Advise & Help needed

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: 1998 NB
  2. I’m based near: Burton on Trent (staffordshire)
  3. I’m looking for technical help or recommendations on: issues starting in the mornings
    in the mornings it will just not catch or fire.

i have replaced all of the following items.

  • Air filter (pipercross)
  • New Panasonic battery
  • Fuel filter
  • Spark plugs
  • HT Leads
  • Coil pack (used of eBay)
  • Cam sensor
  • Air temp sensor (one that’s goes into air box)
  • Crank sensor.
  • Fuel treatment
  • coolant Temp Sensor (rear of engine)
  • 02 Sensor (oxygen sensor )

if its cold or wet it will not fire up,
i have just tried again this morning as i changed the o2 sensor yesterday after using the dignotic LED to come up with error code 15 oxygen sensor (output too low), fired up first time, but over night it rained.

there is no water i can see anywhere.

i dont know what else i can try. hopeing someon here could advice what to try.

2

Hi
You have one of the worst types of problems to solve, intermittent ones!
From your description of what has been done, and that damp may be a cause, I would check the ECU connectors.
The ECU lives under a plate in the passenger foot well, you need to lift the carpet and possibly drill out a few security screws.
Look for signs of water ingress and check all the connectors for corrosion, if there are signs you may have to open up the ECU and check inside.
If you find nothing then the problem is possibly elsewhere, but this is not an uncommon issue.

Good Luck

3

i have pulled the passenger carpet up today and found it damp,
along with some surface rust,

after attacking the rounded rivet things i got the sheild off,

IMG_6150
IMG_61501920×2560 549 KB

the conenctions on the ECU look perfect. no corosion or rust.

IMG_6151
IMG_61511920×2560 397 KB

is there anything i need to check as to why water may be getting in the footwell, are there some front drain holes like the rear ones?

4

I’ve read in the past about earthing problems from battery to chassis causing starting, electrical issues etc. Worth checking all earth straps for good contact.

5

do you know where they all are?

i have done the one on the top of engin near the injector rail / intake
i have also done the strap the goes from engin to the passenger side of the body under the washer bottle area

6

Someone will correct me if wrong. The battery connection from the boot area to an earthing point at the rear chassis.
It’s been a while since I’ve owned a Mk1/Mk2 so precisely where I’m unsure now.

7

And from that point inside the boot to the PPF underneath. The PPF end of that fat cable seems to rot.

8

sorry whats the PPF?
once im back and ive assembled the passenger side again ill rip the boot apart.

9

Look under the car and there is an aluminium girder linking the gearbox to the differential.
PPF = Power Plant Frame.

The chassis cable goes to near the diff end of the PPF .

10

My ECU cover plate looked a lot worse than than when my car ‘flooded’.
The issue was blocked drain tube. I have since relocated the ECU behind the glove box and have an as new cover from Mazdadudes I’m planning to fit when it stops raining

11

where was this Tube? i have cleaned the hood drains out.

ive juts saded all the rust off the plate and primerd and painted it.

12

I was referring to the hood drain tube. Looks like youve found it

13

Morining

a massive thank you, i have orderd a replacement Earth cable & Lugs from Amazon,

following this guide i found
https://www.pugaddicts.co.uk/2019/11/mazda-mx5-na-replacing-broken-corroded.html#:~:text=On%20the%20Mazda%20MX5%20there,snapped%20completely%20(see%20below).

i have jacked the car up this morning and low and behold a snapped earth cable

71240059418__CDB04C0D-8E7E-462F-AA9E-A669903F1710
71240059418__CDB04C0D-8E7E-462F-AA9E-A669903F17101920×1440 195 KB

so job today run new earth cable and see if it starts first time in the morning

1 Like
14

so seems that the broken earth hasnt solved my issues :frowning:

however i have pin pointed it down to the be the cooleant Temp sensor,
if it unplug it ans crank the engine it starts, i can the plug it in whilst its running no issues,

however if i dont disconnect it before trying to start from cold / over night no joys.

now i have replaced this part allready with an offical mazda part. is it worth checking the earth on this cable? as 3x wires go to the plug the onther one a Earth.

15

dont know if anyone has any recomdations

if i disconnect the rear coolant sensor near the coilpack and try to start it,
after a while it fires up.

could i have gotten a faulty sensor?

i dont want another year of having issues trying to get it started, i would juts get rid of it