1984 RX-7 GSL-SE w/ Cosmo 13BRE, S4 TII Turbo, 550 PRI. 850 SEC. injectors, walbro pump, FMIC. Here is the problem i am having. when im just crusing around town the car would start to bog at 3k RPM, but when i'm under boost its fine. i leaned out the injector map but its still doing the same thing. can somebody please help me with this. thanks

 

I would play around with the transition point possibly move it up a little it will allow the primaries to run a little better and take away the bucking. Try 45% or 46.5% just for kicks and see how that works.

 

How do i do that?

 

In the Power FC Settings 5 use the dataloggit ...

 

That is wrong as the secondaries do not come on until around 100+mph while cruising. Most likely a fuel tuning problem. For an average PFC driven rotory engine, run 30%transition and .100 initial MS with overlap of 5/4/2.
I have proved this with charting logs which were posted here years ago.

 

Well thanks for enlightening me on that one Chuck. I thought that for an FC since this is a big step up in terms of injector size that moving the transition point upwards would prevent the bucking at transition as per B. Davies.

Actually, I used moving the transition point higher on an FD with 1300cc's and it helped remove the bucking so I am confused.

 

Extremely difficult to diagnose without posting Datalogit logs of the problem which would include a wideband input.

Also, sometimes bucking under low load can be caused by insufficient timing advance. Insufficient timing advance can be caused by a crank angle sensor that was not installed correctly (timing is too retarded), or a crank angle sensor that was installed correctly but the timing marks are wrong due to a mismatched pulley/hub set. That is not an issue on series 6 engines due to the revised crank angle sensor design. But it is a problem on earlier motors, and I'm pretty sure that includes the 13B-RE.

 

Best to log BASIC and ADVANCE and then look at the problem in CHART mode. That includes logging AFRs.

As for secondary injector transition, do this experiment:
(1) with the engine only turned on and the commander near the TB, record the TPS voltages for when the secondary throttle just starts to open.
(2) Now cruise and slowly accelerate and then maintain that speed where the TPS voltages reach the values from step 1. Record that.
(3) Slowly accelerate until the secondary injectors start to turn on, this requires ths DL.
(4) between points 2 and 3, there is uneven fuel/air distribution coming into the engine.

Unlike a multi barrel carb which secondaries flow fuel as soon as they open, Mazdas system doesn't which can cause lean bucking.
Mine sometimes does it sometimes around point 2. The only way around this lean point, is to run richer in that area than your normal AFR target unless that target is rich. My target is 16AFR. 14.7 should not lean buck there.

This type of tuning is way more complex than boost tuning.

 

the car runs alot better with the changes. thanks for the help.