Mx5 crank no start spark problem

Mx5 crank no start spark problem

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Julian.hutchinson1982

Original Poster:

2 posts

14 months

Friday 20th November 2020
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Hi all, first post on piston heads [first post on any forum for that matter so go gentle!)

I brought an mk2 Mx5 back in July with a view to build a kit car around it’s engine and running gear. It was running lovely up to a month ago when I hadn’t driven it for a few weeks and wouldn’t start due to what I presumed was a flat bat. Tried to jump start but still wouldn’t start.

I work away during the week so decided to take the batt out, recharge it ready for next weekend.

The following Friday, put the batt back in, And to my delight, started first time. Thought it was a bit strange but happy in the knowledge I hadn’t fried my ECU. Saturday morning went to start it and it wouldn’t.

Spent the weekend researching what it could be and ordered a new cam and crank shaft angle sensor, coil pack,HT leads and coil pack, ready for installation this weekend.

Fast forward to today, got back home, reconnected the battery and once again, started first time. Took it out for a half hour spin and drove lovely again. Turned it off, but once again, wouldn’t start. I then proceeded to replace all the bits I ordered the previous weekend, I.e, plugs, HT lead, coil pack, cam and craMk sensor. Wouldn’t start on batt or by jump starting.

This is all leading me to maybe an immobiliser issue but am really clutching at straws.

Any advice would be welcome.

Cheers.

geordiepingu

116 posts

22 months

Sunday 22nd November 2020
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A few things could be at fault, hard to really say from your description.

Have you checked the basics - have you got fuel and have you got spark? I know on a Mk1 it was easy to bypass the fuel pump relay with a paperclip to test, with the prehistoric diagnostics box. Not sure how you'd do that on a Mk2.

It's also an old car, is the wiring to the crank sensor/cam sensor and coil pack in serviceable condition? That would cause a no fuel/no spark if the sensor is not reading a valid input to the ECU.

There's more specific nuances to a Mk2 depending on the year, engine size and ECU code - if you shared both I'm sure someone more knowledgeable on Mk2s can chime in!

If it ran absolutely perfectly before holding it up for a few weeks, it's plausible a relay or fuse could've let go from corrosion or moisture, especially if it's been kept outside.

Daft question, if you're keeping it outside, the roof hasn't managed to leak and soak carpets near where the ECU is stored?

Mr MXT

7,401 posts

244 months

Sunday 22nd November 2020
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Have you got the gap right on the crank angle sensor?

I was very pleased with myself after doing a cambelt, then despair when it wouldn’t start. Turned out the crank sensor was about fifteen miles away from the trigger wheel.

Julian.hutchinson1982

Original Poster:

2 posts

14 months

Monday 23rd November 2020
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Thanks for your reply’s guys. I took it to a Mx5 specialist over the weekend and they suspect it is the immobiliser.
Going to strip it for its mechanical components and pick up a running MOT failure For the electrical bits.

Cheers again,