I am going megasquirt on the S4 13B NA in my 82 RX-7, and was wondering about the TPS a little bit. I know the TPS on the S4 throttle body is only a narrow range, but I was wondering if you guys/girls think the TPS is sensitive enough to be used as a full range using a custom cam setup to progressively depress the TPS plunger as the throttle is opened. It would require an accurately cut cam mounted on the primary throttle shaft, then a custom bracket for the TPS. I know the cam idea would work, its just a matter of the sensitivity of the TPS.

Oh yeah, I should mention that this would be to more accurately stage the injectors, or so I hope. I hope I'm on the right plan of attack here. My overall plan is to use the specified GM coolant temp and air temp sensors, the output from my AEM wideband O2 controller for the O2 input, and since I'm using a 1st gen style ignition, a signal from the trailing ignitor using a heavily sheilded large wire to prevent any false triggers. I hope to use the S4 air bypass valve for fast idle as well, since it is just a simple solenoid. I'm using the fuel only megasquirt btw, probably V3.

 

Yes its fine. You could just throw on a S5 TB instead. I used S4 throttle sensors on the S5 TPS braket and it works perfectly. The only reason I used S4 sensors is because the S5 ones were bad. I don't think there is any difference between the 2 sensors really. If you use the mechanical OMP then just swap the mechanical OMP control lever from the S4 TB.

 

I'm using S4 throttle body and TPS because I have 2 of them on hand right now, so rather than spend more money and get an S5 throttle body and TPS, I'll just stick with the one I have here. The key is getting the cam for the TPS to the right progressive profile, which is not a real big deal because I took cam profiling in college and how to calculate the profile properly.

 

If you can do it, go ahead. A good working S5 TB wont cost much.

 

You need to make your owne bracket. This sensor is from a late 90's mazda 626. It is very close to the altonator but it isn't touching.


and a short video of it working

http://jaxrotaries.com/rx7/MVI_3758.AVI

 

I don't see why to go through all that trouble when you could just swap TBs.

 

the reason is because the rx7 style plunger tps are inaccurate, expensive, and fail often. I know this from my own experience and from searching the board and finding many others with my experience.

 

The throttle sensors them selfs are very acurate.

The reason many think they fail often is due to the reason that all s4 throttle sensors are over 20 years old. You can find good used ones for cheap and even if you buy a new one you wont have to worry for another 10-20 years.

The S5 TB already has a cam for the throttle sensor which is very accurate. I can verify this on my SAFC and watch the % and volts go up and down in a smooth, steady motion.

You could easily just remove the narrow range TPS from the bracket and remove the TPS arm and keep all the full range items.