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A lot of turbo cars are set up to put heaps of fuel into the engine when under boost.

In simple terms this tends to keep the engine cool and avoids pinking .... and dump a lot of unburnt fuel as black smoke

When you open the throttle (WOT) the O2 is bypassed.

It just is a fact of life that if you push any car .... and a turbo one in particular ...... then the mpg will be very low.

At or near full throttle the ECU ignores the O2 sensor and just relies on the AFM (NA6) or MAF (later models) to feed in fuel based on how much air is going in.

Mazda programmed them to go pretty rich (mine was 10.8:1 at WOT at 5,000rpm) on the grounds that rich is safe.

Various piggybacks or interceptors like the Jaycar Digital Fuel Adjuster can be used to get it back to better levels at WOT. Payoff is 5 - 10 extra Kw and better fuel consumption at the track.

manga blue recently put a dfa on his car and is seeing good results from it (he can elaborate further ). i have had one on mine for a while now and its done a good job. initially i was running it n/a with a cold air intake and the improvements over the stock system were easilly noticeable. now i am using it to run my turbo setup with about 110rwkw and it's been great. i'm thinking of upping the boost soon so i'll replace it with something that does timing as well, but for a fuel only piggyback i think it's easilly the best bang for buck item on the market.

greencomet has one as well, there are a few of us running them now, i can't remember all the others but yes they are a proven performer on the mx5 now i reckon.

wire it yourslef, its not that hard if you have any electronics experience.

or wait til i sell mine and you can have a fully tested and working one

Most of us have bought the kits from Jaycar. Start with the Smart Mixture Display, it's about $30 and takes 3 hours to solder together. Buy good side cutters, needle nosed pliers and a mid-priced small soldering iron. Jaycar will help you get started and you'll learn as you go. Then do the DFA and handcontroller, 3-4 hours each, then 2-3 hours to fit to the car. You might be able to borrow the hand controller from the forum.

I used butt dyno and the SMD to tune it first, then reset it back to all zero and put it on the dyno. Dyno tune was almost identical to butt tune and gave +9rwkw on an n/a motor.

Jt-1600 wrote:thanks heaps for the info, makes more sense now. But it just seems strange that it seems to have gotten worse over the past few months. I wasnt sure if something had worn out.
Has anyone had any experience with the jaycar fuel adjustor? Are they a good unit? Or does anyone recommend a good piggyback for a low boost turbo that doesnt run very rich. My car is putting out around 95rwkw.

Just re-read the bit about it getting worse. If things are changing it always pays to work out why. AFM misbehaving? Dribbling injectors? Blocked fuel supply return? Any other ideas Fatty?

how is the turbo tuned?

are you running a piggyback or afpr (adjustable fuel pressure regulator) ?

an afpr changes your fuel pressure whether in vacuum (usually just on stock) or boost (higher than stock, not recommended to go above 95psi rail presurre) .

now the jaycar is a piggyback style setup which modifies the pulse width to your injectors to deliver more fuel within specific rpm ranges (very similar to the hks fcon mini supplied in their kits).

its limitations will be felt on anything higher than 6psi of boost on stock injectors as they cannot modulate the injectors to open more than 100% of the time (upwards of 80% duty cycle for an injector starts runing the risk of the injector ''locking\" open and therefore flooding the car).

My guess is you need to look at your regulator settings if you have noticed higher consumption without having changed anything.

Are you sure its an afpr?

When you have some time, look for a blue box piggybacked near your factory ecu, HKS kits for the 1600 came with an electronic fuel adjusting box. not an afpr.