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Discussion Starter #1
Hi Guys, I posted a thread a couple of weeks ago about electrical short circuit. I have had the battery checked on my 1999 SLK (80,000 miles) and that is OK. They also tightened all the electrical connections and could not find anything loose.

For the third time recently I have been driving along when the engine has cut out and all the lights on the dashboard have lit up. The car lights remain on and also the radio. (I habitually drive with my headlights on, for safety reasons.)

On the two previous occasions I pulled over, turned the key to "off", and then to "on" again and the engine has fired up. Tonight I am idling in nose to tail traffic - luckily - when the same thing happens. This time though she would not start until the third time of trying - absolutely quiet, no trying to start, just nothing....any ideas please?

Thank you very much. :burnout:
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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What means "short circuit"?

If you want to be efficient, take it to have it's MB codes read (not just OBD-II codes but MB codes).

If you want us to guess, here's mine: proactively replace the CPS, and resolder the K40 connections.

HTH
 

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Premium Member 2004 SLK200K
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Have you checked the CPS isn't leaking oil into the cables connected to it ?
This is a known r170 problem which if not attended to , can let oil reach the ECU , causing a very costly repair , but if caught in time is easily and cheaply fixable !
Also might this be an ignition problem , faulty transponder , ignition switch etc ??
Do you have a spare key , try using that just in case , you never know .
I've also heard of cases of the battery being at fault , even after testing and appearing to be fine !
 

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Discussion Starter #5
What means "short circuit"?

If you want to be efficient, take it to have it's MB codes read (not just OBD-II codes but MB codes).

If you want us to guess, here's mine: proactively replace the CPS, and resolder the K40 connections.

HTH
Thank you, efair.
I have had the CPS (crank position sensor - for those of us ladies not in the know) replaced, and was told that the suppliers "hold a lot in stock" for the R170. My wonderful garage did a circuit check with regard to the K40 but nothing was found amiss, so have left it for now. If there are no further incidents then I know everyone was right.
All the best, Ladynoyes.
 

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Discussion Starter #6
Have you checked the CPS isn't leaking oil into the cables connected to it ?
This is a known r170 problem which if not attended to , can let oil reach the ECU , causing a very costly repair , but if caught in time is easily and cheaply fixable !
Also might this be an ignition problem , faulty transponder , ignition switch etc ??
Do you have a spare key , try using that just in case , you never know .
I've also heard of cases of the battery being at fault , even after testing and appearing to be fine !
Thank you, curro101.
With regard to my last post - I panicked when she cut out the third time, and was trying to start her whilst she was still in gear - hence third time lucky when she started. I have had the CPS replaced, and was told that they keep a lot of these in stock for the R170.!!!!
No oil leaks onto the circuit board which was also checked and found to be fine, so have not had the K40 connections resoldered. I am sure she will be fine now, and thank you for your post, Best regards, Ladynoyes
 

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Discussion Starter #7
Have a good hard look at the k40, look for bad solder joints and cracks in the solder that was my problem. I also had to change the CPS which made a big difference for me.
Thank you, livefreeordie - you and a couple of other people pointed me in this direction. I have had the CPS replaced, of which there were "a lot in stock" as apparently they can get damaged by heat. I suspect that the CPS was as old as the car (14 years now, and getting creaky like her owner!). K40/circuit board checked out ok, so hope that the problem has been remedied now. Thank you for your time, best regards, ladynoyes.
 

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K40 / CPS / What Now?

I had the same problem.

I have installed a new Bosch CPS...it snapped into place quite nicely. That didn't solve the problem.

Last night I replaced the K40 RCM (which, Mercedes calls the Engine Mgmt Relay), with a Mercedes genuine part. My car still has hiccups while driving, and dies while stopped. I have found that if I remember to put the car in neutral while idling, it revs a little higher and is less apt to die. But also, if the RPMs start to dip, I give it a little gas and can usually prevent it from dying.

Willing to listen to any and all advice!

Mahalo!
 

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Discussion Starter #9
I had the same problem.

I have installed a new Bosch CPS...it snapped into place quite nicely. That didn't solve the problem.

Last night I replaced the K40 RCM (which, Mercedes calls the Engine Mgmt Relay), with a Mercedes genuine part. My car still has hiccups while driving, and dies while stopped. I have found that if I remember to put the car in neutral while idling, it revs a little higher and is less apt to die. But also, if the RPMs start to dip, I give it a little gas and can usually prevent it from dying.

Willing to listen to any and all advice!

Mahalo!
Hi Aloha Girl, nice to know someone else in the same boat, as it were!....mine has stalled on me once since I had the CPS changed about 6 weeks ago....this time I was sitting in traffic and felt a little shudder, and automatically looked at my dashboard which then lit up - so had to turn off engine and restart. I've only had this cutting out business since I had a new supercharger clutch, and wonder if there is a bit of mis-timing. If I get to the root of the problem I will let you know. TTFN, Lady Noyes.
 

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Premium Member 2004 SLK200K
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What about testing the fuel pressure at idle as well as the injectors?
Now that you mention that , I seem to remember a post not long ago about a random fault in the fuel pump on someones car that only happened ocasionally , due to it being one contact of various being bad and only happened when aligned in a certain way , or something like that ???
 

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Discussion Starter #12
Engine cuts out all of a sudden - usually when idling

Still got this issue guys - have had new crank position sensor, not done the K40 but had it inspected and all seemed well. Car bonnet shakes a little sometimes in idle, so put it into neutral and that clears the shake. Everytime the car cuts out she gives a little shudder, and all the dashboard lights go on. I have not had the fuel pressure checked yet. She cut out on me tonight just as I was going to put my foot on the throttle to go round a roundabout. (Last year had new auto gearbox oil change and new supercharger clutch). Love her but can't trust her at the moment!!!:(
 

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Registered 2012 SLK55 AMG w/P30
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So it appears it's only dying at idle, or when your foot is off the gas pedal? Correct?
 

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Engine cuts out suddenly - no near misses so far

So it appears it's only dying at idle, or when your foot is off the gas pedal? Correct?
Hi Mensra
Yes, that's right, latterly. I was once travelling at about 30mph when the dash lights came up - that was about 6 months ago. Had all the electrics checked and they couldn't find anything wrong.
This week it has happened twice, after a period of 6 weeks problem free.
It always seems to be idling OK, and then dies as I put the foot on the gas pedal...once this week in nose to tail traffic, and then once again as I was about to launch myself onto the roundabout ..
....performance appears to be normal other than that.
 

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Registered 2012 SLK55 AMG w/P30
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Sounds like an issue where the mixture leans out as it transitions from an idle mode to power. That could be a micro switch or a sensor.
 

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Per ardua ad cineris.
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Clean the injectors

You may have partially blocked injectors.
At low revs, the fuel quantity is very small, and a partially blocked injector may not deliver enough fuel during the scheduled opening period.
So use an intensive cleaner.
Halfords (in UK) do "Redex Petrol Advanced" (the equivalent of Techron in USA) for intensive cleaning of the fuel system. (See here)
Or you can buy same from Amazon for less, but with delay.

And when you press the throttle, the throttle butterfly (air flap) may open before the increased fuel has effect, hence fuel starvation.
If this is the case, it probably doesn't happen when cold (ie the engine is "on choke" and more fuel is scheduled).

Your tickover may work OK, since it is closed loop control; if the speed is too low, the ECU adds fuel to get the right tickover speed. However, transient control will not be robust, so adding throttle will move the air inlet before the fuel needs to add more to match.
And trailing throttle on approach to a roundabout may have starved the engine completely; the fuel level would be insufficient to keep the flame alive!
 

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Earth paths

Another thread (here) had a mis-firing engine issue (typically at idle, "at red lights") but it made me wonder about earth straps off the engine.
Your example sounds similar, and makes me wonder about the earth paths.

If you ever get a voltage between the battery and the engine, then the earth chain is not working well, and that would stall the engine.

My inclination would be to check the battery earthing; the reference voltage controls the charging circuit, so loss of this reference may lose power from the alternator as well.

Unless you've resolved it; please let us know.
 

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Thank you, curro101.
With regard to my last post - I panicked when she cut out the third time, and was trying to start her whilst she was still in gear - hence third time lucky when she started.

No oil leaks onto the circuit board which was also checked and found to be fine, so have not had the K40 connections resoldered. I am sure she will be fine now, and thank you for your post, Best regards, Ladynoyes
Can you edit the OP to remove this info about the third start? It might mislead the investigation.

And visual inspection of the K40 is good when the solder joints have overheated, but it would be useful to clean the contacts of the relays in the K40, to ensure regular connection. (Has been mentioned above, by curro101)
And any tests that confirm anything to be OK, when the car has driven in and out of the test location, just confirms it is working at the time; you appear to have an intermittent fault that has happened about five times in quite a few months, so they'd have to be lucky to catch it.

Key points; the failure is "absolute" and kills the engine (so lasts for some time) but can be undone by restarting, immediately.
Most examples are during tick-over (so might be short) but it has happened during normal running.
No mis-fires have been noticed during normal driving; if it fails, it stops the car.
Some issues have been noted during tick-over and the transition to on-power, but this has improved with Techron cleaning. (This might be a different issue, and hopefully has now been cured with a clean-up)

One other thing that might benefit the analysis is to clean the MAF sensor, so that we can remove any pollution (oil) problems there from the consideration.

If it happens when driving, try to notice if the power is cut off sharply (electrical), or if it rolls off (fuel starvation); it may not be possible to detect that, but worth checking. (It is obvious on a carburettor car, but fuel injection doesn't have much of a reservoir of pressure.)
Happy hunting.
 

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Hi I have 2005 slk auto 2oo I believe this is 171 model to day I went to pull off the car died on me very embarrassing had to put in park to get it going sounded rough took 3 turns of key to get her going this has happened about five times in six months what could or be my nephew reckons it a cps sensor issue I know this was a problem r170 also cheers

Gerry
 

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Registered 2001 SLK320
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Hi, my 2000 r170 did all sorts of stupid stuff; I did the k40 fix and that worked; then it would die on me every 30 minutes or so and that was not only annoying but dangerous; so i replaced it with one from AutoZone and fixed the matter. Still the car ran super choppy and power was low so I changed the MAF sensor and that cleaned it up but still had codes about spark timing and some other crazy stuff. I changed all four spark plugs and that helped but the car was still stupid! Decided to have the battery checked and wouldn't you know it was not up to par! Replaced it with a match from AutoZone and the car became the Hulk! No more problems. I suppose all I should have said was check your battery! You might be surprised at how a low battery affect so many different aspects of this particular car. Now I'm trying to determine why my front tires constantly ware out on their insides only; i've ruined a brand new set of tires already.
 
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