the relay box that operates when the brake pedal is pressed - the relay opens the circuit to the +12 to disengage the torque converter clutch when the brakes are applied. The 1/2" diameter harness also carries +12 to the fuel pump. By using the cable harness I was able to avoid going into the passenger compartment for any wiring except a single wire to pick up the brake signal.

I mounted the fuel pump on the drivers side inner fender so I wouldn't have to crawl under the dirty rear of the vehicle yet another time, and also because the fuel lines were already there. I used a Holley inline fuel pump that is less than 1 1/2" in diameter and only about 6" long. Due to the location of the pump, the high-pressure line is only about 2 feet long, and is mostly metal. Since it only carries about 12 psi, it's probably a lot safer than having the pump at the rear of the vehicle. The pump is quiet; you don't hear it running with the engine on. Unfortunately, it cost almost as much as the V6 did!

I grafted the power steering pump pressure line together by observing that the Mercedes pipe that connected to the steering gear was nice and meaty, and the Astrovan line would fit about right lengthwise if it were connected to the Merc pipe. I threaded both pipes and screwed them together, silver soldering the joint to effect a pressure seal. I discovered that the low-pressure return was a similar situation, except that I just needed to slip a piece of tubing into the Merc pipe and silver solder it in place. I also silver soldered the transmission lines together in the same fashion, using a short piece of the tubing that connects to the rubber hoses grafted onto the lines coming from the transmission. Silver solder is good for almost 600 degrees, and I have used it in the past to solder A/C hoses together with excellent results, so I had no qualms about using it for these applications. It all works well, and there are no leaks. I used the Astrovan fan, which has metric spacing for the mounting screws - the Merc fan would have worked if I could have gotten the nuts on! I had to shorten the blades about 3/4" so they would clear the fan housing, and I used a 2" spacer and made up longer studs so the fan would be closer to the radiator. (The new engine is a lot shorter than the old one!)

I decided to use a throttle cable, but retained the M-B linkage up to the rubber piece bonded to the part on the firewall - I cut off the rubber and mounted a cable sector stolen from an old Toyota carburetor. I used a throttle cable I got from a 1994 Toyota Tercel, which was nice and strong, and fit on the engine end with the addition of a couple of washers. I made up a bracket for the firewall end, and it all worked out very nicely. I was careful to weld on the cable sector so there would be the proper length of movement to produce full rotation of the throttle shaft. I replaced the original plastic oil line going to the oil gage with a 3/16" nylon line - I forced it over the fitting at the oil gage after cutting off the Mercedes line, which was a metric size I couldn't find any fittings for, and put a piece of 1/4" rubber tubing around it to protect it from chafing.

I purchased an old GM driveshaft - I looked for one with a small diameter, but failed to locate one, so used one from an 80's camaro/firebird. I then cut off the driveshaft tube close to the U-joint and nose and after measuring the distance, cut off the front shaft of the Merc driveline to the length to fit in the depression in the end of the GM u-joint. Note that nothing is aligned or trued up here, the GM part wasn't machined, and there was no easy way to put it in a lathe, so it's just butted together and welded as close as it would go by sight. The total distance between transmission and center bearing is only 13", so it doesn't matter if it's a little bit out of line, but I may redo it at some point to reduce the possibility of premature rear bushing wear on the transmission tailshaft. It doesn't vibrate though, so it's pretty close. (Actually, we did try to align it, by leaving a bit of the GM tube on, cutting three holes at the U-joint end, then aligning the shaft with three rods to center it - the only problem is that the GM tube isn't round there! It's pressed onto the U-Joint and machine aligned and welded when manufactured.)

I welded the very nice Mercedes exhaust connector to the header pipe on the engine, and redid the Mercedes exhaust to fit. At this point the car was driveable, so I started driving it to work (I have a part-time retirement job that gets me out some mornings.) So far everything is working just fine! The car's exhaust is a little louder than with the turbo'd diesel, and my wife thinks I need to do something about it, but I like the sound myself- it sounds like a corvair on steroids.

UPDATE: The car passed smog fine in the state of Washington with no catalytic converter or air pump, so I'm not going to install them.

The car drives just fine, and the transmission shifts just about where I would shift it myself if I were doing the job. The ECM won't let the torque converter clutch lock up until the engine warms up, but then if the car is going over 35mph and the brake pedal's not depressed the TCC locks up, depending on the throttle position - if you are not accelerating it locks up sooner and if you are under heavy acceleration it locks up much later. The transmission has a terrific low gear ratio which makes for quick getaways (It will squeak the tires), and a 0.7 overdrive ratio for excellent cruise economy. Engine speeds are: 1750 @ 60mph, 2920 @ 100mph. The front of the car must be several hundred pounds lighter than before, as it sits up an inch or two higher, but I haven't noticed any problems with the ride or steering because of it. In fact, the car has a very "balanced" feel, and rides and handles extremely well - the front - rear weight balance is much better than it was. The shift lever has a low, 2, 3, and OD position, so you can put it in 3 if you don't want to use OD for some reason, like towing or whatever. One job left to do is to install the Park/Neutral/Reverse switch - I got a unit from a GM car, and just need to hook it to the shifter, which I will do inside the console, a-la camaro or firebird. I've been getting almost exactly 20 mpg around town (20.1), driving to work, etc. with a lot of starts (over 3000 miles now), and close to 30 on the freeway. It would probably do even better around town if I could just resist the temptation to blast away from the other cars at the stoplights! I recommend this engine swap to anyone that has the time, place, tools, ability and desire to do it - it will take a bit of time to do the job right, but the results are very rewarding.