C15 diode problem

[Ben*17]

Hi to all. I was hoping someone would be able to assist me. I have recently aquired a 55 plate C15 that has problems starting. In my attempts to get to the bottom of the problem I have replaced a diode that is on a wire that seems to feed into the ECU. The trouble is that I managed to destroy the original diode and I am now not sure if I have the right diode. I know that the original was a 1N4007 something or other diode. The new one is also a 1N4007 diode but the other digits from the original are different, but as a dont have the original I am not sure exactly what those digit were. I am hoping someone could tell me if all 1N4007 diodes are the same and what I should be looking for to get the right one. With the new diode in place there is 12V going to it but nothing the other side, so I am guessing this is not as it should be. The diode is in a plastic casing and it is amongst a load of wiring under the air filter.
Any help would be much appreciated.

[Peter.N.]

A 1N4007 is a 1N4007, are you sure you have connected it the correct way round? If its a feed the end with the ring is the output end - plain end to supply.

Peter

[Ben*17]

Thanks for your help Peter.I have tried another diode in there today, made sure it was connected the right way. As soon as I switched on the ignition the fuse for the ECU blew and the diode burned out. Any ideas why this might be?

[Peter.N.]

Well if it is a feed, whatever its feeding must be s/c to earth, is it a supply to the ECU?

Peter

[Ben*17]

Yes I am pretty sure it goes to the ECU.

[Peter.N.]

If it does, sounds like the chip is down, have you got a circuit?

Peter

[Ben*17]

I get 12v between the supply to the diode and the output, but thats all I know.

[Peter.N.]

If the diode is in series with the supply you should have about 12v on both ends, if the output end is being earthed it will blow the fuse and the diode. Are you putting the diode in the same way round as it was originally. Can you measure the resistance to earth of the output end, disconnect the diode first.

Peter

[citronut]

are you sure this diode is to do with the non starting issue, as the BX has a diode in a plastic casing behind the dash which is to do with the ABS,

also what engine is in your C15

[Mandrake]

This whole thing sounds a little fishy to me!

Which ECU are we talking about here ? Engine ECU ?

How and where is the diode mounted exactly ? Seems very odd that it would be mounted externally in line with the wires to the ECU.

A 1N4007 is only rated at 1 amp, an engine ECU will use far more than that as the peak current from the coil packs alone approaches 10 amps, and injectors about an amp each when firing.

It's possible that its not connected in series but is connected in parallel as a back EMF diode - in which case it should be reverse connected. If you then connected it the other way around in this configuration it would instantly blow.

Without a circuit diagram we're just poking around in the dark - if you can confirm which ECU it's connected to and post your VIN number (or PM it to me privately if you don't want to post it publicly) and I will see if I can look up the exact wiring diagram for you tonight and post it into this thread so we can all see it. Then we have a chance of figuring out what this diode is for and where it should be.

PS unless I missed it we don't even know if its a diesel or petrol engine we're dealing with here, that would also be helpful information.

[Ben*17]

Thanks all for your help. I have had another look today and I realised that this diode does not feed to the ECU. But it does blow the fuse for the ECU. I will start again the van is a deisel c15 with a dw8 engine the VIN number is VF7**************[VIN obfuscated, can be read by forum staff]. My original problem was the glow plugs not firing up, after a lot of fiddling about it seems although something is not tell the glow plug relay to switch. In my amatuerish quest to solve the problem I discovered this diode. Unfortunately a destroyed the original diode and am not sure which way it was connected. As you have probably gathered by now I really dont know what I am doing here, any help would be gratefully recieved.

[Stickyfinger]

Would not an hours visit from a mobile Auto|Electrician not pay for itself ?? what is a blown ECU worth ?

[Mandrake]

I will start again the van is a deisel c15 with a dw8 engine the VIN number is VF7**************[VIN obfuscated, can be read by forum staff].

I tried to look up your cars wiring diagrams on my copy of Sedre but although it finds the model and shows a listing of all the wiring diagrams when I try to open any of them they're all blank.

Sorry about that! I haven't had this problem with any other models I've looked up before...

[Ben*17]

Thanks for trying Mandrake. I am still no further on with this problem but I have checked all connections today and will try a new diode in there tommorrow.