Torchy Torchy

[Dave_Q]

Can't tell you what bulb you need but yes, on most cars the alternator gets a signal to charge via the bulb.

[hauserplenty]

Funny, I was thinking about that a few days ago-- if the light was still on, why did the garage give you the car back? They would have seen something was still wrong...

 

UNLESS...

 

I suggest you substitute either the high beam or the bulb warning lamp (chuckle) to see.

 

Service manual (sorry I don't know your specific year)

http://www.w124performance.com/service/Index/104index.html

 

Cleaning those corroded contacts you found is still a good idea. Once you have the instructions for instrument cluster removal, you can proceed. IIRC one must remove the speedometer cable from behind the floor mats, then use a special tool to remove the cluster.

You may have enough room to possibly swap out a bulb or two without resorting to removal of the whole cluster. To do this simply remove the plastic cover, don some safety glasses, and have a look. The sockets are a half-twist and the bulbs could be 194's but I'm not certain. You could also remove one, take it to the parts store, and buy a whole box or so...then pull the cluster later and replace 'em all!

I need a new cluster for mine; the odometer ist kaput.

 

P.s. Although the ignition switch is good to have spare, if not can you take it back? I've heard of them breaking down gradually but yours is probably still OK.

[castros_bro]

*********yellow card*************

 

Alternator giving out 14v ?

 

This light bulb is part of the alternator field circuit ?

 

Shirley if the field coil is not getting excited caused by your bulb an open circuit then the alternator won't give out 14v ?

 

(I am ignoring your no load self exciting scenario)

[hauserplenty]

The speedo cable has to be removed from the transmission, sorry I didn't remember exactly(choose 54-6015)

http://www.w124performance.com/service/Index/Groups/54ChassisElectrical.htm

 

It may be helpful to use a mirror to locate the bulb holders, then see if you can unscrew one or more either by hand or with a small pair of needle-nose pliers. I believe the speedo cable is on the, uh...left hand side. I need to do this same job but haven't had time.

[D Spares & Tyres]

Sounds like you haven't been paying your electricity bill and you have been cut off ☺

[hauserplenty]

"I am serious...

 

If you turn the key to ON, they should all remain lit. When starting, the SRS lamp should remain on for 4-6 seconds.

 

...and stop calling me Shirley." [/Leslie Neilson voice]

[hauserplenty]

The OVP relay connector can be removed, and the contacts retensioned one at a time. Gently squeeze each contact with needle-nose pliers, then reinstallation is &c...Another tip from a Merc specialist I know. The new part may also be defective, which I suppose is not impossible.

Glad you got it fixed!

 

As for the emissions, have them test the oxygen sensor. Also the EGR pipes can get clogged with carbon overtime. A fuel injection service to dissolve the carbon in the cylinders might also be in order.

 

P.s.:

https://mercedessource.com/problems/search

[hauserplenty]

Bad solder joints in the old OVP. Have them retension the contacts and install the new one...nothing to lose!

[richardmorris]

The OVP relay connector can be removed, and the contacts retensioned one at a time. Gently squeeze each contact with needle-nose pliers, then reinstallation is &c...Another tip from a Merc specialist I know. The new part may also be defective, which I suppose is not impossible.

Glad you got it fixed!

As for the emissions, have them test the oxygen sensor. Also the EGR pipes can get clogged with carbon overtime. A fuel injection service to dissolve the carbon in the cylinders might also be in order.

P.s.:

https://mercedessource.com/problems/search

 

 

1989 year won't have a cat or oxygen sensor over in the uk.

[hauserplenty]

RÃœF.

 

Ah, it's an '89.

 

In that case, cleaning as much carbon out as possible might be the way forward. When I changed my head gasket it took me two days to scrape all the carbon off the valves, pistons and combustion chambers with a razor blade. That and cleaning the EGR tube, which was now much more accessible with the head removed.

A fuel injection cleaner which is fed through the vacuum system is preferable as it will clean more thoroughly than simple fuel additives.

[hauserplenty]

The knocking sound could be the climate control. Maybe the blend air door? See if changing the temperature from 90 for a few minutes then back to 60 has any effect.

As for the loud buzz, more information about how it sounds and when it occurs please. Is it constant, or just on startup? Sometimes fuel pumps can make a buzzing or whining sound. A gentle whirring sound is normal; as is a slightly louder whining sound after a long freeway trip. A buzzing sound means the pump is failing.

 

Go on, ask me how I know...

[hauserplenty]

It does sound like a vacuum pump of some kind. You may have caused a leak which is making the headlamp leveling pump run constantly. Find the fuse, and pull it. If the sound stops, you can reinstall it, then use a spray bottle with soapy water in it to check for leaks (similar to checking LP systems.)

 

I can't think of much about the clicking sound, sorry. But it does sound like it may not be too much to worry about. If you don't have an automatic climate control, that seems to rule it out.

 

You may be able to find links to the UK version on www.benzworld.org or through someone on there. It's a great resource, of which I've made quite a bit of use. A service manual for your car, not the USA one is more likely to be helpful. I'll see if I can find a link to one and post it later.

[hauserplenty]

3in1 will work. It's great for the door latches and hinges as well!

Wd40, PB Blaster or similar. Then find the correct location and de-bodge it. Might as well, right?

A length of vacuum line and a few bits of vacuum hose can be used to extend the vacuum line if needed.

Reinstallation is...&c.

[Guest Hooli]

I'd guess it hisses all the time, probably a return feed or something.

[richardmorris]

Remind me what the problem is at the moment-all dash warnings lit all the time ?

[Pete-M]

Mercedes OVP relays blow goats.

 

I've been trying to fix the OVP on an R107 for the last couple of years. Main symptom is the heater suddenly goes to full speed and won't switch off. Secondary symptom is the car flattens its battery after a week parked when the OVP is kicking off. When the OVP is behaving the car will start first go after a month.

 

Ain't cheap, are they....

[richardmorris]

Does sound like a bad connection ( or two). I suspect that they're sensitive to voltage changes - they're not really a relay, more a complex circuit.

 

I hate cars too sometimes.

[hauserplenty]

Is that a genuine M-B relay? If it is, they could both be faulty. If the new one says URO on the side, bin it and fit one from the dealer. Expensive but there is no substitute.

[hauserplenty]

You'll need a wiring diagram then. I would check all the wires one at a time with a meter set to the Ohms scale. Look for a break in one of the wires from end to end. You may also wish to find a known good relay, substitute it and see if there is any improvement. If so, then you have two defective relays. They call it a relay, which it is, but it also incorporates a Zener diode, which has a given breakdown voltage which cannot be checked with a meter. If you can find someone with an oscilloscope, maybe checking the charging voltage waveform would be in order. Or there could be a fault in the wiring to/from the alternator which is yet undiscovered...

[hauserplenty]

That's what the wiring diagram will show you: the entire circuit. When those relays fail, sometimes they're intermittent, which on mine meant if you tapped on it, the engine would stall.

 

Before you start soldering, you need to rule something out. Substituting a known good OVP is one way. Making sure your alternator is not intermittently failing (dirty contact, failing diode, loose/corroded wire elsewhere in the circuit etc.) is another. Without the correct diagram for your car, you will only be barking up the wrong tree. But unless you know for sure, do not proceed on an assumption, lest you make the problem worse...

 

Have you checked all the fuses? The fuse box on these cars is a known weak point. If the fuses are aluminum, they are original and should be replaced with copper ones. The reaction of dissimilar metals comes into play here.

They can appear good but actually be so weak as to fail intermittently. This could mislead you into thinking that moving the wiring harness on the OVP is what caused it to work, when the two events may be unrelated.

 

On my 1990 300TE, I had to:

 

1. File all of the contacts

2. Remove the 4 screws securing the fuse box, then tighten all the Phillips screws to secure the wiring underneath. I was quite surprised how many of them were loose.

3. Be a cheapskate and NOT replace all the fuses.

4. Hope for the best, plan for the worst.

5. Get frustrated.

6. Pay a specialist.

7. Repeat steps 4-7.

8. Sell the damn car.

 

As for the zener, it may not be a pass/fail situation. You could be dealing with a diode which is breaking down at a certain temperature, or a certain voltage level, but well before it should. If one of your alternator diodes is failing, it could be causing the zener to overheat, which it's designed to do. The diode may not have failed completely yet, so at a certain voltage/current level it opens...until the situation rectifies itself...

...I'll get me coat.

[hairymel]

 

When anything goes wrong you then hear things you never heard before 

 

Ive noticed now the car hisses from near the rear wheel arch

 

I know there is a buzzing and hiss when you turn the key as the fuel pump pressurizes but though it stopped once fuel was flowing? or does it hiss the whole time and I have never noticed it before?

 

By the way just wondered is it just estates that have two fuel pumps? will mine have an in tank one too or just the one grouped with the filter and accumulator?

 

 

 

dunno if its the same but my c class has a vacuum pump in the rear d/s wheelarch for central locking etc, and it wirrs for quite a while after unlocking the doors due to a audibly leaky pipe in the drivers door. 

 

trying to track down a battery draining fairy in mine at the moment as well lol

[hauserplenty]

Battery drain: check the voltage regulator first. It's attached to the alternator with two screws.

 

Definitely clean up and replace all those fuses...I don't know from memory but the only fuses for the OVP relay are on the relay itself. However a good electrical baseline must be established first, and this is the best way to do so. There could be a high enough current draw elsewhere, on one of those corroded fuse circuits, which took out the new OVP relay soon after you installed it.

[hauserplenty]

The condition of the fuse box directly affects total current draw, which I believe passes through the OVP relay. It will be well worth it to tighten the screws on the underside of the fuse box as well, as this is a known fault and rules out another potential trouble. 124's seem to require quite a bit of perseverance, which is alright for a Sunday driver, but can be a bit much for commuting to work.

 

The relays may be working, but see above re: zener diode breakdown voltage. It's possible they might be defective, though not likely, unless a high current draw due to the condition of the fuses is causing them to overheat.

 

@hairymel: Try checking the voltage regulator on your car; often battery drains are caused by a worn or defective brush.

[hairymel]

Investigation was halted by a failed fuse in my multimeter, so i fitted a battery cutoff switch instead! Plenty to check when i get a stock of replacement fuses

 

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