NB8B engine cut out

Uncle Arthur · Postby **Uncle Arthur** » Mon Apr 26, 2010 7:20 pm

I'm gonna have to try the main relay, but my cutting out problem is really WEIRD.......

After I start the car if I wriggle in the driver's seat it cuts out. I worked it out when I realise when I get inthe car and start it, the next thing I do is push hard on the floor (foot rest) and wriggle my self tightly into position in my seat.

Now when I do that, for whatever reason, the car falters and cuts out, and then refuses to restart straight away. If I start the car through the open window, without me in it, when I get in, the car stalls.

Trying to think what it might be, my first thought is that tit is like the motion sensor in my alarm is switching the car off, or that there is a wire under the driver's seat/floor pan (particularly the driver's foot rest) that shorts out when I move.

Once the car is properly warmed up, it seems to behave.

It's weird man - really weird

Uncle Arthur · Postby **Uncle Arthur** » Tue Apr 27, 2010 12:13 pm

It looks like it might be the main relay afterall....... now has anyone managed to source an alternative to the mazda part? $150 for a relay is ridiculous!

93_Clubman · Postby **93_Clubman** » Tue Apr 27, 2010 1:09 pm

Uncle Arthur wrote:It looks like it might be the main relay afterall....... now has anyone managed to source an alternative to the mazda part? $150 for a relay is ridiculous!

UA, good to hear you've possibly id'd the problem, but $150 for a relay :shock:

I think I'd be tempted to get a couple of 2nd hand ones if they were available cheap & take my chances.

Caffeine · Postby **Caffeine** » Tue Apr 27, 2010 2:11 pm

Is it the same as the EGI main green one?

I've paid $25 3 times and $5 once for second hand ones of them

manga_blue · Postby **manga_blue** » Tue Apr 27, 2010 7:03 pm

UA, mine behaved pretty much the same way. This morning I pulled it out, pried off the plastic cover, cleaned the points with a really narrow strip of 600 wet and dry, bent the holder of the main point back to what I thought the original gap should've been and whacked it back in. Works like a charm again. It was simply good old-fashioned pitted points. Can't you tell I used to own Anglias and Minis?

Mind you, it's only a relay and they're almost steam technology now. I've ordered a 40A Siemens one from RS-Online for $10 and I'll wire that in. mx5parts.co.uk had new ones (JE16 056700-8780 replaces the original B6S8) for 47 pounds. Sorry I meant to take a photo first to show the pinouts. I'll sketch it and spec it later.

manga_blue · Postby **manga_blue** » Tue Apr 27, 2010 7:36 pm

Here y'go.

MAIN Relay pinouts.jpg

A = 12V+ output to ECU, injectors, coils, pump, cooling fan relay, etc,
equivalent to pin 87 in a std relay
B = 12V+ input (always hot) from ENGINE fuse under dash,
equivalent to pin 30 in a std relay

C = earth from relay coil
equivalent to pin 86 in a std relay
D = 12V+ input from ignition switch to relay coil,
equivalent to pin 85 in a std relay

In an emergency you can remove the relay and hotwire from pin A to pin B with 30A wire and quickfit connectors

Caffeine · Postby **Caffeine** » Tue Apr 27, 2010 7:52 pm

manga_blue wrote:In an emergency you can remove the relay and hotwire from pin A to pin B with 30A wire and quickfit connectors

Or a piece of 'U' shaped coathanger, which I still keep in my front cupholder should it be required again

Benny · Postby **Benny** » Wed Apr 28, 2010 12:10 pm

manga_blue wrote:Just as an afterthought, the Main relay problem is the only one I can think of that you can fix by slamming the door and kicking the car.

I wonder if that would work on Mrs Benny?
She doesn't have any doors, but a good kick might get some action! :mrgreen:

93_Clubman · Postby **93_Clubman** » Wed Apr 28, 2010 1:59 pm

Caffeine wrote:Is it the same as the EGI main green one?

Believe so - black on the NA6s & NA8s I've seen & labelled 'FUEL INJ'.

manga_blue · Postby **manga_blue** » Wed Apr 28, 2010 2:46 pm

Caff, is yours all sorted yet? I reckon that if you keep blowing relays then you might have a problem with the coil side of the relay, either the 12V supply or earth return. That could mean the points don't close properly and keep arcing and burning out.

Caffeine · Postby **Caffeine** » Wed Apr 28, 2010 3:07 pm

manga_blue wrote:Caff, is yours all sorted yet? I reckon that if you keep blowing relays then you might have a problem with the coil side of the relay, either the 12V supply or earth return. That could mean the points don't close properly and keep arcing and burning out.

It hasn't died for a long time, at the moment I have intermittent faults with the tail and brake lights to chase

Uncle Arthur · Postby **Uncle Arthur** » Thu Apr 29, 2010 7:01 pm

Definitely NOT loving the MX5 right now.....

Mark - thanks for getting that injector relay for me - it didn't fix the problem.

I have now possibly tracked the problem further 'upstream' in the electrical system. It seems that there is only intermittent current passing to, or through, that relay - when I turn the ignition key slowly, I can sometimes hear the relay click (not sure if it is the one under the dash, or the injector relay. Sometimes when I turn the ignition, I hear no click, hence no injectors, hence no fuel..... Sometimes when I turn the ignition, the current to/through the inj relay seems intermittent such that the relay 'flutters'.........

This is a sudden failure which is not consistent, and seems related to a bad connection somewhere in the ignition circuit, or a bad switch somewhere. Perhaps it is something to do with the alarm/immobiliser..... I don't know yet. However, a bad connection/faulty connection somewhere seems consistent with the fact that if i start the car and get it to run, it may even cut out as I move into, or in, the driver's seat.

Any considered opinions or suggestions from the Brainstrust of Dodgies would be greatly appreciated, because both SWMBO and I (more her) see Max as a very effective boat anchor right now, rather than a delightful machine to put through the twisties.

manga_blue · Postby **manga_blue** » Thu Apr 29, 2010 10:16 pm

Caff's coathanger solution is looking good.

Maybe he can sell you the design drawings.

Uncle Arthur · Postby **Uncle Arthur** » Sun May 02, 2010 2:17 pm

Uncle Arthur wrote:Definitely NOT loving the MX5 right now.....

Mark - thanks for getting that injector relay for me - it didn't fix the problem.

I have now possibly tracked the problem further 'upstream' in the electrical system. It seems that there is only intermittent current passing to, or through, that relay - when I turn the ignition key slowly, I can sometimes hear the relay click (not sure if it is the one under the dash, or the injector relay. Sometimes when I turn the ignition, I hear no click, hence no injectors, hence no fuel..... Sometimes when I turn the ignition, the current to/through the inj relay seems intermittent such that the relay 'flutters'.........

This is a sudden failure which is not consistent, and seems related to a bad connection somewhere in the ignition circuit, or a bad switch somewhere. Perhaps it is something to do with the alarm/immobiliser..... I don't know yet. However, a bad connection/faulty connection somewhere seems consistent with the fact that if i start the car and get it to run, it may even cut out as I move into, or in, the driver's seat.

Problem found - problem solved.

Previous owner had put in secret switches - basically they kill the car.

At least 10 years of motion, moisture, vibration and current etc had led to cracked insulation in the wires leading to said switches.

Once I found them, it was an easy fix.

93_Clubman · Postby **93_Clubman** » Sun May 02, 2010 5:18 pm

Uncle Arthur wrote:Problem found - problem solved.

Previous owner had put in secret switches - basically they kill the car.

At least 10 years of motion, moisture, vibration and current etc had led to cracked insulation in the wires leading to said switches.

Once I found them, it was an easy fix.

Good to hear it's fixed!

Not sure if it's still popular to install these kinds of switches - they can be useful, but certainly a pain for later owners who haven't been advised of their presence.