Relays..

[theaxe]

I'm planning to keep some spares in the car (when I get it, 96 hours and counting). Are they all the same? If so where's the easiest place to get them?

If not what do I need to have a spare set on a '98 Chim 500?

Thanks guys!


PS. Tried search but it's broken.

[hugepiece]

Recently got mine from www.LRDIRECT.CO.UK for 14 quid each. Bosch part number is 0732014112

[hugepiece]

This is the part number for the Fuel pump relays found in the passenger footwell, I assume this is what you were referring to.

[mgman50]

The original Bosch fuel relays are only £10 each from TVR Carparts, but they sting you a bit on postage (£8)as they don't use the good old Post Office

[theaxe]

So are all of the relays the same? Which ones are critical (ie. not for heated seats etc...)?

[greenv8s]

The two metal-cased relays in the ECU loom are different to all the others, and should only be replaced with identical relays. All the other plastic cased relays in the fuswe/relay panel will probably be generic changeover relays, just make sure you get an adequate rating (some will be 30A but some may be 40A).

[chassis 33]

What excactly is so special about the two metal relays? I've head all sorts of things like oh they have diodes in...well so do loads of fairly run of the mill relays.

As I understand it they are fairly normal in their basic function, ie for fault finding you can swap in any two pole 5-pin (ie two 87 terminals not an 87 and 87a terminal) on off relay. What else do they do over and above this?

Regards
Iain

[greenv8s]

As you say, the critical difference is that they are two pole make/break relays rather than the changeover relays that are used elsewhere. Changeover relays will get the car going but leave the lambda heater circuit powered up with the engine off, which will flatten the battery pretty quickly.

The other noticeable difference is that they are metal cased rather than plastic; maybe this improves heat dissipation or something? Don't know, but I imagine there would have to be some reason for Bosch to go to the extra expense.

Electrically, there's nothing special inside except a small diode. It's been too long since I looked at one of these and I don't remember exactly how it was wired up, but at the time I just glanced at it and mentally ticked it off as a conventional snubber diode in parallel with the coil. Maybe it's in series, in which case it would mean that the relay didn't draw any current when the coil was back fed. Is it back fed? Don't see why it should be, but again I've never checked.

As far as I can see, any twin pole relay with adequate current rating should work just as well, and I've run an ordinary plastic twin pole relay for a few days with no obvious ill effects. I've also run a changeover relay to get me home, and again it worked fine except for the battery flattening effects.

[theaxe]

So if I get a couple of Bosch 0732014112s and a couple of generic 40amp relays I'll be covered?

[chassis 33]

Axe...yes!

Peter...ignoring the diodes; a 5-pin x-over will mean that 87a (the middle pin) feeds the Lambda sensors (presumably on the ignition relay, what does it do on the fuel pump relay?) when the relay coil is de-engergised, but wont feed the lambda sensors when the ignition is on, again fine for testing, not great for running the car below 3100rpm.

Regards
Iain
(P.S. PM me if you don't want to bore these good folks)

[greenv8s]

That's right. Running without power to the lambda sensor heaters would mean they take longer to warm up (normally only takes a couple of seconds with the heaters on) but the heat from the exhaust should warm them up eventually anyway. I didn't notice any particular problems with the heaters unpowered, there was none of the bolshiness that you normally get when a lambda sensor goes bad. But having the sensors powered up when the ignition is off is definitely a quick way to flatten the battery!