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Discussion Starter #1
I have a 2010 Grand Scenic 1.5dci FAP
As the temperature has got colder starting has become an issue
Replaced all glow plugs and nothing changed, so today thought I'd test the voltage on the electrical connection to one of the glow plugs.
Although the car had been run and was warm I was surprised to find 1.3 volts even though the engine and ignition was switched off. When I started the engine the voltage only went up to about 1.5 volts, didn't see 12 volts even flash up.
Is this a viable test on a warm engine and why do I have a voltage with everything switched off.
Does this indicate that the heater unit is faulty and/or it's draining the battery overnight, although cranking speed doesn't appear to be significantly slower
Any advice would be greatly appreciated
 

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Super Moderator Technical Supremo Platinum Member
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Low voltage is commonly measured on glow plugs, even when ignition off.
This is due to the Glow plug module passing a very low current through the plugs to check if they are okay.
Depends on meter used as to whether or not anything is read.

Is starting problem both hot and cold or what ?
 

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Discussion Starter #3
Thanks for your reply
It's only difficult to start when it's been left overnight and is obviously cold. It takes a long time cranking then it splutters for about 3-4 secs and runs fine. Doesn't blow any smoke out of the exhaust when cranking or when running
 

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Good chance it is glows then.
Though I would have expected a Scenic of that age to throw a service light and tell you.

Check them with a multimeter on Resistance, lowest scale so you can read Ohms (not KOhms)

Pull off lead and measure resistance from centre electrode connection of the glow to earth.
Failed will likely show infinity/open circuit
Good is in region of 4-6ohms IIRC.
 

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Discussion Starter #5
Thanks again

Definitely no codes for glow plugs and when I did test them they were ok. I'll retest them and see what I get.
I wondered whether I might have an air leak on the spill pipes but they appear to be fine, there is what looks like a one way valve in the return line into the pump, could that cause a problem. The pipework and valve look original but I can't find a picture which shows the same layout.
Also the hand pump doesn't appear to move anything and there is a big slug of air in the clear pipe. Does the one way valve in this have any bearing in possibly allowing the fuel to run back toward the tank causing a delay in starting?
 

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Yes.
But that sort of starting issue is not usually temperature dependent even though often described as a cold start issue.
It is time that allows fuel to run back to tank, usually due to a minor leak in the feed pipes (which lets in air and breaks the syphon action)

The primer bulb should get hard in a few pumps, if it doesn't that is one issue.
Within the bulb there is a non return valve at each end.
So when you squeeze fuel has to go towards the HP pump. And when you release, it should not come back.
If it is, replace the bulb.


Second issue is where the fuel system is letting in air.
Can be a worn pipe, split primer bulb or poor connections.
Often the latter on the fuel filter with push on fittings as the O ring seals harden and don't seal as well as they should. Grease can help.
Final is injector leaks, that can let air in and fuel run back.
 

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Discussion Starter #7
Thanks for getting back to me
I'll retest the glowplugs and change the primer bulb as that doesn't get firm at all.
I'll also try and determine whether it is a non-return valve in the spill pipe and if it's working.
I'll try greasing the connections to the fuel filter as well.
I can only test one thing at a time as once it's started I don't have any problems with starting for the rest of the day
Cheers
 

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Discussion Starter #9
Also found these are rated at 4.4 volts not 12 volts so I assume I'll never get a reading above that from the heater module. I've tested them before at 12 volts, will this mean that they'll have had it or is the resistance of 0.4 ohms mean they are undamaged
 

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Super fantastic Mod Technical Supremo Nice Guy
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so the heater plugs you have put in, are the same as the ones you took out, DID YOU check,
 

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Discussion Starter #13
Can't recall if I did, I may have assumed they were the correct ones. If I take them out and check the rating etched on them and it's 4.4 volts do I assume that they are ok
 

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A resistance reading suggest they are okay.
As in not burnt out (normal failure)
But as Ourkid says, are they the right ones for the car?
Although 4.4v would make some sense of the voltage readings you took.

Two things you can try.
Meter on DC volts.
Measure between end of loose glow plug lead to earth
Engine cold, switch on.
Should see a voltage change though likely only for a second or two.

If you have a glow plug out, if only just changed should come out easily but put one back in to plug the hole, doesn't matter if a dead one
Try it and see if the end gets hot when touched to earth and plugged into the lead.
Carefull, they can get very hot, very quickly.
 

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Discussion Starter #15
Tried the voltage first thing today, although ambient temperature was around 4 degrees, it did register slightly above the 1.2-1.3 volts it seems to have all the time, then settled for about the 30 seconds I ran it at around 1.8-2.0 volts
 

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Discussion Starter #16
I assume the glow plug will only get hot if the ambient temperature is low enough to call for them to work. I've already run the engine, will the glow plug still get warm or is the test best left until tomorrow.
I assume this will tell me if the control unit is working correctly generally, but will only confirm the plug I'm testing is ok.
Now I've checked suppliers some plugs are 'after glow capable' and some don't state they are. Is this something that they should have
 

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Most modern DCIs are afterglow fitted. It is car not plug dependant.

Modern systems only put on glows during start up for a couple of seconds and may adjust depending on engine temp... my old Scenic would take longer to get to crank after start button pushed in winter then in summer.
I always assumed this was glow plug timing.

Then, after start continue to heat, often at half volts as engine warms... this is the "afterglow" and used to reduce emissions when cold/aid running.
This makes sense of the 1.8-2v reading after the engine started assuming the plugs are 4.4v.
No reading prior can be that the ECU decided no preglow needed. (or very short)

Myself and Ourkid have had the argument before about DCIs not needing glows to start until it gets cold.
I still reckon they don't but he has more practical experience. :grin2:

Was a lot easier with older diseasals and keys.
You knew they needed glows, knew they were 12v and came on when you turned key to position 1... simples.
Just counted to 10 in the summer and 30 in the winter before cranking. :grin2:

Never changed them on my Kia.
Not that it has any to change :grin2:
 

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Super fantastic Mod Technical Supremo Nice Guy
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Pressed wrong key..
Look for AQGS glow plugs ..

Might give you a better understanding of them
 

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Discussion Starter #20
Thanks both for your help
I think I'll probably buy the correct NGK plugs rather than sticking with the ones I've got, then the plugs will be definitely discounted or fix the problem.
I think I could take all the plugs out and connect them together in series to a 12 volt battery. I believe this would provide each plug with 3 volts which should cause them to heat up if they're not faulty
 
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