NB8B electrical issues - HELP

[pezchops]

I've looked thru the wiring diagram and the only thing I can see to draw enough to blow a fuse intermittently on the engine fuse is ignition coils or oxygen sensor. Coils would be my bet, I've seen many times before when ignition coils get hot they short internally, common on Falcons and camrys , never had an mx5 do it before, but there is always a first. If it comes down to it throw some second hand ones on to see if it fixes it, or have the car running and move engine harness around a bit in deferent places to see if it stops or blows fuse. If it does you have a short. I've been a auto electrician for 20 years and these type of problems do drive you up the wall! Good luck

Cheers for the advice.

i have a 2002 nb8b and i can say from experience the engine fuse will blow with a 02 sensor problem.
mine was a short in the wire harness
it may only be american model nb8c?, but you could have 2 sensor's.

[The Green Goblin]

new crankshaft sensor that I am wanting to install
can anyone provide some specific details

http://forum.miata.net/vb/showpost.php? ... stcount=24

this was the post that i was referring to, no pics shown though. called up mania who said all that is needed is:

a) the sensor needs to line up with one of the notches on the timing wheel
b) the gap (between end of sensor/point + wherever it is pointing to) is 'credit card' thickness

thoughts?

[The Green Goblin]

I've looked thru the wiring diagram and the only thing I can see to draw enough to blow a fuse intermittently on the engine fuse is ignition coils or oxygen sensor. Coils would be my bet, I've seen many times before when ignition coils get hot they short internally, common on Falcons and camrys , never had an mx5 do it before, but there is always a first. If it comes down to it throw some second hand ones on to see if it fixes it, or have the car running and move engine harness around a bit in deferent places to see if it stops or blows fuse. If it does you have a short. I've been a auto electrician for 20 years and these type of problems do drive you up the wall! Good luck

Cheers for the advice.

i have a 2002 nb8b and i can say from experience the engine fuse will blow with a 02 sensor problem.
mine was a short in the wire harness
it may only be american model nb8c?, but you could have 2 sensor's.

interesting, i done a quick search & found plenty of common responses to yours. i will inspect wires & perhaps replace the 02 sensor also. it maybe due to wires rubbing against hot manifold or close to.

there is only 1 o2 sensor right?! under the car/near gbox passenger side - which is attached to the exhaust.

thanks.

[93_Clubman]

called up mania who said all that is needed is:
...
thoughts?

MX5 Mania should know their stuff better than most, so go with their advice.

[The Green Goblin]

so heres where im at:

- had auto electrician visit
- we noticed the 02 sensor wire was touching the exhaust manifold & melted/ate through the rubber exposing the wire
- have replaced the CAS
- have replaced front 02 sensor unit + wire (not touching anything hot)

took it for a drive after the front 02 sensor install, after 10 mins got back home & at idle it died again - busted engine fuse again, so it turns out that it wasn't the front 02 sensor that was the issue as originally thought. so now i should be checking ignition coils, alarm system - is there anything else?

i am taking it to a workshop next week.

[93_Clubman]

NB8B usual suspects in approx order of frequency are:
Cam position sensor;
Crank position sensor;
EGI relay;
Fuel tank electrical connector;
Coil on plug setup;
Fuel pump; &
ECU (if water gets into passenger side floor).

Caffeine on this forum who had/has an NB8B also had a persistent electrical issue (EGI relay), which he was eventually able to trace to intermittent faults with the tail & brake lights:
viewtopic.php?f=29&t=67030&start=30
viewtopic.php?f=29&t=38526&p=535895&hilit=brake+tail#p535895

[The Green Goblin]

Thanks mate..

ive purchased the crank sensor so this will definitely get replaced. links are very helpful.

this has been such a pain in the a$$ & ive missed 2 track days because of it.

[The Green Goblin]

so after much time & money spent..

turned out the issue was the rear o2 sensor.. care was not taken by person who installed my exhaust.. the wiring was sitting on the hot exhaust pipe rather than being tucked out of the way (exactly like the front o2 sensor), resulting in melted rubber housing, exposing wire.. the hot pipe melted the wiring which caused the short. ended up replacing the crank sensor whilst car was at the work shop, also had the ECU area inspected & cleaned.

something quite minor, but can cause much headache.. all because care was not taken - lesson learnt.

cheers all for your input.
J.