Mercedes-Benz Forum banner
1 - 20 of 28 Posts

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #1 ·
Hi, Really need help on this before I buy.
I'm having a problem with my load on the car.

Car starts:


{ Volt fluctuations +-.05 }

Battery 13.72v *no accessories

Battery 13.55v *aux fan

Battery 13.30v *a/c on

Battery 13.11v *headlights high beam

Battery 12.89v *hazards on
Engine somehow rattles. I raise the rpm by pressing the gas pedal just to remove the rattling and it does. But when I release it, seems to cut off but it didn't. Then rattling begins again

Car has parasitic draw on .20amp.

The alternator is a stock 80amp. Have already checked VR and serviced the alternator. (Change the bearings)

An electrician told me to get a higher output alternator. So that could supply the parasitic draw and the accessories. I've looked at J&S alternators. And am planning to order 2003 ml500 alternator, which is compatible to the stock based on cross-referencing from autohausaz and as-pl.

The alternator I'm looking at, has an output of 250 amps. Would this work and solve my idle? And any factors I should consider if put this 250 amp alternator like wires, grounds, etc., Would really like your opinion on this. Thanks
 

·
Registered
1989 W124 260E
Joined
·
3,571 Posts
Stapler Never ever come across this idea before ,..Wont change the running of your car engine one bit ..you can use a larger alternator it wont change a thing ..You have other problems sorry to say .. Well i know my alternator is only 70 amp and i have no problems with that . But if your running a mobile cinema at a drive in movie then 250amp will be ok .. .
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #3 ·
Stapler Never ever come across this idea before ,..Wont change the running of your car engine one bit ..you can use a larger alternator it wont change a thing ..You have other problems sorry to say .. Well i know my alternator is only 70 amp and i have no problems with that . But if your running a mobile cinema at a drive in movie then 250amp will be ok .. .
Thanks.👍
 

·
Registered
Your mom
Joined
·
6,229 Posts
The 2003 ML500 alternator (AL0795x) is 120a, not 250. It can be made to work in your w124 by swapping out the voltage regulator but it's not plug and play. As previously mentioned swapping the alternator won't fix your issue.
 

·
W163 and General M Gremlin
Joined
·
8,573 Posts
Lazy indie selling a wannabe bandaid solution, imo.
Find an indie that has the patience to locate the parasitic draw, or diy.
 

·
Registered
1989 C126 560 SEC 2015 W212 220d
Joined
·
107 Posts
Buy yourself a good multimeter - chasing a parasitic draw is not that difficult, you just need to understand the process and follow it step by step. There are lots of How-To videos on YouTube for reference.
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #7 ·
The 2003 ML500 alternator (AL0795x) is 120a, not 250. It can be made to work in your w124 by swapping out the voltage regulator but it's not plug and play. As previously mentioned swapping the alternator won't fix your issue.

Thanks👍👍
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #8 ·
Buy yourself a good multimeter - chasing a parasitic draw is not that difficult, you just need to understand the process and follow it step by step. There are lots of How-To videos on YouTube for reference.
Thanks👍👍
 

·
Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
Joined
·
11,006 Posts
Some really good vids on YouTube for chasing down parasitic drains. Easily find the circuit and then trace from there......

I like this one:


Kevin
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #10 ·
Some really good vids on YouTube for chasing down parasitic drains. Easily find the circuit and then trace from there......

I like this one:


Kevin

Thanks for the video, but do you have other suggestions aside from this. The problem I want to fix is my idle: when AC on it Voltage dips down and begins to show a rough idle. But when I give it a gas, it got smooth. If I release it, as AC is on, rough idle begins again. Really appreciating this forum for education. Thanks
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #11 ·
Stapler Never ever come across this idea before ,..Wont change the running of your car engine one bit ..you can use a larger alternator it wont change a thing ..You have other problems sorry to say .. Well i know my alternator is only 70 amp and i have no problems with that . But if your running a mobile cinema at a drive in movie then 250amp will be ok .. .
Actually I got this idea from this forum.


Font Screenshot Terrestrial plant Darkness Number
 

·
Registered
1989 C126 560 SEC 2015 W212 220d
Joined
·
107 Posts
Actually I got this idea from this forum.


View attachment 2716888
I think you're conflating 2 separate issues here:

1. you have a parasitic draw - find the cause and resolve it. If you have additional extra load on the Alternator due to multiple accessories running, THEN this can be solved with a higher AMP alternator.

2. Rough Idle - if this is due to A/C, perhaps you should start with the ICV (Idle Control Valve) and/throttle body?
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #13 ·
I think you're conflating 2 separate issues here:

1. you have a parasitic draw - find the cause and resolve it. If you have additional extra load on the Alternator due to multiple accessories running, THEN this can be solved with a higher AMP alternator.

2. Rough Idle - if this is due to A/C, perhaps you should start with the ICV (Idle Control Valve) and/throttle body?
Thanks for the two advice👍
 

·
Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
Joined
·
11,006 Posts
The electronics are supposed to compensate your idle if the AC is turned on. But before we get into all that....do as suggested, check out the voltage regulator in your alt AND do some voltage checks straight across your battery terminals. If the alt's VR is bad and you turn on your AC which is affecting your idle, it's because the alt is not keeping up charging your battery. Or you have a bad battery....most likely.

If you have the AC on and other accessories on.....the battery voltage shouldn't drop below like 13 volts. With accessories on, the alt is maxing out it's charge to the battery. If you're down around 12.3 volts or less with all those accessories on, you have a charging problem or a bad battery.

You have to rule out whether or not your alt and battery are 100% before we can go any further with advice. The alt MB used in these cars is just adequate....going to a larger alt is often done especially if owners add big sound systems. But we're jumping ahead here.......

Kevin
 

·
Registered
1990_w124_300CE_M104.980_Automatic
Joined
·
69 Posts
Discussion Starter · #15 ·
The electronics are supposed to compensate your idle if the AC is turned on. But before we get into all that....do as suggested, check out the voltage regulator in your alt AND do some voltage checks straight across your battery terminals. If the alt's VR is bad and you turn on your AC which is affecting your idle, it's because the alt is not keeping up charging your battery. Or you have a bad battery....most likely.

If you have the AC on and other accessories on.....the battery voltage shouldn't drop below like 13 volts. With accessories on, the alt is maxing out it's charge to the battery. If you're down around 12.3 volts or less with all those accessories on, you have a charging problem or a bad battery.

You have to rule out whether or not your alt and battery are 100% before we can go any further with advice. The alt MB used in these cars is just adequate....going to a larger alt is often done especially if owners add big sound systems. But we're jumping ahead here.......

Kevin
Thank you so much. Very enlightening. Thanks😊👍
 

·
Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
Joined
·
11,006 Posts
Thank you so much. Very enlightening. Thanks😊👍
These German cars are very sensitive to a voltage range....they don't like to drop below 12.5 volts without dash trouble lights coming on like the ABS or others. Forget the battery light showing condition of charge....it will come on if there's a physical break in a alt wire etc. Member flooby can explain it better than I.

Kevin
 

·
Registered
1976 BMW 2002. 1991 250TD. 1995 E320. 2018 Honda Africa Twin
Joined
·
2,750 Posts
These German cars are very sensitive to a voltage range....they don't like to drop below 12.5 volts without dash trouble lights coming on like the ABS or others. Forget the battery light showing condition of charge....it will come on if there's a physical break in a alt wire etc. Member flooby can explain it better than I.

Kevin
\
Was about to comment that he really needs to take a closer look at his battery; it's size and condition specifically.

Your idle changing due to the AC being on is because the AC compressor is engaged, and therefore causing a load to your engine at idle. There is supposed to be compensation for it in the form of slightly higher idle controlled by some gizmo.

As already mentioned, these cars get weird when their battery voltage is low. Check your battery, fuses and grounds.
 

·
Registered
W124, 230E 5 speeds Manual, 1987
Joined
·
365 Posts
Hello, Before looking into all of this I would check for 2 things:
1- Belt and Tensioner. If you have a good belt, tensioner, and tensioner shock, You should hear no rattling even if the idle gets low

2- There is output from Klima relay to the ECU that commands the ECU to raise the idle to compensate for the AC Compressor when engaged. you may have an issue here.

Personally, I had a 50A alternator that delivered 14volts when I rev the engine, I replaced it with an 80A one due to some added accessories... but to my surprise, the voltage now is always around 13.5 and gets low to 12.7 if everything is on. i couldn't figure out why this is happening. took the alternator to a shop and they tested it perfect. replaced many regulators without any significant change. tried a thicker cable from alt to battery and it barely increased the voltage. but well it never caused any issue for me and batteries are lasting for a long time 4 years+. so I just forgot about it.

My car is a manual and today because of curiosity I shut the engine off when running downhill car in 3rd gear (without clutching in order to keep the alternator excited) with my voltmeter inside and hooked to the battery. I had a 14.9Volts. even if I run everything. the only explanation I could think of is that the ignition system is drawing a huge amount of current and I can't figure out why. maybe @Floobydust could have an explanation for this also.
 

·
Registered
'95 E300 DIESEL, '91 600SEL, '92 600SEL
Joined
·
18,353 Posts
When you go above 14,5 volts you start damaging the battery.
 

·
Premium Member
2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
Joined
·
1,604 Posts
Hello, Before looking into all of this I would check for 2 things:
1- Belt and Tensioner. If you have a good belt, tensioner, and tensioner shock, You should hear no rattling even if the idle gets low

2- There is output from Klima relay to the ECU that commands the ECU to raise the idle to compensate for the AC Compressor when engaged. you may have an issue here.

Personally, I had a 50A alternator that delivered 14volts when I rev the engine, I replaced it with an 80A one due to some added accessories... but to my surprise, the voltage now is always around 13.5 and gets low to 12.7 if everything is on. i couldn't figure out why this is happening. took the alternator to a shop and they tested it perfect. replaced many regulators without any significant change. tried a thicker cable from alt to battery and it barely increased the voltage. but well it never caused any issue for me and batteries are lasting for a long time 4 years+. so I just forgot about it.

My car is a manual and today because of curiosity I shut the engine off when running downhill car in 3rd gear (without clutching in order to keep the alternator excited) with my voltmeter inside and hooked to the battery. I had a 14.9Volts. even if I run everything. the only explanation I could think of is that the ignition system is drawing a huge amount of current and I can't figure out why. maybe @Floobydust could have an explanation for this also.
First, the shut off and coast test is not valid. The alternator VR gets its voltage reference via the alternator light and the hot in run/start circuit. I'll bet the alternator light glowed somewhat when you did it. With no reference voltage, the VR went to max output, 14.9 volts - nothing to do with ignition load or lack thereof.

As for the low voltage output with the 80A alternator, is this a "reman" unit? With alternators, rebuiliders are barbarians. They don't rebuild them one at a time, but rather, in batches. You might get an 80A stator winding coupled with a 50 amp rotor winding or the other way around. And are the diode packs the correct units? I believe MB uses high current zener diodes to prevent alternator dump. What did the rebuilder use? And are all diodes functioning? An open three phase diode will definitely cause low output. A used alternator can be vulnerable to this. .
 
  • Like
Reactions: Real1shepherd
1 - 20 of 28 Posts
Top