M102 intermittent cut out problem

[horatio]

The engine can cut-out (usually at a junction), when switched off and back on again is fine! Last time it did there was a fairly loud humming noise from the fuel pump. This might just be because it was re-priming after the cut out though?

This is very intermittent, most drives it does not happen (which makes diagnosis a PITA). I have already changed OVP, fuel pump relay, ignition leads/cap/etc. Vacuum pipes are all in good order.

Any thoughts very welcome. I am absolutely lost and don't have much faith in a garage diagnosing it because its so intermittent

Thanks

 

[martyz]

If you can hear the fuel pump running louder than when it's priming there is no fuel in the pump,sounds like you have a fuel restriction pre pump.

 

[horatio]

Useful info thanks

Come to think of it, there has been an occasional slight petrol whiff inside the car. Could well be related

 

[horatio]

Booked it in with aj Robertson. Really want the end of this saga...

 

[stwat]

Faulty OVP relay is a regular problem on these older mercs. I have had a few faulty ones. Once replaced or re-soldered, the cars run beautifully again.

 

[mazza]

Hi

as suggested by stwat's post, check the ovp relay

attached to your throttle linkage, you have a microswith, this microswitch sends 2 signals to the ecu (fuel shut off) (full throttle), sounds like your problem happens when you are approaching a junction with no throttle (engine going onto idle) if the microswith is faulty, it could cause the fuel shut off(without giving way to idle control valve)

hope this helps
mazza

 

[horatio]

Cheers, already changed the OVP!

How do I check the microswitch?

Thanks!

 

[mazza]

Cheers, already changed the OVP!

How do I check the microswitch?

Thanks!

give it a clean and make sure the lever arm is moving properly

you will hear a click as soon as you press the throttle, that click send current to the ecu (full throttle) and the other way round when no throttle is applied

mazza

 

[horatio]

Thanks, it looks ok to me!

Really appreciate the help, cheers.

 

[horatio]

Think its fixed - idle valve was clogged and has been soaked/cleaned. So far so good. I soaked it in meths myself when I changed the vacuum pipes - hence the problem went for 6 months. Pretty obvious, duh!!

Going to swap it for a new one because it will probably go bad again.

 

[horatio]

Spoke too soon! Its done it again a few times.

Really am at a loss now. I really, really don't want to but I might have to give up on the car because its dangerous.

Any more thoughts?

Thanks and happy Christmas!

 

[Druk]

My first Merc was a 230 M102. When exiting a roundabout it would invariably cut out which was eventually traced to an internal break in the large green wire from the dizzy to the control unit on the inner wing. The engine leaning away from the wing would pull the break apart.

Just a thought.

 

[horatio]

Cheers.

Well, I just took off the coil and found the lead connection is manky with and burnt looking. One bit is melted.

Suspicious!

 

[grober]

Try cleaning all the fuse contacts and ends in the main fuse box- they can oxidise giving rise to intermittent contact and weird electrical problems. Other possibility is dodgy ignition switch. Check the engine earthing strap under the car also. How old is the fuel filter? Run with the petrol cap on loose to check you are not getting a vacuum build up in the tank altho a smell of petrol would point to an ignition problem rather than one of fuel supply.

 

[horatio]

Thanks!

The fuel filter has not been changed in my ownership (about 6 or 7 years) and I'm pretty sure the pump is humming louder than it should be

The ignition switch was replaced with an aftermarket job a few years ago. The electrics etc stay on and the car chugs a few seconds before totally cutting out so not sure on that one.

Right so,

1. check/clean fuse and strap connections
2. New coil
3. New fuel filter

Possibly fuel pump and ignition switch.

That will keep me busy. Most would probably give up on the car but I really don't want to...

 

[horatio]

By the way, I'm pretty sure wet weather/humidity makes a cut out much more likely... does this change anything at all?

The inside of the ignition coil terminal has burnt/melted chunks, I'm not sure if this is a symptom or cause (or a red herring).