Torchy Torchy

[Joloke]

The Battery Boy

[Timewaster]

Give us some clues?

 

What car is it?

[HH-R]

Bad earth?

[HH-R]

Are the alternator voltage regulators part of the alternator itself on these? If not, it could be that that's going wrong - might be worth checking what voltage is getting pushed into the battery when it's acting up.

[vulgalour]

I did wonder if it was a Laguna, in which case you'd be screwed.  It's a Mercedes, so it's probably fixable.  This comment is of no practical use.

[Bren]

Faulty regulator causing spikes?

[Urko]

Another vote for bad earth - although dodgy fusebox/relay connections caused by corrosion/water ingress would be another place to look. Whilst there - if it has those big fuse link things, they have been known to be loose or break

[Junkman]

For the record, it's not the Peugeots that have electrical problems, it's the Mercedesesses.

 

Anyway.

What does your DVM say about all this?

How was the faulty* alternator diagnosed? And by whom?

[Danblez]

What is it putting out with the engine running, which will tell you the condition of the alternator?

[Asimo]

Alternators are often mounted on rubber bushes and require to be earthed themselves to the engine. So -  with engine running - measure voltage between alternator and engine and then between engine and battery earth terminal. Should be very close to zero, if not, bad earth.

[xtriple]

Could it be the battery or has that been replaced already?

 

Plus one on the separate earth for the alternator as that is dead easy to forget.

[castros_bro]

Ooooo that looks like it may be a good 6V motorcycle battery you've got there.

 

Carefully measure the volts between the big stud or spade terminal on the alternator and the alternator casing with the engine running,

 

 

If this is 14 ish volts then somewhere between the alternator and the battery is a bad connection to look for.   So you'll have to then do battery earth terminal to alternator casing with engine running etc to trace it through.

[hauserplenty]

^ This. Plus my two cents worth:

Check the OVP relay. It should have a red top with two fuses in it next to the battery. Buy an M-B one, not a Uro relay, as those are worthless. It is a consumable part and faults like these indicate it should be replaced first. It contains diodes and relays to protect various components from voltage spikes, hence the name: Overvoltage Protection Relay. The part cost me $100, since I spent $20 on an URO which I soon found out I needed to change...

Also there is a ground strap between the engine and the body, near the transmission mount. This is a known failure point. Remove and file clean/reinstall. Have them charge the battery, also. If it has been discharged, all this will be for naught. I usually bung a charger on the lead box before I start work, in cases like this. It is very important to have a full charge.

[hauserplenty]

Doesn't matter how good the fuses are. That is only the first step. The box contains relays and diodes. The solder joints fail and produce symptoms as you describe. I had to replace mine twice. Warning lamps, low voltage, and random stalling can all be caused by a faulty OVP relay.

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1572015-ovp-basic-function-test.html#/forumsite/20548/topics/1572015?page=1

 

It's also important to realize that this needs to be ruled out before you proceed. I've learned from buying a Benz, knowing nothing about it, and needing to get it running. I've called in specialists and am by no means an expert. But I do advise that there are several flow charts which must be followed and it sounds to me like all this alternator replacement is down to simply following the wrong one.

[richardmorris]

Ovp is about £60 from Mercedes. A good battery is needed for the charging circuit and a dead cell will confuse things. But the fact that it's still not charging correctly is odd and does point to the alternator or a bad connection.

[hauserplenty]

Correct. Might as well rule both of those out first. Since the OVP regulates the voltages, if they are incorrect, an alternator is not the first item but the second on the flow chart. It seems you have it under control now. OVP relays generally last ten to fifteen years, and are considered a maintenance item. If you do buy one and it turns out not to be the problem,it will still be money very well spent. That is, if you buy an OEM one. The approved Benz part is the only one to use. I found this out the hard way...

[matty879]

try the earth straps,body to battery,body to engine,they can,and do fail

[matty879]

Doesn't matter how good the fuses are. That is only the first step. The box contains relays and diodes. The solder joints fail and produce symptoms as you describe. I had to replace mine twice. Warning lamps, low voltage, and random stalling can all be caused by a faulty OVP relay.

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1572015-ovp-basic-function-test.html#/forumsite/20548/topics/1572015?page=1

 

It's also important to realize that this needs to be ruled out before you proceed. I've learned from buying a Benz, knowing nothing about it, and needing to get it running. I've called in specialists and am by no means an expert. But I do advise that there are several flow charts which must be followed and it sounds to me like all this alternator replacement is down to simply following the wrong one.

please forgive my ignorance,but what is an ovp? im always trying to learn ive been looking after an a209 clk for last 8 years and wondered if its worth me getting a star diag reader.cheers.

[hauserplenty]

http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1562149-ovp-relay-what-does-do-exactly.html#/forumsite/20548/topics/1562149?page=1

 

If your car has OBD-II, I.e. HFM, it does not have an OVP. But they are worth knowing about on cars equipped with the Bosch KE-Jet CIS systems.

 

HFM is an abbreviation taken from the German for what us Yanks call a mass air flow sensor. As for the Star diagnostics, I do believe there are aftermarket (ahem) versions of it available, not that I've ever seen* one, of course.

 

 

http://www.peachparts.com/shopforum/general-information/310495-mercedes-startek-have-done-right-thing-help-you-do-right-thing.html

 

 

Here's a link to my Benzworld thread, in which I have posted a picture of the old relay and the shit aftermarket one side by side:

 

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1926193-climate-control-blower-not-running.html#/forumsite/20548/topics/2451969?page=1

 

Benzworld.org is where I've learned most of what I needed to get my car running in the first place. I found it by googling my car by year, make and model. You never know what might turn up. If I find a thread or a site useful, I bookmark it and Bob's my uncle.

[matty879]

all I can say is bring back plugs points carbs and dizzys,im oldschool,and I probably have an inability to learn this tech,even though I own some of it,i feel sorry in a way,that our next generation of technicans are merely guided by a laptop or similar hand held device and instructions,what ever happened to good old diagnosis and hands on expereince?

[hauserplenty]

...They don't make 'em like that anymore... :'(

[Danblez]

Did they even to bother testing it after putting a new alternator on it and letting you drive home?

[castros_bro]

Ignore this if it's the sucking grandmother's eggs situation.

 

There are two connections for the electricity from the alternator to the battery, the -ve is through some short cables and the metal bodywork  whilst the +ve is through some cables and miscellaneous components.  You have done the basic in measuring 14v at the alternator. 

 

Next you just* need to check with one DVM the voltage (with engine running) between the        alternator +ve out put (big terminal)           and the battery -ve terminal (not the battery clamp but the battery terminal it is attached to) , if this is the same as the alternator output ~ 14 v then  -ve / earth side of the alternator/battery connection is good.

 

If the -ve side is good you then have to systematically follow the +ve path either from the alternator end  or battery end  using a DVM till you find two adjacent points of a connector or component where one is 14v from the alternator and the other is the battery voltage

 

If you suspect the OVP then one side will have alternator 14 volts and the other side will be battery +ve voltage.

 

on a If you have TWO faults the you are royally buggered

[castros_bro]

Thanks for the advice

 

So + of the DVM to Big output lug on alternator and - of the DVM to - battery post?

 

Just don't understand what you mean in the next bit?

 

i know basics but sometimes (lots of the time) need things in laymans terms.

 

 

Yes, If you have 14v from your alternator then do this and also get 14v tween battery -ve and alternator this checks that the alternator case/earth/chassis/battery-ve connection is good. 

 

The next bit is to follow the 14v +ve from the alternator big lug along the big lug cable to next point which is the other end of the same big lug cable, check there is  14v between this cable end and the battery-ve which shows this cable and its connections are good.  You continue along the path of cables/connectors/components which are between the alternator big lug and the battery +ve terminal. When you reach a  connection which does not read 14v that is where the problem is, if it's something like a fuse where one side is 14v but the other is not then bad connection or blown fuse.

 

 

If there is something crimped on the end of a cable then read the voltage from the the crimped part rather then the wire inner in case the crimp connection is bad. Access to some bits will be difficult so there are ways to cheat like using a sharp pin to push through the cable insulation connected to the DVM to check the cable voltage. Bon chance.

[twosmoke300]

What he said ^

Had a transit in a few months ago that wasn't charging since the customer fitted a starter . He had put the wire from the alternator onto the output terminal of the starter solenoid ! So basically it only charged while it was cranking 😄

[hauserplenty]

Exactly. The links to Benzworld will explain the OVP in greater detail than I could at present, but I will say that castrosbro's advice is spot on regarding a broken connection. Using the flow chart approach, first rule out the OVP by replacing it, but if the battery still is not charging:

 

1. Remove (-) cable with a 13mm wrench.

 

2. Attach one meter probe, ideally with an alligator clip, to the (+) terminal. Set to the ohms scale/beep tone setting.

 

3. Follow the (+) cable to its attachment point, which should be a terminal block in front of the battery.

 

4. If the meter beeps, or shows 0 ohms, attach one meter lead to the (+) terminal on the alternator, and the other to the terminal block. If the meter beeps, touch the probe to the (+) battery cable. If it beeps again, there is a complete circuit. But there may be too much resistance due to corrosion, which a static test won't always show.

 

5. Remove the battery, then remove, file and clean the terminals one post at a time. If it only beeps once, you have an open between those two points. Start by cleaning all the terminals with a file, in fact, I suspect your alternator (+) terminal is corroded and these tests should help you narrow it down. I would be remiss if I did not mention that this is a different method than castrosbro suggested, but that you are testing the same parts of the circuit as above. His test is a dynamic test; mine is a static test. The advantage to static testing is that it is much less risky. A short circuit can make your simple problem much less so. Horses for courses and all that. But he did say it first and I agree with him anyway.

 

Since the $100 OVP is used to prevent voltage spikes from destroying the $3500 ECU, and the $500 MAS unit beside it (integrated fuel pump controller/relay), it is designed to fail before those components do. My Benz specialist friend told me, in fact, that he's seen some of the best mechanics frustrated by jobs which would be straightforward on other cars. So your garage chaps shouldn't feel too bad about this one.

 

He also said, "It's usually something simple."

 

Das beste oder nicht...

[twosmoke300]

I find mercs the most frustrating of all cars to work / diagnose things on .

[Lacquer Peel]

I find mercs the most frustrating of all cars to work / diagnose things on .

 

 

You're not the only one, odd-voiced YouTuber Scotty Kilmer agrees.

[hauserplenty]

Mr. Kent Bergsma, on the other hand, is here to help you fix that Mercedes-Benz you bought:

 

https://m.youtube.com/watch?list=PLaxhnEQGGF3yaUEu3vv4_2IlyrcCX8Fs_&v=pBrjzYUYyNg

 

https://mercedessource.com/problems/electrical/troubleshooting-an-electrical-problem

 

https://m.youtube.com/playlist?list=PLaxhnEQGGF3yaUEu3vv4_2IlyrcCX8Fs_

[hauserplenty]

Just clean the connections at the junction box, as decribed above. Then remove the 3-pin and clean/retension the pins. A small screwdriver will usually work. Of course with the battery (-) cable disconnected! If the continuity is good, you may have a plug which is not seating and not making contact.

Have a nice vacation, anyway. It's down to a single circuit path so I'm sure you can fix it.

Bad wiring is much less likely than a loose connection.