D1 30 glow plugs staying on

[bavman]

Any experts here - this is an update I put on our local YBW forum without any success so giving this a go.
Just a update folks , firstly I've had the boat from new. I have now connected the yellow wire to the alternator from where it had been missing for i dont know when.
didn't seem to make any difference to charging circuit . engine running battery's charging at 14,5 v.
Now the original fault - the glow plugs re energising after the engine start cycle. I have what I believe narrowed the problem down to the orange wire Terminal 6 terminating at connection 86 on the glow plug relay (thereby going positive momentary after engine starts and start button released.
(the negative end of the Diode positive on same supply - the diode testing good)
I now need any ideas where this orange T6 can get its supply from.
Somehow the alternator seems suspicious but my expertise end there - so any suggestions gladly accepted.

By way of further information I have spoken to Volvo technical in the past and they say this is a simple set up with Glow sw to relay. (both changed!!!)

[Dsanduril]

The black box on the engine should have three large wire connections (in addition to wiring harness connections). The center one is +12V, to one side is the orange glow plug wire, to the other side is the starter solenoid wire.

The relay inside the black box can be frozen, or the switch at the panel can be stuck, or some connection between the panel and the engine could have a short. Easiest way to check it to put a voltmeter on the orange wire, then disconnect the wiring harness connectors from the black box (the ones that go to the instrument panel). If the glow plugs stay on then the problem is a frozen relay. If the glow plugs go off with the harness disconnected then the problem is a short at the switch or in the harness.

On the alternator side of things, the yellow sense wire is only really needed (and will only really make a difference) if there are some losses between the alternator and the battery (like a diode separator). If the yellow wire becomes disconnected the regulator controls to the voltage at the alternator output terminal. If there are not many losses then that is pretty close to the voltage on the yellow wire (and it is the original harness, and you have not connected the yellow wire direct to the house bank then it is really the same voltage). I suspect the two problems are not related (other than belonging to the same green engine).

Here is the wiring diagram,

Volvo Wiring.PNG Views: 100 Size: 88.5 KB ID: 217481" style="margin: 2px" />

The red wire is +12V, the orange runs the glow plugs, and the red/yellow runs the starter. Since the switch on the panel does double duty as both start and pre-heat it is, IME, not usually the problem. Instead the relay inside the MDI gets stuck.

[bavman]

Many thanks for your reply , much appreciated.
My boat 2006 has the older / simpler?? set up with 2 bosch relays (start and glow plugs).
both relays have been replaced along with 2 toggle switches so dosent have the MDI system.
My guess is the orange wire is re-energised when the engine / ALTERNATOR is fired up!!?? based on slight delay. But only a guess without understanding how the alternator functions.

[a64pilot]

I have no idea how to fix it, but feel certain if they have been coming in after start, they are burnt up by now, unless it’s controlled.
I assume this MDI thing is some form of computer? I ask as it’s pretty common for modern Diesel engines to energize the glow plugs after start for short periods to help with engine warm up, my Duramax would energize both the intake air heater and the glow plugs after starting, I believe duration was temp dependent though

[Dsanduril]

Does your panel have a key switch? Or just a start pushbutton? If you take a look at this, the glow plugs are activated when you use the glow plug switch and also when you use the start button. The diode in the line from the start button keeps the starter from being activated when the glow plug switch is on. So I would think no problem with the start button. Which would lead me to believe a problem with the glow plug/alarm switch. Is that still the original?



[Edit] the Red/Green wire on terminal 7 runs the glow plug light and is connected to the orange wire at terminal 86 on the relay. Any chance there is a problem in the light display (short or something) that is keeping this energized when running? I ask, because the light (and the wire) next to that is the charging indicator, which would then possibly explain the observation about when the alternator comes on (does the glow plug come on when the charging light goes out?).

[Cadence]

As a wild ass guess. Is it wired such the glow plug remains on till the oil pressure comes up. Could just be an oil pressure sending unit?

[Mike Banks]

Your problem is most likely in the starter switch. Replace it.

[NorthCoastJoe]

You might have bad replacement parts, it is not uncommon to get replacements that are crap. I would use a simple test light to see if the switch or relay is stuck on. It should be an easy fix. I have had brand new parts that were defective.