How to adjust the Fuel/Air Mixture

What for? There are seveal "tricks" for specific purposes. Alter air temperature readings Change air flow readings. "Clamp" the O2 sensor reading These really only work for/during open loop, or for a very short time in closed loop, since the O2 sensor is going to cause the ECU to adjust the mixture in closed loop. The O2 clamp has some longer term possibilities, if the "rich lean" change is enough to fool the ECU. It may also be necessary to alter the second O2 sensor signal.

The usual thing is to fool the ECU and add more fuel with a timing retard as well.

After replacing the intake, building a cold air box for said intake, and a high-flow exhaust from manifold back, I seem to be running a bit lean...

I figured as much, but thought I would ask...

Original question below:

'97 STO, "Chouki"

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In your case, I'd be thinking about the placement of the air flow sensor. It may be that it's not reading quite what you need. The timing retard is usually only needed if you add forced air (turbo/supercharger) I'd also replace the fuel filter if you haven't already done so. Another thing to do is to see if the fuel pressure drops below normal at higher throttle settings.

Why do you say so? You should be putting only a small percentage more air through the system as usual.

Apparently, the JR uses a resistor in the air temperature circuit to trick the ECU in adding more fuel. You could try the same with a much smaller resistor. I do not remember what the resistance of the JR kit one is, (if I ever knew,) but you could try the power forum on miataforum.com.

Following chuck's advice in insuring the proper operation of the OEM system first seems like a good idea, though. You hate to have to take out the resistor later again after you replace the fuel filter or fuel pump, say.

Leon

Chuck -

Thanks for the lead. The car has ~43K miles on it. Having owned it for only 6 months, I've not changed the fuel filter.

Leon -

My reasoning for the "running lean" assessment is due to the blueing verse s bronzing of the RB 4-1 stainless header.

I agree that changing the filter is a first option over adding a resistor of unknown size...

- L

'97 STO, "Chouki"

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I don't know if that's a good indication these days. The feds insist that the engine run leaner than they did in the old days when we used pipe discoloration to judge rich/lean.

Chuck -

I've talked with a few other gear-heads and have come to the same conclusion. -- Based upon the lack of CEL and the relatively unchanged fuel consumption post exhaust upgrade, I am guessing things are OK...

Thanks to those that chimed in...

- L

'97 STO, "Chouki"

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