1993 220TE intermittant starting problem

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1993 220TE
Greetings all,

For the last couple of weeks I have had an intermittent starting problem which is becoming more frequent.

The engine will turn over but will not start or attempt to fire.

Normally, after turning the ignition on and prior to starting, there is a short whirring sound from the rear of the car (fuel pump?) and a couple of noises from the engine compartment. Then all is quiet, turn the key and the engine will start.

At the times when it will not start, these normal noises do not occur which is a major clue.

Looking at the Haynes manual, there is a fuel pump relay which operates a cold start valve. The relay perhaps is activated by the KE control unit, wherever that is. So I'm suspecting a bad contact on the supply to the relay coil.

Not knowing where these normal noises emanate from after turning the ignition on, I do not want to prod around in the dark so to speak as indiscriminate prodding is not good for intermittent fault finding.

I would be very grateful if anyone can tell me what these normal noises are and what components are involved. Also where these components are situated and what actuates them (or is not actuating them when the problem occurs).

Any advise would be well received.

Best regards
 

robparker

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The Haynes manual is confusing elements from the older engine here. You have a fuel pump relay which is behind the cover behind the battery and is a small green relay with a fuse on top, that will probably be the problem, or a bad connection to it. You don't have a cold start system as such or a KE control unit.
 

kth286

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Your Mercedes
E320 Coupe 95
and it could be the overvoltage protection relay which is also there.

It is bigger/higher and may have a cover on top with a fuse built in.

It is a critical component (which everything else is dependent on) and the solder joints do go bad on the earlier versions.

Try and get a specialist Merc Indie to loan you one to try (for a charge), unless you know
of someone.
 
OP
C

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I did not see a small, green relay with a fuse on top, but there is a tall, metal cased relay with a 15 amp fuse under a clear, plastic cover which is probably the same thing.

I took that out and cleaned the contacts as there was slight corrosion. With the ignition on and the plug just touching the contacts, I found the relay does work and actuates the other components.

So, touch wood, I think it's fixed.

Many thanks Rob for such a quick reply and also to kth286 for the warning about the over voltage protection relay.

I'll give it a few days and then hopefully post if it's still good.

Best regards.
 

kth286

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Your Mercedes
E320 Coupe 95
you found the OVP relay - good.
 
OP
C

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Same problem this morning so I'm not there yet.

This time the tachometer needle was moving erratically. I must be in the right area.

The relay I took out (with the 15 amp fuse on top) was next to the two control units behind the battery and fixed to the bulkhead. I think this is the OVP relay comparing it with the item in the Haynes manual which shows seven contacts and what looks like the fuse on the 2.5mm. wire.

This was working yesterday and the contacts are clean, so it maybe it is the soldered joints inside as you suggest.

I think I will bite the bullet and order a new OVP relay.

My nearest Indie is the marvelous Andy Overs in Warwick but he's a day's trip away.

Rob, can you supply a new OVP relay?
 
OP
C

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Looking at Haynes a little more, the coil in the OVP relay is powered from the fuel pump relay so it could still be the fuel pump relay that which is causing the problem.

Rob, I have not found the small green fuel pump relay as you describe, could you give me more info on it's position.

Thanks in advance.
 

robparker

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The fuel pump relay will be in the area you are looking somewhere, there are a whole bunch of ecu's and relays there, I think it will be on the side furthest from the wing, but it should be there in that area.
 
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Found the fault. One of the tubular contacts in the OVP relay plug base had opened out (they have a split). Closed it up for a tighter fit with a small screwdriver.

Thanks to all.

Regards.
 

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