Now that the leaning issue has been solved, its time to get to tuning.

One of the steps I took attempt to solve said issue was to toughen up the fuel map. By roughly 10%-25% thought the boost areas. Once the injectors were flowing as they should this resulted in pretty terrible afr's. Before I went to lean the maps out, I figured id toss on the cosmo afm I picked up so I wouldn't have to tune it twice.

I wired the s5 plug into my s4 harness in parallel so I could do back to back comparisons or run an s4 afm if I needed to for any reason. Not sure if that affects the readings.....?

Interestingly, when fully depressed by hand, both units registered the same value (on the palm). However during the idle test the s4 afm read higher at the same rpm/vac level. This was confirmed during the driving test as it was just barely too lean to idle. However it ran much better during cruise and boost, registering about a full point more lean. Before afr would drop to 10.x then 9.x in boost now it maintains mid 11.x I guess I won't need to do as much tuning as I thought.

 

I think part of it has to do with the amount of air that is bypassing the measuring plate. It is my understanding that the Cosmo AFM is s5 style like this:



and the s4 is like this:



I suspect each has the air bypass passage adjusted differently.

 

Makes sense, as the port size goes RE> REW>s5>s4. I'm just hoping I can get my idle back w/a combination of variable resistor and TB adjustments.

 

Ugly little things. Good luck, glad you got the issue resolved!

 

Me too, I was about ready to park my car in a bad area of town and call the insurance company, lol.

I will be posing some logs for comparison once I get this idle adjusted. I'm curious though, since the n390 runs 11.x afr w/ all that extra fuel, should n't I be make more power? It definitely seems faster, but not as much of a difference as I was expecting considering how much fuel was "added"

 

That looks like the s5 afm, due to the bypass tube near the bottom of the diagram. The cosmo afm has a larger opening and no bypass tube. Looking at the diagram and a spare s5 afm; it uses the bypass tube because the cone seals completely against the inner bore of the unit.

The n390 has no bypass tube because it does not seal against the inner bore. The small gap between the cone and the wall acts as the bypass as far as I am able to tell.

 

Here are the comparison logs I ran for the N318 and N390. I hooked the units up and manually depressed the actuators fully, then I went inside and started the car to get the value for "idle" (the car was completely cold, so its a little high)

Both units maxed out at 732.5 mystery units in a static environment (I am aware that other factors are involved in airflow calculation under load)
however when when running:
@ 1200 - 1300 rpm the N318 fluctuated between 27.5 to 30 units
@ 1150 - 1250 rpm the N390 fluctuated between 20 to 22.5 units

 

Well, I have come to the conclusion that this afm cannot be made to idle on an rtek w/ 550cc primaries.

Since there is no control over idle fuel mixture there its no way to compensate for the greater volume of bypassed air when upgrading to the n390 afm. Theoretically operating 720cc injectors on the "550" setting should provide enough extra fuel fort it to idle, of course the rest of the map would need to be corrected accordingly.

 

No luck with variable resistor?

 

Nope. It really doesn't offer very much adjustment at all, just some nearly insignificant fine tuning. The bac was a non-factor as well, it was set to full open, full closed, and somewhere in between. The throttle plate stp screw was set for minimum air as well, all to no avail.

The closest it came was a very brief pause@ 500 rpm, before stalling. That was bac= closed, throttle plate = mininum, and VR= middle.

 

You would have to run an SAFC or something. That's just a pain in the ***.

 

No safc for me, I'll just wait till I upgrade to 720 primaries then it should be ok on the 550 setting as it will be injecting roughly +30% fuel.

In the mean time.....I'm trying to figure out why my car now revs to 2000 everytime I start it, and stays there as long as the key is in the "on" position. This comes after installing a relay to fix the very common sticky starter issue.

 

If the BAC valve is unplugged, does this occur?

 

The reving? Yes. The bac has no effect on or off or disconnected.

It has been determined that the problem is that the starter will not disengage. This is because mazda in its infinite wisdom decided to wire the ignition and interlock switches into the blower motor. So The wire used to trigger the relay never had less than 5v and therefore once closed, the relay will not te open, even though the 12v stay signal is no longer present... More details here:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/ive-solves-2nd-gen-sticky-starter-mystery-896013/page5/