Do MX5s tend to run rich?
Discussion
Just back from the MOT: passed with no advisories - result!. However, she struggled a bit on the emissions test. The tester kept her revving for a fair while and eventually got the required result. I queried this and his comment was that all Mazdas - not just MX5s - from that period seem to run a bit rich and need a bit of coaxing to get through the test. Mine is a 95 1.8 Eunos, incidentally.
First I'd heard that that was a common Mazda tendency and wondered if anyone else has been told that?
Helpful guys at the MOT station, incidentally. I've used them for years and they're happy for me to watch and to take a closer look underneath while it's on the ramp. One of the headlamp bulb clips had sprung loose, leaving the bulb awry and they were happy to lend me a screwdriver to fix it, rather than just fail it as many garages would have done. Turned out that one of the testers owns a Mk 2, which probably helped as well!
First I'd heard that that was a common Mazda tendency and wondered if anyone else has been told that?
Helpful guys at the MOT station, incidentally. I've used them for years and they're happy for me to watch and to take a closer look underneath while it's on the ramp. One of the headlamp bulb clips had sprung loose, leaving the bulb awry and they were happy to lend me a screwdriver to fix it, rather than just fail it as many garages would have done. Turned out that one of the testers owns a Mk 2, which probably helped as well!
Well they do tend to run rich but not at idle or fast idle. It should be reading the O2 sensor and running from that so it should fine. They run rich over 4k, especially 1.6 as the AFM goes out of adjustment. 1.8 has MAF so should be much better. If it's running rich then it might have a problem with O2 sensor, temp sensor, cat or something. What sort of mpg do you get?
The print out from the MOT shows:
At average engine speed of 2,580rpm CO = 0.167% against limit of 0.2%; HC = 13ppm against limit of 200ppm; lambda = 0.998 against limit range of 0.97 - 1.030
At idle engine speed of 845rpm CO = 0.244% against limit of 0.300%
So on paper it looks fine but it took quite some time before it settled down to those figures. I'd taken it for a drive beforehand to warm it up but but only for 15 mins or so. In future I'll drive it further and make sure it's properly warm. On this occasion, I discovered at the last minute that the rear fog wasn't working so that rather upset my schedule!
In terms of economy, the last time I measured it, tank full to tank full, including a drive into central London, some gentle pottering about and a bit of more spirited stuff, it came out at 29.5mpg, which struck me as probably about right.
At average engine speed of 2,580rpm CO = 0.167% against limit of 0.2%; HC = 13ppm against limit of 200ppm; lambda = 0.998 against limit range of 0.97 - 1.030
At idle engine speed of 845rpm CO = 0.244% against limit of 0.300%
So on paper it looks fine but it took quite some time before it settled down to those figures. I'd taken it for a drive beforehand to warm it up but but only for 15 mins or so. In future I'll drive it further and make sure it's properly warm. On this occasion, I discovered at the last minute that the rear fog wasn't working so that rather upset my schedule!
In terms of economy, the last time I measured it, tank full to tank full, including a drive into central London, some gentle pottering about and a bit of more spirited stuff, it came out at 29.5mpg, which struck me as probably about right.
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