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My 4g15 swap into my 4g37 1G
I’ve been meaning to post this for a while. A little over two years ago I did a motor swap into my 94 1.8L Eclipse with the help of Iceminion. It’s been my daily driver ever since and been a damn good car. Totally gutless, but cheap to drive easy to fix and still kind of fun to pilot it’s a perfect beater.
Swapping a 4g15 in place of a 4g37 in a 1g eclipse:
While this car likely was not worth putting a motor in to replace the junk 1.8, my irrational love of the thing made me do this, and I really didn’t want to scrap it. I was just going to remove and replace the 1.8, but they don’t seem too plentiful in junkyards, and they want lots of money for high mileage motors.
Iceminion advised me against R&Ring the old 1.8, claiming these motors have design flaws that make them fail prematurely. Despite my better judgment, I accepted Iceminion at his word that a 1.5L 4g15 would work well for this car and be a really easy swap. I probed about the specifics but he was vague about some details and so I forged ahead on my own.
I went to Upullrparts in Rosemount; never been there before and I’ve never met a more unhelpful staff at a junkyard. Seems their service is limited to operating the cash register and saying no to customer inquiries. Anyway, I grabbed a mostly untouched 1.5 liter 4g37 out of a 1994 eagle summit 165,000 miles for 200 dollars. I rolled it over a few times with a breaker bar before pulling it and it seemed to have compression in the right spots, but looking back that was likely just the valve springs pushing the cam around. The Summit was a manual so I left the clutch and flywheel attached to the motor. I also disconnected as many lines and hoses and kept them as intact as I could, which was very helpful later as I ended up using almost all of them.
Back home I did a leak down check and was really disappointed to have a total failure on the 2 and 3 cylinders, and dismal results on the 1 and 4. I pulled the head to find it warped and in dire need of a valve job. Normally I do my own valve work but my grinder isn’t set up to handle stuff this small so I took it over to Kelley Auto who did the whole works for me. The shortblock looked like new so I just cleaned it and painted it. Although I spend about double what I expected to on the motor, the thing is like new now and should be good to go another 150,000 without issue.
The install issues started almost immediately. The transmission bolts up to the motor just fine, but starter won’t fit with the 4g15 upper clutch cover. Some engineer decided that they should rotate the starter motor 3 degrees between the two engines, so the covers won’t swap and you have to use the cover to match the transmission you are using. The lower clutch cover is also different. The angle of the pan rails is different on the 4g15, so you need to use the 4g15 lower cover with the 4g37 upper. The clutch and flywheel are the same dimensionally, but the 4g15 flywheel is lighter with less mass on the backside.
On the summit donor car the front and rear motor mounts are on the transaxle and not the motor. The 4g15 has the same bosses as the 4g37, but they aren’t used. Although they are spot faced, drilled and tapped, 17 years of non use filled them with rust and needed to be cleaned out. Seems an m12 1.25 is an odd size according to Craftsman so I had to get the tap from Fastenal. The 4g37 front and rear motor mounts bolted right up to the new motor and dropped right in.
The driver side mount looks real close, but is an inch or so too low, half an inch too short and a quarter inch too far forward. I ran it through the bandsaw and welded a hunk of 3/8” plate to it in what I think is my least proud moment in fabrication. As a token of my own humbleness I’m posting a picture.
The throttle body from the 4g37 replaced the 4g15 unit, to use the 4g37 electronics. There are various vacuum taps on the top for EGR and emissions things, depending on the engine. The only vacuum line on mine was the “P” line from the vapor recovery from the fuel tank. I just reconnected that line. My old 4g37 had no EGR provisions while the 4g15 had it. As yet, I have just left the valve on the intake and left it unhooked, namely because there is nothing to attach it to, and no electronics to control it. I would like to make it work again for gas mileage and out of concern for the air we breathe.
The throttle body is warmed with engine coolant, and the lines are different from the 4g15 to the 4g37. The lower hose from the 4g37 works but the upper hose is about an inch too short. I cut a piece off a scrap hose and joined them with a tubing nipple. The throttle linkage mount is in a different place on the 4g15 and the cable ends up being mounted about an inch too short. I mounted it with just one bolt for now but will see about going back and welding on some bosses to get a proper mount. Nothing is more embarrassing than having your car fail because of broken linkage. Throttle cable clips are off the 4g37, screwed onto the new valve cover.
Heater hoses were reused from the 4g37 while the big vacuum line for the power brakes is from the 4g15; the intake nipple is in a different location on the 4g15. Fuel supply and return lines are from the 4g15, the 4g37 lines were too short.
The O2 sensor on the 4g37 is in the exhaust manifold while 4g15 unit is under the car near the catalytic converter. I saved the bung and rewelded it up near the manifold. The 4g15 O2 sensor is different so the 4g37 unit was reused in the new location. The new headpipe from the 4g15 was made to mate up to the old exhaust system.
The distributor on the 4g15 sticks out of the back of the head rather than off the side like the 4g37. As such, the harness wires were a bit short after the swap. I was able to unwrap the harness back to the firewall enough to pull out the 6 or so wires for the bigger connector and reroute them under the throttle body so they would be long enough. Routing was not optimal, but it was better than splicing 6 mission critical wires. The two prong connector for the coil was just cut and extended.
The coolant hoses and thermostat housing were a bit of a hassle. The 4g15 had the radiator cap in the radiator whereas the 4g37 had it on the motor. As such, using a 4g37 radiator with a 4g15 motor leaves it with no radiator cap. I was thinking of just swapping the thermostat housings but the distributor precludes any swapping of parts in this area. Instead I cut the backside off the 4g37 housing and welded on a nipple to make an inline cap. I assumed that all the hoses are the same size, which was wrong. The 4g15 uses a smaller hose coming out of the thermostat housing which expands to the larger size when it meets the radiator. I was able to piece together enough to make it work, with the thermostat housing connected to my inline cap with the original upper 4g15 hose and the inline cap joined to the radiator with a hunk of the 4g37 upper hose. The goofy routing makes it rub on the distributor and could rub a hole in it over time, so I might need to fix it someday. The inline cap also interferes with the hood prop storage location which isn’t great. The lower hose is a 4g37 hose with about an inch cut off the engine side.
One of the temp sensors on the thermostat housing is different, so it was just swapped into the new motor from the old one. All the rest of the wiring matched up, including the fuel injectors and distributor. I assume the back box that was on the 4g37 distributor is a power transistor or noise filter. I drilled out the mount hole attached it to the new motor.
The intake hose from the air box now runs in the same space as the new distributor and now sits on top of it. The new intake mounts the throttle body a bit closer to the driver side now and leaves the intake hose a bit short. The interim solution was to leave the air filter unbolted so it can sit about half an inch left of where it should be. The solution will be to make up a new duct that is the right length and that misses the distributor.
With all this done and a good battery it started right up and fell into a nice idle despite the two year old gas in the tank. Results from the first tank of gas were 34.5 mpg, with the 1.5 injectors rather than having swapped in the other set from the 4g37. For reasons that are not clear to me, average mpg on the highway have been around 40 once the motor settled itself in.
I did an autopsy on the old 1.8 4g37 and found that one of the timing belts that drives one of the balance shafts had turned upside down somehow. It also had a hole in the block from a rod beating its way out of the crankcase. Given the extra complexity of the 1.8 over the 1.5, and that the 1.8 really doesn’t have any more power I am thinking I agree with Iceminion’s recommendation to replace the 1.8 with a 4g15.
Overall, the 4g37 to 4g15 swap is pretty easy as motor swaps go. I described the hang ups above, and although there are a few things I need to do yet, it has been working well. About the only thing I might have done differently had I been thinking would have been to shop around for a motor. For the same money I could have got one off the shelf from a junkyard who would compression test it for me, and save me the hassle of pulling it myself. I would have had to deal with some cut hoses and such, but that is something a bit cheaper and easier than spending a few hours in the snow at the u-pull-it yard pulling a mystery motor.
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