Glow plug relay wiring

[steve_a]

Hi All,

We have a 1996 2.5L diesel Ford Freda. After having some starting issues (starter turns, but engine won't fire), I have been investigating the glow plug electrics. I want to eliminate problems here before I remove seat (side conversion) etc to get to plugs themselves.

The fusable link from battery has tested ok. I have removed glow relay and tested voltages in situ. I have attached a pic so I can describe wires. I see a good (identical to battery) voltage at the thick blue/red supply cable (bottom right in pic). When I turn the ignition I get a voltage on the thin purple wire (top left in pic) which then goes off after 10 secs or so - I am assuming this is the control voltage for the coil, and the other thick cable (removed in pic, connects to pin on top right) is the output feed for the plugs? I do not see any voltage at all on that pin when the purple voltage is there. I would assume from that there is a problem with relay? I just want to make sure I have the wires correct - I can’t find anything online with info on which wire does what. I know one is also earth, but unsure if that is the thin black or what I was assuming goes out to plugs. I am trying to work out if I need a new relay, or if I need to now proceed to checking the plugs. I guess I could bypass the relay and see if the van will start? What sort of current would you expect the glowlpug rail to pull?

Thanks in advance for any help.

[teenmal]

Check the wiring (colours) and voltage on the glow plug rail you are looking for about 11volts.The power to the glow plug is constant until a predetermined RPM and or Engine temperature is archived, in actual fact the glow / heater plugs could be working all day in certain circumstances.



Good luck.

[g8dhe]

All the wiring diagrams are on-line here;


For yours the details are;

[steve_a]

Thanks for the help guys.

Geoff - your diagram confirmed my thinking about the wiring.

So, I removed the relay and then ran a fly lead from the battery +ve to the glow plug feed lead that comes off the relay... and the van started.

So, it is a knackered relay I assume.

Having look at this post:
viewtopic.php?f=3&t=51193&p=516585&hili ... ir#p516585

I took the relay apart, hoping I could fix it. But I can't actually see much wrong with it visually (no loose wires, no nasty looking contacts, ..). There is good electrical contact between the battery +ve in / glow plug out terminals when the switch is activated manually. However, it looks like an open circuit across the relay coil, so I think that is where the problem is. A new relay I guess. I haven't yet checked to see if the switch activates with a 12V control signal. If it does, then I am perplexed, as the problem must be in the relay somewhere.

[g8dhe]

The coils have been known to fail and also the contacts to weld, they do have to handle a lot of inrush current when they first operate which explains the welding, poor design and waterproofing probably accounts for coil failing as they don't appear to be sealed.

[steve_a]

Thanks again Geoff. Have found an original Bongo (used) replacement relay for £32 with 3 month warranty. Decided to risk that rather than £90 for a new one. I guess there is no telling whether it might also fail at some point in future. Might try and seal it up a bit better as a preventative measure. They do seem to come supplied with a stylish rain cover, but there has to be a gap in the cover for the mounting bracket, so not sure how useful it is!

[steve_a]

Sorry to ask another question on this, but I wondered generally about the use of the glow plugs on the Bongo. I was a bit surprised that the van refused to start at all with no power to the plugs, even in relatively mild ambient temperatures. Is it the case that the Bongo engine always needs the plugs to be active at start up (independent of how warm the weather is)? Or have a I just got unlucky this past week?

Just curious to learn more...

[g8dhe]

I'm no expert at all on engines, but its both temperature and pressure that causes the fuel to ignite, so if perhaps your a bit on the low side for compression then the heat from the glowplug may become essential.

[steve_a]

Just to report back --

Replacement glow plug relay fitted, and now all works fine.

Thanks again Geoff for the help.

[teenmal]

I'm no expert at all on engines, but its both temperature and pressure that causes the fuel to ignite, so if perhaps your a bit on the low side for compression then the heat from the glowplug may become essential.

Yes that looks very much like low compression could be causing a Bit of this problem. An engine with Good compression should start without the aid of glow/heater plugs in this weather, unless you are in a cold place?.

[steve_a]

Yes that looks very much like low compression could be causing a Bit of this problem. An engine with Good compression should start without the aid of glow/heater plugs in this weather, unless you are in a cold place?.

OK - thanks. I did wonder. We are in Yorkshire, which is not *that* cold (despite what the Southerners might believe...).

So that might a cylinder issue or even a head issue...? Something tells me I might not want to know....

This might explain though why we were able to start on our weekend away when we first had the problems. By chance it was roasting in the Lakes that weekend, and the van had been sat baking in the sun a good while before we started it. Makes me realise we were probably lucky to get it going!