NB8B cranks but not starting

[aviper4u]

Hello,

Apologies if already on here though the no starting threads I have seen have many dead links in there.

Got a NB8B that won't start though its been a shed dweller for several years though I usually leave it chilling with no battery but connect to run it every now and then to run it.

Usually after leaving it on reds till all the checks are done it starts after a few cranks though not today.

What I have tried.
- LED faults though only one light then nothing (https://mx5diy.blogspot.com/2015/04/ret ... r-mx5.html)
- Took a spark plug out to check for spark, it is sparking though the plug is dry... not sure if car engines flood like mowers etc though does this indicate fuel pump/relay issue OR does the spark plug fire regardless of any crank/cam sensor fault on these?

Thanks!!!

[greenMachine]

First, that guide is misleading - it is for the poms, you have an NB8B according to your profile, that has OBDii (if it is an ADM car). You need a proper scanner to read the OBD codes. IIRC there is a way to get the CEL(?) to blink them out, long time since I had an OBDii ECU though.

Troubleshooting the old fashioned way:
Is the fuel pump coming on when the ignition is switched on. (if not, check fuel pump fuse/relay)

Sounds like a fuse or relay, check both/all. If the fuel pump is making fuel pump noises, and the injector relay + fuse are ok, disconnect the fuel line as close to the injectors as you can, and while holding the loose end in a jar/can/etc, have someone switch the ignition on BRIEFLY - objective is to see if fuel is coming through the line (possible blocked fuel filter) - note you only want to see fuel come out for a moment, as loose fuel in the engine bay with ignition on is not recommended by 9 out of 10 WH&S courses, for the obvious reason. I would not do this step without a fire extinguisher handy.

That pretty much exhausts the checklist. If all that looks ok, check that you don't have rats chewing your wiring - that might break a circuit without necessarily causing a short to blow a fuse. I am assuming a fully standard car, that has had no, repeat NO work done on it since it was last running. If it has, thoroughly check out that work for loose connections etc.

I'd usually be pointing at the CAS sensors, but if you have spart they sound like being ok.

Let us know how you go.

[greenMachine]

From the horses mouth ...

[aviper4u]

Yea I have a NB8B which is the earliest variant as in the late 2000 model build.

Many steps are highlighted and I am now back at work so next chance I get will be exciting.

Thanks for the wisdom

[93_Clubman]

you have an NB8B according to your profile, that has OBDii (if it is an ADM car)

have a NB8B which is the earliest variant as in the late 2000 model build.

ADM NB8B didn't get OBDII until 2002.

NB8B usual suspect issues 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).
As GM mentions frequently with NB8Bs the issue is the cam position sensor or the crank position sensor.

NB no start guides: viewtopic.php?t=59479&start=15
NB8B fault codes: viewtopic.php?t=67370
NA no start guide: http://wiki.miata.net/tiki-index.php?pa ... tart+Guide

[aviper4u]

From what I can tell by reading up on no spark plug spark threads on the many Miata threads that exist online if I am seeing spark the cam/crank sensors are alright though I will need to test this more by unplugging them and seeing if the spark plug fails I guess.

I am hoping it a relay or something though as the car is mainly in storage I am thinking it is very likely to be a fuel delivery issue and hopefully not a blockage or pump problem...

I'll update as soon as I know more though thanks for the wisdom again!!!

[greenMachine]

Thanks Clubman, I stand corrected. Never a day goes by do I not learn something ...

[93_Clubman]

As GM mentions, initially very carefully check that fuel is getting through to the motor. Also In the context of the combustion triangle, worth checking that a large cloth has not been suck into the air filter - have seen this following a dealer service!

Ref fuel pump - doubt it's this as seemingly more frequent on the NA, but fuel pump wiring loom & connectors at the inside top of the fuel tank can be an issue as this is where the so called black wire problem manifests itself. Following details the issue as well as MB's observation about ultrafine metallic power at the top of his fuel pump: viewtopic.php?f=55&t=46425

As pic links in my original post above are US, the following shows the fuel pump loom connector, which plugs into the inside top of the tank, which is where black-wire issue occurs:
viewtopic.php?style=3&f=55&t=70835

[StillIC]

What is the battery voltage during cranking? I have found with my MX5 and my Celica past, that even with a reasonable crank of the starter, if the voltage gets too low during cranking the ECU won't fire the engine. An unloaded 12.3V on the battery won't start my MX5; 12.4V might in summer but not winter. Cranking voltage drops into the 11s.

[bruce]

Yes, always look at the most obvious (and simple) explanation first.
If not battery, do you have good fuel?

[aviper4u]

Update

Battery voltage is 12.5V and 10.5V when cranking, sounds very fast

Fuel has been in the tank for close to three years though I have added 20L in about a year ago, took a spark plug out and dry. Should bad fuel make no running or just bad running?

Fuel pump connector provides 12V when cranking though when I connect a 12V AC adaptor to the pump I hear nothing, how wattage does the pump need?

Lastly a mate of mine that was around when I was cranking smelt fuel at the exhaust but I could hardly smell anything, is that a sign that the fuel is bad or the pump is not working and only residual smell from the exhaust system?

[greenMachine]

Lost a lengthy post.

Short version: use a jump starter battery, report back.

[aviper4u]

Lost a lengthy post.

Short version: use a jump starter battery, report back.

I'd be surprised if it's the battery as I got it off a mates write off when in the car less than one month and it started fine last time also charging the battery between tries though like I always say I like being wrong for the right reason!!!

[93_Clubman]

Fuel has been in the tank for close to three years though I have added 20L in about a year ago, took a spark plug out and dry.

Lastly a mate of mine that was around when I was cranking smelt fuel at the exhaust but I could hardly smell anything

Have found year old unleaded sufficient to start a car. If the plug was dry shortly after cranking then it would seem fuel's not making it to the combustion chamber. Re fuel smell at rear, fuel filter is just forward of the rear driver side wheel. As GM says, first try a known good jump starter & check plug afterwards if it still doesn't start.

[greenMachine]

Lost a lengthy post.

Short version: use a jump starter battery, report back.

I'd be surprised if it's the battery as I got it off a mates write off when in the car less than one month and it started fine last time also charging the battery between tries though like I always say I like being wrong for the right reason!!!

Possibly, but 10.5v seems low. It is simple and worth a try.

I have started cars with old fuel, doubt that is the problem. Fuel pump may be the issue, check the injector fuse and if that is ok check the fuel pressure.