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Discussion Starter #1
Hi All,

I've got an 04 R171 350 with 72,000km on the clock, and around 9 months back it started to misfire a little after it had been running for a while. I used to turn the car off and on again and the problem would immediately go away. Would happen around once per week. Eventually, I had my local mechanic follow the fault around by switching coils. Bingo - found the issue and replace the coils around 2 months ago - all good.

Less than 4 weeks later, the problem is back, but now easier to reproduce. Seems that after I have been driving for around 45-60 mins, and the temp has come up to around 94-100 Celsius that the misfire is back again. Started as cylinder 3, then moved to 2, and on a bad day it might get to 1 as well. Note that it's been winter out here in Australia, so temps have been around 15-20 Celsius.

When the car cools down, i.e. overnight/few hours - it will run beautifully again for around an hour before the problem starts again. Turning the car off and on, does NOT fix the problem anymore.

I've done plenty of reading and searching, but what has me stumped is the aspect where it runs perfectly until it seems to heat up. Anyone got any ideas? I doubt that the brand new coils are stuffed already, unless there is a problem upstream causing the issue.

Keen to get some thoughts from the group before committing to the offensive local costs of the dealers here, that charge USD$170 / AUD $250 per hour to look at it. My gut feel though, is that I may need to take it in for their extensive diagnostic.

Notes:
Oil and filter were replaced about 2 months back.
Ran a can of fuel system conditioner through it - no change.
Car has a full MB service history and has been very well cared for.
Transmission fluid replaced at last service.

I've been running Torque on Android to keep track of the faults, and what's shown below is quite typical:

Fault log report generated by Torque for Android
=================================================

Vehicle VIN: WDB1714562F047153
Vehicle Manufacturer: Mercedes-Benz
Vehicle Calibration ID: 00144683401502110004484810150002

Current Fault Log
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P0300: Random/Multiple Cylinder Misfire Detected
P0302: Cylinder 2 Misfire Detected
P0303: Cylinder 3 Misfire Detected
P0353: Ignition Coil "C" Primary/Secondary Circuit
P2015: Intake Manf Runner Position Sensor/Switch Circuit Range/Performance bank1

Pending Fault Log
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P0352: Ignition Coil "B" Primary/Secondary Circuit

Historic Fault Log
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ECU reports no historic faults
Other discovered fault codes
(possibly pending, current or manufacturer specific)
----------------------------------------------------
P0524: Engine Oil Pressure Too Low
P0629: Unknown code - More information may be available on the web
P0633: Unknown code - More information may be available on the web
P0641: Unknown code - More information may be available on the web
P0649: Speed Control Lamp Control Circuit
P0981: Unknown code - More information may be available on the web
P0989: Unknown code - More information may be available on the web
P0997: Unknown code - More information may be available on the web

End of report.
 

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Administrator - Founding Member
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92,875 Posts
cps crankshaft position sensor cheap fix my opinion
 

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Random and i do not think related to your issue but will not harm if you have not had it done yet , change the fuel filter in the tank.......slim slim chance some dirt getting through to the injectors

think filter was a change at 10 year old item
 

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Agreed - make sure you're up to date on the maintenance first, and if the problem persists replace the (inexpensive and easy-to-reach) CPS. Buy an MB-branded one. This is the classic symptom of a failing CPS, and they are notorious for failing without a specific code..
 

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My SLK doing the same thing for about a year now.

Seemed to be fixed by two high speed, full throttle runs from zero to 90mph.

Well see if this really holds... If not I'll try the CPS replacement.
No doubt, a DIY link is here on the forums!
 

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Discussion Starter #7
Well, it's not the CPS. Had it changed today, and the car does exactly the same thing.

Leaving it with the tech for them to take another look tomorrow.
 

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Discussion Starter #13
Latest update: Car ran cleanly for a few hours after the replacement of the intake manifold, then started throwing misfire codes on cylinders 2,3,5. Prior to that it was complaining about 1,2,3.

Mechanic has now had the car for 18 business days, and the bill is up to AUD$3400 for parts and labour. :-/ He is quite apologetic, but is running out of ideas now. Checking electricals to the ECU, as well as checking EGR for issues.

Parts replaced so far:
Crank Angle Sensor
Intake Manifold (new unit)
Coils

Parts Checked
Injectors
Plugs
Coils
(moving plugs and coils results in consistent issues on cylinders 2,3,5)
 
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