Engine cutting out

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[NitroDann]

Well I can't fault that.

Dann

[siege]

Does the tacho reading dropping instantly mean that it has to be one of these two sensors?
Because if that's the case and there is no other possibility then it's as simple as returning the faulty CMP sensor for another replacement

Or could it still be coil pack or fuel pump?

[siege]

I've done some more fiddling this morning

Cleaned the ground strap but it looked pretty good anyway
Set idle spot on to 850rpm
base timing still at 14 degrees warm

Idled until hot and cut out again
Lifted the bonnet to cool for a couple of minutes each time it cuts out to allow it to start again

Now with my timing light hooked up and trigger constantly on I idled it watching the light and the revs
On lead 1 the spark goes at the same time as the revs drop to nothing each time whether idling via the ecu or mechanical idle
On lead 3 an interesting thing happened. The engine happened to misfire once before cutting out. Spark on lead 3 dissappeared with the mis then returned until it cut out, when it misfired the revs only dropped to 500rpm and it sounded like it was continuing to run on the other two cylinders for that moment.

So my interpretation is that maybe the lead 2/3 coilpack is getting heat soaked?

[Red_Bullet]

What ECU is in it? Can you borrow an ECU?

[siege]

It's the factory MY00 ecu
The car doesn't have a check engine light

I don't know anyone else with an mx5 whose ecu I can borrow, but I do know there is a factory immobiliser so unless that was swapped as well it would have to be an aftermarket ecu.

[greenMachine]

My money is on a/both coil packs. If crank and cam sensors are good, that would be my next stop. Borrow a couple of coil packs, and see if that fixes it (obviously, ones that you know are working).

The other suspect is the main engine relay (I think that is the one), which causes similar symptoms. Do likewise.



On preview: I am nor aware of the factory immobiliser causing problems, but aftermarket ones, well that is something else.

[Locutus]

Faulty fuel pump or coil pack doesn't explain why the tacho immediately drops to zero while the engine is still turning (e.g. with the car rolling in gear). The ECU does not get any feedback on whether the fuel pump is working or a coil pack is firing.

Have you tested/inspected the main relay?

[The American]

This sounds like main relay to me. I would have expected the coil packs or sensors that are heat affected, to break up when load is increased and cause misfiring. Whereas, the main relay is either on or off, and will cut power to these other things (sensors and coil packs).

The fuel pump should not be able to prime though until the relay cools and recovers. Maybe the periodic fuel pump cycling is happening each time the relay ‘recovers’ a little causing it to break contact again.

*I’m not a mechanic.* I do have some deep main relay scars. I once had a flat tyre that I am certain was caused by the main relay.

[siege]

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Had a look at the relay. Couldn't see any corrosion. Photos attached. I have just cleaned all the contacts for relay, cmp, cks, MAF as well as the MAF itself and throttle body with crc MAF cleaner.

Cuts out exactly like before once idling warm.

Do jaycar carry this relay or am I going to have to wait another weekend for postage from mx5mania?

[siege]

I've replaced the coil packs and the main relay today (managed to get one from mx5factory so I wouldn't have to wait on Australia post).

Not fixed

Let's call the coil packs preventative maintenance and the relay a cheap spare haha.

Since I'm loath to take it to a mechanic who will repeat all the steps I've already done and have to charge me labour for it, any further ideas?

I've read elsewhere about the coolant temperature sensor causing problems. Is there a reason why that shouldn't be the cause of this hot start issue?

[bruce]

Gosh. You've done pretty much everything.
I wonder if the ECU has gotten wet/corroded? It's been said that the ECU cover bolts need grinding out to get to it?

[Magpie]

Spark plug leads?