NB8B electrical issues - HELP

The Green Goblin · Postby **The Green Goblin** » Sat May 21, 2016 7:41 pm

guys,

to cut the long story short, I've had some electrical issues with the car this past week. on 2 occasions now whilst driving, the car randomly switches off & doesn't turn back on once coming to a complete stop. the engine/starter motor ticks over but the spark/explosion aspect does not happen. the car is regularly serviced & I know its not a spark or fuel issue.

the first time around I had a mechanic look at it & he was able to use the plug in adaptor diagnostic tool, it turned out that the 15 amp engine fuse had burnt out (fuse box situated under/near driver side foot well area), so it was replaced & the car turned on straight away. after this happened, I took it for a 15 min drive, only for it to die again, I was looking at the fuses again & replaced the engine fuse again (even though it didn't look blown), but no luck, the car wont start now.. has anyone had such issues like this & how did you go about resolving?

from an electrical point of view the car has been untouched except for a basic after market mongoose alarm system which was installed about a year ago. the only other thing I can think of is about 3 weeks ago, the OEM cruise control system was unplugged & the unit removed from engine bay however, the wiring is still there & was just tucked away near the engine bay fuse box.

I am now considering calling up a mobile auto electrician to sort this out asap, can anyone recommend someone who is decent & isn't a grub?

cheers,
Jas

JBT · Postby **JBT** » Sat May 21, 2016 8:34 pm

Can you get to the redundant cruise wiring and make sure it isn't shorting out on something under the fuse box?

bigdog · Postby **bigdog** » Sat May 21, 2016 10:13 pm

Can't hell with the electrical issue, but I would be interested in the cruise control unit - mine has a broken cable

datfreak · Postby **datfreak** » Sat May 21, 2016 10:39 pm

Could be 1 of 1000 things but start with the simple stuff first.

You can test the nb (and na) engine fault codes using only a resistor and led. Less then $2 bucks at jaycar. There are a few writeups but thie one is straight forward:
http://www.mx5diy.com/2015/04/retrieving-engine-fault-codes-for-mx5.html

Unsure on nbs but with the na:
the fuel pump relay under the dash often dies (test for this is removing the relay and bridging the + and the pump wire and see if the car starts with the relay bypassed)

the fuel pump itself is getting old and can fail (test with a na is the above relay bypass test BUT use a hose from the fuel return side of the fuel rail and test if its pumping into a jerry can)

CAS ie camshaft angle sensor are know to fail- there is a way to test them but most people just swap it for another one - check our forums or ebay if you think yours is suspect

The blown fuse maybe a concern- check for a short under the dash and engine bay.

good luck sorting it.

The Green Goblin · Postby **The Green Goblin** » Sun May 22, 2016 4:30 pm

JBT wrote:Can you get to the redundant cruise wiring and make sure it isn't shorting out on something under the fuse box?

Yes checked this out.. There was some gunk within the plug/head connection, so I cleaned it out & used duct tape to cover it all up. I don't believe it's this as I tried to fire it up after I cleaned it.. Still didn't turn on.

The Green Goblin · Postby **The Green Goblin** » Sun May 22, 2016 4:31 pm

bigdog wrote:Can't hell with the electrical issue, but I would be interested in the cruise control unit - mine has a broken cable

Happy to sell this to you if you want it. PM me.

The Green Goblin · Postby **The Green Goblin** » Sun May 22, 2016 4:37 pm

datfreak wrote:Could be 1 of 1000 things but start with the simple stuff first.

You can test the nb (and na) engine fault codes using only a resistor and led. Less then $2 bucks at jaycar. There are a few writeups but thie one is straight forward:
http://www.mx5diy.com/2015/04/retrieving-engine-fault-codes-for-mx5.html

Unsure on nbs but with the na:
the fuel pump relay under the dash often dies (test for this is removing the relay and bridging the + and the pump wire and see if the car starts with the relay bypassed)

the fuel pump itself is getting old and can fail (test with a na is the above relay bypass test BUT use a hose from the fuel return side of the fuel rail and test if its pumping into a jerry can)

CAS ie camshaft angle sensor are know to fail- there is a way to test them but most people just swap it for another one - check our forums or ebay if you think yours is suspect

The blown fuse maybe a concern- check for a short under the dash and engine bay.

good luck sorting it.

Very informative mate.

It's not the CAS.. Checked this & all is fine. I've been told it could be the 02 sensor but doubt this also.. Will need to get under the car to check though. The car once on functions as normal.

I have a feeling there's a short somewhere, most likely the alarm system.. There is definitely something stopping the car sparking/ignition cut..bad wire or something.. Needs a proper diagnostic.

Was given McArthur auto electrical details so will try them tomorrow. If anyone knows a good auto electrician around Wetherill park way please let me know.

Ta.

Todd77 · Postby **Todd77** » Mon May 23, 2016 11:37 pm

Hi mate, what number fuse is it? What does it say it's for? What you are describing To me sounds like a cam or crank angle sensor and by fluke it started after the mechanic changed the fuse,, trust me it happens all the time! Fuse could have been for something unrelated ( cig lighter or interior light) You think you have found the problem, but u haven't. Plus fuses don't blow for no reason. I haven't had any problems with mongoose alarms ever so would doubt it would be that. Get someone to check injector and ignition feed and pulse when not running, if you have feed ( battery voltage) but no pulse ( trigger ) to either I would say it's either crank or cam sensor. Cheers

The Green Goblin · Postby **The Green Goblin** » Thu May 26, 2016 12:23 pm

Todd77 wrote:Hi mate, what number fuse is it? What does it say it's for? What you are describing To me sounds like a cam or crank angle sensor and by fluke it started after the mechanic changed the fuse,, trust me it happens all the time! Fuse could have been for something unrelated ( cig lighter or interior light) You think you have found the problem, but u haven't. Plus fuses don't blow for no reason. I haven't had any problems with mongoose alarms ever so would doubt it would be that. Get someone to check injector and ignition feed and pulse when not running, if you have feed ( battery voltage) but no pulse ( trigger ) to either I would say it's either crank or cam sensor. Cheers

Thanks for the info.

It's definitely the engine fuse.. Blue 15 amp, I think it's number 19 or 20 off memory. I have ordered a new cam sensor.. Once installed the only way I will know if it was the CAS failing, is that it won't switch off this time around when driving.. It's all trial & error and some auto electricians are telling me it's hard to pin point as its intermittent. Otherwise all my wires in engine bay look like they're in good shape (car is only at 94k kms). really is painful.

Does anyone know where I can find a wiring diagram for my NB (it's actually an nb8c).

Ta.

93_Clubman · Postby **93_Clubman** » Thu May 26, 2016 4:44 pm

http://www.mellens.net/mazda/
http://neomiata.com/garage/index.php?pa ... 1997-2000/

Todd77 · Postby **Todd77** » Thu May 26, 2016 11:10 pm

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

The Green Goblin · Postby **The Green Goblin** » Fri May 27, 2016 11:56 am

93_Clubman wrote:http://www.mellens.net/mazda/
http://neomiata.com/garage/index.php?pa ... 1997-2000/

You are a legend.

The Green Goblin · Postby **The Green Goblin** » Fri May 27, 2016 11:59 am

Todd77 wrote: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.

The Green Goblin · Postby **The Green Goblin** » Sat Jun 04, 2016 2:43 pm

Fellas,

back again with the new crankshaft sensor that I am wanting to install.. it all seems pretty simple in terms of replacement & accessibility from the top of the engine however, whilst doing a quick search have realised that it needs to be 'gapped' a certain distance to function correctly which involves turning the engine & aligning the teeth on the crank timing wheel - can anyone shed some light here & provide some specific details + pics if possible?

cheers.