WTF burnt wire content

[craigieeb]

As most of you know iv got an M50 turbo in the 325i,
its been running flawlessly for a while now,
until today....

i was out in the car a couple of days ago for a lengthy journey and it was perfect when i came home and sat it on the drive,

so today i went out to the car, plugged in the laptop (running vems) and the laptop could not find the ecu, hu a bit strange i thought,
but then i realized i couldn't hear the icv buzzing or the pump priming,

so popped the bonnet,
gave everything the once over and it all seemed in order,
all fuses in tact, gave all the relays a little tap, even changed the dme relay,
but still no icv and no fuel pump,

so as i was sitting in the passenger seat trying to connect the laptop to the vems, out of the corner of my eye i seen a little poof of smoke coming from the glovebox


so i jumped out the car like a stabbed rat, disconnected the battery,
ran back opened the glovebox
couldnt see anything obvious, so started grabbing things with my hand
and there was only 1 thing that was warm.........









so questions...
wtf is it?
and
why the fuck has it burnt?

[DanThe]

Its the loop that replaces the factory OBC/immobiliser
Its probably burnt due to a bad connection, cant really be anything else if the rest of the wiring is fine.

[craigieeb]

I dont think that loop in its self has caused the problem

is just about how im feeling right now ....

opened the ecu before to make sure it wasnt damaged in any way, as soon as it was opened the smell just hit me, then i seen this






so has the ecu caused the wire to burn out, or has the burnt out wire/dodgy connection somewhere fried the ecu

i just dont fucking believe it, just when everything was going sweet!!!!!

[Speedtouch]

It looks like your output transistors have been over-stretched beyond their safe working current, causing them to run too hot, which has also caused the excess current on that wire loop.

Looks like you'll need to re-evaluate the wiring to the ignition coils, or maybe use a higher impedance set of coils that draw less current.

I presume you've used suitable heat-sinks with these transistors?

[craigieeb]

I presume you've used suitable heat-sinks with these transistors?

Couldnt tell you Maurice,
i bought it, plugged it in and iv been using it and it's been fine, for oosh the past 18 month

[Speedtouch]

Well, power transistors like that are designed to be mounted against a heat sink (or at least, to the face of a metal casing), hence why they have the metal tab on the back!

What's probably happened, is that over a period of time, the excess heat has caused one or more transistors to fail, causing the short circuit that has melted the wire loop.

You'll probably have to replace one or more of the transistors, and look into providing proper cooling for them, and ideally a fused power supply in the event of another failure.

[craigieeb]

Well, power transistors like that are designed to be mounted against a heat sink (or at least, to the face of a metal casing), hence why they have the metal tab on the back!

in that case, yes,,
they are held down by a strip of alloy bar and the bar is screwed to the casing of the ecu,
there is also some form of heat sink strip on the side of the case where they meet up

if that makes sense.

do you know where to get replacements from?

[Speedtouch]

Yes, I remember there being some form of heat-sink arrangement when I replaced your burnt-out chip.

It's best to use heat-conductive paste to mount the heatsinks rather than what appears to be hot-glue though!

You can buy replacements on E-bay:
http://www.ebay.co.uk/itm/ISL9V3040P3-4 ... 5659a340b0

Or you may be able to get them from the likes of RS/Farnell/CPC, etc.

[craigieeb]

That sort of thing?

http://www.ebay.co.uk/itm/Arctic-Silver ... 5aefaa29eb

[Speedtouch]

Yes, that's the gloop!

[craigieeb]

Nice1 thanks mate,

I might pop over RS tomorrow and take the ecu with me, to see if they have any replacements

[kam-325i]

Nice1 thanks mate,

I might pop over RS tomorrow and take the ecu with me, to see if they have any replacements

Remember to lube up first !!!!

[craigieeb]

This is when trade accounts come in handy

[DanThe]

What ECU is that Craig?

[Speedtouch]

He has a VEMS of some description.

[craigieeb]

Yeah it's the Vems Dan, its just out of warranty aswell

[Speedtouch]

Have you tried the ECU since the fry-up, to see if it still works at all? With a bit of luck, all that's blown is the wire loop - use a multimeter to measure its resistance, which should be close to zero ohms.

[craigieeb]

I havn't,
iv pulled the whole loom out and im about to start dissecting it
just to make sure there isnt a dodgy connection anywhere,
or even anymore damage

[magpie]

deep down that car loves you craig,it just likes playing hard to get !

fingers crossed it's a relatively cheap fix with a soldering iron .

can you hook up a small fan to the ecu ?

[craigieeb]

the loving feeling isnt mutual, trust me!


i'v never seem any other vems with a fan, so mine shouldnt need one...?
need to find out exactly whats went wrong before i look into fixing it tbh

[DanThe]

Yeah it's the Vems Dan, its just out of warranty aswell

I'd still give them a call.

Indeed, but check out the rest of the ignition circuit first as they will try to blame your car first regardless.

[craigieeb]

Well, i'v had the loom in bits, allover the sitting room floor and there was nothing a miss,
i checked every single wire and connection to the vems and nothing is burnt/melted,
had the fuse box out and thats all in order,
been under the dash like a little ferret and cant find anything there either

so it is all pointing towards the ecu throwing the hissy fit

[DanThe]

Well, the majority of the current drawn from that Green wire is from the coils, as standard.
Does the thick part of the wire still go to the coil loom? Or has it been broken into and tee'd to the ECU?
Normally the M50 ECU only needs a small gauge Ignition feed wire.

Get some pics up of the ECU plug connections onto the loom

[Speedtouch]

Are you using a coil pack designed for use with that ECU?

[craigieeb]

Well, the majority of the current drawn from that Green wire is from the coils, as standard.
Does the thick part of the wire still go to the coil loom? Or has it been broken into and tee'd to the ECU?
Normally the M50 ECU only needs a small gauge Ignition feed wire.

Get some pics up of the ECU plug connections onto the loom

From the looks of it, it's still coming from the coils..



than branches off to the ecu,







and a random shot of the ecu connections

Are you using a coil pack designed for use with that ECU?

i'm just using the standard M50 coil packs.

[DanThe]

Maybe the coils are just working harder due to the extra compression

[craigieeb]

possibly,
and with me using it for longer and longer everytime im out,
everything will be getting a hammering.

What else draws currant through that wire?

[DanThe]

Just coils IIRC, and to let the ECU know the ignition is turned on

[gromgsxr]

Was it a m50 or a m20 loom to start with?

[craigieeb]

It started life as an M50 loom, that was converted to go into the e30,
then that was converted to connect to the vems

[craigieeb]

So a week on...........

I sent an email to VEMS, and STILL no reply as of yet
so I decided to buy some replacement IGBT's and solder them on to the board myself,

which was simple and straight forward really,
once they were replaced, i put the engine loom back in the car, connected everything up,
connected the ecu then the battery,
plugged in the laptop, turned the key
and the ecu and the green wire behind the glovebox instantly got hot to the touch and started smoking
so just switched it off, pulled the ECU and it looks like the same igbt's have overloaded yet again.

im sending the ecu back off to gunni tomorrow, who has been an enormous help,
to see if he can find any fault with the bloody thing.

I just dont understand how it can go from being on absolutely top form one day, then a smoldering wreck the next

[kam-325i]

that sounds like something has gone short somewhere....

[DanThe]

Have you checked inside the coil wiring box on the loom Craig? Its the only place left

[Brianmoooore]

As far as I can see, you haven't found out why the original driver transistors failed.
Have the replacements gone the same way, or running very hot?
These transistors are being used as a switch in his application, and, if they were a perfect switch would dissipate no heat at all. Example - assume that a coil draws 2A at 12 volts. With the transistor turned off, there will be 12 volts across it, but no current flowing. Heat (watts) = voltage x current = 12 x 0 = 0. With the transistor turned fully on (won't quite happen in practice), there will be 2A flowing through it, but 0 volts across it. 0 x 2 = 0, so again no heat.
If the circuit driving the transistor develops a fault, and only turns the transistor half on, then we now have 6 volts across it and 1 amp flowing through it. 6 x 1 =6, so we now have 6W of heat being produced by the transistor, which it won' like for long!