1990 NA6 Running Stupidly Rich

[Bill2032]

Hey Guys,

So I'm fairly new to this forum, I've been trawling it for quite some time but never really posted. The car is a 1990 MX-5 with a 1.8 engine swap from the previous owner. Anyway ever since I purchased my car I've had quite crappy fuel economy (200-250kms to a tank) and the car seemed to be running quite rich, smelling of raw fuel etc and I've been researching and fixing things to try and correct this but no go, nothing has changed.
So far I have changed

- Plugs
- Leads
- O2 Sensor
- Coolant Temp Sensor
- Fuel Filter

This is all over the process of a year trying to fix this and due to finally finishing college, I've just now been able to dedicate time to trying to fix this issue. As far as I know there are no fuel leaks, I spent the past hour trying to look for them and no luck. I'm coming to my wits end as to what the problem could be. I just checked the plugs in the car and they don't show any resemblance of a car running rich so im quite confused as to what the problem could be! Anyway here are photos of the plugs from the front cylinder to the rear.

[plohl]

Fuel pressure regulator? Check the vacuum lines.
Sticky/dirty injectors?

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[Bill2032]

Forgot to mention I've checked for vacuum leaks and none found, checking the fuel pressure reg tomorrow and if thats not the suspect I'll get the injectors cleaned and go from there

[hks_kansei]

Those plugs don't look rich to me, they're white/brown which is usually lean/perfect.

You mention it's a 1.8, have you by any change used the plugs from the 1.6 in it?

B6 and BP use different spark plugs, different temperature from memory. Using B6 plugs in a BP causes them to be white and the car runs like sh*t, may misfire, etc.

ages ago I had similar issues to what you're describing, in my case it was a combination of buggered plug leads, and an o2 sensor on the way out. (mine was fouling plugs though, so they'd come out wet and dripping)


also note, the BP (in the NB anyway) used a heated o2 sensor (4 wire, I think the NA8 used a 3 wire, but same thing) where the NA6 used an unheated 1 wire sensor, again, maybe wrong sensor?



edit: a healthy MX5 should have the spark plugs come out as slightly black and dry. They run rich per standard.

[Bill2032]

Those plugs don't look rich to me, they're white/brown which is usually lean/perfect.

You mention it's a 1.8, have you by any change used the plugs from the 1.6 in it?

B6 and BP use different spark plugs, different temperature from memory. Using B6 plugs in a BP causes them to be white and the car runs like sh*t, may misfire, etc.

ages ago I had similar issues to what you're describing, in my case it was a combination of buggered plug leads, and an o2 sensor on the way out. (mine was fouling plugs though, so they'd come out wet and dripping)


also note, the BP (in the NB anyway) used a heated o2 sensor (4 wire, I think the NA8 used a 3 wire, but same thing) where the NA6 used an unheated 1 wire sensor, again, maybe wrong sensor?



edit: a healthy MX5 should have the spark plugs come out as slightly black and dry. They run rich per standard.

That's exactly what is confusing me about my cars running condition! and just checked at my work as well as the NGK site and definitely using the plugs for a BP. They're the NGK BKR5EIX-11 Iridiums that are in there at the moment. Yeah mines always run the single wire O2 sensor ever since I've had it and I just replaced like for like, however I did read up and apparently when doing the 1.8 swap you use all 1.6 electrics. Im just stumped as to what it could be but I'll test the FPR tomorrow and go from there.

Some additional info is that the car also likes to sometimes idle seek, confirmed again no vaccuum leaks but is it possible a dodgy ISCV/IACV could cause the issues that I'm seeing?

[hks_kansei]

I wouldnt bother with the iridium plugs, the cheap regular old copper plugs work better anyway (takes less energy to spark)
The only downside with copper ones is they need replacing more often, but their low cost makes up for it.


I don't know that much about using 1.6 parts on a 1.8, but my gut instinct would be that it's far from ideal.

[speed]

What's your timing set at?