My wife inherited a 1993 Mercedes 400SEL that is in amazing condition (near like factory condition). It was stored in an inside air conditioned garage and only has about 85,000 miles on it. The car runs perfectly and has no problems, except.... it does one thing. Also BTW, I can't plug in my OBD2 scanner as that was introduced to these cars in 1994, so it has the old "pin ports" and I have not built a code reader for it yet (but being an electronic engineer I plan to in the near future for fun that will actually have a digital display instead of a blinking LED).
Anyhow, the problem.
If you let the car sit for more than 1 day without starting and running the following day after you start and drive the car for about 10 minutes (it does fine up until that point) it has a near total loss of power. If you attempt to accelerate the car will it will totally bog out, might backfire once or twice and then stalls out. Any attempt to restart it will not work unless you wait around 30 - 40 minutes. If you wait 30-40 min it starts up fine and typically runs perfectly. It might drag a LITTLE for about 1-2 minutes after the restart but once it gets going it is fine and runs like a champ.
As long as the car is started and run for at least 10-15 minutes every day it NEVER does what I described above.
Example:
Monday, car was run.
Tuesday car is not started at all.
Wednesday, car will start, run 10-15 min and then do what I described above.
If it had been at least started and run for 10 min on Tuesday it would have ran perfectly on Wednesday.
Sorry for the odd way of describing things above but I just wanted to make sure I was very clear on what it is doing.
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To date I have replaced the soft vacuum lines and I have also replaced the Fuel Pressure Regulator with a new Bosch part. Neither of those replacements have solved the problem.
Sure, I could keep replacing components until I eventually find what is causing this problem but I figured it was worth asking here what you feel could be a likely cause of this type of behavior. With you advise maybe the next thing I replace might happen to help instead of just going down a list with my fingers crossed and maybe save a few diagnostic dollars along the way buying unnecessary parts. 🙂
Thank you very much for your time.
What you need to do is don't throw parts at it but do some diagnostic work when the problem occurs. When this happens what is the fuel pressure? What is the voltage at the battery terminals? Are you getting spark to all the cylinders? Etc. That thing is over 30 years old, so all components are suspect.
Well first of all, I am not a mechanic... only a amateur DIY'er (and an Honorable Member here 😉) but when I read your post the first thing that I thought was that perhaps your problem is related to a failing fuel pump. Then when I read the comment from @chucktobias "When this happens what is the fuel pressure?" I again thought of the fp and I remembered this video from Scotty a few weeks back. I don't understand the erratic nature of your particular dilemma but perhaps a fp going bad can act in this manner. Anyhow here's Scotty:
https://www.youtube.com/watch?v=SpsMF1zS3Io
There is no problem with the voltage at the battery terminals and there is spark to the cylinders, this I have tested. I do not have a way to test the fuel pressure at the moment but I will purchase a gauge to test that. What puzzles me is why a fuel pressure condition, that can totally be repeated over and over, only seems to occur when the car has not run for 1 day... and then only after it has run for about 10 minutes -- that always resolves after it sits for 30 minutes. If the car is driven every day (or at least started and run) the problem never happens. Also puzzling to me is why after it sits for a day does it run for 10-15 min before the problems develops. If it was a fuel supply issue why would it not be present when you first try to start and drive the car?
It is bizarre to the point that it is so consistent that it always seems to happen at exactly the same place on the road. I live in the country and exactly 9 miles from my home is the first traffic light.... just about the point of hitting that traffic light... BOOM.... problem manifests. Same place, same distance and time, every time. It is so so so weird.
So we are dealing with the problem right now on days we don't plan on going anywhere by at least starting the car and let it idle for 10 minutes or so and and shut it off. The next day the car will run fine, no problems. 🙂