I have a s14 240sx Ka-t with a s13 Calum ECU. I had him copy over a tune from another tuner and was wondering what value makes it so the A/F does not change depending on outside temp. When the temp is 50's-60's+ the A/F are in the 11.5-11.7 with 15 pounds or so. Now since the Temps are in the 30's-40's it jumps up to high 12's to low 13's. I saw this a few weeks ago and turned off the boost controller so it is only running 7 psi or so at 13's A/F. Since then I do not drive it very hard now. There has to be away for the ECU to detect the changing temp and add/subtract fuel to compensate. I could do 2 tunes for cold/summer but that is not what I really want. :( I use TunerPro RT and was wondering what setting pertains to this, if there is a setting for this. My air intake temp sensor is connected also.

idk, i could be way off but i wonder if it has anything to do with the cooler air being denser? i dont think the ecu detects cooler air and leans out the mixture.

The 16 point table/scale at &H0320 is used as a coolant temp based startup injection on the 16 bit ecus, but on the 8 bit ecu it seems to be used as as startup injection as well as running correction.

Might be something to look into.

I just reread your post, quite a conundrum.

Are these A/F taken at the same elevation?

I'm not sure why this is happening. The way I understand it (which could well be wrong), our MAFs should compensate for density differences associated with changes in air temp or altitude. This from Wikipedia --

"Hot wire sensor (MAF)

A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. This is achieved by heating a wire with an electric current that is suspended in the engine’s air stream, not unlike a toaster wire. The wire's temperature increases with the wire’s electrical resistance, which limits electrical current flowing through the circuit. When air flows past the wire, the wire cools decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The amount of current required to maintain the wire’s electrical resistance is directly proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the measurement of current into a voltage signal which is sent to the ECU.

If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow. Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume. (See stoichiometry.)

Some of the benefits of a hot-wire MAF compared to the older style vane meter are:

* responds very quickly to changes in air flow
* low airflow restriction
* smaller overall package
* less sensitive to mounting location and orientation
* no moving parts improve its durability
* less expensive
* separate temperature and pressure sensors are not required (to determine air mass)

There are some drawbacks:

* dirt and oil can contaminate the hot-wire deteriorating its accuracy
* installation requires a laminar flow across the hot-wire"

I just reread your post, quite a conundrum.

Are these A/F taken at the same elevation?

Yea. I'am going to be getting a TurboXS knock light so I can see if it is knocking at all when it leans it self out. If it is now knocking at all then I guess it will not be damaged. When it warms up it goes back to 11.5-11.7. That is how I blew up my stock engine ***. I was at the dyno when it was about 50 ouside and went to 13's under 12psi and popped a ring land on the stock engine.

Thats what I was thinking...

Ive never had this happen to me before, at least not this drastic of a change in A/F ratio. Thats why I asked about elevation, its the only other part of the equation (but it should be compensated for by the MAF).

You would have to do a maf or ecu/tune swap to isolate the problem.

One thing that could be causing this is voltage drift of the ADC reference. I would consider this just as likely as a problem with the hotwire. The drift could be happening at the MAF reference, or the ECU ADC itself which is a little less likely.

I do have a extra 300zx maf I will try. Will also clean out the MAF I have now to see if that does anything. So like I thought the ECU/MAF should compensate for the change in temp. Now the fun part is trying to figure out what is causing this GRR

So what ever happened with this?

Forgot about this post. :)


Well looks like it fixed it self in a way. I messed with the ECU tune and changed things around to see what it would effect, and it does not do it anymore. A/F stays constant now so I guess what ever I messed with fixed it. Wish I could give a more direct reason to why it stopped but it is fine now.

Everything runs awesome now. I did a retune for the water/meth injection and it has so much more power. No problems @ 18-20psi in the summer with 91 octane. Knock light is at setting 7 (10 the highest senstivity) and it only blinks a little bit at night and when I shift. I have drivetrain noise so I think it picks it up some.