W124 E300d OM606 fault find question.

[Charles Morgan]

After replacing the glow plugs on my OM606, recently on start up the following has been happening - ABS warning light on, Rev counter stuck on 0, and idle too weak to move the car when in gear. This is intermittent but becoming permanent. It either all happens together or no faults at all.

Just checked the fuse on the OVP relay which was fine (but will be replaced anyway).

Any other suggestions to check?

 

[roadhog]

Maybe the OVP relay itself? A functioning fuse does not necessarily mean the relay is ok.
Have you checked your alternator output? I've had two fail in my time, both times the first symptom was the ABS warning lamp. The rev counter is a voltmeter I believe, maybe your battery is sucking up what little charge there is available from an ailing alternator?

 

[Charles Morgan]

The battery is not in the best of shape but was fully recharged before I fired her up. I'll check the OVP relay.

Another suggestion made elsewhere was the loom might be in poor shape, which is certainly the case with the glow plug relay loom.

 

[grober]

Another vote for the OVP ABS light is a classic fault indication OVP supplies abs controller, engine ecu and motorised rotary fast idle valve [ on petrols at least] the soldered joints crack with vibration
Numerous guides how to resolder them online.
here's one.-- other guides may be available.
[YOUTUBE]/zPSSXSVMiJk[/YOUTUBE]

 

[Charles Morgan]

My old skills have returned. Removed the OVP relay, cleaned all the connectors, removed the metal shell, re-tinned the connections as per the vid and lo, the car now won't start and the ABS light remains on...

My initial thought is the loom is the likeliest problem. Getting the OVP relay in and out of the connector required a fair bit of tugging.

Starting to think the car needs to be disposed as it has far too much to do to get it running, even before all the work on the body required.

 

[grober]

SOME BASIC VOLTMETER TESTS
OVP - basic function and test - Mercedes-Benz Forum

 

[Charles Morgan]

Thanks Graeme, I'll have a check to see if it is the OVP relay at fault.

 

[brucemillar]

Thanks Graeme, I'll have a check to see if it is the OVP relay at fault.

let me know if you wish to test with my OVP. My car is laid up for winter.

 

[grober]

http://www.w124-zone.com/downloads/MB CD/W124/w124CD2/Program/Chassis/54-0242.pdf
SOME CIRCUITS

 

[Charles Morgan]

Tested just now. The relay is clicking away intermittently but testing the pins as per the link above, the highest voltage I got was 2.4 on one. So the OVP (or my testing) looks faulty.

 

[grober]

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1993/300D/SYSTEM WIRING DIAGRAMS/4455.pdf

time to try a substitute relay?

 

[Charles Morgan]

That will be the next thing.

 

[Charles Morgan]

Very kindly indeed, Neilrr just popped over with 4 OVP working relays so I can test away with enough to be certain whether it's the OVP or the car. The forum at its finest!

 

[Charles Morgan]

Success! First OVP relay in and it fires up, idles properly, rev counter works and ABS light gone. Many thanks Neil!

So now to get all the manifolds back on after changing the glow plugs and get the car back on the road.

 

[grober]

Result! Might be worth getting your alternator output checked at some point as a precaution?

 

[Charles Morgan]

Is that something an electrocution prone idiot with a cheap Chinese multimeter can do or should I get someone else to do it?

 

[brucemillar]

Charles

Easily done (even by my accident prone standards). You should be seeing (Volts DC) 14.x across the battery at 2.5k rpm. This would then drops to 12.x at idle and further drop to 8.x when cranking.

On my 300te the brushes failed (they were 30 years old). This was evident by fluctuating voltage seen in the headlights (bright to dim) and on a volt meter across the battery. New brushes are available from ebay for about a tenner. Have a look at your alternator and see if the brush pack unscrews from the rear. On mine it was two phillips screws, visible from above the car and reachable with a stubby driver.

If in doubt it is worth a try, as when they go, they are dead and they will always fail in heavy traffic, at a major junction, with a fire engine on blue lights, trying to get around you, in the pouring rain.

 

[grober]

My concern would be for some form of AC or voltage spike breakthro damaging the zener diode/s in the relay. However your OVP may have just died thro old age. These basic voltmeter tests should reveal if anything is wrong.
[YOUTUBE]LGB6ZEjGm7Q[/YOUTUBE]

 

[Charles Morgan]

Can't get it up to 2.5k on my own, but at 1.5k it is putting out 14.3, and at idle 13.5v (the battery has been fully recharged though last night). No fluctuation on the voltmeter.

 

[grober]

If these basic tests check out you probably have nothing to worry about.
You would need a clamp meter to measure the current output.
http://www.aa1car.com/library/charging_checks.htm