Ok so, I'm having a lot of issues with my '86 420SEL. For starters my battery (brand new) won't stay charged for even 24 hrs. I've replaced all the fuses and that didn't help. My engine is doing some pretty weird stuff too. Whenever it's in park my engine keeps revving up without me touching anything, and whenever I put it in reverse the rear end hikes up really high, and whenever I put it in drive it wants to shoot off. My car does have 199k miles on it though.
Do a search here, google is better than the BW search feature, those topics have been well covered and also, please fill out your profile (UserCP at top of page) so we don't have to try to remember what model car you have and your location as well, you never know there might be a member just around the corner from you
You didn't mention changing the alternator and I believe that's your battery problem. I ended up having to change mine three times before I got one that was rebuilt properly. Pretty easy to test: check voltage at the battery with the engine running (alt. turning). You should have something over 13.5 V. If it's lower, replace that alternator.
Get that sorted first, then move on to other issues.
Chances are it is your alternator. As stated previously, check with a multimeter your voltage across battery terminals with the car running. If it is low, change the voltage regulator in the back. If you're still on the original alternator, you may want to bring it to a shop to have it rebuilt though. I'd check the shaft that the brushes rub against to see how worn it is.
Excellent recommendation so long as you can find a shop that still rebuilds in-house.
I completely forgot about that tact as there hasn't been such a shop in my locale is quite some time. I reckon they were put out of business by the box stores. Damn shame, really.
I agree. Can't hurt to replace the voltage regulator while you're trickle charging the battery outside the car. Every German car I've owned needed a new voltage regulator at about that mileage. I will say I've never needed a rebuilt alternator. New regulators have fixed all of them.
And speaking of the alternator, you might want to pull and check the voltage regulator from the back of it. I haven't had this problem with my SEC . . . . . yet, but on the SE over the 12 years I owned her I put three regulators. The brushes would wear down and although the dash light would glow it was so dim I could only see it lit at night. I think the poor thing (factory alternator ?) just finally wore out because with the third regulator the whole thing gave out on an Atlanta to Memphis road trip, likely the shaft just wore down where the regulator couldn't maintain contact
I have acquired two spare alternators plus an additional regulator here JIC
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