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I turn the key, hear the fuel pump, starter motor fires, but the cranking is weak, slow and sometimes fails to start, even after half a dozen cranks.
I know mx5s are said to have week starting but this is worse again.

The car is a 2004 SE with 112k on the clock. Standard turbo with aftermarket intercooler, large injectors, standard coils, aftermarket ecu and a conservative tune for about 150kw.

Off to Sandown, early morning, started ok. Stopped for 98ron but it would not start. Slow cranking, No start and cranking getting slower and slower until battery gave up. Push start ok and starting at Sandown fine all day but each time with my heart in my mouth. Slow cranking problem.

The Panasonic battery was load tested and is said to be good. I am trying to isolate the problem. Next is the starter motor. OEM are pricy so I don't want to replace it if its not the problem.

Has anybody in the Melb east area who has a known good starter that I can borrow to test whether mine is good or not?

Or any advice would be greatly appreciated.

First points of check

all wiring to the starter motor itself. Clean if required.
also check battery terminals.make sure they are secure & clean

I picked up a NB starter motor for $20. It was probably mates rates. but $50-100 second hand should be doable

They are a pain to change. Not hard just difficult to reach bolts at gearbox.

I would be surprised if its the starter motor itself. But not impossible.

If youre not inclined to do the work yourself.....it gets exy. I agree

My SE's starter also turns over slowly - similarly to how other cars sound with a near flat battery. But mine will start ok after four or five cranks. It always leaves me with a feeling there is something not right though even after three years ownership. I've read quite a bit that NB's have a slow cranking starter fitted and that it's normal, but I often still wonder if it'll start on those first couple cranks.

Stan's suggestions are certainly where to start by checking all cables and connections especially all earth connections. Spark plugs in good condition and good spark. Fuel getting through. Others will give much better experienced suggestions than I can...

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The Zork wrote:The Panasonic battery was load tested and is said to be good.

Appreciate what you've been advised in quote above re battery, but if it's running it's original 2004 Panasonic battery then it could go anytime as the originals lasted up to 13 years, so trying out a new battery before replacing the starter motor might be more prudent. In addition to the previous suggestions, check & clean-up if necessary the main relay, aka EGI relay, in the engine bay fuse & relay box.

I would still be looking at the battery.

The Zork wrote:aftermarket ecu

What are you using for alternator control? The alternator should not be charging while the engine is cranking.

Check earth straps, esp the one from the back of the PPF to the chassis near underneath the battery. For some strange reason this strap seems to affect starting more than any of the others.

bruce wrote:I would still be looking at the battery.

Many thanks to all of you for your advice and suggestions. I will need to check the wiring and earth points before doing anything else. As far as the battery is concerned, I think 93-Clubman and bruce are right to point out that the original battery will last up to about now, so a new battery is in my not too distant future. So I will start with that.

The place that tested my current Panasonic told me no-one has a replacement Panasonic and he advised a Federal. Is this a good thing or is there something else with more cranking power, small and light and suitable for boot mounted applications.

Another confusion from looking at starter motors yesterday. Some quote 1kw and other quote 1.4 kw. What is the factory starter rated?

Only Mazda sell the Panasonic battery. Expensive, maybe ring around a few Mazda dealers to see if you can bargain a little.

Locutus wrote:

The Zork wrote:aftermarket ecu

What are you using for alternator control? The alternator should not be charging while the engine is cranking.

I know nothing about this Locutus. How can I tell?

Has the car always had this problem, or only recently? How long have you had the car? Did you buy it before or after the aftermarket ECU was installed?

All earths, EFI relay (cheap to replace as a precaution), battery (it should have died approx 3 years ago).

Locutus wrote:Has the car always had this problem, or only recently? How long have you had the car? Did you buy it before or after the aftermarket ECU was installed?

It,s been slow cranking since I bought it. My rx7 could sit in the garage for 6 months and start strong every time. Not the mx5.

Most ECUs require an always-on power supply so they can at least remain in standby when the ignition is off. This means they don't waste time rebooting whenever you go to start it. Battery drain for this function can be quite significant for some ECUs.

If the problem is one of losing charge over a day or two because of your ECU then you either need a bigger battery or a trickle charger.

Alternatively check that someone hadn't wired up the ECU so that it is constantly fully powered up.

The Zork wrote:place that tested my current Panasonic told me no-one has a replacement Panasonic and he advised a Federal.

Last read that US Mazda dealers stopped selling the Panasonic battery years ago, so not sure if new stock is available here anymore. Worth checking what MX5 Mania are selling &, given you're in Melb, trying to obtain same locally: http://mx5mania.cart.net.au/epages/mx5m ... /Batteries
Recent replacement battery thread might also give you some ideas: viewtopic.php?f=55&t=75150