Date registered: Jul 2003
Vehicle: 98 slk 230
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bad stuff is happening
After posts to this forum and consultation with a few folks, here is the general summary. The car runs very, very rough and stalls and sometimes backfires. I toyed with the idea of a fuel delivery problem and replaced the filter, which was long overdue (I suspect) as the car has 80,000 miles on it. I have not checked the fuel pressure, but when I popped the pressure regulator, there was definitely pressure in the fuel rail. Plus, when the car runs, it reeks of unburned fuel. Conclusion = not a fuel delivery problem.
OBD II diagnostic connector pulls codes for misfires in cylinders 1 and 4. I thought maybe the 1/4 coil was bad so I swapped them - still miss on 1 and 4. OK...not likely a coil problem. Interestingly, I read today that the flywheel reference notches for the crank sensor are positioned at TDC for 1 and 4.
I replaced the plugs with Bosch +4's and had no luck. I tested spark with an in-line strobe, and all cylinders seemed to be firing well.
So....fuel and spark but almost can't even run....timing problem, I'm thinking.
Further, the O2 sensors were replaced in June and I just put in a new map sensor and air filter. I checked all the vacuum lines for leaks and ignition wires for shorts.
hmmm.....here is where I really began to think about visiting the MB dealer. Still hinking this has to be a timing problem of some sort, I checked the resistance of the crank sensor. It tested at 1100 OHMs. I heated it to 200 degrees F in my oven, and it then read 1200 OHMs. I made a quick visit to the used auto lot where I bought the car, and they were nice enough to let me hit another 98 slk they had on the lot with my multi meter. The crank sensor read 700 OHMs.
So my conclusion is that the crank sensor is sending exaggerated readings to the ECU (or whatever MB has to do that job) which is "advancing" the timing and causing this problem.
Is this conclusion worth gambling $100 of my pully upgrade budget....?
but...the illuminated door sills look great....
99,000 miles and still like new.