Starting issues...Glow plug relay?

[Trystan92]

Hey Bongo community.

First post on here after months of reading other topics and solving my issues that way - love this forum, its a great resource.

We bought a '95 diesel 2.5 TDI a few months back and after starting without any issues at all since then, this morning it hasn't been able to start. It was 12 C today so not particularly cold, she was starting reliably at -2 earlier in the winter! Engine ticks over on starter motor but won't ignite. I've narrowed the issue down to glowplug related: no voltage detected on glow plug rail. I checked all relevant fuses which are fine, the fuse wire directly out of the starter battery +ve terminal is also in good shape and has continuity. voltage is going into the relay, but not out. when I turn the key 2 clicks to "ON ll" I can hear the relay clicking, but no voltage is coming through. I hooked up an old spare battery directly to the glow plug rail and it started straight away (!) and after 30 seconds of the engine running, when this spare battery was disconnected from the glow plug rail, the engine started to shudder and noticeable struggle (I guess as loss of glow plug heat caused engine to cool), which ceased as soon as power was re-supplied to the glow plug rail. So I suspect a dodgy relay.

Took the relay out and opened it up - no obvious damage (in fact it looked brand spanking new) and the waterproof sheath over the relay was also in good shape so I don't suspect water damage. I did notice that one of the single copper wires was not making contact with the large copper coil (not sure if it should or shouldn't be), so I tried to make contact again, but snapped off the wire (bugger). found some old copper wire of slightly larger diameter than the original (0.5mm diameter) and replaced relay, but still no luck.

Basically, I think I need to buy a new glow plug relay but wanted to get a second opinion that I have narrowed down the problem enough before forking out 90 quid on a new one to find the problem still persists. Battery is in good condition and not draining, fuel supply to engine must be good as engine started first time with spare battery powering glow plugs. Is there anything else obvious that could still be causing the lack of power to the glow plug rail? Would anyone in my situation just go ahead and buy a new relay? maybe I should bring it to a mechanic for confirmation?

Thanks all

Trystan

[g8dhe]

Yes if you know the the fusible link is OK and the full 12v power is getting to the relay contacts then it sounds like the wire between pin and contacts has failed, given that you can hear the relay click implies that the coil side is working OK.

[teenmal]

It would be worthwhile having another look at the relay gubbins for a broken wire or bad soldered joint,there is nothing special about these very expensive relays that can see. The last time I had one up the spout I replaced it with an ordinary relay I think it was about 70amp? costing under a tenner.

[Trystan92]

Thanks both for replies, I had another look at the relay and seems fine to me, I plugged it back in with the cover off to see if I could see the contacts 'click' when the ignition was turned on, and I couldn't see the magnet activate (the click I heard must have been some other relay under the hood). When I pushed the relay contacts together, power went straight through to the glow plug rail and engine started immediately. I did notice though that there is no voltage in the purple wire coming through the white connector. I think this is the power going from the ignition to activate the relay? maybe the issue isn't the relay itself, but rather the ignition not correctly activating the relay? orange glow plug light comes on on the dash, but maybe no power is getting to the relay to actually activate it...?

Thanks again.

[g8dhe]

The signal on the Violet wire comes from the ECU itself, the light is just a timing light it doesn't indicate power to the glow plugs at all. The violet wire comes from the 1K connector on the ECU, so worth checking there as well.

[sotal]

The only thing that doesn't make sense compared to my findings with the bongo was on your first post you said that you put a battery in and heated the glow plugs, then started it, left them on for 30 seconds then removed the power to the plugs and it struggled??

From what I've tested, the glow plugs don't stay in for long after, you can hear the click when they go off and this is normally only a few (maybe 10) seconds after the light goes off and doesn't affect the running of the engine. I once tested the glow plugs and confirmed that per did stop when the relay clicks off.

I also sometimes wait until I hear the click before starting - the idea being that the starter motor then isn't fighting against the glow plugs for power. It doesn't seem to make any difference to the way the engine starts.

Just thought I'd add my findings in case they helped at all.

If all else fails and you can't find a break in the violet wire, then you could always wire a switch to the glow plugs and manually control them. A little bit of a bodge but much cheaper than a new ECU.

You could even get fancy and use some kind of timer switch, I'm thinking a momentary push button, linked to a 555, which supplies power for 1 minute each time you press the button. Can't forget to turn it off then - probably cost about £2 for a ready made circuit. You can then adjust the pot to lengthen the time if required.

[rita]

The only thing that doesn't make sense compared to my findings with the bongo was on your first post you said that you put a battery in and heated the glow plugs, then started it, left them on for 30 seconds then removed the power to the plugs and it struggled??

From what I've tested, the glow plugs don't stay in for long after, you can hear the click when they go off and this is normally only a few (maybe 10) seconds after the light goes off and doesn't affect the running of the engine. I once tested the glow plugs and confirmed that per did stop when the relay clicks off.

I also sometimes wait until I hear the click before starting - the idea being that the starter motor then isn't fighting against the glow plugs for power. It doesn't seem to make any difference to the way the engine starts.

Just thought I'd add my findings in case they helped at all.

If all else fails and you can't find a break in the violet wire, then you could always wire a switch to the glow plugs and manually control them. A little bit of a bodge but much cheaper than a new ECU.

You could even get fancy and use some kind of timer switch, I'm thinking a momentary push button, linked to a 555, which supplies power for 1 minute each time you press the button. Can't forget to turn it off then - probably cost about £2 for a ready made circuit. You can then adjust the pot to lengthen the time if required.

Hu Sotal ,The glow/heater plugs remain active until the engine temp reaches aprox 30/40c or the RPM exceeds 1500 rpm. In actual fact its possible that the could stay active all day depending on your journeys.

Hence the reason why the OP engine started to splutter when he removed the power from the rail, hope this helps you to make sense of the situation.

Take care.










Hi Sotal, a bit of information for you that will probably help you make sense of the way the glow/heater plugs function .

[sotal]

My testing does not confirm this theory, although I have seen it mentioned before on here, however it simply doesn't appear to test that way.

Put a meter on the glow plugs and monitor, when you turn the ignition on they power up, once the light goes off they stay on for another 10 seconds maybe a little longer in cold weather but certainly not a huge amount of time. Once the relay clicks off they go off.

If you start the engine as soon as the light goes out they continue to be on for the same amount of time, literally a few seconds. If I wait for the click prior to starting then they aren't on at all after.

If course I've only tested one and not in enough different scenarios to be one hundred percent sure, so it genuinely would be interesting to see if any others do stay on longer but I'm fairly sure you'll find they don't. It seems to be a very basic system.

[rita]

My testing does not confirm this theory, although I have seen it mentioned before on here, however it simply doesn't appear to test that way.

Put a meter on the glow plugs and monitor, when you turn the ignition on they power up, once the light goes off they stay on for another 10 seconds maybe a little longer in cold weather but certainly not a huge amount of time. Once the relay clicks off they go off.

If you start the engine as soon as the light goes out they continue to be on for the same amount of time, literally a few seconds. If I wait for the click prior to starting then they aren't on at all after.

If course I've only tested one and not in enough different scenarios to be one hundred percent sure, so it genuinely would be interesting to see if any others do stay on longer but I'm fairly sure you'll find they don't. It seems to be a very basic system.

Hi Sotal, I am hundred percent sure, it is a basic system that was devised for the WLT engine with a pre combustion chamber.

We used to get customers coming into the garage a try to tell us how to repair their vehicles, for a laugh we would put a spanner in their hand and say " Fix the friggin thing yourself".

[sotal]

We used to get customers coming into the garage a try to tell us how to repair their vehicles, for a laugh we would put a spanner in their hand and say " Fix the friggin thing yourself".

Hence the used?

Give it a try, I had read about the supposed function, so tested mine to see what was happening and found that the glow plugs do not stay on for long at all. That was relatively cold weather at the time, not sub zero but cold enough to need the glow plugs to start. As I say I would be genuinely interested to see others results rather than just hearsay, I know what mine does but there is every chance that mine doesn't do what others do.

[g8dhe]

You will need to bear in mind that there are LOTS of different versions of the ECU I suspect that they changed on a much more frequent than we know!

[Trystan92]

I couldn't find anything visually wrong with the connection from the ECU to the GPR, but its an absolute snakes wedding of wires behind the glove box so who knows if I missed anything. Booking the Bongo into an auto electrician that knows Bongos for tomorrow, so I'll report on what they find.

I've been driving the Bongo a bit the last week, heat up the glow plugs for 10 seconds with a spare battery and let run idle for 5 mins with a bit of revving to warm her up. Once glow plugs are disconnected she runs absolutely fine and once warm can be switched off and on again even after 30 mins rest so long as there is a bit of heat still in the engine.

If nothing comes of her visit to the garage or something like a new ECU is needed, manually wiring in a Glow Plug switch into the dash might be a reasonable course of action!

[Hazzobongo]

Relays are just an automatic switch, in your case the relay will be energised by the ECU, that power/signal will pass between two pins of your relay, pin 85 & 86 when the ignition is the on position, the output to the rail will come from 87 & 30 or 87a 87 and 30 so if you have power from the ecu to 85 & 86 but nothing at 30 I'd be replacing the relay for another either five or four pin and the same amp rating, you can pick up relays for between 5 and 12 quid brand new on ebay, anyone charging 90 quid for one should be carrying a gun and wearing a mask.

[Trystan92]

Report from mechanic/auto electrician after 2 weeks at the garage:

confirmed no power from ECU to relay - suspect a dodgy ECU. Wired in a manual relay switch to bypass ECU. This worked but the mechanics were uneasy about this as a final solution, since a dodgy ECU engine module may also be causing underlying problems to the vacuum pump and choke system. They sourced a new ECU module (we have a 2.5 diesel manual which is rare, so module was hard to find, but they managed to get one!). Replacing this didn't work... They suspected that the alarm system and immobiliser may have been installed poorly and that could be the reason for lack of signal in/out of ECU module. Once removed, the same immobiliser and alarm system cannot be reinstalled. I reluctantly agreed. and Voila - problem solved. Engine works better than ever.

So the whole problem turned out to be a dodgy connections somewhere on the alarm/immobilizer system. Whether this has always been a problem, or has just appeared, I do not know since we only bought the Bongo 4 months ago.

[g8dhe]

Ugh, nasty one to identify especially when you have 3rd party items involved i.e. the alarm! At least its been identified and you have a working vehicle which is by far the most important aspect, another alarm can be fitted by professional installer if you want the alarm system.