mx5cartalk.com

I have recently purchased a stock 94 Na8 and I love it heaps. Was recommended to this site by my mates step dad (99MXV). I've been lurking around for reasons as to why I have very little power/torque at 2700-2900rpm. I have cleaned the throttle body out but that's about it.
It's stock as a rock nothing aftermarket on it at all. I'm an apprentice mechanic so feel free to talk very technical with me.

I was thinking maybe weak ignition or alternator? Or map sensor issue?

Or possibly O2 sensor.
I am told a faulty one can cause a flat spot in the mid range.

Snowmotion wrote:Or possibly O2 sensor.
I am told a faulty one can cause a flat spot in the mid range.

That actually sounds like it could be it. My girlfriend owns a 02 BJ 323 with the the 1.8 do you think it would have the same O2 sensor? I could swap them over before I go and spend a few hundred bucks on a new one.

New 02 should be way less.

For 200 you can get a wide band with a gauge and controller. Replacement bosch sensors for these after market wideband are only about 60 bucks.

Sent from my GT-I9100 using Tapatalk 2

Bosch replacement O2 sensor is about $150 (that's just a shop price, you can probably find cheaper on ebay etc, but then you need to wait for postage etc)

Check the part numbers for the 323 and the MX5, I would assume they're the same (the o2 sensors are fairly universal) but check to be sure. (I don't think the later 323s used the B series engine)

Most O2 sensors are a universal fit, with no plug, you just need to use the provided diagram to wire them up to the factory wiring.

On the NA6 it's only a single wire, on the NB it's 4 wires (NB one is heated)
Not sure what the NA8 had, but it will be one of those.

Alright thanks heaps for the info I've looked more into it and it definitely looks like the O2 sensor has reached its used by date. A wise man once told me that if you have to replace something, upgrade it. So what is my best bet for a wideband O2 sensor kit? There is a few out there what is your guys experience with them?

stock ecu can only deal with narrow band.
However most good widebands have a narrow band output aswell.
The Innovate LC-1 is generally well regarded.

An NA8 runs in closed loop mode when revs are below 4500 and you're just using light throttle. In closed loop mode the ECU uses the O2 sensor to help it set mixture.

It runs in open loop mode above 4500 or when you're giving it at least half throttle. In open loop mode the ECU only uses its internal fuel map to set mixture and the O2 sensor is not used.

So if you're getting that flat spot when you've got your foot down then changing the O2 sensor won't fix it.

edit: fixed

Well the issue is at light to mid throttle below 4500. Above 4500 at full throttle it runs fine no hiccups even at light to mid still runs perfect. Idle is very steady about 950rpm at operating temp. It just really feels like there is very little power at all below 3000rpm at light to mid throttle...

Let me know how you go with the Innovative Wide band if you do the install.
Sounds interesting and perhaps something to do in the near future.

Jelzahar wrote:Well the issue is at light to mid throttle below 4500. Above 4500 at full throttle it runs fine no hiccups even at light to mid still runs perfect. Idle is very steady about 950rpm at operating temp. It just really feels like there is very little power at all below 3000rpm at light to mid throttle...

OK, potentially O2 sensor then, although it usually shows as poor fuel consumption rather than a miss because the car will tend to run way too rich when the O2 sensor is worn out.

Plugs and leads are much more common causes of misses in these cars.

The NA8 uses a 4 wire sensor. Normal sensor life for an early type 4 wire one is about 80,000. Genuine Bosch, NipponDenso or NTK is the way to go. You should be able to get a Bosch Universal for under $100, you need to cut the old connector off and splice it to new connectors supplied with the universal kit. Otherwise a Bosch BF Falcon one should work if you don't mind cutting and soldering 4 wires.

Wideband is a total waste for a car with a stock ECU. Your ECU is only capable of reading narrowband.

Given you've only recently purchased it, if you've not already, it would be worth baseline/fully servicing it to ensure all consumables are serviceable & all settings are correct. As manga_blue says on the NA8 a miss is usually plug leads.

I've dumped the oil and replaced the filter, pulled a plug out and seems alright and the leads seem fairly new. But I'll whack a multimeter on the leads and replace the plugs. If this doesn't fix it I'll have to go for the O2.

well ive replaced the plugs and no difference, have an O2 on its way to my place so hopefully should have it in next week, will report back with results

I know this is real basic and overly simple ... but has the fuel filter been changed?

Sent from my GT-I9100T using Tapatalk 2