MX-5 Mk 2 1.8 Sport Running Rich & emmitions problem

[Sarahr1335]

Hi All, I'm hoping someone can help me with the problems I've been having recently please.

I have a 2000, MX-5 1.8 Sport mk2. The last year or so ago the car started misfiring and the idle was very erratic. It would misfire for a while, and loose power then the power would kick in and it would drive like nothing had happened. I took it to many garages but they could not detect the problem as it always seemed to be running fine when it was in the garage. They said it needed to misfire while it was in the garage to detect the problem.

I researched this problem and had the plugs and leads changed, however the misfire continued and no one seemed to know what was causing this. I had a full service in November and they replaced the leads again, as i was told they was not fitting correctly... so that was two sets in one year!


Well the problem persisted, then after more garages later i was informed the coil pack had gone and when it came to having its MOT it failed on emissions.

Since then i have replaced the coil pack with a new genuine mazda part, a new catalytic converter,which was completed blown due to the misfire problem, I was advised to changed to airbox as it had a air conduct kit... this was already fitted on the car when i bought it 6 years ago.. But was slightly cracked, I was told this could be sending messages to the sensor to send more fuel through, therefore could be culpret. So I have replaced the airfilter and box back to its original.

However, when the car went into its second MOT, The car has still got an emissions problem and only just scrapped through. I have been informed that the petrol in running too rich and it still has a slight misfire onn start up... its very jumpy but driving is fine and seems to be driving well.

Have I caused any serious damage driving with that intermittent misfire fault?

The ABS light keeps coming on too.

Any advice on what could be causing this?

Thanks in advance.

Edited by Sarahr1335 on Saturday 13th April 13:39

[skinny]

You've replaced all the usual suspects. I'd suggest you temperature sensor might be duff, telling the ecu its colder than it really is so it's putting too much fuel in. The other possibility is the o2 sensor misreading so again too much fuel is going in. Both are fairly cheap and easy to replace.

Have the garage run a diagnostics check to see what fault codes are being thrown up?

I think your abs fault is unrelated unless your ecu is going funny and needs a reset or something...

[fatjon]

Had a quite similar problem and changed all the things you have plus the lambda, crank and cam sensors. Turned out to be a duff MAF sensor. £30 ebay replacement and ran perfectly after.

Symptoms, bit of a pig to start hot or cold. KInd of tried to start but hard to get it to "catch", surging on constant throttle, smelled rich and lumpy idle.

Test:

the MAF has 3 connections, 0v (ground), 5V (supply) and output which varies with air flow over the sensor wires. Can't remember which pin is which but should be easy enough to work out with a meter. On mine the output did not change when I blew on the sensor wires, it was stuck at 0.7 volts. Tried cleaning it etc but it didn't fix it. With a working one you see an immediate swing in output if you blow on the sensor wires.

[skinny]

isn't it a map sensor on the mk2?
worth a try.

[MX-5 Lazza]

skinny said:

isn't it a map sensor on the mk2?
worth a try.

From Mk1 1.8 onwards it's a MAF (Mass Air Flow) sensor replacing the Mk1 1.6 AFM (Air Flow Meter).
MAP (Manifold Air Pressure) sensor is for forced induction or cars with replacement ecu

[Sarahr1335]

Thank you all for your replies, very helpful.

I have taken it to many garages in my area, but as the management light is not on they all have not got the diagnostic equipment to see where the fault is.. They said it is over their heads!!

Could anyone recommened a garage or someone who can tell me which sensor has gone, or where the fault is please?

Kind regards

Sarah

[youngsyr]

Hmmm, I've had a similarly persistent problem with my 1999 Mk2 1.8.

The issue is that the engine will drop 2 cylinders (fired by the same coil pack) only when it has been run for at least 30 minutes and then left turned off for at least 30 minutes.

The engine will fire up fine from cold. It will also fire up fine when hot, e.g. if driven for 30 minutes, turned off, then restarted a couple of minutes later: no problem.

When the problem does occur, it can sometimes be cured by pushing hard on the tab of the plug that connects the engine loom to the coil pack.

I've tried changing the coil pack (notoriously dodgy on these cars), plus having the plug on the loom replaced, but the problem has come back. Car also has new HT leads and spark plugs.

Emissions have been an issue at the last two MOTs, which I put down to the CAT being killed by all the fuel that's going through there when it's running on two cylinders.

Has anyone seen anything like this before, or can they suggest a possible solution?

[youngsyr]

Sarahr1335 said:

Thank you all for your replies, very helpful.

I have taken it to many garages in my area, but as the management light is not on they all have not got the diagnostic equipment to see where the fault is.. They said it is over their heads!!

Could anyone recommened a garage or someone who can tell me which sensor has gone, or where the fault is please?

Kind regards

Sarah

I'm not a mechanic, but as you'll see above, I've had some similar problems - I know how frustrating it can be when "experts" can't diagnose a problem!

Here's what I'd try:

As you've changed leads and plugs after the coil pack. We can rule out those being the cause.

The next time it starts misfiring, pull over and pull one HT lead off of its spark plug at a time. Start from the front of the engine.

If there is no change in how the engine runs then you know that cylinder isn't firing. If the engine runs worse or stalls, you know that cylinder was firing. Repeat this until you've tried all four cylinders in isolation.

If you have one or two cylinders not firing from the same coil pack (trace the HT leads back to the coil pack, there are two coil packs taking two HT leads each). You could try swapping the coil packs and see if the problem moves with it (i.e. the other two cylinders stop firing and the ones that weren't firing start firing). This would indicate a coil pack problem.

If you have two or more cylinders not firing that are powered by different coil packs, then you'll need to do the above but actually unscrew the spark plug and reconnect it to the lead and check it's sparking for each cylinder in turn. This will tell you whether it's an ignition problem or a fueling problem. [Edit: you could actually use a spare spark plug, rather than unscrewing each one as you've got brand new plugs in there, so we can rule them out as a factor, we just need to see if each plug lead is delivering power].

If the plug isn't sparking at all, and the issue doesn't move with the coil packs, this would suggest an electricl problem before the coil packs, i.e. between the ECU and the coil pack.

If the plug is sparking and the problem doesn't move with the coil packs, it would then indicate a fueling issue.

At that point I'd get a garage to start testing fuel pressure and swapping the injectors around to see if those are a problem.

It might also be worth changing the fuel filter as a precaution.

Edited by youngsyr on Friday 19th April 14:01

[skinny]

Sarahr1335 said:

Thank you all for your replies, very helpful.

I have taken it to many garages in my area, but as the management light is not on they all have not got the diagnostic equipment to see where the fault is.. They said it is over their heads!!

Could anyone recommened a garage or someone who can tell me which sensor has gone, or where the fault is please?

Kind regards

Sarah

Whereabouts are you? There are some specialists dotted around the country that will be a lot more useful than a dealership etc

[trackerjack]

Totally unable to offer much but if the thermostat was stuck open it would make the car run rich, does it get better if it gets hotter?

Have you got a friend with the same type of MX and swop parts until the fault transfers too.

[Sarahr1335]

skinny said:

Whereabouts are you? There are some specialists dotted around the country that will be a lot more useful than a dealership etc

I'm in Telford

[Sarahr1335]

trackerjack said:

Totally unable to offer much but if the thermostat was stuck open it would make the car run rich, does it get better if it gets hotter?

Have you got a friend with the same type of MX and swop parts until the fault transfers too.

When the coil pack was changed the garage said it still had a slight misfire problem on start up and running rich, not sure if that changes when hot. No I don't know anyone else with a MX5.

[Sarahr1335]

Can anyone help please? my ABS light is permanently on, does this mean one of the sensors need replacing? if so how can I tell which one?

many thanks

[Sarahr1335]

fatjon said:

Had a quite similar problem and changed all the things you have plus the lambda, crank and cam sensors. Turned out to be a duff MAF sensor. £30 ebay replacement and ran perfectly after.

Symptoms, bit of a pig to start hot or cold. KInd of tried to start but hard to get it to "catch", surging on constant throttle, smelled rich and lumpy idle.

Test:

the MAF has 3 connections, 0v (ground), 5V (supply) and output which varies with air flow over the sensor wires. Can't remember which pin is which but should be easy enough to work out with a meter. On mine the output did not change when I blew on the sensor wires, it was stuck at 0.7 volts. Tried cleaning it etc but it didn't fix it. With a working one you see an immediate swing in output if you blow on the sensor wires.

Thanks for the advice

[Craikeybaby]

Does the ABS kick in if you brake hard in the wet?

With regards to fault codes, you can get diagnostic readers that will read out the trouble codes.

[youngsyr]

You definitely need to know the code.

The battery light came on permanently in my MK2 - no other problems or symptoms noticed. Battery charged fine and the car ran perfectly.

Turns out that the inlet temp sensor had been disconnected in the garage and had not been reconnected. Plugged it back in and the light immediately disappeared, never to be reseen! Why an unplugged temp sensor should throw a battery light is beyond me!

[vescaegg]

Sounds like you havent had much luck! Mine was more straightforward

I had the same issue for a couple of weeks and tore my hair out trying to figure it out. This was the culprit in the airbox intake pipe - between the filter and the engine! Somehow!

[Shotgun Rider]

Sounds like you've borrowed my car as mine had an erratic idle and was running rich. After taking it to three different people who proved no use at all I ended up buying a MAF sensor on Ebay which solved the problem.

I also had the ABS light come on intermittently which turned out to be a faulty sensor. They are horrendously expensive new. £180 odd.

http://www.mx5parts.co.uk/sensor-front-mk225-p-190...

[Sarahr1335]

Thanks so much for all your replies

been to a few garages who are supposed to have all the diagnostic kits, one said had to go in as mx6 due to age of car.. was told all the sensors are fine and then its probably the ECU, and charged £45 for the privilege then my friend used a bit of wire to check all the sensors and said its the passenger front sensor which I suspected. Can anymore suggest a good garage that won't rip me off and know what they are talking about to do the work?? as if I can't I might regrettably have to get rid of it

[Craikeybaby]

Where abouts in the midlands are you?