Low voltage to glow plugs?

[Agile]

Since the weather became cold I have had problems starting my Peugeot 106.

The symptoms were typical of faulty ( o/c ) glow plugs.

On Sunday I fitted two new ones but blindly because I did not have a test meter with me. It made no difference! So I swapped over one of the old ones but still no start.

Today, I applied battery voltage directly to the plugs and it started immediately.

Later I will see what voltage is getting to the plugs but its obviously not enough.

Where and what is the device that times the plug activation? How does it monitor engine temperature?

I have not encountered this before on any diesel cars. Is it common and is there any particularly likely cause of the voltage loss?

Tony

 

[seco services]

May not be getting any voltage.
Maybe the relay faulty.

 

[Burnerman]

Follow the thick wire that goes to the glowplugs back to the timer / relay.....when energised by the ignition switch, the plugs should come on with the dash light for a few seconds. Once the dash light has gone off, you can start up. Power to the glowplugs may continue for a short while afterwards and may intermittently appear for the first mile or so.
John

 

[Peter.N.]

The light will probably go out well before the plugs switch off, listen for a 'clonk' as the relay drops out and don't try and start the engine until you hear it, if the engine is tired the extra heating may allow it to start.

Try connecting a voltmeter from any glow plug connection to earth, switch to the glow plug position and check the voltage, if all the plugs are good you should have 10-11 volts for about 15 seconds, if one or more have failed the voltage will be higher, if the voltage is much lower you have a relay or wiring fault.

Peter

 

[Agile]

It is supplying a lower voltage, not yet measured but probably about 7v.

So what provides the timing and how is that controlled by the engine temp?

Tony

 

[Peter.N.]

Follow the thick lead from the glow plugs as burnerman says, if it dissapears into the loom look for a box about 3" square with thick wires, same as on plugs, connected to screw terminals, that is the relay.

The temperature only affects the length of time the glowplugs are on not the voltage.

Peter

 

[Mursal]

Low voltage plugs to ensure full power even if the battery is on its knees at -10 in the middle of winter.
Coolant temperature sensor should/will control length of "ON" time via control relay. Series resistor drops the voltage measured across the plug. So to get s true voltage (when measuring) always have the plug in the circuit.

 

[Belle427]

identify the black box as suggested, you can test for 12v in and out there
not uncommon for the connections to become loose on it

 

[Agile]

Right, I have further information after checks today which is not encouraging!

The control box is on the offside screwed to the rad header tank.

Contrary to what I thought, the glow plugs are being supplied with over 10v for the normal duration! All plugs are fine!

So what could cause poor starting just when cold? Until a week ago it was no problem. It seems starting at 10 C is impossible whereas at 14 C it was fine.

When it does start there is lots of white smoke from the exhaust so there seems to be plenty of diesel getting to the cylinders!

The car is sluggish at slow engine speeds but at motorway speeds it has plenty of power to cruise at 80+ mph.

The fuel consumption averages about 62 mpg with mixed London/motorway use. So no serious fault there!

Any suggestions for non starting when glow plugs are fine and diesel present?

Tony

 

[seco services]

Is it loosing coolant ?

 

[Burnerman]

Just a few other checks.....
Each glowplug should have a resistance of about 1 ohm.
Check the battery voltage doesn't drop below 10v whilst cold cranking. Apart from starving the glowplugs, the cranking speed may be too low.
Its not uncommon for glowplugs to be rated at 11v so they get very hot when full battery voltage is applied. Some glowplug supply is in fact pulsed.
Look at the fuel injection pump and spot the throttle cable. Is there another bowden cable that comes from the thermostat housing on the block? If the thermostat is closed, this pulls the cable tight to operate a cold start mechanism (the movement of the lever is very slight - about 3mm or so).
Chuffing white / light blue smoke on start up is a sign of poor ignition or a very cold cylinder head.....it wouldn't be a bad idea to have a compression test done on the engine just to see what sort of condition it is in.
John

 

[Agile]

The battery is very good and cranks at a good speed.

I have three of this model and this one cranks just like the others.

As it does 62 mpg I think the engine is in good condition. It has only done 102k compared with another which has done 173k and is still running well and starts easily as all my 106s have done except this one.

The cold start device is working! But how does it work? Operating it while the engine is warm causes a change in sound and slight reduction in RPM.

I need to remind you that even when directly powering the plugs from the battery thus giving full battery volts it is still difficult to start although obviously better. This is what I am doing to try to get it to eventually start.

On some web sites there are comments on timing as a cause of poor starting. I did wonder about the rather sluggesh performance at lower revs. But how is the timing adjusted?

Tony

 

[Mursal]

Current flowing to all 4 heaters and good cranking speed?

Hopefully you have air getting into the fuel line overnight, otherwise it looks like an expensive fix, regardless of what miles are on the other engine.

If you have a manual fuel pump for bleeding, endure its hard before trying for a start.
We find keeping an open mind until you find the problem saves time/money in the long run

 

[Peter.N.]

Are you certain all four glowplugs are good? Your 10v + across them would seem to indicate so. As mursal says try pumping the the primer before you start, do you have white smoke from the exhaust when trying to start.

Its unlikely that the timing is out unless the belt has just been changed and it would also cause lack of performance and economy. It would make it difficult to start if it had slipped a tooth but this would be accompanied by uneven tickover and smoke even when it was hot, it would also be quieter then normal.

The compression could be low due to incorrect valve clearances, if all else fails get the compression checked.

Peter

 

[Burnerman]

The cold start mechanism actually advances the injection pump timing slightly, and should increase the idle speed fractionally at the same time....I'm confused by your idle speed reducing!
John