mx5cartalk.com

As the title suggests, my Nb has a new gremlin!

When on a drive up some hilly roads last weekend, the engine twice stopped suddenly, without sputtering or any other warning. It's as though I've turned the key off. After a period of time (cooling I suspect) the engine would restart and run fine. This happened twice during the drive.

I googled, and it sounded like many others have had similar issues with the Cam Angle Sensor or EGI relay. After no issues during a hill climb event today, and after replacing the Cam Angle Sensor, it happened again twice on the way home. I replaced the EGI relay on the way home after the second occurrence, and then after another 15 minutes driving it happened again for a third time.

This leads me to conclude that neither the CAS or EGI relay were to blame, and something else is!

What other part is able to cause a complete cut with no warning?
ECU power supply?
Crank Position Sensor?

I've had a similar fault and it turned out to be the fuel pump.

Fuel pump is new. No sputtering as though it's running out either

There is also a Crank position sensor in addition to the Cam angle sensor.
I imagine if the Crank position sensor was on the way out you would have a similar outcome.
an old VP holden i had suffered a crook crank position sensor and acted the same .

Id go crank position sensor. I replaced both the crank and cam angle sensor on my nb8b and it made a hell of a lot of difference. Was having starting issues and running rough when warm occasionally before they were replaced.

Noting your signature block says NB8B, the usual suspects are:
EGI relay (weakened but not necessarily blown due to faulty light bulb connector);
Cam position sensor;
Crank position sensor; &
ECU (as a result of getting wet).

Earlier MX5 issues include above as well as:
Electrical connector at inside of top plate of fuel tank which affects the fuel pump (more common on NA, but not unknown on NB);
Coilpack wiring loom weakness - lack of support resulting in wires breaking inside plastic insulation (NB8A); &
Coilpacks (NB8A).

Most of the issues are mentioned over the 3 pages of this, but page 3 covers some of the outstanding ones: viewtopic.php?f=29&t=60295&hilit=Caffeine&start=30

Fuel tank connector issue: viewtopic.php?f=55&t=46425

Thanks 93_C, I will report back. Crank Sensor is next.

Ok!
I changed the crank position sensor on Friday night, and on Saturday evening, went for a long drive. I suspect it was not hot enough to cause the fault to appear (or it was fixed).

This afternoon, I drove to Mt Glorious and back, and a block from home the engine died. This time I tried to check what wasn't working, and although the engine would crank, the fuel pump was not priming. I popped the bonnet and gave the replacement EGI a tap and tried the key again. The fuel pump primed and the engine started. So I'm back to the EGI relay as the culprit.

Note: the EGI relay was very hot. I think heat weakens the effectiveness of electromagnetic devices? What could cause the relay to heat up so much?

The relay was a second hand unit from Mx5+, and the nearest I had to a known good one.

Read Garry's post re EGI.
Would a piece of wire work OK, as a test?

Bruce, I've hunted around and I'm not sure who Gary is. I can find a few references to Caffiene and a light bulb issue, but no clear description linking that to the EGI.

The symptoms I've identified so far:
- engine stops completely without warning, no sputtering.
- tachometer drops to zero immediately even while the engine is still turning.
- fuel pump is not priming
- EGI relay is very hot, and a tap on the relay is enough to get the car to restart.
- all other electrical appears to be working.
- Ambient temp is a factor - I've only had the fault after more than 40 minutes driving around 2:30pm (around peak daytime temp).

I thing the EGI relay failing is the cause of the first three issues. But I don't think 'failed relay is the root cause', because swapping it has not fixed it.

So the question is: 'Why is the relay overheating?'

This fault has occurred within a few hundred km of installing a 450lph Walbro fuel pump, larger injectors and an ECU, so there have been some electrical changes to the system.

I don't have a good understanding of the common reasons a relay overheats. if load is a factor it might be possible that these new devices are too much for the relay to handle. If wiring fault is a factor, perhaps there's a poor connection somewhere.

Look in audio, electronics, lighting section

Given the work you've recently had done it would be worth checking all electrical connections in vicinity of work as well as all earths.

The original reference to Caffeine's EGI relay issues being linked to a dodgy light bulb connector was here:
viewtopic.php?f=29&t=60295&p=817873&hilit=dodgy#p817873

I'm sure you'll have found it by now, but for anyone looking in the future, Garry's recent thread:
viewtopic.php?f=55&t=67086

american commented "EGI relay is very hot, and a tap on the relay is enough to get the car to restart". I would think thats a fair assumption to link a prob with the EGI relay and perhaps to borrow one for a cross check/ drive. How much is a relay i.e. maybe cheap enough to just replace.

Mr Morlock, thanks for contributing. The relay replacement was the second thing I replaced. The replacement also became hot, and cut out after only 10 or so minutes of operation. I think the hot relay is a symptom of another cause.

Does your new fuel pump draw more current than the relay is capable of handling? Perhaps bypass the relay with a piece of heavy gauge wire and see if it re-occurs. (bear in mind that bypassing the relay means that the fuel pump (and fuel gauge) will be powered up even when the ignition is off, so don't leave it in that state for long.)