NB8B cranks but not starting

Engines, Transmissions & Final Drive questions and answers

Moderators: timk, Stu, zombie, Andrew, The American, Lokiel, -alex, miata, StanTheMan, greenMachine, ManiacLachy, Daffy

User avatar
aviper4u
Fast Driver
Posts: 258
Joined: Sat Jan 23, 2010 12:36 pm
Vehicle: NB8B
Location: Sydney
Contact:

Re: NB8B cranks but not starting

Postby aviper4u » Wed Jan 10, 2024 10:48 am

Ok so I got it running

Tried to post yesterday though the site seems to be intermittently down with a counter error...
Can you remember your first drive?

User avatar
aviper4u
Fast Driver
Posts: 258
Joined: Sat Jan 23, 2010 12:36 pm
Vehicle: NB8B
Location: Sydney
Contact:

Re: NB8B cranks but not starting

Postby aviper4u » Wed Jan 10, 2024 10:57 am

So I was working solo yesterday so I took videos of voltages with and without the jump starter
Battery 12.5V & 10.7V
Jump starter 12.5 & 12.5 noticibly faster cranking

No starting though

So then I started opening the back shelf and testing the fuel pump connector it was getting 12V at cranking like it should.
Then I checked continuity and all good and put a AC adaptor which didn't work so I tried the jump starter which did make the fuel pump make noise which then the car started instantly.

So I want to ask if a stock 2000 NB8B should prime the fuel pump on ignition reds/run position or only work when starting/running.

So ATM I'm leaning towards intermittent fuse/relay issue, thoughts?
Can you remember your first drive?

User avatar
greenMachine
Forum Guru
Posts: 4053
Joined: Thu Apr 24, 2003 11:00 am
Vehicle: NB SE
Location: Sports car paradise - Canberra
Contact:

Re: NB8B cranks but not starting

Postby greenMachine » Wed Jan 10, 2024 11:53 am

My 2004 (SE) definitely does prime the fuel pump on the 'run' - ie turning the ignition on, past 'acc', to the setting prior to activating the starter motor. It runs for a few seconds then stops. My understanding that is controlled from the ECU, to ensure the lines/rail are pressurised for the injectors. IIRC my 98 NB8A did the same.

Presume that when it started, it ran happily enough?

Yes, sounds like relay, could be a fuse, replace the lot, including the main engine relay (which is a known troublespot). Keep an eye out for anything that looks/suggests 'loose connection', corroded contacts, etc.

Glad to hear progress is happening!!

:mrgreen:
I never met a horsepower I didn't like (thanks bwob)

Build thread

NB SE - gone to the dark side (and loving it 8) )

User avatar
aviper4u
Fast Driver
Posts: 258
Joined: Sat Jan 23, 2010 12:36 pm
Vehicle: NB8B
Location: Sydney
Contact:

Re: NB8B cranks but not starting

Postby aviper4u » Wed Jan 10, 2024 1:42 pm

greenMachine wrote:Presume that when it started, it ran happily enough?


Yea it ran well though as I ran through all the gears etc though the ABS dash light came on as the car is on stands and the wheels speed sensor might error as the front wheels aren't spinning like the rears?

When I have time again I want to short the Fuel pump to ground pins in the diagnosis box in the engine bay to test if bypassing the fuse/relay helps as when it was running I saw the fuel gauge stop showing and I jiggled the fuel pump four pin connector which made is show again so something is a miss though I am not sure exactly.

Not registering anytime soon so I'm not concerned though I'll need a few parts changed in the future.

Thanks all!!!
Can you remember your first drive?

93_Clubman
Speed Racer
Posts: 11852
Joined: Mon Aug 08, 2005 11:35 pm
Vehicle: Clubman
Location: Melbourne

Re: NB8B cranks but not starting

Postby 93_Clubman » Sat Jan 13, 2024 10:49 am

aviper4u wrote:opening the back shelf and testing the fuel pump connector ... tried the jump starter which did make the fuel pump make noise which then the car started instantly.

aviper4u wrote:when it was running I saw the fuel gauge stop showing and I jiggled the fuel pump four pin connector which made it show again so something is a miss

Given above, perhaps worth keeping in mind the black wire issue mentioned in my earlier post as gauge & pump can be affected by it - it's an in-tank degraded wiring connector, which the direct connection of the battery jump starter may have overcome:
93_Clubman wrote: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


Return to “MX5 Engines, Transmission & Final Drive”

Who is online

Users browsing this forum: No registered users and 8 guests