Injectors misbehaving but trying to understand the numbers

[CitroJim]

I've had a look Darren and on the face of it the control looks simple - 2.6V on pin 8 should turn on the glowplugs but I don't believe it's that simple given there's a diagnostic line on pin 3 of the relay...

I believe it's a digital CAN Bus-like signal from the engine ECU that controls it with a revertive diagnostic to report back to the ECU that all is happy or not.

The only things you can easily check is that it has a healthy supply from the battery that does not 'sag' when the glowplugs are commanded to turn on due to a high resistance between the battery and the relay. Ditto with the earth connection. A high resistance here from relay to earth could also cause an issue.

A good, close look at the fusebox and fuse F02 might be useful...

Putting an oscilloscope on the control and diagnostic lines I'd expect to see a 5v (or so) peak-to-peak squarewave of variable mark-space ratio encoding the digital signal to control the relay. An ordinary voltmeter applied to the lines will see 2.6v'ish as it will be measuring the RMS value of the squarewave signal.

If supply, earth and control signals look OK then possibly the ECU may be sending it duff data...

Does the dash warning light ever come on?

[darbuck]

Hi Jim, I thought I had replied to you earlier, thanks for that. I have some direction now and a lot to think about. Will check what you have said and I will hook up the hantek and see if the signal is as you described. The glow plug wait light stays on constant key on engine off. it goes off more or less instantaneously once the engine is started and running. I need to rule out all you have suggested . yes the money light comes and the depollution fault comes up as well, I will report back when I have had a chance to look at it, hopefully after work this evening

[darbuck]

Hi Jim I have checked all you suggested, the live feed has a bad connection, which I discovered by moving cables around while watching the voltmeter. I got it to stay in this condition which allows the glow plug light to go off. The ECU seems to think the glowplugs are working, However when I run the activation test the relay doesn't click. See the video attached of voltage bouncing..
I checked f02 all good, the control wire is giving 2.5V. ground has a reading of 2.5ohms and the ignition wire was reading 10.8V while battery voltage is 11.4V so a slight voltage drop between battery and ignition. I haven't had a chance to do the scope.

[darbuck]

I found this drawing of the relay online. It shows a microcomputer inside the relay which I had guessed was the case. It appears it is more intelligent than we thought there is essentially two way Comms between the glow plugs and the controller. Well at least a method for bypassing the relay to ensure monitored power is maintained to the glow plugs.. It could be just for illustration purposes but it seems to have an interface between the plugs and the microcomputer. My connector isn't in great condition so I might cut it off and replace with a good used one I know this is not ideal but it could easily be the cause of the issue. One side of the slide is partially missing and so is part of the seal. Any opposing views?

[CitroJim]

I think that's a good plan Darren...

[darbuck]

Thanks for confirming Jim. I will try to get to it this evening or tomorrow. I'm off tomorrow so might do it then.ive to drive to Waterford and back today so might not feel like it this evening. It's 300km round trip so a good bit of driving.

[Paul-R]

I found this drawing of the relay online. It shows a microcomputer inside the relay which I had guessed was the case. It appears it is more intelligent than we thought there is essentially two way Comms between the glow plugs and the controller. Well at least a method for bypassing the relay to ensure monitored power is maintained to the glow plugs.. It could be just for illustration purposes but it seems to have an interface between the plugs and the microcomputer. My connector isn't in great condition so I might cut it off and replace with a good used one I know this is not ideal but it could easily be the cause of the issue. One side of the slide is partially missing and so is part of the seal. Any opposing views?

Not so much disagree but more of a comment. The diagram shows each glow plug fed separately. Is this actually the case? It's more usual to have a single feed linked across from one glow plug to the next.

[darbuck]

Hi Paul they are all individually fed yes. So the drawing looks accurate

[darbuck]

Ok so changed out the plug glowplug light comes on and goes out more or less instantly. No fault codes detected. I can hear the ECU bleeping for the relay but I don't hear the relay clicking. I think I will just do the master cylinder and get it through a test and see how it behaves. I have done what I can for now.

[CitroJim]

That's a great result Darren

I don't hear the relay clicking.

You won't - all the switching is electronic - it's a relay in name only.

You can prove 100% by hanging a voltmeter on one of the glowplugs and seeing if it registers a voltage very briefly. It may not given it's summer'ish as they only come on to pre-heat in very cold weather... You may see a minute or so of post-heating though as they come on after starting to to keep emissions down. Post-heating is not indicated by the dash light. This only lights for pre-heating...

All best with the Master Cylinder and MoT

[darbuck]

Thanks Jim , it fought me something terrible on the connector. I couldn't solder it my iron is too weak for the cables going to the glow plugs. Ended up using butt connectors and heat shrink. Absolute nightmare I hate butt connectors, I don't trust them but needs must. I must of about 20 of them before I got good connections.She loves to fight me.

[CitroJim]

She loves to fight me.

Because she's French They all do in my experience

[myglaren]

She loves to fight me.

Because she's French They all do in my experience

[darbuck]

Same as, the Jap yolks are even worse.

[CitroJim]

Macron's missus is a bit feisty by all accounts...