Preheat relay timer not working

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paul in normandy
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Preheat relay timer not working

Post by paul in normandy »

Strange problem with a 99 Berlingo 1.9 D preheat relay. The relay clicks in and back out again within seconds - the two clicks follow immediately after one another. Have got another unit from the local breakers - its a Nagares PPC/7-12 other numbers on it are 96 165 823 80 and this one does exactly the same. Are they prone to failing in this way or should I be looking somewhere else? The dash light is coming on and off again immediately in time with the relay.
Thanks in advance,
Paul
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Post by CitroJim »

Hi Paul,

Normally, they're a paragon of reliability :?

It's basically trying to work so that means it's getting the right signals to it. If it were on a late TD then I'd say there might be a problem with the injection ECU as that controls the basic timing and post-heating but on a D there is not normally any post-heating to worry about.

One thing I suspect is that the controller may have some over-current protection built in and this may be activating because of a faulty (short-circuit) glowplug. I've seen one instance of this happening where the connection ring crimp to No.1 glowplug had moved and was shorted against the thermostat housing.

I'd firstly inspect the bus cable that spans the glowplugs and ensure it s not shorting to earth anywhere and then disconnect it. Then retest with all glowplugs effectively disconnected. If the timer now works correctly, you know you have a short-circuit glowplug. Reconnect each in turn until the fault reappears.
Jim

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Post by paul in normandy »

Its had new glowplugs fairly recently, so could have been put back incorrectly - will have a look tomorrow morning. Its got a cable to connect direct to the battery, when you do that it goes first turn - no problem.
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Post by wheeler »

I assume this is a DW8 engine, I think Jims right about the short, on this engine if one of the glowplugs short internaly it cuts of the relay operation. Undo the glowplug rail thats bolted to the side of the inlet manifold & put a normal test lamp (ideally the filament bulb type) onto the feed wire if it illuminates the light you have a faulty glow plug (assuming the rail is ok).
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Post by paul in normandy »

The engine is a DW8 unit. The story so far, if you disconnect the glow plug circuit at the joint on the side of the inlet manifold the relay acts normally, ie stays on for a while, then goes off. Disconnecting a glow plug at a time makes no difference - its on and off straight away as before.
I then disconnected the bus wire from all the plugs, cleaned it, checked for continuity - its about the only function on my tester I'm fully conversant with :) , all seems Ok, reconnected it and we're back where we started. There does not appear to be anywhere the odd small uninsulated parts of the bus wire can touch, so does this mean that its perhaps been fitted with the wrong type of glow plugs, or that they are all faulty.
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Post by wheeler »

Either do a continuity test individually on each plug with the rail removed or remove them & test them direct on a battery.
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Post by paul in normandy »

Checked each one indidvidually, using a bulb they all lit up, connecting them singly into the relay circuit they all caused the relay to go on and off quickly.
Appears that they are all US.
In view of this I suspect that they had not been replaced. Would the failure of one then mean that the rest were then more likely to fail?
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Post by CitroJim »

No, but they may have replaced them with the wrong type Paul.

Not all glowplugs are the same, even if they look ore or less identical.

The D and TD use differing types and if the wrong type is used they can burn out very quickly. This applies to using the D (quickheat - not specified for post-heating) types in a TD (or a D with post-heat) where the post-heating will very quickly destroy them.

Being a very late IDI engine, I'd not be surprised if the DW8 has post-heating which can leave the glowplugs alight for up to three minutes after starting. Quickheats are only designed to be alight for 20-30s.

Been there, I know from making the same error :oops:
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Post by paul in normandy »

That sounds logical.
Connecting the bus bar to the battery for a few seconds results in a quick start from cold, but having to put the bonnet up all the time is a pain, looks like this will have to be the first investment in our 'free' car! :)
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Post by paul in normandy »

Back again!
Just fitted a new set of glow plugs, much cheaper to buy them in the UK, and lo and behold the same thing happens.
Hve now changed glow plugs and relay box and the problem still hasn't gone away - any further suggestions anyone?
Thanks in advance.

Off out to play with the BX now! :)
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Post by paul in normandy »

Been to have another go - went back to the beginning.
Disconnected the bus wire from all the plugs.
With it disconnected from all of them the relay does exactly as it should.
Connected the relay to one plug - on/off quickly. Connected it to all the plugs individually the result was the same relay on/off quickly.
Surely the odds on all 8 plugs shorting out - 4 nearly new ones and 4 brand new ones must be fairly long.
Totally baffled now.
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Post by myglaren »

It is looking like a faulty relay again, sods law that your replacement relay has the same fault as the original.

That or an earth leak in the relay wiring.
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Post by spider »

I think (although not ideal!) I'd consider a standard heavy duty relay (ensure it is up to coping with the current) and wiring a push button up on the dash to that so I could just manually operate the glowplugs...

Having said that it does sound like you do still have a faulty relay to be honest.
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Post by paul in normandy »

I think that sounds like a good plan, we did it once with a diesel Renault 18 with about 400k miles on the clock and it worked fine on that, mini starter solenoid from memory. Will try one other relay from the breakers first, they did say they would swap it if it was not working.
It was much simpler in days gone by, my mate's dad had a Fordson Major I think it was, you pulled a piece of bent metal in the dash, waited till your finger got warm, then pressed the starter button, and bang off it went. :)
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Post by paul in normandy »

I think that sounds like a good plan, we did it once with a diesel Renault 18 with about 400k miles on the clock and it worked fine on that, mini starter solenoid from memory. Will try one other relay from the breakers first, they did say they would swap it if it was not working.
It was much simpler in days gone by, my mate's dad had a Fordson Major I think it was, you pulled a piece of bent metal in the dash, waited till your finger got warm, then pressed the starter button, and bang off it went. :)
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