mdalke

Hello,
My mother owns a 1992 420 SEL. She has had it serviced regularly at an independent MB mechanic for 15 years. 18 months ago she complained of the car stalling within 5 minutes of filling up the tank with 91 octane fuel. The mechanic immediately replaced the FPR and the car ran fine in the test drive. Once my mother drove the car in normal conditions, on a hot desert day, the car would stall in exactly the same way, but restart immediately and run fine for another hour or so. Once the stalling happens, the car can be started up and driven again no problem. The stalling only occurs when her foot is not on the accelerator. The check engine light came on a few weeks ago after a stall, but she has not had it back to the mechanic, she just avoids driving.

She lives in Riverside County CA, where the summers are very hot, and the winters are never below 60 degrees during the day.

She puts about 100 miles per month on this car. Any idea what this problem might be? So far, she has never left the shop with less than $1200 worth of service. I am hoping we can get some suggestions, so that I can take the car to an indie, and ask for a specific part to be replaced.

To recap... short, cold drives: no problem. Long hot drives, stalls at stop lights, then restarts and runs fine for 10 or 20 miles, or until the next stop light. The car always gets 91 Octane fuel from 76, and has had all routine oil changes.

Thanks in advance.
Mike Dalke
2002 e320

Mom's car: 1992 420 SEL

dsmith

Not sure a 1992 420SEL was sold here, but let's assume it's a 1991. Could be many things. My free guess is that the crank positioning sensor is starting to fail. Unless it becomes a no start issue long enough to diagnose what's good and bad, you can only guess.

mdalke

Thanks for the advice. I was just minutes away from delivering the car to the mechanic for a new CPS, then when my mother got further into the symptoms, it sounded like a fuel delivery problem. Since the FPR didn't fix it, then the CPS was next on the list.

The mfg plate in the door jamb lists the mfg date as 09/1991. It does have 180k on the motor, and still has the original CPS. My 2002 e320 needed one at 95k. My symptoms were very different. Mine only came about upon re-start after being parked for a few minutes. The engine would misfire for 10 seconds, and shut down after the starter stopped turning. Engine light would glow after the next start, then go away after a half hour or so. It did this 3x before I had a shop replace the CPS it for about $225.

What would your guess be for that part/service at an indie? There is a pretty wide range of prices for the part on the 1991 420 SEL. One supplier even suggested that the car had 2 CPS's one on the front of the block, one on the rear. Info seems foggy, since the car is 20 years old, and most dealers are not seeing many cars of this age in their shops.

gogi

crank sensors don't usually go bad on the w126 but you might be having a problem with ignition control module, its usually located on the drivers side fender under the hood. you can probably smell it and know its bad.
Dave