Strange starting issue after driver's side flooded

  1. My model of MX-5 is: nbfl 2005 1.8vvt icon
  2. I’m based near: bradford
  3. I’m looking for technical help or recommendations on: starting issue
    I have had the car for over a year and never had any problems with it starting until the end of August.
    I had been away for a month and came back…the car started up fine - no problems whatsoever after not moving or being charged for a month.
    I go away again for a week and come back to find that the driver’s side is full of water…at least an inch of it - the drain holes had clogged.
    I emptied and dried up the carpets etc as best I could.
    However, ever since then I have to use a booster on the battery to get it to fire up the engine.
    I connect the booster to +ve terminal and -ve to battery bracket retaining bolt and the engine fires straight up.
    I have removed the battery and charged it…it was fully charged. I also can see that the alternator is charging it as I have a device to tell me what the voltage is when am driving. So I know that it isn’t the alternator not charging.

Amy ideas?
I have looked at the immediate earth point from the battery and it is like new! The lead that then carries on from it appears to be good too.

I have had a brief look at the loom running along the driver’s side footplate and cannot see any break or water that may be causing the issue I am having…

Any ideas?

I’ll let someone else answer this who’s more familiar with the mk2.5 but I’ll hazard a guess at water ingress (yes I know you mention it.) probably in the ECU but I’m not sure where that is on this model.

ECU on the NBFL is under the nearside carpet so there’s a chance if water was in the drivers side…

A friend had to do a marathon drying out session in one to resolve all sorts of electrical related oddness.

1 Like

The passenger side was bone dry :slight_smile: it just seems strange that if I boost it with power pack it fires straight up…I did think it could be an earth issue but everything does seem to be dry except for the soundproofing under the driver’s side.
I will just try and get it drier and see if that makes a difference :slight_smile:
Thank you

Had the same problem with a MK3 I bought, usual thing drain holes blocked, water in cockpit. Had to take out sound deadening material, carpets and dry out all wiring and connections. Surprising where water gets not a quick fix. Left if Two or Three days to dry out before putting Carpets back. Kept fingers crossed no electrical components were damaged. ( also painted floor with rust inhibitor before putting carpets back ).

1 Like

my first thought was an earthing issue if it fires up with a booster on positive battery but not on negative battery terminal, so using an alternative earth.
Have you tried the booster on the negative as well as positive battery terminal?
Could it simply be that the battery is knackered and the flooding is a coincidence?

It starts up with both booster leads on battery too… I tend not to do that too often as I was told many moons ago that with newer cars there is a risk of damaging the ECU. So I always just do booster -ve to body. So it looks like it’s going to be a drying thing…battery charge was full so I don’t suspect it is a failing battery.
It’s an enigma!

Hi D,
Have you checked the voltage across the battery while cranking using just the car battery? What does it dip to? If you can pop the result on here for a diagnosis it may help.

Sounds like the battery to me.
I would at least get it tested.

Thanks everyone that has given some input…so the winner was…think there were a couple of things at play…definitely water ingress…took seat out and pulled carpet back and the soundproofing was still soaked :frowning: so have dried that out. However I think it was compounded by the fact I have heated seats and I think that the connections were damp too.
But after a couple of hours of drying the car out some more it is firing up every time…yay go team MX5’ers.

Now to find out what is causing a rumble underneath the front passenger side…doesn’t look like it’s suspension and have noticed that the air intake seems to move a bit…might pad it to see…

Hi Malc,

No I didn’t. Have sorted now by drying out the carpet some more and drying the heater connectors on the seat. I also cleaned off the rust on the exposed part of the seat caused by the water ingress. Thank you


Sounds like you got the damp problem sorted, well done. What the rumble is, not sure, is it very loud.

No, it doesn’t always happen and does seem to be over uneven roads…all the time then lol.
It seems intermittent and does not always occur over rough roads or speed bumps.

Droplink, broken spring, loose arch liner, I even had rattly brake pads but that was on the rear of my Mk1.

1 Like

Yeah I was heading in that direction…it has had all new discs, pads and calipers in last 12months so don’t think it is that.
Will check suspension again :slight_smile:

Droplinks were replaced…think I have found the issue…but won’t know till I get a chance to extract the damaged bolt…driver’s side bolt that holds the vent shroud and undercarriage tray in place.


The engine tray and the wheel arch liner lol.
The bolt looks like it has sheared so there is nothing holding them in place against the wheel arch.

Looks like the chassis rails are crusty, hence bolt sheared.:-1:

It’s another job possibly on my list… although still thinking of building ANC replicar so body wouldn’t matter…but fell in love with the car and even it’s colour …now redundancy has delayed my potential plans for the conversion…so we shall see :slight_smile: