Blowing Fuses in manual Preheat circuit - HELP!

[shaunlfc1]

Evening all,

After weeks of diagnostics, researching etc.... I've finally taken a few peoples advice on installing my own manual pre-heat system for my Pug 405 TD.

This is what I have done:

Taken feed direct from POS on battery into one connection on a push switch i've installed in dashboard.

Then taken another feed from the other connection on the push switch straight in engine bay and put straight on number 3 glow plug which then feeds rest of the GP's via busbar. (removed original wiring from glow plugs)

Now, I've included a in-line fuse which is situated 2-3 inches from the battery positive in the first feed going to the switch in the dash.

Firstly I put in a 25amp fuse, as thought this might give a bit quicker protection.

So did all this work all went well, and did my first test of system. Here goes.....

Sat in drivers seat, pushed button and held for 10 seconds then attempted to turn over car, with no joy, just cranking no firing, which instantly means the GP's have not been on!

So I checked inline fuse, and the thing had exploded, glass smashed in half etc....

So then put in 30amp fuse and did same test and the same thing happened, although this time no glass explosion just a split fuse wire within the fuse....

Well this means I still have no pre-heat and am curious to know why I am blowing fuses, as this is something mechanics within our club and other clubs have advised me too do, as far as I know I havent got anything stupidly wrong, as I think from their descriptions and info its a pretty much simply idiot proof circuit.

I've spoken to my electrician mate, who hates car electrics, but he seems to think its blowing fuses because its "earthed" through the engine, and needs a neutral to prevent this, but as far as my knowledge goes the original preheat system on the car is purely LIVE FEED from alternator/battery into the relay/ECU, and LIVE FEED coming out of relay/ECU to GP's with the 5-pin connector on the relay being the ignition switch on, various warning lights and sensor inputs, so I disagreeumption is the original system is identical to my new system apart from the relay/ECU.

So why is mine blowing fuses?

Is the Original GP system fused? If not, is this the reason Im blowing fuses because the particular nature of my circuit/system doesnt require a fuse?

Should I perhaps have the inline fuse after the switch in the feed, feeding the GP's, rather from the battery?

Anyway, I bodged the break in circuit between the fuse ends just to test out circuit, and it seems to work fine, as car starts fine after holding switch in for 10 seconds or so. Although I have noticed the switch connectors on rear are getting a little hot once they've been on constantly for 10 seconds is this something to worry about?


I think thats it..... i've come so far and the bl00dy thing still isnt playing ball..... im sure im doing something stupid or obvioulsy wrong due to my limited knowledge on car electrics etc.... So please help if you can!!!

Thanks all have good weekends,


Shaun

[frank]

you need to fit a relay of at least 40amps or you will end up with a fire. just a normal 4 pin one will do, car acessory shops sell them and are the safest way to do it

[shaunlfc1]

Where do I fit the relay?

Is my switch man enough?

My switch is a push type, surely risk of fire is low as GP's will only be on whilst finger is on switch???

Cheers.....

[Donaldiesel]

Glow plugs draw approx 18 Amps each when first switched on. The current reduces to about 10 Amps as they heat up. Therefore the wiring needs to be able to handle nearly 80 Amps, which is why a relay is used in the preheat timer box. You are playing with fire here. Letting go of the button wil not stop a meltdown once it starts. You have already seen how the fuse exploded, so dont mess with this energy.

You have not given any information to suggest the preheat timer is faulty. Try sorting out the ignition feed to the timer. See my reply on your previous posting. Sorry, been away so missed some of this thread.

Regards,
Donaldiesel

[shaunlfc1]

Im keen to use the relay solution as, now I've installed my switch, all I need to do is put relay in connect it up and away I go.

Do I need to get a 80amp relay or Like Frank suggested just a 40 amp one?

Do I still need to put a inline fuse, and where is best for this?

I can use my switch to turn on relay which then takes power/charge from battery and sends it to glowplugs, hope this is right?

Thanks again for all your help, I know I sound amatuerish but, im learning, and at least I've not blown anything up yet apart from a couple of fuse's!!!

Cheers....

[frank]

I know I sound amatuerish but, im learning, and at least I've not blown anything up yet apart from a couple of fuse's!!!
YET!
get somone else to do it before you set fire to it

[shaunlfc1]

I've come this far, I wanna finish it myself.

Just some further pointers on the relay, and answers to the simple questions I asked in previous post would be most appreciated.

I dont have the money to put it in a garage where they will charge me silly money.....

I've spent 3 sats all day to get where I am, im sure with that final bit of advice I can finish the job.

Cheers again for your time....

[Donaldiesel]

The preheat timer box already contains the heavy duty relay needed for the glow plugs. You just need a new ignition controlled supply to the five pin connector. See my recent reply in your previous thread. Use your new switch for the 12v supply to the five pin connector if you must.

[shaunlfc1]

Thank you for the previous post in my other thread, it was very helpful.

You said not to go cutting wires, so I havent, this is why I wanna use my new circuit.

If I use my switch to engage the original ECU box I will have to cut into the wiring in the 5-pin plug no?

If you recommend me to do this, then I will as it'll save me getting a new relay and having to muck with the ignition etc.... which is something im not interested in doing.....

Thanks again.....

Shaun

[Donaldiesel]

What ECU? I thaught we were dealing with the preheat system. Assuming this is still the case, the preheat timer box has a five pin connector. The wires are:

CC5 - Ignition key controlled 12v supply
105 - 12volt supply from starter solenoid (only while engine is cranking on starter)
M115 - 'earth' negative connection to chassis
1394 - negative connection through postheater relay and injection pump - (coolant temperature controlled).
436 - 12volt supply to preheat warning light.

As I understand it, you are not getting an ignition controlled supply to wire CC5. This wire should be 12volts when the ignition key is turned to position 2. The wire must be broken, corroded or disconnected somewhere between the timer box and ignition switch. You can connect your switch to this wire (CC5) at the preheat timer box, or better, provide a new ignition controlled supply from fuse 12, or the stop solenoid on the injection pump, which will keep the system automatic. If you use a scotch block connector you can tap into wire CC5 without cutting it.

Are you sure wire CC5 isn't damaged where it goes into the five pin connector? You are getting power to the stop solenoid, since the engine did start. The same wire from the ignition switch supplies the stop solenoid, preheat timer, postheat relay, diesel advance corrector relay and fuse 12 (rev counter and some warning lights). The fault in the wiring must be close to the preheat timer since you don't mention any of the other items being faulty.

If you use your manual switch, you will need to hold it in for a few seconds after starting in very cold weather (Postheat) to avoid lumpy idle and smoke.

Regards,
Donaldiesel

[shaunlfc1]

Thanks Donald that last post is spot on, loads of info and enough for me too definitly fingers crossed nail this problem once and for all on Saturday.

When I say ECU I meant Preheat timer box, on other forums people refer to it as a ECU. Sorry about that.

I'll let you know how I get on.

Cheers Again...

Shaun

[shaunlfc1]

Hey all....

Finally got the old gal starting and running fine.

In the end I had to use my manual push switch and after market 70amp relay as what ever I tried with the cars' original pre-heat system simply didnt work.

Donald, using fuse 12 as a ignition controlled live 12v feed is not correct as this fuse/feed is constantly live regardless of ignition being on or not, luckily I put a multimeter on the 5-pin plug at the preheat box end with ignition off by chance and got 12V's coming through, otherwise I'd of kept it connected and drained my battery.

Anyway, fuse 12 would of been fine running through my new switch, by I opted to run a feed straight from battery to my switch then onto relay etc....

It works fine, nothing gets hot, its all fused up, all wiring is heavy duty, and I must admit I think she starts better.

Anyway, I wanna say a huge thankyou to everyone who through in there info and advice, as without you I'd of been forced to put it in a garage which im sure they'd of said it needs a whole new circuuit and system, as I still dont know whats wrong with the original system.

Anyway, thanks again, if you need to know exactly what I did and what I used incase you have similar problem then just hola!!

Cheers,

Shaun

[scottyman]

It would seem i have just gained exactly the same problem,
looks like i'll be making a bypass relay then

[shaunlfc1]

Well if you need any help then I've spent the past 5 weeks of saturday's trying to sort out this problem and put in the new circuit and system.

DonaldDiesel seems the most knowledgeable on here, try everything he has suggested to me, you never know you could find the problem with your system and be able to fix it unlike me!

Again if you need to know what I used and how I used it just shout.

Good luck,

Shaun

[Donaldiesel]

Hi Shaun,
Good you finally got it working. Checked my wiring diagram for 405 turbo diesel from 1992 - shows ignition key switch supplies fuse 12. Sorry if this is different on your car, and good job you checked. Any ignition controlled supply will do to to replace a faulty feed to the preheat timer. For reference, wires sometimes break inside the insulation and cause intermittant faults which are very annoying and difficult to trace. So it is important to always also test the negative wire to chassis. Sharp bends in the wiring loom are a clue. Anyway, your new system has done the trick so well done.
Regards,
Donaldiesel