I had been slowly sorting out the wiring and I had reached a point where I had a pretty good stripped down harness constructed from the remains of the OEM unit. Many calls to DIYAutotune, the place where I purchased my MegaSquirtPNP G2 MM9900 engine management and Innovative LC-2 wideband O2, and hours of web searches now had me at the point where I could attempt a first fire up. I would still need to balance the throttles and calibrate the sensors first however.
Balancing the throttles is a two part process. I needed to first set the opening of the throttle to at least get the air flow close to identical at idle and while the butterflies were opening. I came across a good .pdf file that really helped out in getting the basic settings built into the throttles before I attempted a start (Toyota ITB EFI) . I would need to balance them later at idle with a syncometer to make sure all the throttles pulled the same air.
The next step was to make sure I set the calibration for both the engine sensors and the Innovative wideband O2. The O2 was very straight forward, leave the O2 out of the pipe, disconnect it from the included harness, keyed power on, wait for red light to appear on the Innovative box, key off, connect the O2, key on, wait for solid green light then you are set to install the O2. You need to be careful with the O2 as it gets very hot during the calibration, just a warning. As for the MegaSquirtPNP, that was a little more complicated as the install and the calibration takes a bit of research. I was planning on using ITB Mode which comes with the MegaSquirtPNP and makes life a bit easier when starting out. I would still need future tuning but its a great place to start. Basically ITB mode blends Speed Density and Alpha-N to make driving ITB powered cars smoother. Its dependent on a few things but most importantly it needs a good working and properly wired TPS (Thottle Position Sensor), more on that in a bit.
Here was my initial set up and the results after a full day of messing around in TunerStudio. I calibrated my TPS, but noticed the range for the ADC count was short and seems to be very high in numbers. I calibrated the IAT (Intake Air Temperature, GM), which I also purchased from DIY. Then the Coolant temp sensor and a few others. I found this document helpful in getting started (Gant_Semester_Project). This is actually a very simplified explanation of what I did for the set-up. I spent many hours with a meter checking wires and resistance in preparation for the start-up and I believe in having everything worked out before an issue can occur. Even with this approach a gremlin slipped in.
I pushed the Catfish into the driveway and took out my fire extinguisher, just in case the first fire up was my last. Safety first. I turned the key to on and made sure that all of the appropriate lights on the Megasquirt and the Innovative O2 box lit up and looked at the gauge ion the fuel rail to make sure the fuel pump was primed. I stopped at this point to go over the fuel lines from from to back and looked for a leak or even the smell of raw fuel. So far so good. I moved back to the key and got ready to see what would happen. Fire on the first turn! It actually kind of scared me a bit. After a few revolutions it died so I tried again. This time the same issue presented itself so I manually opened the throttles a bit and tried again. This time I was able to get a mildly rough idle but the engine still wanted to die. I noticed the coolant temperature climbing as I made adjustments in Tuner Studio and fiddled with the throttles. About the time I was able to balance out the air going into the throttles with a syncometer coolant temp hit 200 degrees. Things seems to settle out and sounded much smoother. The idle settled down to around 1100 rpm’s and everything seemed ok on the outside, I looked back at Tuner Studio and found the AFM was way out of wack and the engine was running very lean. I decided to give it some throttle and wanted to see if it would add more fuel and if the engine would rev evenly. This is where I discovered the issue with the TPS. The throttle response was erratic and I noticed that even though my O2 AFM gauge read lean the exhaust looked very rich, I also smelled fuel in the exhaust, not good. I checked the oil for fuel after shutting down and decided it might be smart to change it just in case, which I did the following morning. After a few emails back and forth with DIY I pulled the TPS and rechecked the wires from the stock wiring harness and the resistance of the pins on the Toyota TPS. For anyone looking for the test here it is:
The resistance between the VREF (IDL) and ground pins will remain constant.
The resistance between the ground and signal pins will be low with the throttle closed and high with the throttle wide open.
The resistance between the VREF and signal pins will be high with the throttle closed and low with the throttle wide open.
What I found was my issues were two fold. First during my initial wiring of the Miata OEM harness to the Toyota TPS I had switched the VTA and VREF wires, that was easy to remedy. The second issue was that the Toyota TPS (89452-22080), that came with my used throttles, was bad. The VTA signal would just erratically or sometimes show nothing at all. I went out and purchased a new TPS and prepared for my next attempt the following day. Before doing so I re-calibrated the O2 and reset the tune back to the base tune in Tuner Studio. I always like to reset at the base and start again.
This time was much different. The engine fired quickly again and with a very little help it held idle and was fairly steady during warmup. I knew there was still weeks if not months of tuning to get the most from the engine, but I finally had a base tune for the ITB’s. The revs were steady and the engine sounded powerful and even. The idle was still a bit high at 1100 rpm again and I was seeing an AFM way to far to the lean side but most of the major items seem to have been sorted. I shut it down and decided to take a week long break before additional tuning and messing about.
Second ITB Set-up and Test Day
I will have more soon, I am now deep into tuning and getting ready to do the body work and modifications. See you next time.