What is this thing and what does it do?

[tuvok4711]

Dear community,

this is possibly a newbie  question but surely most of you will know and could soothe my curiosity:

What is this kind of button-thing mounted in my 1999 K-Series Supersport and what is it good for? It is mounted right beside the heater on the passenger side.

Thanks!

Steven

[michaelf]

It's the inertia switch, turns off the fuel pump in an accident, there are quite a few threads on this site about them.

[Jonathan Kay]

Please let me know if you would like an Assembly Guide and Handbook.

Jonathan

[tuvok4711]

Thanks all!

So it directly affects the fuel pump, right? Because I sometimes experience that the fuel pump does not work when starting (the immobilizer has been correctly turned off though). And I am thinking if this switch might have anything to do with that? (malfunctioning somehow?)

 

@Jonathan: thanks; actually you already did send me those a couple of months ago ;-)  (maybe should have looked there first but sometimes a quick question gets the faster answer ;-)

[Jonathan Kay]

"So it directly affects the fuel pump, right? Because I sometimes experience that the fuel pump does not work when starting (the immobilizer has been correctly turned off though). And I am thinking if this switch might have anything to do with that? (malfunctioning somehow?)"

*It does.

But it's going to be hard to find out what's happening: intermittent failure and lots of possible causes.

When you don't hear the fuel pump does the engine crank normally?

Does it always start eventually? 

Have you got a multimeter?

Jonathan

* Unlike the immobiliser!

[tuvok4711]

When you don't hear the fuel pump does the engine crank normally? --> yes, but it does not start

Does it always start eventually?  --> no. The last few times I just waited until next day while as a precaution charged the battery. Next day all was good; engine started directly.

Have you got a multimeter? --> yes

[Wrightpayne]

I had a problem with my 1998 car when new. Just down the loom from that switch is a crimped connector inside the loom tape. Soldering the joint fixed the problem on mine. Possibly a complete red herring but something to check / be aware of.

The MFRU can also be a problem.

 

Ian

 

[tuvok4711]

@Wrightpayne: which cable on your photo do you mean? hard to tell; the loom toward the inertia switch on mine seems to look different; maybe has been renewed by previous owner, don't know. The colour of the cable should be the same I guess; if I could tell from your photo which cable it is I can try to compare it with mine...

 

btw: what is that brown cable which just ends without connecting to anything? I have exactly the same somewhere in my engine room dangling around rather indifferently ,-)

[Wrightpayne]

Twin yellow wires with green tracer - that goes to and from the inertia switch (One goes to the fuel pump). You will see a bit of black tape around one of the yellow/green wires - thats where the connector was and is now soldered.

 

there is usually a purple wire plugged into the brown wire connector. Engine was out at the time of the photo.

[tuvok4711]

Thanks! Will check tomorrow. Will also try to find the brown/purple connection. 

 

Cheers to the isle from Germany!

[Tom_Arundel]

Just a thought....The inertia switch has a`snap` connector plug for the wiring. The locating lugs on mine were moulded the wrong way around which could enable the plug to easily disengage. I reported it to CC at the time but haven`t heard back. Might be worth checking the plug is locked into the inertia switch properly.

[David aka Blue7]

"Does it always start eventually?  --> no. The last few times I just waited until next day while as a precaution charged the battery. Next day all was good; engine started directly."

I think that comment may indicate the problem.  I would suggest before you go delving into electrics and fuel supply that you check the condition of your battery, how old is it?  I have experienced similar problems in the past, engine turns but does not fire and eventually the battery goes flat. New battery always solved the problem.

David

[John Vine]

There are many reasons why a K won't start, but you can easily eliminate the inertia switch by shorting across the connector. 

With the ignition off, detach the 3-way Econoseal connector (two Yellow/Green wires) and insert a wire between the two terminals. Turn on the ignition, listen for the pump priming (a couple of seconds) and then try to start.

JV 

[Jonathan Kay]

Identifying cables:

You have the wiring diagram. It can save time when identifying cables by looking them up in the "standard" British wiring colours, eg:

https://www.autoelectricsupplies.co.uk/cms/files/colour_code_for_vehicle_wiring_-_new_order_2.pdf

Caterham usually adhered to these.

Eg that Brown is very likely to be a "Main battery feed".

Jonathan

[Jonathan Kay]

"When you don't hear the fuel pump does the engine crank normally? --> yes, but it does not start

Does it always start eventually?  --> no. The last few times I just waited until next day while as a precaution charged the battery. Next day all was good; engine started directly."

Good advice above.

1 Have a good look at that inertia switch and the wiring connections. Inspect, wiggle, disconnect, clean, reconnect. 

2 Have that little jump wire available in the car so that you can try shorting out the inertia switch the next time it happens.

3 Identify the fuse for the fuel pump. Check that it is gripped nicely. Remove, clean, and put it back in.

4 If it's the type of battery that needs topping up then check the levels.

5 Measure the battery voltage at rest, the minimum seen during cranking, and at 3,000 rpm. Tell us what they are. Cranking is the most convenient DIY load test and will tell you about the condition of the battery before it fails. Or that the battery isn't the problem and that you don't need to replace it blind.

Jonathan

[tuvok4711]

Thanks all! Very good advice and clever thoughts. I like the one about simply being able to shortcut the inertia switch in case it happens again. Thats also a way to rule out whether the inertia switch is the problem at all or if it lies elsewhere.

Have yet to find the fuse for he fuel pump in order to check it. I doubt, though, that this is the cause of the problem. But checking doesnt hurt ;-)

And: yes, the battery definitely is a problem! A new Banner is already one the way. I do have my old one on a CTEK in winter constantly but it still seems to be hard on the edge in cold weather. The banner was just 60 EURs lately (incl delivery) so I will just put in a new one. Having problems with constant draining, though. I am still studying all the posts where others describe the same prob plus give multiple advice to check it out.

I will check the drop of voltage when cranking of the old battery (voltage at rest is 12.65V, so approx 80% capacity up to my knowledge). What´s the value it should not drop under when cranking? 10V ?
 

[Jonathan Kay]

"I will check the drop of voltage when cranking of the old battery (voltage at rest is 12.65V, so approx 80% capacity up to my knowledge). What´s the value it should not drop under when cranking? 10V ?"

Probably something like 10.5 V. Some electronics might drop out below that. The strange thing is that it might still be able to crank at a decent rate.

I recommend measuring this routinely in the same way that we check oil levels. It's probably the easiest way of detecting deterioration as early as possible.

Jonathan

[tuvok4711]

[John Vine]

12.65v is nearer to 90% according to this chart:

I'd agree that, on a K, 10.5v is probably the threshold.  I assume you have the standard MEMS ECU.  MBE ECUs seem to cope with lower voltages (at least, mine does).

JV

[tuvok4711]

I assume you have the standard MEMS ECU. 

No; the previous owner managed to program and install a SCS Delta 400 and get the legal requirements necessary in Germany.

I do not have any knowledge about ECUs whatsoever but this things works just fine so far and helps the VVC to some extra horses ;-)

 

[John Vine]

You could ask SCS Delta what minimum ECU voltage is required during cranking.

JV

[David aka Blue7]

I would bet money that it is the battery, sufficient juice to crank the engine but not enough to create an adequate spark to the plugs while cranking.  It is so easy to suspect something more complicated.

My battery is ok at present but when it starts to fail I am thinking of fitting a lithium replacement as recently fitted by one of our local 7 owners, here

https://jackwebbmotorsport.co.uk/JWM-PS-12-LiFePO4...

[Jonathan Kay]

There are some specifications and experiences in Li ion batteries, including a single mention of that JWM PS-12.

Jonathan

[Rex]

My switch gave me trouble over the years, though my car came new with a Zetec engine. I finally bypassed that switch and have had no problems since. Sometimes the slightest thing would make it malfunction.

[SLR No.77]

The switch is a safety feature, unless it's a race car which is expected to be bouncing off kerbs IMHO it's wise to ensure the switch is fitted and functions correctly. It's a small minority of owners that have problems, they do usually work as intended!

Stu.