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I'm having trouble with the poor old girl cutting out intermittently while driving. Looking for some help with the diagnosis.

I think I've had two different issues recently. A week ago I had a no start, no spark problem. Was towed to mechanic, no fault codes, ended up replacing the crank position sensor and it drove great for most of the week including two long spirited drives to celebrate.

Now I've dríven to the city and back, and while cruising at 80kph the engine cut out. Revs immediately dropped to zero, speedo, water temp, oil pressure, fuel gauges all still functioning, radio playing as I coasted to a halt. Turning the key the car would crank but not start. After sitting for about 10 minutes it started up again and I was able to drive 1km before the same thing happened. Repeated this process and I got home.

Today I replaced the fuel filter as its due soon and I thought maybe the E10 I'm using had loosened up some debris and clogged it. Started up fine, no leaks. I test drove it up and down the street for about 10 minutes and it accelerated smoothly. Then on one of my u turns at almost idle it cut out and wouldn't start. Coasted down the road to park, Waited 5 minutes. Started up again. This time I just let it idle. And it was very smooth, no misfiring at any time in all of this. After 2 minutes it suddenly cut out again.

I'm a bit confused now. The plugs and leads are all new this year, mechanic tested the coils last week and said they were good, its running intermittently so I can't imagine a sensor is dead.

Any ideas?

Possibly fuel pump, they often get very intermittent before total death.

Otherwise, when you said at 80kph the revs dropped, was the car still in gear at the time?
Because if it's in gear, and at speed, the revs can't physically drop (unless the rear wheels lock up)

Replace your cam sensor. The cam sensor signal is poor at the best of times, but deteriorates when heat soaked in exactly the way you've described as they age.

In an NB the tachometer is electronic and dríven by the ECU. The ECU requires both crank and cam sensor to determine engine position so if it loses track of either, it will stop injecting fuel.

Not saying this has anything to do with the problem, but any pre NC MX5 is not on the list of cars that are suitable for e10.

I noticed my fuel pump started to get a bit noisy after running E10 for a while. The pump would be next on my list of things to rule out.

siege wrote:mechanic tested the coils last week and said they were good

On NB8As usually one of the two coils in the coilpack breakdown when they are very hot, so can depend on when they were tested, ie hot or cold.

Cheers guys

I have ordered a replacement cam angle sensor. Fingers crossed with express post it will arrive tomorrow and I don't have to wait until after the long weekend. I also ordered a replacement used MAF as mx5mania only had one left and at $40 I thought it was worth a crack since the postage was already paid for. Both are easy to replace.

Intetesting to hear that the fuel pumps can play up intermittently before they die.

If the sensors turn out not to be the problem which pump should I buy? I'm pretty keen to continue using ethanol.
I'm finding GOSS, Bosch, options. Walbro and dw being more expensive.

What about the fuel pump relay?

you can get a list of say 6 things it could be and replace them all one by one cheapest to dearest. Or you could let someone who looks at cars daily and see if they can diagnose the problem. I had a mechanic who guessed a problem for me- guess i.e. for a person who is around cars daily- and his guess was right. Coil packs seem a common failure point if they old and 93 may well be right. At least a set of coils is something that has an ongoing value- i.e. life of possibly 10 years.

Relays are easy to test, just remove it and check with a multimeter and a battery to see if it switches properly.
or, the lazy way, try and start the car and listen for the relay clicking.


With regards to the pumps, you'll need to contact each manufacturer and see if they're rated for ethanol fuels.
ethanol is pretty rough on rubber components, so they need to be the right type to be ok for use with it.

I bought a Denso fuel pump when mine went last time, works fine and the same brand that Mazda used from factory.
HOWEVER, the ones Denso sell now for the MX5 are just a universal pump, so you need to cut the factory plug off and wire the pump yourself, and use the old filter sock, since the one provided is the wrong shape.
And you'll also need to modify the OEM rubber base to allow the pump to fit securely and not block (the Denso supplied base doesnt work with the MX5)

Personally, i'd not bother with a Denso one, try and find a company that makes one that fits without having to re-do half the stuff.

Thanks champions

Replaced the cam sensor today and drove it around for 10 minutes, idled for 10 minutes, drove another 15 minutes. no more cutting out!

One possibility is:

Intermittent broken wire at the Cam angle sensor plug. This has been identified before. It was fixed by replacing CAS plug pins and reterminating the wires.

So don't throw out your old Cam angle sensor just yet!

Red_Bullet wrote:Intermittent broken wire at the Cam angle sensor plug.

hmmmmmmmmmmmmm.....

Try this (note the position of the cable tie)


Then do this if it works

Looks like it needs heat shrink

So I'm not out of the woods yet. Each fix seems to work for a little while...

So the engine is still cutting out intermittently and I have been able to characterize it further:
- Occurs only when hot. Hot weather, once the engine has warmed up
- If I open the bonnet and let it cool for a few minutes it will start again, otherwise just crank
- Occurs only near idle, actually while idling or coasting in high gear, or with the clutch in while slowing down to do a U turn. Mostly while idling.
- Tacho drops to zero immediately, speedo registers properly
- All other electrics in the car continue to work
- After it has cut out while idling and the key is still in the run position, the fuel relay will periodically click like it is trying to prime the lines?

The following are new:
Crank sensor, Cam sensor, Fuel filter, MAF, plugs and leads

The mechanic said the coil pack tested fine

I tried zip tying the cam sensor in place as pictured above but that made no difference, cuts out while warm at idle all the same. The wires didn't look damaged nor did the connector look corroded

I pulled the fuel pump today, The fuel line connected to the pump had no splits in it. The fuel pump wires didn't look corroded.


I could just buy a new fuel pump and try that next, but now that it all seems so closely related to underbonnet temperature I'm a little less inclined to do that. What's next, buy a can or electrical contact cleaner and hit every plug with it?

Its the cam or crank sensor, got some really good closeups of them installed so we can see how theyre fit up?


... or its the worst invention for cars ever, farking ever... an aftermarket immobilizer.

Dann