OM 605 250 TD starting issue (?Heater plugs?)

AMH

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Hi everyone. I'm posting on behalf of my dad. He has a 1998 Merc 250 TD (OM 605) which has covered 55k miles. It's a UK car, owned by him since 2007.

On cold starting, the engine is very rough and the heater plug lamp on the instrument cluster stays illuminated for around 2 minutes before extinguishing. The engine also runs poorly during this the time that the heater plugs lamp is on.

We're used to diesel engines and everything points to one (or more) of the heater plugs being duff. However, I've read some terrible stories about these plugs snapping and stripping in the head when you try to remove them (as far as we know these have been in there since 1998!).

So, dad has been applying PlusGas to the tops of the plugs for a few weeks now (the car is not being used) but he's keen to find out how the wire to the top of the plugs is removed(?) so that he can get a better look at things before he even starts to apply any socket to the top of any of the plugs.

Can anyone advise on whether we're right on this or whether it is likely to be the heater plug control unit or relay that's throwing things out?

Any advice - or links to articles on this - would be very much appreciated.

Thanks!

Adrian.
 

om613

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Lube is good, take it steady!
Get a DVM on the relay connection and earth to find which plugs are down.
Push fit on OM605/6.
They pull off upwards and can be stiff.
 
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AMH

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Ok thanks om613. This might be a daft question; but will the reading be accurate if I measure the resistance of the plugs whilst they are still in the head - i.e.. without removing them first - so that I can see which ones are down?

Thanks.
 

umblecumbuz

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Just unplug the glowplug lead, take a wire with bared ends, put one on the glowplug terminal and touch the battery live terminal with the other.

A weak spark will tell you that the plug is functioning. No spark will confirm that it is duff.

Umble.
 

yorkshire1

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If a plug does test dead I,d advise replacing the whole lot whilst you,re at it as ideally the easiest way to do the job is with the inlet manifold removed,and you dont want to do that more times than you have to (you,ll also need new manifold sealing "O" rings,cheap anyway). Ive had the most luck with the Bosch Duraterms
to test the controller/relay cycle the ignition and test all 5 relevant output for power as sometimes a duff plug will blow a fuse inside the controller aswell (each one has a separate fuse) the controller can be dismantled and new fusible links soldered in if required
 

Steve@Avantgarde

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I would rather he learned how to measure the resistance of the glow plugs using a multimeter than using a battery and a good old spark.

At least he would get a solid form of diag then...just saying like.
 

silestanix

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Just replace the whole lot. They're not pricey and at least you'll eliminate the need to take the inlet manifold off again, as above do ensure you get new manifold seals and o rings, take care removing the glow plugs as they can seize in over time.

Edit - the plug leads come off, pull upwards firmly but not ham fistedly lol.
 

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I would rather he learned how to measure the resistance of the glow plugs using a multimeter than using a battery and a good old spark.

At least he would get a solid form of diag then...just saying like.

agreed. ive seen glow plugs short out part way down so that the tips dont get hot but they do still complete the circuit so that the in-head battery test makes them appear ok. removal and full testing or a resistance check shows the short (glows in the wrong place or resistance is lower than expected)
 
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AMH

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Hi folks. Ok, thanks for all your input (so far) - please keep the suggestions coming. Have (verbally) forwarded all the info on to dad today. Plan is to go 'round to his place and see things in the flesh either tomorrow or Friday.

I get the feeling that dad is tempted to sell the car on as spares or repair, though - as any failed attempt at removing any of the plugs would be a head-off job and he's thinking that it might be better to cut his losses and sell it on with the issue and let someone else make the decision about how to remove them - or not. It's a shame as the rest of the car is mint (for it's age) and it's only done 55K miles!

Will report back.....
 

yorkshire1

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not as daunting as it sounds but if he does decide to sell send me a message as I would be interested
 

brianbrian

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Have it done if as you said the car is in good condition, you could replace the car and have the same problem. Glow plugs are like light bulbs, some last years, some last months.
 

turbopete

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i used to use a guy who could remove most glowplugs without removing the head. he was a member here but not seen him on for quite a while. he is based in Carlisle and i still have a phone number for him (somewhere!)
 
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AMH

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UPDATE: Hi everyone & thanks again for your help with this. Have spent the afternoon looking at this and (IMO) none of the heater plugs are duff.

On starting from cold - turn the key to light up the plugs - plug light extinguishes - turn over and the engine fires immediately and runs as normal (no extra cranking, she just fired and ran). However, heater plug light then comes back on and stays on for around 1 minute and then goes out and stays out. Engine running normally (albeit IMO a bit slow on tick over (circa 600rpm) but my father says that's what it should be(?))

It might also be worth mentioning that the service spanner light is currently also illuminated and reads -37 miles. Dad says that he's going to remedy this with someone he knows ASAP - but not sure if the fact that the OBC is saying that the car needs a service and is throwing out a red herring with the heater plug light coming back on(?). The car has covered 56K miles.

One other thing that's worth mentioning is that we're also currently clearing out some oily gunk that's appeared in the air inlet manifold - which is made from black plastic, not aluminium. I noticed that there's what looks like some sort of sensor or sender with a tube coming off it at the 6o'clock position on the front end of the air inlet manifold. I'm just wondering if that might have also been effected by the build up of oily gunk and could be making her run slowly - or might be having any other adverse effect? She's not using any oil at all and there's none in the expansion tank, BTW.

So in summary, there's some sort of electrical fault, but unless it's just one of the heater plugs that's down and that this doesn't effect the way that the engine starts, it seems to be related to the heater plugs but they're functioning (as heater plugs) correctly. I only say that as, in a previous experience, I had one heater plug go down on a 4 cylinder diesel Citroen XUD engine (best engine I've ever owned) and you had to crank the thing over for ages with your foot to the floor to get it going. This was followed by a huge cloud of black smoke from the exhaust.

Dad's car is not behaving anything like this.

Any ideas what's causing this heater plug lamp to re-illuminate?
 

EmilysDad

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A failed glow plug will put the light back exactly as you describe. A single failed plug on mine caused no starting issues at all. ;)
It could still be the relay though
 
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AMH

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Thanks. Wouldn't the relay effect all the plugs and make her really hard to start? Are you able to point me at the relay and suggest how to test it?

Many thanks.
 

EmilysDad

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Thanks. Wouldn't the relay effect all the plugs and make her really hard to start? Are you able to point me at the relay and suggest how to test it?

Many thanks.

Apparently not. STAR indicated a single plug when the light first came on but when the light still came on with a new glow plug I replaced the relay. Problem solved.
If it's the V6 diesel, then it's right at the front, near the top & slightly over to the driver's side.
 

yorkshire1

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youve got to take the washer bottle out and the relay/controller is under it,can be tested as per my last post,symptoms though indicate glowplug as suggested above

That tube on the front of the inlet manifold runs to the MAP sensor (senses boost pressure and sends signal to ECU )

black gunk is partly crap from the EGR valve and oil from the crankcase vent recycling back into the engine and nothing to worry about
 

om613

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You've one or two plugs down, that's what the light dash is telling you.
Your car is not a CDI (common rail).
It's an IDI.
On the CDI, the same GP fault shows up but make no difference to starting in UK temps.
 

charlysays

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The push fit connectors can be dodgy... sometimes you need to unclip the lid on them, take the contact out and squish it a bit tighter with some pliers, carefully so as not to crush it completely. They can get corroded too.

Seized glow plugs will usually come out if the engine is really hot (run it with the IM off making sure nothing can fall in the inlet ports). It's usually a screechy quarter turn out, quarter turn in affair to slowly break up the packed in carbon and remove the plug. One took me 10 mins to get out once. If I'd just hauled away at it with a long handle ratchet it would've snapped off.
If they do snap is almost never a head off job provided you know what you're doing.
 


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