I am new to this forum, after only recently purchasing this MX5. However my first issue with it has come about and I have turned to the internet for help!
The situation is: Sunday night after a weekend away I come home, and of course the first thing I do is fire up the MX5 just to check she is alright! However, It was not starting, I eventually get her going after jump starting it, however it did take 10 mins of charging just to get it to go. So I think I have a dud battery, so I got and buy a brand new Bosch S5 and that seems to solve it.
However then I think, maybe the battery was just a bit flat and switch it back to the old one (hoping to save £130), now the starter motor just keeps on turning over without it ever firing and the imobbillisor warning light comes on from time to time. I put the new Bosch battery back in and it does the same, the engine just keeps on turning over with plenty of power but it doesnt catch. It does occasionally fire up once but then instantly the revs just cut out, as if there is no fuel. (there is half a tank). I even try to jump start the new battery and all it does is make the starter motor turn over quicker and still doesnt get going. Also it intermittently doesnt crank at all and when you turn the key you get nothing.
Update to today, all the car does is make a very fast clicking noise in the engine bay.
I have bought a diagnostic reader however it doesnt seem to show any error codes, even though the engine and battery warning lights come on when you turn on the ignition.
Any suggestions would be greatly appreciated! I am only a student and stupidly spent all my money on this car so have no money left for garage fees!
Can post videos of the symptoms if that would help. I am only a novice in this area! Alternatively if any kind people are out there in the surrey area and fancy giving me a hand I would be highly grateful!
In that case I would suggest you take a look at the car’s ecu as it is possible the recent weather has created a scenario where water has got into the car and got to it!
You need to get the passenger footwell carpet up, remove the cover plate and inspect. You are looking for obvious sign of damp and corrosion.
Where exactly is it in the footwell is it? Would make a lot of sense as last week I hired a carpet dr to get the smoke smell out and the interior got quite damp. What do I do if it is? Will check Once Home.
The ‘ECU’ (actually named the PCM - Powertrain Control Module) is on the sloping section of the passenger footwell, you need to take the carpet it to see it. There are two covers, an outer compartment cover, and a second inner cover over the PCM. This has two security screws that need a slot chiseling in to remove (not for the faint hearted) so see if there’s any sign of water or dampness before trying that. If the carpet cleaner used loads of water, then it could be a problem, though you may have difficulty getting any acceptance of blame from him (or her).
In my experience, damaged PCM’s are a rare event, but it does happen with lots of water in the footwell. There are other reasons why a car won’t start, and your symptoms match various other possible problems. From my viewpoint, worth waiting for other suggestions before you take the expensive PCM/Immobiliser replacement route. (You need both even if only one is faulty - they are a matched pair.)
The Cam Angle Sensor (CAS) may be faulty for one, other problems are various. (I’m an electrician - not a mechanic). For battery replacement, I always recommend buying a Panasonic, it’s the original fitted battery, and on a Mk2.5, probably past its best by now. Mine was replaced at twelve years old, some last longer.Very few other batteries fit, or don’t meet the requirements (no vent point provided - which is important, long term.)
Another possibility - the immobiliser may be faulty, but as mentioned, you will need to replace both units.
I have found the section and have come across those annoying rivets. Do you chisel a cross head into the top and then screw them out? It doesnt seem particularly damp down there, however once the car was cleaned it was steamed up for a number of days so maybe damp got inside it then.
I went back to the place I got the battery from and got a replacement Bosch (incase the last one was faulty or flat) but now it doesn’t do anything at all! No clicking or anything, very strange.
The imobilisor does make sense as the key light Was intermittently coming on, is the light meant to come on when he ignition starts up? it also makes sense as it used to randomly Start up and drive fine after a lot of times it wouldn’t start up. I have seen people mention you can damage them by jump starting the car and causing a surge?
I have sold over 120 ECU sets in around three years. The main reason is water damage to the ECU. More recently there has been increasing evidence that the Lucas immobiliser that is coded to the ECU is starting to fail as well. If either ECU or immobiliser fail, a matched pair + coded transponder are needed to replace.
The two bottom fixings on the cover plate are sheer security fixings. Originally there would have been a hex nut on top to facilitate tightening and once the required torque was reached, the hex part snaps off leaving the metal dome. I use an old screwdriver as a chisel and hammer this onto the edge of the dome to shock it into undoing(anti-clockwise). This is the cleanest method but watch your hand and the car when hammering. Others grind off, cut slots, etc but that just creates metal particles in an area prone to damp and rust. If these undo as planned can usually be reused or probably better to replace with standard 10mm bolts for ease of removing next time.
Given the MX5’s vulnerability to water ingress I recommend that any owner of a MK1 - MK2.5 MX5 check out their ecu. This is particularly important with the 1995 on UK cars with the associated immobiliser and transponder - expensive and a nuisance to replace.
Rob - Lets see - according to the Daily Express, 25.022 Mk 1’s and 43,170 Mk 2’s (including Mk 2.5’s) were sold between 199o and 2005. That’s a total of 68,192 cars, of which you’ve replaced 120 PCM’s.
Update: With a different battery it unreliably starts if you balance the throttle just right once in every 3/4 goes. Any suggestions for what needs happening now? I didn’t manage to get into the ECU but uncovering it maybe helped get moisture out and get it going (who knows!)?
I am surprised the figure is only 68192 cars - would have guessed at least four times as many. Frightening how many I have known to be broken and lost forever.
No m8 if my little speciality business has sold 120 in three years you can be sure a lot more have needed replacing. In the early days cars were scrapped because Mazda were quoting £2000 for an ECU but could not get an immobiliser let alone code it to the ECU. I get ECU sets from breaker colleagues all the time and quite a number cannot be sold because received with water damage. It is a common problem to be taken seriously. Any sizeable quantity of water that gets into the car will end up in the absorbent sound proofing in the passenger footwell - road camber and parked downhill on an incline will see to that. The superior Mazda carpet serves to hold the water in. Once the damp is there it just stays and corrodes the vital parts of the PCB.