2002 MX5 NB, 1.6
100k miles on the clock.
Bit of a backstory. Last year the car sat idle for several months and the fuel filler cap filled with water and some of that water made its way into the tank.
Some of the water in the tank made its way into the engine and then the engine spluttered and died.
Tank and injectors were flushed by my mechanic.
All good. Car drove fine for a while.
Now, if the car has been sitting for a few weeks it seems to cover 15-20 miles of enthusiastic driving (getting the rust off the discs) before it splutters again and dies.
It's as if there's no fuel getting into the engine.
Leave it overnight and it fires up again just fine.
Let it sit there and idle at 2.5k revs for half an hour or so and no probs.
Reluctant to drag it to the garage as it's on the other side of town, money is tight and we're wanting to sell the car ASAP.
Are there any additives that I could pour in to help?
We've tried the Italian method and all seems fine until on our way home (15-20 miles drive) before it dies.
Bumping.
Doesn't sound fuel contamination...
Other than flushing it again theres no magic answer if it is fuel.
Cant see how it is related to the initial water in fuel issue. If liquid water gets into cylinders then usually its permeant damage...water is not compressible so can even cause con rods to snap if enough of it in there, but generally they're not very tolerant to even small amounts of liquid water in the cylinders. Is there any smoke at any point...on start up? during acceleration or off throttle? maybe just replace spark plugs and HT leads..if the car has been sitting idle for long periods these may have degraded. Was the fuel filter changed after the water contamination event and the fuel system subsequently flushed (should have been). All these are things you can check or do for little money.
I'd also be considering checking the injectors and fuel pump...can try something like Redex to clean injectors in case they're not atomising correctly. And maybe a cylinder compression test too to confirm thee has been no mechanical damage due to water contamination (but wouldn't necessarily explain intermittency of the issue).
Also can check for vacuum leaks...spray some WD 40 or something around the air intake and vacuum lines to check for leaks...any raise in idle RPM when you spray over a leak then there is a leak...a loose jubilee clip, spit hose etc.
Does the 15-20 miles correspond to the engine warming up? If so might be a temp sensor in the AFM/MAF or however the engine management system manages choke, so engine runs fine when cold and mixture is rich, but as it warms the system doesn't compensate.
It could be all sorts of things...
Partial Fuel line blockage perhaps? closer to the tank so enough fuel drains into the line when left than it's not starved until 15-20 miles in a journey?
Fuel pump knackered?
Still getting some water in the tank? - maybe just Brim it with posh petrol?
Injectors not seating when up to temp?
Old Plugs worn/need gapping?
Head Gasket leaking, but again only when up to temp?
How old is the oil, did your mechanic change it when her flushed the fuel system?
Alternator?
I'm sure an actual MX5 expert will be along soon.
Something simple like a paper air filter being damp and collapsing in a way the air filter blocks the air intake. I had exactly this in a previous car.
I'd go for fuel filter first. All the fuel (with a bit of water) gets sucked up into the filter, after 20 miles its full and stops the fuel going through. Stop and it drips back down into the tank, and you can do another 20 miles.
otherwise something expanding when it gets warm and messing around with the air/fuel mix.
What did the flush of the tank entail? I've had debris in a fuel tank that blocks the outlet but then moves as the fuel swishes about. Only cured by taking the tank out and having a look inside/ slosh around fuel and pouring it out to see all the crud that came out.
When the tank was flushed the fuel filter was also changed.
The air filter is a K&N jobby.
When it does splutter and die, giving it some revs and putting your foot to the floor keeps the engine running for longer, but it still dies.
Spoken to mechanic and he has driven it daily to work and back (60km one way) back in December and had no issues.
Got an immobiliser that cuts the fuel maybe?
It's been a while since I owned a petrol car, the symptoms you describe seem to appear once it's warmed up so it could be any one of a number of things.
IIRC fuel pumps tend to make a loud whirring noise before they fail - or at least they did on my old Golf GTI. I don't know whether the MX-5 has one pump or if there's an auxiliary lift pump in the fuel tank itself, but it's worth checking for.
Other than that, something obviously triggers the issue once up to operating temp, so the obvious culprits would be sensors, gaskets, seating of spark plugs etc.
Fuel level in the tank when it sits? If half or less, I'm going with condensation forming in tank. Causing repeat of original problem.
I’d go for fuel filter first.
Yep. You need to eliminate potential problems. This is a cheap and easy one to do.
Had the same issues on a motorbike, it was the fuel pump. Cold, fine no issues. Hot day and/or low fuel, the bike would run rough, cut out, kangaroo. Leave it for 30 mins and it would be fine for a little while.
Fuel pumps are cooled by the fuel around it, mine was overheating and turning the fuel to vapour (confirmed by turning on the ignition with the tank/bike warm, priming the pump and it was like a jacuzzi in the tank. No air was getting in anywhere else, so it had to be the fuel being turned into gas by the pump and then coming back into the tank via the return line. I could also feel the fuel tank getting very very warm on a hot day, as the fuel pump overheated which heated the fuel which vaporised, and repeated the cycle.
Replace the fuel pump.
Also check the filter(s). There will be the inline filter but also a teagbag strainer directly on the pump, if this is blocked not enough fuel will be getting through, making the pump overheat. That was actually my first issue. So many issues caused by a 2 inch square bit of plastic....
don't mess around, you need to pin it down.
Buy a cheap fuel pressure gauge and bodge it (carefully to avoid leaks and subsequent firey death obvs) into the fuel system.
If the fuel pressure falls and the engine splutters, then it's pump, filter, pick up or similar.
But if the fuel pressure doesn't drop, then you can ignore all that and look for something else
Trust me, guessing and changing random stuff gets you nowhere fast!
I had the same on an old saxo, it was the lambda(?) sensor. I'd be driving along just fine then it would start to cough and splutter, then die. It would eventually restart and run for a while then do the same.
Must be something to do with heat / fuel. Worth buying a fuel pump pressure gauge.
Thanks folks....
Problem is I've not got the space to do any of this as I'm in town.
Ironically I can't get the car into my wood workshop. The workshop is on an old underground car park and the angle of the ramp is too steep to get the car down there without seriously bottoming out (car is lowered 50-60mm).
Maybe just sell the car on a cold day... 🤔
And not let them get too far on the test drive... 😁
My mum had the same thing on an MX-5 several years ago. It went into the local Mazda garage several times and they never got to the bottom of it. She traded it in eventually.
Possibly the air vent for fuel tank blocked - release the cap when it happens to see if a vacuum has formed.
Or as people say fuel pump likely a problem.
Seeing as it happens after a set time I'd investigate something getting hot as you drive it then the heat causing it to stop working. The classic part that does this is HT leads, coils and sensors. Seeing as it doesn't do it when left idling it's got to be something that gets hot under load (revving an engine while stationary doesn't generate much load) so that's where I would start.
Fuel pump could be a culprit.
Does that engine have a single lead to the coil or is it coil packs?
My guess would still be water in the fuel system.
When it cuts out, try taking the fuel cap off.
If you get a whoosing noise as air rushes in, and the car then starts/drives normally, there's an issue with the tank breather system.
Either something got put back on wrong when the tank got flushed, something got trapped, or the breather system has a blockage somewhere.
@Symes, I think that's it too. Water got into the tank probs thought the cap, breather inside cap now sealed, tank builds up a vacuum, engine gets starved and dies, gradual release of the vacuum over time and repeat.
Isn't vacuum a strange word?
Lol
Cheers folks.... Food for thought.
OK, first step is going to be open the filler cap and take it for a spin.
Liking the theory that the filler cap valve is done for. Especially as they are only 20-30€...😁
If that doesn't do it then I'll look at the fuel pump. Looked it up and it's fortunately relatively easy to swap.
Failing that drag it across town and drop it off at the mechanics yard.
Many, many thanks!
@mucker I'd say this should be new enough to have a completely sealed fuel cap. IIRC petrol vehicles have had to have an evaporative emissions control system fitted since at least the mid 90s.
Essentially the fuel tank vents through a carbon canister so you never get petrol vapour anywhere around the vehicle, and then once the engine is running, a valve allows the gathered vapour to be drawn* back in from the carbon canister and burnt in the engine.
My guess is if the issue is resolved by removing the fuel cap, then the vent line from the tank is blocked. If it was the vent from carbon canister, then the engine would quite quickly get starved of fuel due to the high vacuum on overrun, whereas 20-30 minutes is probably enough time for a vacuum to build due to fuel being burnt.
However, it could be a totally unrelated fault, but start with the easy tests first.
*I say drawn, but in engineering/fluid dynamic terms, gasses/fluids are pushed from higher pressure to areas with lower pressure, not drawn by the lower pressure.
What Symes said was my guess.
Sounds just like my BMW engine, but without the water history. Just traced it to faulty coil packs on cylinders 3 & 5 so replacing those tomorrow and that should fix it (hopefully)
Saddle tamk isnt it on an mx5
Wont be the breather, mazda use a decent set up, some have a charcoal filter
My guess is internal transfer pump fail
Or failing running the main hp pump dry as the other pump is hvlp
Can you get a code reader to plug in? Faults don't always throw a check engine light but a reader might give you a chance.
Has the fuel filter been changed as part of it's servicing history or when it was in for water in the tank? It's cheap and quick to replace, it might still be full of water.
Fuel pump switch? anything thermostatically controlled?
Mmmm parts darts.
I'll take HT leads and coil for 50p.
Running it with no filler cap might set a code (not sure about 2002 mazda but others)
If water got in through the filler cap, have you resolved that issue? Pretty sure a 2002 should a sealed cap and vent elsewhere.
It's an old car. Punt the blighter and be done!
Previously water got in because the drain was blocked and the area around the filler cap filled with water.
I (or rather the GF, I'm drunk) can give it a run tomorrow without the filler cap and see what happens.
On a side note I have no idea what coils are, nor coil packs nor HT leads.
before it splutters again and dies
I think therein lies the clue..are you running it low on fuel and there is dirt in the tank with lying? still think the filter could be needing replaced(if not already) I'd be asking on the Mazda forum in case it's common to all MX's.
Previously water got in because the drain was blocked and the area around the filler cap filled with water.
I'm pretty sure that shouldn't happen. The filler cap should seal. In its own it wouldn't cause your problem but a new one is probably on the cards. If it'll let water in it'll let fuel vapour out, and air in.
I think you need a code reader. A camshaft or crankshaft position sensor would cause the problem you describe but 'should' trigger the mil light. Unless it's in the early stages and is only intermittently failing, so will set a stored code bit not the light.
HT = high tension - the wires with lots of electrons that go to the spark plugs. Coils generate the high voltage for the plugs. Coil packs are a bunch of coils together.
Totally different vehicle but I had similar on my Mk6 Transit, would do about 50 miles from cold, then die. Leave for an hour or so and it would do another 10-20miles then die, leave it overnight and it could do 40 again.
It was the circuit board on the fuel pump getting hot and warping slightly, breaking some contacts, let it cool and it was fine again. No idea how similar a petrol Mazda is but symptoms sound similar
On a side note I have no idea what coils are, nor coil packs nor HT leads.
After seeing this Punt it as is or take it to a garage.
Your relying on people who have not seen or heard this car do diagnose your issue and your getting some fairly obscure and car (other than mx5) quirks as a results.
It's going to cost you money
It’s going to cost you money
That's what I'm fearful of!
Other than this issue the car is in great condition.
No rust, sills and frame have been sorted.
Bit of a shame, really.
Well by cost you money I mean if you start playing parts darts it'll only be luck that fixes it based on the symptoms you have described. So you could easily spend considerably more than required.
If you get a garage to fix it. They will repair the fault ...it'll cost you X.
If you sell as it is faults declared. It'll likely net cost as much as the garage fixing it although it'll sell easier fixed.
Does the temp gauge work ok?
It's true, trail rat is giving the hard but honest advice, here you can only get random guesses and suggestions, sometimes good ones but unless you can do them you are getting nowhere, the fix is probably not expensive if they can find the problem, but finding problems can take all day and time costs money, switching out filters, pumps and so on can be more expensive if you don't know what you are doing, a good mechanic might know what it is and just order a part.
Alternately selling with a problem is less money, not declaring is potentially getting it back after it breaks down 20 miles later, it's just one of those things, cars need fixed, solution is either know how to fix it cheap or have a mechanic you trust, and buy him beer occasionally, that goes a long way.