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1975 Mazda REPU - Build and Repair thread

:
'86 RX-7 Base, '79 RX-7 GS
I mounted my vacuum manifold as high as possible to avoid that. Fuel has to make it through two 90 degree bends to get in there but somehow it still does. The lines going to the FPR, MAP sensor, and brake booster all trend upward so hopefully that'll keep the fuel out as a backup to the filters and check valve. I'm going to clean out the lines and swap in new filters in the near future to see if what's in there was from before I moved everything around. If I'm still getting a lot of fuel in the lines I'm probably going to put one of those inline air filters for air power tools on my vacuum block.

It looks like the Adaptronic transient functions are a little more advanced that the Haltech options I have with the PS1000 and ECU Manager. I'm sure the Elite has better functionality as well. I think my problem lies with the asynchronous fuel injection settings. I think I need a higher asynchronous injection percentage than I originally thought and at higher engine speeds. I bumped up the numbers for my drive today and transient throttle response seemed to be a little better. It's hard to make good adjustments because I'm in the car by myself.
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
While I wait for the IACV to arrive I ran the new wires for it and cleaned up the harness so I could tuck the wires tightly behind the fuel rail. They’ll be out of sight when I put the air filter back on.

 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
So the 2-wire Ford style IACV is not going to work. What I have ascertained is that they require a significant amount of air volume and consistent vacuum to stay closed. In resting state, a spring keeps the valve open. Suction through the valve will somehow pull the plunger and seal the opening. Sending power to the solenoid will open it back up. Sending a frequency power signal can keep it partially open, assuming of course the motor is drawing enough air to pull against the plunger.

My engine just doesn’t draw enough air so the valve never closes. Looks like I’ll be returning this one as well and seeking out a 3-wire valve that can forcefully close itself electronically.
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Played with the Ford style 2-wire valve a little more this afternoon and I simply cannot get it to close. I shut down all the other ports on the intake and closed the throttle as much as it would close and still it wasn’t enough vacuum to pull the valve’s plunger and cut off the air supply. So enough with that. I’m running another wire so I can use a BMW style 3-wire Bosch valve. It’s more expensive, but I don’t see another way to affectively meter air.

 
:
'86 RX-7 Base, '79 RX-7 GS
What's your target idle speed again? My idle vacuum is around -7 psi at 1000-1100 RPM. However, mine will pull more vacuum at slightly higher engine speeds, which is why I've relied on a zero throttle fuel map. My heaviest electronic loads are the electric cooling fan, exterior lights, and cabin blower motor. I haven't had all three on at once but the cooling fan + blower at maximum only drops my idle by ~100 RPM. I've been told you can make use of a stock FC RX-7 bypass air control valve (BAC valve) for idle control.
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
I’d like to get it idling back down at 750-800 RPM. That’s what it used to do with the carb. However the bigger issue is that the truck needs to really warm up before the idle can drop below 1,500. Normally the choke would be open for the first 10 minutes of driving, even in warm weather. So the IACV is basically going to serve that same purpose, plus the Adaptronic can then compensate for loads. I’ll start simple with just adjusting for the cooling fan but there is also a table that will finely tune injector output based on voltage so as I power up lights, heater, radio, etc, I can dial things in and keep that idle low and slow without stalling.

The FC BAC valve would serve the same purpose but it falls into that 2-wire category that may rely on vacuum to operate. If I had one lying around I would certainly try it but they are very expensive (unless you buy a questionable eBay used one). You’ll have to fab up an manifold adapter whereas the Bosch unit above can be connected with just hoses and won’t be dependent on vacuum to open and close.

 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Guess I never posted the bracket.



Winter has arrived so progress has slowed. I’ve taken it out here and there and messed with the tuning software. The fuel map seems fine but the transient throttle is still touchy and I haven’t solved the stalling issue. Last time out I moved on to using the ignition PID controller for idle control and had a thought about a way to solve the off throttle stalling. I’m going to advance the timing on the ignition map so when I lift off the throttle it has some torque to hold a faster idle...and then I’ll get the idle control to drop the RPMs down further. Makes sense in my head, just not sure i can get the software to do it. This is sort of how my stock FB RX7 does it. First it opens a valve to let more air in under decel, but it also seems to hold the mechanical advance momentarily before it drops down into idle.

In other news, I picked up a spare 60k mile ‘85 12a off a guy on Craigslist for short money. It looks like it will run, but I dropped it off to get street ported. It’ll likely end up in the RX7, so street porting the motor in the REPU will have to wait. Honestly, if I could get this running smoothly, I don’t think it needs all that much more power. With skinny tires and a lifted stance, more power will only lead to bad things.

 

bazooka joe

No words
Moderator
Contributor
:
2016 Miata Club, 2014 CX5 Touring, Honda 1976 XL 175
Looking forward to spring and more progress on your build, ��!
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Small update. I’ve been driving the truck a little more now that the roads are drying out. Lately it’s been a battle with the ECU not doing what I want it to and a lot of head scratching with regards to idle control. It would run fine in open loop but as soon as closed loop kicked in things got real bad. After more time than I’d like to admit I think I tracked the issue down to the following: I have no speed sensor, I have no clutch switch, and I have no neutral switch. That was putting the software in some odd state where it didn’t really want to let the car idle and it was throwing out whacky values for the idle air control valve, pretty much ignoring anything I tried to set.

A speed sensor or neutral switch isn’t an easy task for an old truck, but I figured out a 1st gen RX7 clutch switch drops right in.



I’ll need to put some more miles on it and play with the PID idle control settings but I think this will solve the stalling at stop signs. To get past the neutral switch issue I used the logic settings to make an assumption about neutral. If throttle is 0% and RPM is below 1200, assume transmission is in neutral regardless of clutch switch.

All of a sudden the ECU started catching the falling RPM and changing gears was a little smoother. The battery died on my laptop before I could log a drive and fine tune things, but I’ll head out again this week as long as we don’t get more snow.

 

bazooka joe

No words
Moderator
Contributor
:
2016 Miata Club, 2014 CX5 Touring, Honda 1976 XL 175
Small update. I’ve been driving the truck a little more now that the roads are drying out. Lately it’s been a battle with the ECU not doing what I want it to and a lot of head scratching with regards to idle control. It would run fine in open loop but as soon as closed loop kicked in things got real bad. After more time than I’d like to admit I think I tracked the issue down to the following: I have no speed sensor, I have no clutch switch, and I have no neutral switch. That was putting the software in some odd state where it didn’t really want to let the car idle and it was throwing out whacky values for the idle air control valve, pretty much ignoring anything I tried to set.

A speed sensor or neutral switch isn’t an easy task for an old truck, but I figured out a 1st gen RX7 clutch switch drops right in.



I’ll need to put some more miles on it and play with the PID idle control settings but I think this will solve the stalling at stop signs. To get past the neutral switch issue I used the logic settings to make an assumption about neutral. If throttle is 0% and RPM is below 1200, assume transmission is in neutral regardless of clutch switch.

All of a sudden the ECU started catching the falling RPM and changing gears was a little smoother. The battery died on my laptop before I could log a drive and fine tune things, but I’ll head out again this week as long as we don’t get more snow.

[emoji849] wow, but I know you really enjoy this hunt!!! Don’t get the truck all salty!
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Well, my tune was good enough to get me to the top of Mount Washington, temps never went over 205.







 

Matt22

On my 14th Mazda.
:
90 RX7 Vert
I like rereading this thread to pick up on other stuff I need to get done to my truck.
 
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