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1989 260e
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13 Posts
Discussion Starter · #1 ·
Greetings all!



Earlier this year purchased an awesome 1989 260e, mint car with only 157k km (97k miles). Had a ton of work done but it's been an absolutely awesome car to drive.

One major issue I've had however is that at some point i started having electrical issues whenever headlights and / or heater was on (rough idle at stop lights, dimming lights, ABS and / or SRS lights coming on intermittently) and RPMs dropping to the point where car almost dies but doesn't quite. As soon as driving forward everything was fine.

Naturally after researching I replaced the old 1 fuse OVP with a brand new 2 fuse OVP the other night. Seemingly the problem went away where I was driving with full lights on at night without symptoms. However, the problem returned as soon as I put the heater or AC on specifically.

Tested the voltage and noticed it was the normal 13-14v range but then when heater was turned on it dropped to about 9.6v. Similarly afterward with car off when I tested it was also 9.6v while key on but engine off.

Coincidentally these issues first seemed to start not long after I had to boost the car (having left headlights on for about 10 minutes while adjusting them) and also after first time driving in the rain once or twice. Not sure if those would have contributed to the start of these problems.

Through process of elimination I've now ordered a new voltage regulator.

Any other advice would obviously be really helpful.

Cheers.

-Paul
 

W163 and General M Gremlin
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Welcome to BW Paul,

Please Complete your Profile to show the year and model of your car next to every one of your posts.
Members are not likely to search for the one post the model of the car is mentioned.

OVP ===> generic or oem?
Checking your alternator VR - noted
Battery age? Voltage tested?
 

Registered
1989 260e
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13 Posts
Discussion Starter · #3 ·
Welcome to BW Paul,

Please Complete your Profile to show the year and model of your car next to every one of your posts.
Members are not likely to search for the one post the model of the car is mentioned.

OVP ===> generic or oem?
Checking your alternator VR - noted
Battery age? Voltage tested?
Thanks, I've gone ahead and done that.

OVP hard to say, I believe is generic but looks identical to OEM. Purchased from "Haas Classics" in Florida and that's also what they list under the brand name for it. It's a two 10 Amp 9 pin type as opposed to the old 1 fuse, 7 pin i pulled.

Didn't check the VR but about to pick up a new one I ordered.

Battery is of the larger heavy duty variety and almost new, put in by my mechanic / project manager (I trust his judgment as he has 30 years experience and 3 w124s and they're his specialty).

I did some more voltage testing through a cigar lighter plug in today. No lights on, the car drives at 14.2v, lights on at 14.0v. For idle they're around 13.8 and 13.2 respectively. Where things take a nosedive is when the AC or Heat is applied. At idle voltage drops to about 9.6 when parked, then even lower to about 9.1 when going into drive or reverse and that's when ABS / SRS shows up, revs drop and even the blower starts cutting in and out.
 

W163 and General M Gremlin
Joined
14,848 Posts
Sure sounds like the VR on the Alternator - the drop symptom.
Which brand VR?
With these era cars, oem (as best as possible) <=== recent discussion

Not familiar with the OVP differences and the one you installed in yours (presuming it was recommended to you)
I personally dont like the idea of swapping in a (non-oem) replacement unless it's been verified as working correctly.
That's just me.

Others can chime in on the OVP swap - (original oem7pin? vs. the 9pin you have)
 

Registered
1989 260e
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13 Posts
Discussion Starter · #5 ·
Sure sounds like the VR on the Alternator - the drop symptom.
Which brand VR?
With these era cars, oem (as best as possible) <=== recent discussion

Not familiar with the OVP differences and the one you installed in yours (presuming it was recommended to you)
I personally dont like the idea of swapping in a (non-oem) replacement unless it's been verified as working correctly.
That's just me.

Others can chime in on the OVP swap - (original oem7pin? vs. the 9pin you have)
Yeah I'm figuring as much as well. Just through the process of elimination I'm going with the VR first. Yeah I know it's blasphemy but it's a Beru, so not OEM. Worst case at least it'll work in the short term and I can rule it out and get a better one later.

Only thing that makes me think it's not the alternator itself is that the battery holds a charge well. Starts on a dime fine the next day or even after car sitting for a few days. The Heater specifically seems to be the one big drain at this point.
 

W163 and General M Gremlin
Joined
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Blasphemy!
Forgiven though.
Others on the forum may get somewhat snarly with comments, but meh! Your dream, your rules.

Perform a parasitic drain test.
Blower motor regulator?
 

Registered
1989 260e
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13 Posts
Discussion Starter · #7 ·
Blasphemy!
Forgiven though.
Others on the forum may get somewhat snarly with comments, but meh! Your dream, your rules.

Perform a parasitic drain test.
Blower motor regulator?
I'll try that if new VR doesn't rectify it. For now I've misplaced my tester so I've got to find it. Where is the blower motor regulator?
 

W163 and General M Gremlin
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300te 4Matic, 1992, 225,000 miles. W447 Vito Sport Long 116cdi, 2018, 70,000 miles.
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Voltage regulator Or. I would just change the whole alternator with a proper make one for ease. Then check and repair the original to keep as a spare.
 

Registered
1989 260e
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Discussion Starter · #11 ·

Inspect the fan resistor too (as a precaution)
Thing is the blower is new.

One other thing I'll say is once the heater / AC is turned on and the problem starts, even once it's turned off the voltage does jump back up but never quite returns to as high as it was before having used the heater....and later in the same trip it even begins to dip to similar levels if headlights are on. Only when the car is started for a new trip is it back up to what it was before the heater was ever turned on.
 

W163 and General M Gremlin
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I was referring to the resistor under the blower motor.

Cable Wire Composite material Event Font
 

Registered
1989 260e
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13 Posts
Discussion Starter · #13 ·
So to hell with, I've decided to purchase a new alternator as well just for the hell of it 馃お

My only question is from what I'm seeing I can't seem to find any remanufactured Bosch ones that are higher Amp such as 115 or more listed for my car specifically most places. Only ones seemingly available from most parts sources for my 2.6 260e are 70 and 80 Amp ones. Is that normal?
 

W163 and General M Gremlin
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If you upgrade to higher amp, you're going to want to beef things up.
 

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1989 260e
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13 Posts
Discussion Starter · #15 · (Edited)
If you upgrade to higher amp, you're going to want to beef things up.
Truthfully I think 80 Amp would be enough anyway. Only modifications I'm running is the euro spec headlights and (when I get around to it) a single din aftermarket kenwood stereo running with the stock 1989 speakers, no subs, no nothing. Nothing extraordinary I would think.

Firsr I'll try just replacing the VR and if that doesn't correct the problem I'll get an 80 amp remanufactured Bosch AL165X.
 

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1989 260e
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Discussion Starter · #16 ·
Small update, tonight I took another trip, this time to work. Even though I didn't run the heater I had the headlights and all, car maintained around 13.5 - 13.7 while driving but kept dipping down to 12.0 - 12.2 while stopped at red lights. Once or twice it dipped into the 10s and 11s while idling or switching from park to drive / reverse.
 

Premium Member
1986 Mercedes 300e 124.030, M103, 1986 Mercedes 560 SEC 126.045, M117.968
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Unfortunately neither the voltage regulator or a new alternator will cure your woes. You have excessive voltage drop in your circuit if I read your initial post correctly. The key information I picked up from your post was with the key on engine not running the voltage also drops to 9.6 volts when the HVAC is turned on. If that is indeed correct what you have identified is excessive resistance in your electrical system. I will break out the wiring diagram later and guide you to check it out if you want. If you want to try the voltage regulator first no problem just ask when you are ready.
 

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1989 260e
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Discussion Starter · #18 ·
Unfortunately neither the voltage regulator or a new alternator will cure your woes. You have excessive voltage drop in your circuit if I read your initial post correctly. The key information I picked up from your post was with the key on engine not running the voltage also drops to 9.6 volts when the HVAC is turned on. If that is indeed correct what you have identified is excessive resistance in your electrical system. I will break out the wiring diagram later and guide you to check it out if you want. If you want to try the voltage regulator first no problem just ask when you are ready.
The 9.6v with key on but engine off seems to have occurred only right after the voltage problems after using HVAC. Every other time I went to cold start the car after its been sitting for a while it seems to be higher.
 

Premium Member
1986 Mercedes 300e 124.030, M103, 1986 Mercedes 560 SEC 126.045, M117.968
Joined
300 Posts
Personally I think your issue lies between the battery and the dashboard or it could also be a grounding point with high resistance. Some simple first steps to check.
1) with engine running and the blower fan and lights on check the voltage at the battery terminals. Should be at least 12.7 volts which will increase to at least 13.5 volts when engine speed is raised to1500RPM鈥榮 . Voltage regulators usually fail in one or 2 ways they either full field the rotor causing voltage to run away which the OVP relay is designed to come into play or the brushes are worn and you have no charging at all.
2) if you have long enough leads measure from the positive battery post to the cigarette lighter center pin with your consumers are turned on. Anything over .3 volt and you have excessive voltage drop. Do the same with the negative post and the outside shell of the lighter socket. Same readings apply.
 

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1989 260e
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Discussion Starter · #20 · (Edited)
Personally I think your issue lies between the battery and the dashboard or it could also be a grounding point with high resistance. Some simple first steps to check.
1) with engine running and the blower fan and lights on check the voltage at the battery terminals. Should be at least 12.7 volts which will increase to at least 13.5 volts when engine speed is raised to1500RPM鈥榮 . Voltage regulators usually fail in one or 2 ways they either full field the rotor causing voltage to run away which the OVP relay is designed to come into play or the brushes are worn and you have no charging at all.
2) if you have long enough leads measure from the positive battery post to the cigarette lighter center pin with your consumers are turned on. Anything over .3 volt and you have excessive voltage drop. Do the same with the negative post and the outside shell of the lighter socket. Same readings apply.
I hear you brother. This is all vauable and i'll definitely take it into consideration. At the moment I don't know where my tester is and i haven't used it in years, so for now I'm using the lazy methods. As soon as my voltage regulator arrives I'll replace it and see if maybe that'll help any (incidentally do I need to disconnect the battery to replace just the voltage regulator if I'm not removing the alternator? I've heard different opinions on this issue). In any event on closer inspection it appears both that and the alternator are original and both look their age.

Another interesting development is that after a few hours of it being parked I then went to start the car, voltage read 10.3 with engine off. It took 2 tries to get the engine going but once it did the revs shot up and the voltage went up to 14.0. Then started driving with lights on and the driving voltage dropped to about 13.3 - 13.8 depending on city or highway. However, at red light stops when idling it still continued to drop down to between 12.0 and 12.2 and at least at one stop it behaved erratically, dipping as low as 10 then jumping to 13. When I got home and shut the car off and immediately went to start it again the engine started quick. Another thing i'll mention is also it seems like some of the times its done this the headlight bulb warning light comes on and 1 headlight is off, but then the next day I could turn them on and it'll be fine. Completely random. May or may not be related.

P.S.
What do you mean by "full field"? Sorry I'm not the most electrically inclined.
 
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