'smoke' from the exhaust of a 2001 Mk2.5 1800 sport,

the easiest way to see if your running rich would be to get a hold of a WideBand 02 sensor. Innovative motor sports sells a logging wideband with Gage for around 180.00. you could ether install it alongside the original 02 sensor, you can get a muffler adapter and use it as a temp tuning tool or replace the original 02 and run the analog wire to the narrow band connection on the car ( if it is a 1 wire 02). long story short that will be the most difinitive way to determine what your A/F ratio is. if it smells like gas for the first few min then most likely it is running rich. it could be an issue with the cold start system. is the smoke pure white? or does it have a tint. also try holding a white rag near the exhaust and see what color any particulates are or what smells it is giving off.

I would say if its white smoke,then its just normal condensation that builds up in ex. systems in humid conditions,0-1 volt is normal switching of 02 sensors,just pull a spark plug,if its rich it will be black,wet ,dry,if its normal it will be tan or white,if the check engine light is not on I would not worry,plugs tell you at a glance what is going on during combustion,no scan tool or fool needed,hope this helps.

Thanks for both your comments, it could well be condensation just seems more than I would have expected! plugs are blackish but not overly so, Sensors are 4 wire heated I did wonder if they were nearing the end of their useful life & sluggish or even if the heater had failed. I did have a misfire a while ago but changing the plugs from BKR5E that were fitted to 6E (Cooler) helped along with new 8 mm leads and a new coil pack finally cured the misfire. The mx5 appears a bit susceptible to misfires. Cant understand why the timing drops below 10 that won't help, just wondering if I should advance it a tad

its generally controlled by the ecu. (timing advance) if you wanted to chip the ecu or to modify the map with a custom ecu but that would be spendy. and for those who will suggest it, it is possible to do it manually but then the overall timing is slightly off and not just the advance. also when you are checking the timing you may want to make sure that you don't need to put it into "timing mode" i know on the obd1 computers from mazda to time it correctly you had to jumper Ten and GND before you could time it correctly. in my experience 10 deg + or - is usually just the computer advancing or retarding.

Thanks Paul, I was thinking of doing it manually perhaps checking with a good old fashioned timing light. The cam belt was recently changed & I wondered if the crank sensor was possibly disturbed slightly.

timing lights are not relevent any more,the computer does all the changes by itself,which is a good thing,thats why it always starts every morning,unlike the sports cars of yesterday,if it aint broke you cannot fix it. if it has wierd misfires look at the distributer sensor housing,if its full of oil the sensor is on its way out,did mine at 105,000,when it was a customers car,now mine.

Thanks burner but what do you mean by distributor sensor hosing full of oil I thought this was solid state these days?

the cam sensor is at the back of the right cam, if you are looking at it with the hood open,it tells the computer tdc #1,and provides the input to ecm for ignition also,if its getting full of oil it will fail,just like all of us ,have a great day!

If the timing belt or cam was put in wrong the computer will not be able to correct for the issue, using a timing light will at least let you know if the timing is correct.

If the cam timing was wrong,you wont be going anywhere fast and SEVERAL codes would show up,mainly in your ass computer.

no, if the sensor is faulty and the cam is slightly off it is possible for the car to run just poorly. I have seen it happen. All i am saying is sometimes a trusty double check is better then relying on telemetry form a computer. computers can fail and give faulty readings and an engine can still run.

Thanks for all of your input Burner & Paul its all very helpful, The car is running fine using more fuel than I would have thought but then I do a lot of short trips so the engine doesn't get warmed up properly. I still think sensor upstream of the cat could be worth replacing on a 2001 model with 62 k on the clock it may be getting sluggish. put a stainless bid & back box on from mx5 parts which seems to have helped I think the cat may be iffy MOT due in 2 months so I should soon find out

Thanks for all of your input Burner & Paul its all very helpful, The car is running fine using more fuel than I would have thought but then I do a lot of short trips so the engine doesn't get warmed up properly. I still think sensor upstream of the cat could be worth replacing on a 2001 model with 62 k on the clock it may be getting sluggish. Put a stainless steel mid & back box on from mx5 parts which seems to have helped I think the cat may be iffy MOT due in 2 months so I should soon find out

my mx5 does the same thing. it like goes to choke mode and chucks out white smoke . it always passes the mot no water loss no oil loss . my bloke said it is running too rich. try the coolant ecu sensor and go from there