I'll start with a simple question, which someone may know the answer to, then elaborate below - I warn you, it's a bit long winded!!

On a 1990 MX-5/Eunos/Miata, what are the key components that need to be live when the key is turned from 'on' to 'start' in order to get a 'spark' and the car start up, i.e. why can I jump start my car in 'on' but when I turn to 'start' - and the starter motor DOES engage - do I get no spark / car doesn't start?

The details....

It's not starting (no spark when key turned to 'start'). Engine turns over, can hear fuel pump hum into life, but no spark/firing up. We've already replaced the Cam Angle Sensor and Igniter, we can see these are fine because with the key in position 'on', if we turn the CAS, we get a spark. In fact, we can also jump start the car in 'on' position... so it's just turning the key to to 'start' that doesn't work.

We figured it could be the aftermarket immobiliser playing up - but we've found the only 2 wires off the back of the ignition switch that we cut/go via the immobiliser and have re-joined them/bypassed the immobiliser (I can now
get power in 'on' without using the immobiliser key fob) - still no joy/spark in 'start' though.

Took the ignition switch off, pulled it apart, cleaned the contacts and reassembled... no difference. Also checked the wiring diagram (http://www.madracki.com/miata/wiring.html) and this forum
http://forum.miata.net/vb/showthread.php?t=324204 and touched a wire from the white to the black/blue as suggested - and it fires the starter motor (I can hotwire a car, cool!). Still no spark/starting though!

It has an aftermarket ECU (Adaptronics) but that appears fine, connected up the laptop and everything looks fine.

Don't think it's the coilpack, once started runs fine.. (this issue was intermittent with starting for weeks but now has given up completely).

All the fuses in the engine bay look fine... checked the main 'INJ' relay and this engages in 'on' and stays engaged in 'start'...

I've also borrowed my Dad and his multimeter to check the blue connection from the ignition is live on the coil pack connection and the ignitor connection in 'on' position, we thought turning to 'start' may go via a fuse or relay that was broke and perhaps we would loose the power to the ignitor/coilpack - but it's still present.

So what else needs power?? The coilpack/ignitor have power (at least from the blue ignition wire - should I check another wire?) when the starter motor fires, so why is there no spark? What is the different between jump starting
the car in 'on' position - which works - and firing the starter motor with 'start' position? I assume something else isn't getting a signal/power, what should we check?

I appreciate that the 'on' position is different to the 'start' position in that it's not just everything in 'on' plus starter motor, other things will turn 'off' to avoid drain on the battery, so only the minimal components required are live.

I figured that we could run a live signal straight to the starter motor in the 'on' position and, in theory, the car will actually start??? BUT: can't easily get to the starter motor/work out which wires I would have to touch... and it's not the 'proper' solution...

If anyone can help please, this has been driving me nuts for several weeks now, I'm not electrical or even that mechanically minded, had a lot of peoples help and thank god for Google but at the end of my tether now :(

Thanks
Ross

 

One thing I haven't checked is the Circuit Opening Relay. Could this be the cause of issues? Should it be in a different position (engaged/not engaged) between the 'on' and the 'start' position?

 

Cam sensor?

 

Quote:
"We've already replaced the Cam Angle Sensor and Igniter, we can see these are fine because with the key in position 'on', if we turn the CAS, we get a spark. "

Cam Angle Sensor already replaced with a mates...

 

My bad, it's my bed time. TL: DR.
In for results.

 

Explain in detail how you are starting the car in the on position. I think you mean push start but I can't be sure.

Check how much voltage is getting to the coil when cranking, and also, is your cranking weak/slow? If you have any skills with a scope, see if the igniter is doing what its supposed to while cranking.

I know of someone who had a problem with their car starting because the cranking rpm settings in their ECU were set high, and the Miata battery is tiny, its not exactly going to crank the engine fast. Might wanna check that. There was also a TSB for some Nissan (can't remember which one) where the starter was too weak and the PCM wouldn't see the rpm it wanted. Updated starter fixed the problem.

 

Hi... I'm trying to start in one of three ways, all with the same result:
1) Turning key to 'start' position (either having used the immobiliser key fob or having bypassed the immobiliser with direct wiring into original connections)
2) Pushing aftermarket 'start' push button
3) Having key in 'on' position and touching white wire to black/blue wire
-all crank but there's no spark at the plugs.
When I do this, in 'on' and at 'start', there is 12V at the blue wire at the coil.
The cranking is pretty strong, well it was, my battery started to go flat so have taken out now for a recharge...

"If you have any skills with a scope" - erm - what's a scope?!?!

You can take that as a no

We swapped out the igniter for a mates that we know's works anyway.

ooo the ECU comment is interesting... I've just had a play with WARI, the Adaptronics software, but can't see anything obvious... I'll ask a few people who are a bit more clued up on the Adapt.

Cheers!

 

Ok, we found a min crank RPM setting on the ECU - and mine seemed a little high! Set it lower...

NO DIFFERENCE.

Damnit.

Today I've been out in the freezing cold and done some more tinkering.

I've had the multimeter out and have made a few tests, the results are as follows. With the key in the 'on' position 2 this is what I get:

Cam Angle Sensor - unplugged and checked connections on the 4 pins
1 - black & light green - 0V
2 - white & red - 12V
3 - white - 4V
4 - yellow & blue - 4V

Coilpack - unplugged and checked connections on the 3 pins
1 - Red - 0V
2 - White - 0V
3 - Blue - 12V

Ignitor - unplugged and checked connections on the 8 pins
Won't list them all - they were all 0V except for the blue one (from ignition) which was 12V

When I turned the key to 'start' / position 3:

THE SAME.

Well, all the 12Vs dropped to about 9V, but believe that's normal.

I didn't loose any signals nor gain any.

Is that right??

We thought there should have maybe been a signal at the cam angle sensor on the first wire - on the wiring diagram I can see this is perhaps a shared earth?? Don't really understand wiring diagrams that well to be honest... checked the loom again for the CAS connections and did a continuity test on the muttimeter and they all looked fine...

Anyone know if I'm supposed to be getting a signal somewhere when I 'start' that I'm not???

 

Ok - new theory.

When I said

Well, all the 12Vs dropped to about 9V, but believe that's normal.

I've now been informed this isn't true, it shouldn't drop. If we link another battery in - we actually get a spark!!

Although... it's still only just above 9V and the spark is tiny and yellow (rather than blue?) and the car won't start.

Found and cleaned 7 earths in the car, made no difference.

It's now been suggested that it could be the ALTERNATOR to blame?! Apparently the alternator is supposed to do something to STOP the voltage dropping from 12V... this ring true with anyone? Could it be the alternator?

 

i have the same problem. as i was driving home one day my car shut off and turned back on like it choked or something. drove fine on the way home after that. parked it, woke up in the morning got into my car and it cranks but no spark. any ideas?? i also replaced the spark plugs since they looked bad and the coil pack... still no spark:/ need help!

 

Hi mate, all it was in the end, ridiculously, was a bad negative battery terminal!! Clean up you terminals and make sure they're nice and tight, may help...?