Started cutting out - Can anyone help???

[DougE280]

My 1995 E280 (W124 24 valve) has started cutting out when warm. It's usually when travelling at 50 mph or so. The car loses all power and starts to slow - but whilst slowing, the tachometer starts "jumping about" between 2000 and 5000 rpm but the engine isn't revving up at all.

If I try to start the engine straight away, it won't start but the tachometer "jumps about" as before.

If I leave it for maybe ten minutes, it starts immediately and runs fine. No other symptoms - it runs really well all the rest of the time.

Tonight, it decided to stop on the M25, so it needs sorting out sharpish!

I'm assuming it's as electrical fault......can anyone tell me what mysterious "black box" may be at fault!

Thanks, Doug

 

[talbir]

Sounds like a faulty Crank Position Sensor - when this is faulty, it usually plays up as car reaches operating temp, as heat increases, sensor resistance increases to above the max of 600ohms.

The Crank Position Sensor is a feed to the ignition ECU and if the CPS is faulty, engine will give loss of power and with it loss off/erratic tacho signal.

I recommend getting the crank position sensor checked and then the ignition ECU. It's usually the thick green/black single cable lead on the ECU and runs to the bell housing where it's held on bya 5mm allen bolt.


talbir

 

[Andy]

Hi Doug

From the symptons you are experiencing. I would replace the overload protection relay. The relay supplies the main electrical feeds to the engine ECU. We have problems with a dry soldered joint which plays up when hot.

Try this first & NOT and tdc sensor.

Regards

Andy @ www.mercedesservicing.com

 

[mjtray]

Doug

I also have a 280 (1993) and exactly the same thing was happening on mine.

I replaced the Over Voltage Protection relay...will cost @ £45 from your friendly Merc dealer.

Once replaced I have never had the problems again.

Apparently the original OVP relays that were fitted were sub standard and the replacement relays now come with a different part number from the original as it has had a slight re-design.

It's located behind the battery....you have to remove the battery, then remove the plastic shield infront of the ECU and the relay sits to the right of the ECU. It has a black plastic cover over the top of it and is about 4 inches high. Held in with 2x 10mm bolts.

Best money you will spend........replace it pronto and your worries will fade away.

Good luck

 

[DougE280]

Thanks for the advice chaps,

I trawled the Mercedes forums last week and came to the same conclusion! I bought an overload protection relay from Europarts in Wembley for £30 plus vat and swapped it Friday evening - an easy (and clean) job! Since then...........well perhaps better not tempt fate!

This seems such a minor job compared to replacing the crank sensor that it was certainly worth a try.

Thanks again,

Doug