• The Forums are now open to new registrations, adverts are also being de-tuned.

Immobiliser?! 1992 W124 300TD Estate

Nothing wet or even damp in the wiper relay box area. Vacuum pump (under rear seat) totally dry and looked fine. What is your theory on the vacuum pump? The doors all lock fine from the driver's side and the rear boot/trunk gate, but not the passenger door.
As i have been checking on the site for the alarm it did say that some electrical items for the alarm are in the passengers door lock. Its all in the 124 site i left you.
 
Thanks everyone for keeping up with this thread. Here is an update from today that might be a breakthrough:

So I just checked the fuses. The number 9 read 5-6 volts. That fuse controls:

diagnostic term.6, hazard warning system, clock, front roof light (electronic radio, vanity mirror light, relay comfort circuitry term.86)

Then I checked 'C', right next to it. It read 11 volts. I'm assuming this should not be reading this high. It controls:

rear roof light, trunk light, rear door locking system, safety belt handover alarm, rear back arrester (central locking system, door lights, reading lamps, aut. antenna.)

So have I found the drain? Or should 'C' be reading 11 volts?

Now that I'm reading through the w124performance manual, 'C' is on Circuit 30 which is apparently always 'hot', as is number 9. But should it be 11 volts 'hot', or some lesser amount?
 
Last edited:
As has been mentioned, the earths all need to be checked.

Dec

[YOUTUBE HD]wcbMuGE3rL4[/YOUTUBE HD]
 
Moonshine Scotty is good too.

Dec

[YOUTUBE HD]BcGT1bNrsAM[/YOUTUBE HD]
 
If the battery is 12 V at rest then all the fuses should be 12 V as well. You have corroded fuses and/or bad earths and/or other electrical problems

The starter circuit is pretty simple: the key pulls in the solenoid which powers up the starter. If the starter is turning over slowly you have either a low voltage at the starter or a mechanical problem with the starter

As I said some time ago, wipers running, lights flashing & etc are typical signs of low voltage when starting a W124

There are very few parts to test to find the problem. It doesn't lie in the fusebox, in the central locking pump or in the N10 relay, it lies somewhere in the starter circuit or battery

If there's a current drain somewhere that's flattening the battery, or it has a bad cell, or both, you won't be able to diagnose the problem properly. So I'd start by testing the battery

Nick Froome
 
If the battery is 12 V at rest then all the fuses should be 12 V as well. You have corroded fuses and/or bad earths and/or other electrical problems

The starter circuit is pretty simple: the key pulls in the solenoid which powers up the starter. If the starter is turning over slowly you have either a low voltage at the starter or a mechanical problem with the starter

As I said some time ago, wipers running, lights flashing & etc are typical signs of low voltage when starting a W124

There are very few parts to test to find the problem. It doesn't lie in the fusebox, in the central locking pump or in the N10 relay, it lies somewhere in the starter circuit or battery

If there's a current drain somewhere that's flattening the battery, or it has a bad cell, or both, you won't be able to diagnose the problem properly. So I'd start by testing the battery

Nick Froome
Sorry I've made it sound like I don't know much about the starting/charging system. I'm familiar with how it works, which is why this problem has left me dumbfounded. I used the multimeter to test whether there was voltage going in to the fuses by removing them and touching one lead of the meter to each side. But it appears both of the circuits that showed power going to them were supposed to have power going to them when the car is off. Number 9 for clock, etc. had 5 volts, and the other one labeled 'C' read 11 volts.

The alternator seems to be putting out enough power, but my multimeter doesn't read anything but whole numbers, so if it needs to be more accurate I'll have to get another one.

I'll get the battery tested/charged today and start again from there.
 
Post 30 minute EDIT:

Sorry I've made it sound like I don't know much about the starting/charging system. I'm familiar with how it works, which is why this problem has left me dumbfounded. I used the multimeter to test whether there was voltage going in to the fuses by removing them and touching one lead of the meter to each side of the area that holds the fuse (can't think of what that area should be called).

It appears both of the circuits that showed power going to them were supposed to have power going to them when the car is off. Number 9 for clock, etc. had 5 volts, and the other one labelled 'C' read 11 volts and is always hot.

The alternator seems to be doing its job as measured from + terminal on battery to alternator was 13v, as was + to - terminal on battery.

As previously stated, I installed a new voltage regulator. The old one was knackered, worn unevenly on one of the leads/magnets. But that hasn't seemed to fix the issue.

My multimeter is a bit old and doesn't read anything but whole numbers, so if it needs to be more accurate I'll have to get another one.

I'll get the battery tested/charged today and start again from there.
 
The battery should float at about 12.6 Volts when fully charged. The voltage at the battery should rise to 13-14 Volts when the engine is running & the alternator is charging. The voltage across the alternator and across the battery will be the same as they are connected together

A common battery failure is for one cell (of six) to fail & go high resistance. This won't pull the battery voltage down a huge amount at rest but it will limit the current delivery capacity of the battery quite dramatically

The internal resistance of a car battery is incredibly low which means it is capable of delivering hundreds of amps to the starter motor. If the resistance of the battery rises, due a bad cell or a poor connection, the voltage drop across that resistance may prevent the battery delivering enough current to turn the starter

Those diesel engines need a battery that will turn the engine over long enough & fast enough for it to start. The fuel pump is mechanical so the engine has to turn for fuel pressure to be generated. In my experience with the early diesels, a battery that won't spin the engine fast enough won't start it

Nick Froome
 
The battery should float at about 12.6 Volts when fully charged. The voltage at the battery should rise to 13-14 Volts when the engine is running & the alternator is charging. The voltage across the alternator and across the battery will be the same as they are connected together

A common battery failure is for one cell (of six) to fail & go high resistance. This won't pull the battery voltage down a huge amount at rest but it will limit the current delivery capacity of the battery quite dramatically

The internal resistance of a car battery is incredibly low which means it is capable of delivering hundreds of amps to the starter motor. If the resistance of the battery rises, due a bad cell or a poor connection, the voltage drop across that resistance may prevent the battery delivering enough current to turn the starter

Those diesel engines need a battery that will turn the engine over long enough & fast enough for it to start. The fuel pump is mechanical so the engine has to turn for fuel pressure to be generated. In my experience with the early diesels, a battery that won't spin the engine fast enough won't start it

Nick Froome
Exactly.

I took the battery back to where I bought it. They tested it while the car was running, then shut it on/off through several cycles. With no warning, it just lacked the ability to turn the engine over. They gave me a new battery and Oh how I hope that it was just the battery and all will be well. I'm not holding my breath, though.

Thanks for all the assistance. JD
 

Users who are viewing this thread

Back
Top Bottom