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Discussion Starter #1
Alright guys,

2000 SLK230, bad sputtering. It misfires on 2 cylinders, pressing gas makes it move, but only just. It actually moves more if I press and release the pedal. Only code thrown was for the Throttle Actuator, which works perfectly. I got this car recently, and when I reset the computer to see if my CD player in fact worked, this began. Checked K40, no bad solders, air filter is brand new K&N, Throttle Actuator works, supercharger is engaging. Transmissions fine, this car SHOULD run perfectly. Changed plugs recently to see if that was the problem, no difference. TPS is working as it should, nothing clogging intakes, cleaned MAF. I've tried everything pretty much. The only thing I haven't taken a close look at is coilpacks.

Is it possible when I put the cable back on the battery it fried a coil? I just can't see it happening. Help me out guys, please.
 

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Discussion Starter #2
Is it possible it's the computers sorting out everything? I kept looking it up, do I need to do a driving cycle?
 

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Discussion Starter #4
Already did, the only code it threw was from a while back, and it was the air bypass for the supercharger. I checked it out and it works as it should. No check engine light nor BAS light.
 

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Discussion Starter #6
Okay so, pretty sure it's coil packs. Both of them. When I switched them it shuddered horribly as before, and it's emitting a strange smell. I'm going to buy some and will replace them next week. I will update progress when I find out. Thanks all.
 

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Per ardua ad cineris.
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My SLK 230, once I've had the battery disconnected for quite a while (four hours or so) forgets how nicely it should be running, and struggles horribly to run for about 10 minutes; it suddenly remembers, and starts to run as it should.
The only time I found this didn't happen was once I'd cleaned the MAF; that was such a quick job, I might not have exceeded the time for the memory to be lost.

So, to get it going again, let it tick over for a while, then try revving it mildly (at which point it splutters like it's just never going to run right again) and finally, after about 5 minutes, you will get some revs (but not confidence), and after another 5 minutes, thing will start to run OK again.

This may not be your problem, but may be useful for others who have disconnected their battery and so entered this dark world of "doesn't seem to work any more"
 

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Per ardua ad cineris.
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Coils

The coils are relatively inert high power items, and so would not be affected by a power pulse when you connect the battery. In fact, a coil is normally used to control an inrush, to define a soft-start (in non-electronic designs) so is really safe.

But the support circuitry (effectively Capacitive Discharge Ignition) might just be able to suffer. But the normal failure mode for these is to fail, not to become intermittent. Again, it is power circuitry, so robust (and should be supported by robust design).

Dodgy connections (and broken wire harnesses) will make intermittent operation; pulling the cables might help this show up clearly. But all of these would run the same for

And some items (like low pressure fuel rail) will cause bad operation, even at tickover, and worse when throttle is applied. (Good option as described)
Leaking air would affect tickover, but as more throttle is applied, so the effect of leaking air will decrease. (Not applicable in this case.)

You could check the plugs to see what colour they are running at; at tickover, the plugs should be black to beige. When you increase the throttle, running under no load, they should go to beige. If they come out wet with fuel, then the plug and coil are not igniting (properly), if at all.
If you run the engine for a short while, and then whip out the plugs, you can confirm which plugs are running, and which are just getting warm from the compression of the cylinder.
However, if the fuel system is the problem, rather than the ignition system, then the plugs will all be dry, the plug colour will be light beige (since it's running lean) and they will all be the same temperature.
Happy spannering.
 

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Discussion Starter #10
Sorry to dig this from the grave but...Alright the parts finally came in, tried to start, sputter and died for the first couple times. Then, it starts, sounds better, then back to horrible. Where to next? Spark plugs, done. Coils, done. MAF clean? Done. No gas on spark plugs, awesome. Still missing, exhaust is LOUD. Cam position sensor? Pushing gas pedal to get higher revs is all wrong. I have to floor it then release the pedal, then the revs go up.

Ideas?
 

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Discussion Starter #11
Also already checked k40, no bad solders on it. One looked a little rough so I went ahead and re-soldered the sucker. Figured it couldn't hurt.
 

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Seems whenever you have adequate vacuum the engine runs properly. That's what happens with the RPMs go up and you suddenly let off the throttle, the plate snaps shut and the engine drawdown the vacuum and then starts to run again. On a carburetor car, that would be the engine pulling more fuel into the system. You might want to check your fuel pressure.
 

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Discussion Starter #13
Okay so I went out and started it, it fired up shaking horribly again. Thing is..I can't help but wonder if the dealership was lying to me. They said, "It threw a code for ignition." So I've replaced plugs and coils, checked all spark plug wires but no difference, and wires are good. I've bought a bluetooth OBDII reader so I can read codes myself. I'm tired of relying on dealerships here in Germany. BLEH I just want the car to work. BLEH.
 

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Fuel Filter changed???
 

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Discussion Starter #15
Fuel filter was supposedly changed before the car was sold. However, I am now unsure as to the credibility of the previous owner. It ran perfect up until the day I unplugged that battery for 30 minutes. Then all went bad.
 

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I had this problem recently so changed coil packs and plugs.Also found the MAF sensor was 'oiled up' so cleaned that too. Runs like a dream now.
 

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When you crank the car and let it run for a minute or so to run all the fluids through, after that minute, does the idle stay under 1000rmp and stay constant? Or does the idle speed go up and down when you are not pushing the gas pedal?
 

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Let it run

Not clear from the posts above, but have you tried to run the car for about 10 minutes, as if you were trying to drive it away?

As mentioned above, I found mine was very bad running after the battery had been disconnected, but after trying to drive it (so used to get-in and go) it took quite a while of spluttering and then I could drive it, and before I got back up the hill to home, it was working OK.
 

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Discussion Starter #19
The idle speed stays about the same but there are some misses, you can feel it.

I reset the computer yet again and let it sputter for about 10 minutes, then I revved it a little to see what it would do. For a 1-2 minute gap it ran what felt like perfectly, then it started to stutter again. I noticed if I hold the pedal the RPM's climb and fall with no pedal movement, but no I haven't driven it yet. I feel like it won't move. Should I try and drive it sputtery? If so, how long before I should give up?

Thank you everyone. You have no idea how much this helps.
 

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Discussion Starter #20
Idle does however stay under 1000 rpm, sometimes it jumps, it seems like it's trying to learn but I don't know, so I didn't move the car.
 
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