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Discussion Starter #1
2012 451 with 128,000 trouble free miles (75% freeway)

Been having the following issue for the last 8 months. I’m getting close to having to take it in.

Cylinder 1 misfire and occasional random misfire codes and a post catalytic fuel trim lean code. It was also stalling at idle when I came to a stop

So; I replaced all three plugs and coils. Ran sea foam in the throttle body and use MMO. I also replaced both O2 sensors. This cleared the fuel trim lean code, no longer stalls and reduced the random cylinder misfire codes. I did a vacuum leak check and couldn’t find any leaks. I’m still getting a cylinder one misfire code.

I am going to replace the fuel rail and injectors this week.

It’s getting to the point where I may need to verify fuel pressure and consider a fuel filter change? Even if the filter isn’t the cause it’s proably due for a change anyway.

If i pull the plugs, run a borescope will I be able to see the valves easily from this vantage point? I am also not sure how to do a compression test either. That is uncharted territory for me.

Is there anything I’m missing? Considering bringing it in after I rule out the injectors. That would leave a bad valve or fuel pump and or filter right?

It runs fine once driving but idles rough.

Thoughts?
 

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Before anything else do a compression check. If it is an intermittent code, run the MMO fix a few times. my 2008 does come up with a minor evap leak code when the tank gets down about 1/4 from full, engine just warming up and I get stopped at a stop light for awhile. CEL comes on but resetting it makes it go away until I hit that magic spot again. Only in cooler weather though....Been doing it for over a year now. New coils, plus, and regular MMO every 4th tank. All hoses look good, checked with spray and no change in rpm's
 

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Discussion Starter #3
I’ve run MMO for a few months already. No change. I get random misfire as well but not as much as I did before I changed O2 sensors. The random misfire is leading me to think it’s not a valve issue. I’ll figure out how to do a compression check anyway.


Thanks


QUOTE=jimvw57;1656858]Before anything else do a compression check. If it is an intermittent code, run the MMO fix a few times. my 2008 does come up with a minor evap leak code when the tank gets down about 1/4 from full, engine just warming up and I get stopped at a stop light for awhile. CEL comes on but resetting it makes it go away until I hit that magic spot again. Only in cooler weather though....Been doing it for over a year now. New coils, plus, and regular MMO every 4th tank. All hoses look good, checked with spray and no change in rpm's[/QUOTE]
 

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I suffer a random cylinder 3 miss fire code. I did everything you mentioned, and even replaced the crank sensor and will be replacing the cam sensor soon.

Still need to do a compression and leak down test as well.

Frustrating...
 

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The SAM is very very sensitive to a misfire. I pulled my head off mine at 37,000 for burned valves. Put it back together. It now has 52,000 on it and occasionally I will get a random misfire code. It doesn't light the CEL but my scanner sees the code. Jdykstra and Pete000 for both of your situations I would suspect a burned valve. There are 4 per cylinder and they are small as a valve in a Briggs and Stratton engine. Mine is a 2011. I have noticed that some of the Fortwos in the 2011 and 2012 seem more prone to valve issues.

Do a compression test (the spark plug hole is smaller than a standard one). Then squirt some oil in the cylinder and retest. If any of the readings come up it means the rings are worn, but f it stays the same it is probably a valve if you get a low reading. The rule is the lowest cylinder reading shouldn't be anymore the 25% lower than the highest reading. My cylinders was 1- 160, 2-150 and 3 was 90. That triggered the light. I never felt a miss in the engine it seemed to run fine, but the CEL kept being triggered.

Dropping the engine down is a pretty involved task. I did mine because I am a mechanic. Taking it to a dealership for replacement is very pricey. If you do it yourself you will have around $750 tied up in it to replace valves, grind the seats, set the shim buckets, gasket set, timing chain and gears etc,... Keep up the MMO it really keeps the engine crystal clean inside if you do oil changes when they are supposed to be. I tow trailers with my Smart frequently so I do oil changes every 5,000 miles. I use Mobil 1 European blend (Walmart). 3 quarts of Mobil 1 and 1/2 quart of Marvel Mystery oil. Once a valve doesn't seat properly sea foam or MMO will usually not clean the carbon off the valves if they are carboned bad. If you drive it with a burned valve it will erode the seat over time and you won't be able to re-use the head because the seat is ruined. DCO

This was my valves at 37,000 miles. I had just purchased the car. It belonged to an older school teacher who had passed away. He babied it around town with the engine lugging. In automatic mode it tries to get to 5th gear as soon as possible. So the valves were all carboned up from low RPM use.


 
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