W124 Diagnostic Testing BEDS SG18 area

[Clark300CE]

Does anybody know somebody who can do mobile diagnostic testing on a 91H W124. Car is based in Biggleswade and I've only just got it running. Now time to tackle the long "To do" list. Electric gremlins are in abundance.

 

[grober]

DIAGNOSTICS are limited on cars of this vintage. This may help
http://www.diakom.ru/CARS2/pribor/cs1000/manual/cs1000_mb.pdf
you can build your own blink code reader [ easy and cheap] or buy a ready made one
Mercedes Diagnostic Code Reader Tool W124 Obd1 300e 320e 400e 190e and others | eBay
how you use it

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First thing to check are the basics Clean up all the fuse holder clips /fuses -they corrode-- check all body earths [ brown wires] for corrosion including the often missed engine earth strap. Next port of call would be vital relays like the OVP [ overvoltage protection relay] and FPR [ fuel pump relay] and their socket connections.

 

[Clark300CE]

Thanks. One has been ordered from Ebay for about 20 quid. It will be interesting to see what codes if any are present. I did reread that as a precaution that the OVP relay is best replaced in most cars? Is that necessary?

 

[grober]

The OVP [ over voltage protection relay] supplies the ABS unit, the engine ECU and the motorised rotary idle valve. If its faulty it can give rise to some very odd faults. There's more than one type so its important to get the right one. Usually the small circuit board inside develops dry joints or cracks where various components are soldered to it. Its often enough to simply remelt the soldered connections to effect a repair. In the absense of faults its not necessary to replace it but if you have lots of electrical gremlins then its not a bad idea. There are one or two fuses on the top which should always be checked for continuity or corrosion on their holder connections. Of more importance is the EZL ignition unit if the car has one. These are bolted to the inner wing with a heat sink compound to help unit cooling. If this dries out the unit will eventually overheat leading to intermittant and then complete ignition failure. They contain an internal ignition advance map designed for the specific car so are not readily exchangeable from car to car. They are a sealed unit so almost impossible to repair. Due to their rarity they are very expensive to replace now when they fail so renewing the heat sink compound is a wise precaution.