A couple 'lectric questions

[ben711200]

Evening

As part of the Volvo's bid to (consistently) achieve over 20 to the gallon, I'm going to be upgrading the LPG to closed loop. This involves fitting a lambda probe..

These come with a variety of numbers of wires, from one upwards.
1 wire- signal wire (presumably earthed through it's body)
2 wire- signal wire, earth wire
3 wire- signal, earth, heater
4 wire- signal, earth heater, heater.

Can't say I really understand the need for two wires to preheat the thing, unless it's a separate earth for it or something. So I think I will be going three wire as I can't tuck it right up in the exhaust manifold so as to not really need to have it heated.

This leads me to the first question.. Since I have no existing lambda wiring, do I just assume that the heater wire requires a 12v feed?

That then in turn leads to the 2nd question.. Since I'm gathering more extra electrical bits floating about around the engine (kenlow, switching stuff for the LPG condenser, Lambda, possibly a more meaty horn when I get around to it) I want to tidy it up and do it a bit more properly by having an auxiliary fuse box.

My idea for this is to take a switched 12v feed from the ignition, run to a relay (amperage as yet undecided. Bigger the better?), which allows me to use a wire straight from the battery. Good idea? And why is it that fuse boxes have individual inputs, and not just one 12v connection with a series of fuses taken off of it? Can I just piggyback them together?

Cheers ;D


**Apologies for lack of technical terms and the vague descriptions, I'm sure you know what I mean**

[RobinJI]

With regards to the last question, unless the volvo's a top spec, every-option-ticked model, then you may find there's actually quite a few unused fuse's in the original fuse box. I know there's a fair few on an average scirocco, and the passat I just stripped had a whole bunch too, despite having lots of optional toys. So I guess using them would be the neatest option if there's enough.

[Steve]

Wouldnt the closed-loop setup come with some rough wiring diagrams? or is it just an upgrade to your existing setup?

Steve

[ben711200]

Perhaps, but I have a funny feeling they're all used and I think the tidiest option will be to make an aux fuse box. Gives me room for further expansion as and when I need it too

[ben711200]

Apr 12, 2010 21:22:46 GMT Steve said:

Wouldnt the closed-loop setup come with some rough wiring diagrams? or is it just an upgrade to your existing setup?

Steve

-

It works on the assumption that you already have one fitted and only needs the signal wire

[Steve]

That just sounds too simple.........i don't believe it ;D

Edit: I just googled "closed-loop lpg wiring diagram" and looked at an aftermarket setup and it looks like your right. One wire (poss purple/white or purple/black ) off the sensor is the signal wire and a black wire which goes to ground .........and it should work like that

[ben711200]

Yeah, the purple one It's not the wiring of that I'm too concerned about, it's just that if I keep adding electrical gubbins, I'd rather wire them in nice and tidy.. And find out about the heater wire on Lambda thingies.

[Steve]

I think the heater part might be a bit more difficult to control unless the lpg ecu thingy has the facility to monitor it its something alot of modern setups will be able to control but yours might not

[ben711200]

hmm, you could be right. The other thing to note, is that because it is LPG, I always start on petrol to warm up first anyway, which I imagine could negate the need for a heater. Should have thought of that before really...

[RobinJI]

Apr 12, 2010 21:23:46 GMT ben711200 said:

Perhaps, but I have a funny feeling they're all used and I think the tidiest option will be to make an aux fuse box. Gives me room for further expansion as and when I need it too

Fair play, what about something like this?

2 inputs (could be used as ignition live and permanent live maybe) with 4 fuses/outputs for each input.

Although I've definitely seen a fuse box somewhere that just had a single, big, fat input to it, and a whole bunch of fuses and outputs.

[Clamity]

I was reading up on the MS forum about lambda probes a little while ago. Couldn't quite digest all that was said, but I think the ECU has to control the heater as the resistance varies a lot with exhaust temp. Maybe connecting directly to 12V when cold will draw enough current to wreck the wiring.

Depending how far the bung is mounted from the exhaust ports, the heated type might be necessary for times when the car is idling for a while, unless the ecu expects the probe to go cold and ignores the signal in that case.

[cobblers]

From my experience, the most common type is a 4 wire lambda, which means they are easy to get off ebay cheap! 2 wires are for the sensor (signal and ground) and 2 for the heater, which is not really necessary unless you are mega picky about it working from cold.

4 wire lambdas have white, black and 2 grey wires. White is signal, black is ground and the 2 grey are either side of the heater.

You can more or less directly swap a 1 or 2 wire in it's place (if you don't need the heater, which you probably don't), but they seem less common and economies of scale are at play.

From memory, looking at the wiring on a mid-90s 106, the heater is wired inline with the fuel pump, so on all the time the engine is running.

[ben711200]

Apr 12, 2010 22:15:57 GMT RobinJI said:

Apr 12, 2010 21:23:46 GMT ben711200 said:

Perhaps, but I have a funny feeling they're all used and I think the tidiest option will be to make an aux fuse box. Gives me room for further expansion as and when I need it too

Fair play, what about something like this?

2 inputs (could be used as ignition live and permanent live maybe) with 4 fuses/outputs for each input.

Although I've definitely seen a fuse box somewhere that just had a single, big, fat input to it, and a whole bunch of fuses and outputs.

That's the sort of thing, though I'd be a fussy blighter and moan that it's pre-wired and has writing on it that's irrelevant to my needs..

This from here would be spot on, though I may be showing my tightness at not wanting to pay £20 plus VAT for it


and this one would be better because it's half the price, and uses the same type of fuse as the rest of the car (no point having to carry more than one type of fuse..) A six way bridge is available for it separately, so it would then fulfill my criteria a bit better.


Calamity and Cobblers.. Thanks I don't think it will make too much difference at idle to be honest so it looks like whatever 2/3/4 wire one is cheap on eBay is the ticket, and then just not bothering with wiring up the heater if it has one.

[jrevillug]

The Megasquirt manual shows a 3-wire lambda sensor with the heater supply just connected straight to the +12v feed on the fuel pump.

[ben711200]

Apr 13, 2010 10:42:04 GMT jrevillug said:

The Megasquirt manual shows a 3-wire lambda sensor with the heater supply just connected straight to the +12v feed on the fuel pump.

Interesting I could always wire it up, and if it burns out, it's not going to do any harm..