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Discussion Starter #1
Hello,

Backstory:
I was having some issues with my 99 SLK230, at first it was throwing these error codes: P1420, P1525, P1236, P0304, P1235, P0443 . I've done enough research to find that it was potentially the k40 relay being burnt... So I took it out of its casing and sure enough the A3 was semi-crispy... So I re-soldered that area as well as a few others that looked weak (I used a professional soldering tool that heats high)... Plugged it back in and it ran even worse then before! I was thinking maybe I soldered wrong because when I would accelerate it would chug as if it's going to die. Then I let it run for a few minutes in idle came back out and it would move forward and reverse with extreme chugging. I scanned it and now it shows only P0304 & P0303 ... PROGRESS!

Issue:
The P0303 & P0304 is causing it to chug horribly, I can't WOT the gas pedal or it'll kill the RPM's to around 500. I see these are misfirings and you can definetely hear it... But I am unsure what would cause not just one, but TWO misfirings.. including one new one.

I haven't checked the injectors or spark plugs yet (I have however added some fuel additive [NOT TECHRON] that is supposed to help clean the injectors), I havent cleaned the MAF (I have cleaner), I havent swapped the coil packs yet either...
I do not want to do a compression test yet until all other routes have been taken.

Potential solution:
I was thinking about cleaning the MAF with some cleaner & letting it run for a good 5-10 minutes on idle and test it out. Or potentially going and swapping the spark plugs and injectors.

Thank you all,
Alex

PS: Sorry for my poor writing skills. Also sorry my first thread isn't an introduction thread!
 

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Discussion Starter #3
UPDATE:

I cleaned the MAF using a liberal amount of the cleaner. I let it dry and put it back on, let the car sit (off) for about 5-10m while I ate... Came back and it still has the same issues. Check engine light is off when starting, then revving it it misfires and then the check engine light comes on.... But after trying to rev it in park over and over it finally gets up to 4k (still vibration in cab.. but less so), and then the check engine light FLASHES at this point. It usually never flashes unless i'm really working the engine /w this.

No idea what to do except maybe replace spark plugs/injectors/coil packs.
 

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Keep in mind the time difference as some of the forum experts are in the UK. May/will take till tomorrow a.m. to get some help
 

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Discussion Starter #5
Keep in mind the time difference as some of the forum experts are in the UK. May/will take till tomorrow a.m. to get some help
Totally understand! I'm just tinkering /w it as we speak... I don't want to let the engine misfire too much so I let it take a break.... I am planning on swapping coil packs eventually and seeing if it'll follow it.

Every symptom:
Intermittent rough idle (Sometimes there is, but ONLY in drive/reverse... doesnt do it in park after fixing the k40)
Cannot wide open throttle, ever.
Cannot rev past 2k unless feathering the pedal... And even then it only does it after I let it warm up by attempting to throttle past 2k.
Smells like gasoline when I leave the car, after trying to rev it to 4k for about 5 minutes.
CEL stays on, except when I finally reach 4k RPM's and cycle through those 2-3 times.
Misfiring on two cylinders.


Things I have done:
Re-soldered multiple joints on the k40
Cleaned the MAF (Could still be broken)

There's not much I can do in the immediate future as far as parts go.. because it's going to be sunday tomorrow.
 

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Discussion Starter #7
UPDATE:

I've been looking around and someone said on another forum to actually remove the plug from the MAF and test how it runs like that. (I never cleared the code yet) It revs up perfectly now! STILL truthfully sounds like a potential misfire going on, but it sure does rev up right away. I'll take it for a 2-3 minute drive around the block to guarentee this was the issue. I'll be ordering a replacement MAF from MB on monday if this is the issue. Will reset codes before taking test drive, of course.
 

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Discussion Starter #8
UPDATE:
It's still bogging down. I guess the 4k rev was a fluke maybe? It wont even accelerate w/o it plugged in now.

Haha I go faster in idle then I do accelerating w/o it plugged in!
 

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So many possibilities, it sounds like you have multiple issues. You're saying it ran ok for a while with the MAF disconnected, then failed to do so? I would check the vacuum lines, and check your fuel pressure with a gauge, and check voltage at every fuse next. If those look ok, and you don't receive any more helpful codes, throw some money at it with a new crankshaft sensor. They're pretty cheap.
 

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Don't lose sight of that K40 even though you re-soldered it. As you probably know, the power supply for the fuel pump comes from there. And K40's are reknown for intermittent problems. A fuel pressure test as suggested by efair is a good idea (as are his other suggestions).
 

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don't lose sight of that k40 even though you re-soldered it. As you probably know, the power supply for the fuel pump comes from there. And k40's are reknown for intermittent problems. A fuel pressure test as suggested by efair is a good idea (as are his other suggestions).
^^ this ^^
 

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Hi,

Just caught up with this, some excellent advice above ;) ..............

Whoever suggested un plugging stuff is an idiot :frown:

That practice has no place in diagnosing problems on vehicles with Electronics, the only reason it makes a difference is because the ECU sees and flags a fault and then refers to "Basic Tables" to keep the Engine safe and all it actually achieves is putting other fault codes in the ECU!! It tells you nothing.

If this came into my workshop, first thing I would do is read it on SDS, Clear it, get the fault back and Re Read !!

Now, assuming I then had Misfire Codes, firstly all plugs out, lay them in order, and Compression test ........... know if they are good or not and know that I am not flogging a dead horse !!

Now swap the Spark Plugs and Coils on the misfiring Cylinders and see if the fault migrates, if it does, now swap the Coils back, if it now moves back again it's Coils if not replace all 4 Plugs.

Under 1 hour and very very likely fixed, if not you know it is not Ignition related and can now look at Fuelling :wink:

HTH, Cheers Dave
 

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Discussion Starter #14
So many possibilities, it sounds like you have multiple issues. You're saying it ran ok for a while with the MAF disconnected, then failed to do so? I would check the vacuum lines, and check your fuel pressure with a gauge, and check voltage at every fuse next. If those look ok, and you don't receive any more helpful codes, throw some money at it with a new crankshaft sensor. They're pretty cheap.
I will check voltage across every fuse & vacuum lines. I do not have a fuel pressure gauge, but I can get one. As for parts I have in my 'cart'... Camshaft sensor, crankshaft sensor, spark plugs, and coil packs

Don't lose sight of that K40 even though you re-soldered it. As you probably know, the power supply for the fuel pump comes from there. And K40's are reknown for intermittent problems. A fuel pressure test as suggested by efair is a good idea (as are his other suggestions).
It could still be the k40, I have 0 idea though. They were resoldered properly I believe... but the board itself could be bad!

Hi,

Just caught up with this, some excellent advice above ;) ..............

Whoever suggested un plugging stuff is an idiot :frown:

That practice has no place in diagnosing problems on vehicles with Electronics, the only reason it makes a difference is because the ECU sees and flags a fault and then refers to "Basic Tables" to keep the Engine safe and all it actually achieves is putting other fault codes in the ECU!! It tells you nothing.

If this came into my workshop, first thing I would do is read it on SDS, Clear it, get the fault back and Re Read !!

Now, assuming I then had Misfire Codes, firstly all plugs out, lay them in order, and Compression test ........... know if they are good or not and know that I am not flogging a dead horse !!

Now swap the Spark Plugs and Coils on the misfiring Cylinders and see if the fault migrates, if it does, now swap the Coils back, if it now moves back again it's Coils if not replace all 4 Plugs.

Under 1 hour and very very likely fixed, if not you know it is not Ignition related and can now look at Fuelling :wink:

HTH, Cheers Dave
The unplug method I was told was to test to see if the MAF was working or not. They said if it runs better without it plugged in its broken... As far as the plugs and everything, I will be doing that today.

Thank you all for the help!

Alex
 

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Discussion Starter #15
UPDATE:

While the system re-learned the MAF (I'm assuming) the car was dying shortly after startup... On the 3rd start up it finally stopped but I couldn't get the throttle to raise the RPM's. So I went to the engine and manually did the throttle and I heard a whistle of air each time I throttled. Could this be the misfire or is this a vacuum leak?
 

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In regards to the K40, did you do the re-solder or someone else? I ask because if done "by eye", some cracks/joints are easy to miss.

It may be worth while to check it anyways. Use a magnifying glass to inspect. You may find some hairline cracks the naked eye can't see and will need re-soldering.
 

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Discussion Starter #17
In regards to the K40, did you do the re-solder or someone else? I ask because if done "by eye", some cracks/joints are easy to miss.

It may be worth while to check it anyways. Use a magnifying glass to inspect. You may find some hairline cracks the naked eye can't see and will need re-soldering.
I took it to an electronic repair shop. He told me that there were a few 'weak or about to break joints'. He resoldered them for me. He did not however use a magnifying glass.
 

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Discussion Starter #18
UPDATE:

I have swapped coil packs, so far it does not chug too bad (havent attempted the wide open throttle yet)... You can SLIGHTLY hear the backfiring at lower RPM's, and you can barely hear it at higher RPM's (Like almost non-existent).... But it still does accelerate like a granny. It still throws CEL's... And here are my new ones:
P0300 - Multiple/Random misfire detected
P0304 - Cylinder 4 Misfire
P0302 - Cylinder 2 Misfire
P0170 - Fuel trim (Bank 1)

(It was throwing 2,3,4 cylinders misfired from my device awhile ago though...)

After warming the vehicle up and swapping coils it revs and gets up to speed (Slowly but surely).

EDIT (Finally got the button): Researching all this it sounds like the MAF... But I think its a vacuum leak as I hear a whistle coming from the RIGHT (Driver side if you're in the US) when I accelerate.
 

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It's also a pretty common problem for the pedal sensor to fail. It would be good to monitor the pedal position with a good scanner.
 

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Discussion Starter #20
It's also a pretty common problem for the pedal sensor to fail. It would be good to monitor the pedal position with a good scanner.
With an ODB2 scanner? I can have access to an expensive one that gets relatively good detail.

However,
I just got done driving it around town (Its my birthday) for about 2 hours.. About 80% of the time it slowly accelerated (with what I would say is quiet backfiring.. doesnt sound like a honda with a fartcan) and 20% of the time driving it went into a similar sluggish limp-mode.
 
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