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Discussion Starter · #1 ·
Hi everybody, gonna need some help here:bow:?

My r171 slk200 is having some strange problems, when idling, the m271 engine is having sporadic misfire in only cylinder 2, but when i put my foot down to the gas misfire is not happening at all. (Monitor by DAS)

I did try to swap the spark plugs and coil packs, but the problem stays with cylinder 2.

Do you guys think i am having a PCV hose problem, or my car is having valve issue?

Please help:sob:
 

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I recently bought a new coil for cylinder 2 on my car. Unlike your problem, my misfire started after car was warmed up and revving. The new coil fixed it. Sounds like you just swapped the coils around to see if the misfire changed to a different cylinder. Since you've checked the easy stuff yourself, I would take it to a good Indy and have them look at it. I wouldn't want to risk serious engine damage trying to troubleshoot the more complex stuff myself.
 

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**Premium Member 2004 SLK350
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Check you injector and then a compression test but with a proper tester. If you do a compression test and crank from you key you will have false readings.
 

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Registered 2000 SLK320
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Hi everybody, gonna need some help here:bow:?

My r171 slk200 is having some strange problems, when idling, the m271 engine is having sporadic misfire in only cylinder 2, but when i put my foot down to the gas misfire is not happening at all. (Monitor by DAS)

I did try to swap the spark plugs and coil packs, but the problem stays with cylinder 2.

Do you guys think i am having a PCV hose problem, or my car is having valve issue?

Please help:sob:
You have logically checked the coils and plugs so it has to be down to low speed fueling problem if it is only there on tickover.

May be a build up in the injector that's blocking it slightly at low rpm but fine when you put your foot down.

Try some Chevron Techron additive see if it will get rid of the deposits on the injectors, worked for me.

Regards Stuart
 

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* Founding Member #2
2008 SLK55 AMG
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.....
Try some Chevron Techron additive see if it will get rid of the deposits on the injectors, worked for me.

Regards Stuart
I second this move.
Use the Techron Concentrate (not the more dilute Techron Fuel additive). Link: http://www.slkworld.com/general-dis...ock-sluggishness-hesitation-top-tier-gas.html

Also, make sure you are getting the "proper" fuel for your engine as stated in the owner's manual.

In the USA, it states use minimum octane 91 fuel (R+M/s method). The octane number is different for different countries as the method for publishing the octane number varies. Moreover, use fuel that has good proprietary additives, like those from Chevron or Shell.
 

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**Premium Member 2004 SLK350
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*Premium Member
2005 SLK55 AMG /2005 SLK350
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+1 for this is informative article. It sounds like the special tool is nothing more than a jumper that allows you to engage the starter motor continuously without the injectors injecting any fuel. Normal key use with a typical compression gauge screwed in would result in the car starting, with 1) lots of raw fuel dumping into the exhaust and cats (which can't be good for them), and probably 2) misfire error codes. Also, I'd hate to think what could happen if the secondary air pump kicked in on a running but compromised engine with a bunch of raw fuel in the exhaust. Also, with the key it's not possible to engage the starter continuously - the ME decides when to stop, not you - so you might not get the full compression reading.

Getting back to the original poster's issue - I would suspect an injector problem as earlier suggested. I'd consider replacing the injector seals, and perhaps swapping a few as done with coil packs. Otherwise, you can test with a squirt of light oil at the injector seal to see if it improves? I've also heard of using propane to test for air leaks (the engine RPM will increase if any is ingested - but this can be dangerous if you're not careful). I don't know if a hose leak at the manifold could impact just one cylinder like that - something about the gas laws IIRC? Or have those been repealed since I was in school?
 

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**Premium Member 2004 SLK350
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@efair
Starting the car with the acceleration pedal to the floor ( kickdown ) will cut off all the petrol going in injectors. Also you remove all the spark plugs NEVER try the test with only one removed.
Even applying this trick will not give you a correct reading for compression test.
As per secondary air pomp slk 200 doesn't have one.
 

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*Premium Member
2006 SLK55 AMG
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@efair
Starting the car with the acceleration pedal to the floor ( kickdown ) will cut off all the petrol going in injectors.
Are you sure about that. I believe that the ECU will go through its start cycle independent of the throttle position so fuel will be injected even with the throttle to the floor.

In fact the ECU actually controls the starter motor which is why the owner’s manual says to "Turn the SmartKey in the starter switch to position 3 and release it again immediately. The engine starts automatically."
 

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2005 SLK55 AMG /2005 SLK350
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Maybe I missed something, but I just started my 350 with the pedal to the floor and it started (and revved up). Scared the bejesus out of the wife who just saw me jump off the couch, grab the key, and head to the garage without a word.
 

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**Premium Member 2004 SLK350
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Are you sure about that. I believe that the ECU will go through its start cycle independent of the throttle position so fuel will be injected even with the throttle to the floor.

In fact the ECU actually controls the starter motor which is why the owner’s manual says to "Turn the SmartKey in the starter switch to position 3 and release it again immediately. The engine starts automatically."
Maybe I missed something, but I just started my 350 with the pedal to the floor and it started (and revved up). Scared the bejesus out of the wife who just saw me jump off the couch, grab the key, and head to the garage without a word.
The pedal to the floor must be done with the coil pack and sparks out ( if not using a DAS )

From DAS
not sure how is reading the values ...


From 3.04 min

Post nr 2 for m271 ( in slk 200 ) but C class
http://mbworld.org/forums/c-class-w203/420033-m271-compression-test.html

I did 2 engine and i didn't smell any gas from cylinders
 

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Discussion Starter · #15 ·
In the passed few weeks i have done both of the front leakage magnets and a cylinder pressure test.

1 cylinder : 150 psi
2 cylinder : 130 psi
3 cylinder : 150 psi
4 cylinder : 150 psi

So i think i may have the carbon build up issue....

Let me put some Techron in the follow next refill and give results to you guys.
 

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Discussion Starter · #16 ·
Finally the workshop did a Re-build of my engine, change all four set of Piston Rings and 4 valves (2 in 2 out for cylinder 2).

And all the symptoms are gone. Engine idle as silky smooth.

Workshop said the problem is the the piston ring is not working well and leak when it doing compression.

Cost me HK$43000 with new radiator with pipes (as the workshop found a small leak when they took out the engine), new engine mount, transmission box mount.

Which is kinda expensive, but i love my car so everything worth it :grin:
 
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