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Have a check engine light on and throwing codes for multiple miss fires and miss fires on cylinder #2 . Changed out all plugs and coils and still have CEL and codes for misfire on #2 . I made an appointment with MBI Motors next week. In the mean time they suggested I do a compression check of all cylinders. They would do that first thing but it would cost $250:eek: I just did the compression check and, on a cold engine, the pressures read 150 for #1 , 90 for #2 , and 120 for #3 . I will check the #1 again but my question is: Is 90 PSI on #2 a terribly low number? All 3 of the plugs look identical...light tan with no oil or fuel residue. Wife is panicking...we can't afford a new engine right now and this is our work car. Any input will help.
Thanks, Brett
 

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I dealt with the same problem. I had misfires on cylinder #3 which was P0303. I had burned valves. Your highest reading for your compression was 150 which is good. Your lowest compression reading should be no lower than 25% of your highest reading. So your lowest cylinder would have to be a minimum of 113, which is 25% of 150. So you have a low cylinder.
A misfire can result from either bad piston rings, burned valves, blown head gasket, bad iginition coil or a faulty fuel injector, or even a hole in a piston. Usually you would see from your engine codes which cylinder had the misifre as you have already found out. Then you would move your spark plugs to a different cylinder and also switch your coil packs around to different cylinders to see if the misfire moved to another cylinder. That you tell you if it was a coil pack or a spark plug.
If the engine isn't overheating, smoking out the tailpipe , have water in the oil or oil in the antifreeze you can probably rule out a head gasket. I would put a few teaspoons of oil in the low cylinder with 90 pounds and retake the comression reading. If the reading comes up your have a piston ring issue because the oil temporarily seals the rings. If it doesn't come up you probably have a burned valve.
Chances are very very slim it is a bad fuel injector. A bad injector will cause the engine to spark knock severely if it is not sprying enough fuel or if it was not spraying properly or too much you would have black sooty deposits on the spark plug for that cylinder.
At any rate to remove the head and get new valves installed and the shim bucket set back up for the proper valve clearance is a costly endeavor. I did the head removal and reinstall myself because I am a mechanic, but just the parts alone for gaskets, new valves and guides cost me around $600. Then the machine shop fee for doing the valve work and shim buckets was close to $300. Then you still need to change the oil. Also if you are going that deep into the engine you might as well replace the timing chain and possibly gears and tensioners.
So it is a very costly thing to do or have done. I wish I had better news for you. There are threads here on getting the head off. What makes a burned valve an even bigger headache on a Smart is you only have 3 cylinders to begin with. When the computer detects a misfire from a cylinder it will shut off the fuel injector to that cylinder so that the cylinder isn't dumping raw fuel into the exhaust. So you are running on 2 cylinders then. When you shut it down and restart it may fire that cylinder again until it detetcts another misfire, then it's the same thing all over again. DCO
 

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You drive it till it will no longer move down the road...!!! Get every "CENT-Out-Of-It"...YUP... MB would put a NEW HEAD on it, So-Use-That-One-UP...
NOTE: You can Buy a Whole new-to-you USED Smart for what MB would Charge you with out all the BS... Smart's Have-No-Resale-Value...<:-(( BUT... that's good for you if looking for a used Smart, or to get a engine out of a used one, and think of the Extra Parts you get with a Used-Parts-Car...
NOTE: Don't pay no attention to the cel light... ~ Drive-On "Grass-Hopper" ~
 

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Sadly, if you are still getting a miss after changing plugs and coils, and your compression test shows a low cylinder, it is cheaper to find another used smart than to repair what you have, unless you have extremely low miles, or a lot of cash tied up with modifications. Repairing a motor is just not worth the cost. If you do it yourself, you will save the labor cost, but when you are done. you still will have a lot of money in a car that just doesn't have much resale value.

It is possible you might have a stuck ring and some Marvel Mystery Oil has worked on a number of smarts to increase the low cylinder (if it still runs with the CEL on)
 

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Thank you everyone for the detailed answers to this issue!

Is there any upgrades that can be done while doing all this work that may make it worth it? (Just a thought).
 

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There's just not much out there to upgrade performance. You could go with an aftermarket muffler. I would love to put a nitrous kit on mine just for a little boost on interstate, but it's just too expensive. May be a turbo kit but that too is well over a grand. Would love to have about 100 horsepower. You need to take a ride in Jetfuel's turbo Smart, it will make a believer out of you. If you love your Smart like I love mine it is worth it to fix it. Not practical or cost effective for sure but if you enjoy it, fix it. It can be torn down with basic hand tools. I did a video of the valve job and my computer hard drive died and I lost part of it, but it can be done. Timing it is the hardest part of it.DCO
 

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My thoughts were in the line of enlarging bore and increasing stroke. This is what AMG, Brabus, and US based RennTECH have done to Mercedes models. (Maybe even Carlsson and Lorinser, but not familiar with them as much).

They would increase bore, and maybe even stroke, to increase displacement and hence power? Just curious if reasonably doable as you have it disassembled.
 

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My thoughts were in the line of enlarging bore and increasing stroke. This is what AMG, Brabus, and US based RennTECH have done to Mercedes models. (Maybe even Carlsson and Lorinser, but not familiar with them as much).

They would increase bore, and maybe even stroke, to increase displacement and hence power? Just curious if reasonably doable as you have it disassembled.
I would contact Larry Wu (he's on the Facebook group, too) about that one. I think he did something like that with his bonkers smart.

If you want to make the most speed out of the smart's engine, you pretty much have to turbo it or swap it for some other engine. If money were no object, I'd make a dual engine smart. :D

To the OP: 90 PSI on the #2 isn't great. I'd give it a good dose of Marvel Mystery Oil and see what happens. Worst case scenario is that it doesn't do anything. If it doesn't help, you may be looking at an expensive fix.
 
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It sure has! :) It's been a while since I've last put some in, yet the car's still chugging along. Car used to throw misfire codes for two cylinders every day, now it runs pretty well!
 
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I don't know if undersize pistons are available for the engine. And probably stroker cranks are non existent. the Mitsubishi "I" used the same 3b21 engine and they made the "I" with a much larger access panel to get at the engine. The engine is so small I guess they just planned on it being a throw away engine. They are already running 10 to 1 compression. I read somewhere that the enigne only weighs 125 pounds. But they wrung alot of power out of a small engine. 70 horsepower isn't much but that is a small engine in the motorcycle range of displacement. If one could find beefier rods and could flash the ECU to remove the rev limiter, then port and polish the heads, then slightly larger fuel injectors and aftermarket exhaust, I'm sure you could get a few more horsepower out of it. Somewhere here on the forum I remember someone stating that the 3B21 engine would hold together for up to 125 horsepower or something like that, can't remember for sure. So many people just have a stigma against a 3 cylinder engine. If I could afford a turbo kit I would be happy with the acceleration. Max handles great and rides better with my mods. It has always stopped well. If I could just increase the horsepower by 30 percent up to around a 100 it would perform so much better on interstate. We have some pretty hefty hills here in WV. DCO
 

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I would try what Jim suggested, a shot of Marvel Mystery oil, I've had to replace my head gasket and it is a very labour intensive (expensive) job as the motor has to be dropped out of the car. As others have said it might be better to find a used one, though buying used you could just wind up buying into another headache. Depends a lot on condition of yours, model eg Brabus, Passion, Pure and mileage. Are you the original owner?
 
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