W124 300TD ABS light on won't tickover, revcounter stopped working

rattlecrank

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Just started up the old dear to investigate my as yet untraced rattle. The important thing to note here was that I was not touching anything when the engine stopped running. On attempting to re-start, nothing happened until I depressed the accelerator to take it past idle speed. It then fired up and ran normally when over 1000rpm. Foot off the accelerator and stopped. ABS light was on and rev counter had stopped working.
Is there some mysterious relay at work here? Strangely, even with the electric idle control removed off the back of the injector pump the symptoms were the same.

As for the rattle, no it's not the tappets, not the timing chain or tensioner, not big or little ends, not the vacuum pump bearing, but it does sound rotational and definitely coming from the engine - could it be the oil pump chain drive? Even using the stethoscope to listen it's difficult to pin down.

All help appreciated.
 

television

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OVP relay could cause these faults, I would slip the belt off the front of the engine to see if the rattle noise goes away, the idler is known to do this
 
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rattlecrank

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Sorry, should have said I've replaced the belt tensioner/damper - can you tell me where to locate the relay?
 

television

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Up on the bulkhead under a plastic cover, it has a fuse on top
 

Bolide

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603 or 606 engine? I assume it's a 1993, not a 1973

Engine stopping on its own is odd. The only way you can stop these engines is to operate the (vaccum-operated) stop valve, or stall it mechanically

ABS light does sound like a bad OVP

Nick Froome
 
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rattlecrank

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I'll go and hunt down the relay, I presume it's in the box next to the fuses?
Sorry, it is a 1993 vintage, how do I tell if it's a 603 or 606 engine? The refusal to idle also bothers me, but everything happened at once so I've made the presumption they're all linked. Engine still runs but simply refuses to idle - just cuts out as soon as you take your foot off the accelerator.
 

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OVP as above. Its behind the cover behind the battery, your idle will return after its replaced, as will your rev counter and the abs light will go away!
 
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rattlecrank

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Just located the relay - next to the battery. 10A fuse on top had popped - put another one in and the same thing happened............does this mean the relay is faulty? If so where can I get another?
 

television

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Yes this means the relay has blown its diodes unless you had a dead short on the ABS ECU

You should do a resistance check from pins 87 to ground
 

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As above re. faulty relay - or one other possibility is that the engine wiring harness has a short in it, blowing the fuse, which is not uncommon on these.
 
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rattlecrank

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New relay on order, just took the casing off the old one, and couldn't see anything obviously wrong with it like overheating etc. So here's hoping, I'll do an update post on it and do a video post on the mysterious rattle when I can get the tick over back!!

Thanks for your responses.
 

television

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At the worst if there is a fault on the car the fuse will blow without damage to the new relay
 
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rattlecrank

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Ordered a relay and will let people know the result when fitted. Will also post a video with the mysterious noise when I can get it to tick-over again!!

Thanks for your responses.
 
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rattlecrank

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Just done a resistance check on the three pins marked 87. There is resistance between them but nothing to ground. Fuse pops as soon as the ignition is turned on. I'm hoping it isn't anything in the loom as suggested in one of the replies - everything looks sheathed and rather difficult to uncover!!
 

television

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Sounds OK to me then, these relays contain 2 x zener diodes that go short circuit should any voltage be exceeded or reversed flow
 

Alex Crow

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Just done a resistance check on the three pins marked 87. There is resistance between them but nothing to ground. Fuse pops as soon as the ignition is turned on. I'm hoping it isn't anything in the loom as suggested in one of the replies - everything looks sheathed and rather difficult to uncover!!

Do you literally mean it is a dead short to ground (no resistance)?
Or is it actually high resistance/open circuit to ground?
 
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rattlecrank

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Postie placed a new OVP relay in my hand - fitted as quickly as I could. Same fault occurring I'm afraid -
10A fuse at top of new relay going pop, symptoms are still no rev counter, ABS light on and will not tick -over. I can get it to run but that has to be at around 1000 rpm with use of throttle - over those revs engine running normally.

Not being an electrical whizz, I'm now getting just a wee bit despondent!!

On the bright side, still a few days holiday left to sort it out!!!

Thanks for all your suggestions so far, I'm sure you'll help me nail the problem in the end.
 

television

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OK you have a short on the ABS or something else that uses the OVP relay and this must give a reading to ground.

I will try and work out what uses the output from the OVP relay
 

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