76 280z microsquirt project

[Datsunpowers]

Darom, wanted to say a big thank you. My PTZ throttle body was making the same whistling noise, and it was driving me crazy. Grinding the sharp edges off tonight reduced the noise to an acceptable level. It's much improved now!

 

I hope I can help you out with your closed loop idle settings. I spent a lot of time working to get my car to idle properly at 750 RPMs with the PTZ throttle body. I had to recenter the throttle plate and close the throttle screw closed more with a little grinding on the stop. I also had to change out the GM IAC motor with a different model. The one that came with the throttle body would not close and seal for me all the way. So, I went to the junk yard and pulled several different GM IAC models. The IAC that is working for me I think it came from a Grandprix V6. Here are my Megasquirt closed loop settings. I hope this helps you out.

Thanks, Tom

[darom]

Hi @Datsunpowers Tom!

I appreciate your time posting your IAC setup here.

 

I wish Protunerz would grind the sharp edges at their factory. I talked to them, they are aware of all this whistling business with their intakes. They are great guys and I got quick tech question responses from them. But the noise is an embarrassment to a pricey car part.

 

I have a few questions for you:

- Do you set up your throttle blade to be completely closed and then configure your IAC to provide additional air to get your target 750 rpm?

I went over this subject on a msextra forum as well, and it appears there are 2 ways to do it. One is to open the blade a little and IAC completely closed at idle. Another - the throttle blade is physically closed and IAC is providing air for idling target speed.

 

I went with the 1st option, since I couldn't get my IAC to provide predictable behavior. One day it would be idling at 900 rpms, next day - 800-850 rpm, another - around 1000 rpm. I figured the IAC's min steps and step size needed to be played with and per Madcaw's advice, I left it on 'Always On'. This helped somewhat. I also bought another IAC for a 1999 Camaro V8 (Ultra-Power AC162) to test (10$ special from Rockauto), but I haven't installed it yet. I suspect my IAC is not completely sealing the opening, thus these fluctuations.

 

- Open-loop vs closed-loop question

I removed my a/c a while back, and I have a 5-speed. I thought the closed-loop idle control is suited for the cars with big electrical loads (like electric fans, a/c compressor kicking in) or an automatic transmission. I have a belt driven fan. All my headlights are converted to using relays. I set up the open-loop since it was the easiest option.

Would you recommend for my car to switch to the closed-loop idle control?

 

If you don't mind checking my tune/idle and a driving log, I'd appreciate it.

 

What are your car's specs? Can you share your tune?

 

Thanks!

Den

2025-05-18_13.51.43.mlg 2025-05-18-adj-IAC.msq 2025-05-10_11.12.19-driving.mlg

[Datsunpowers]

Den, I agree with you that the ProtunerZ guys are very helpful, and stand behand their products. I am so glad that the car doesn't whistle anymore. 

 

I am no expert here, so take this as advice. Your mileage my vary. 🙂

 

The car is a 71 240z. I live at 8,000 feet and I see a lot of altitude change to 5,600 feet in CO, so I am running %Baro.

 

Here is the setup on my engine:

3L Turbo Stroker, 88mm JE forged pistons 8.43:1, Max Speed rods, ARP head, rod, main bolts, Electramotive L7 Cam, Garret GTX Gen II 3071 turbo, Water-to-Air Intercooler, ProtunerZ intake, turbo manifold, downpipe, Arizona Z Car 7 QT oil pan. Megasquirt V 3.57 with the expansion daughter board, sequential injection, 280zx Turbo CAS, GM Truck COP, Bosch 440CC injectors with 43 Psi. This is a new engine that has about 2,000 miles on it. Its running very well over the stock turbo engine I had in the car.

 

I did set up the throttle blade to be completely closed and then configured the IAC to provide additional air to get to the target of 750 rpm. This has allowed me to have it start in the cold at -10F and 90F and warm up properly. I do find it likes a AFR of 13.5 for a good smooth idle at 17 degrees of timing at 750RPM. I enclosed my MSQ tune file

 

Looking over your setup I noticed a couple things you should check. I will make the assumption the engine is stock with no cam and stock cam timing.

 

1. SYNC LOSS: (This is not good. fix this first otherwise you're chasing your tail) Your RPM signal has noise on it and two dropouts where the rpm goes to zero in a four-minute period. You need to confirm your sending a clean signal to the ECU. This is not my area of expertise with a hall sensor and tooth wheel as I am running optical from the 280zx turbo CAS. Check your sensor gap and grounding and shield grounding. Others here have way more experience in this area.

2. The throttle position sensor: You have 464 steps where mine has 679 steps. I would make sure it has full travel and re-calibrate it. I also noticed that your sensors are unlocked. This could be the sensitive throttle you mentioned.

3. Timing: It can't hurt to double check your base timing. I would confirm it at (Fixed Timing setting set to 15 degrees) with a timing light. Make sure you confirm zero TDC with the piston at TDC. I have had a couple harmonic balancers spin on me. I am not sure how the missing tooth crank wheel bolts to the balancer, so I could be incorrect here.

4. TPS WOT Curve: You have it set to start a zero and it keeps firing off your acceleration enrichment at idle. Your AFR is going rich to 10.4 when that happens. Move the starting point rpm so it just starts to fire when you start to accelerate. Take a look at my tune for a starting point. You don't want to fire off acceleration when its idling.

5. MAP sensor: Looking at the one warm up idle log. The timing moves from 19 to 23 degrees with no TPS input. Then is settles down to 14.8 while the MAP remained fairly steady at 41 kPa. You would think this would change with the timing swings, so check your MAP hose to the MAP sensor and the MAP sensor wiring. I see you have a GM-1Bar sensor configured. On my engine I have a vacuum of 27 kPa. It could be normal for your engine but check for vacuum leaks also. Here is a great article from DIY Auto Tune on closed loop ldle. MS3Pro Closed Loop Idle - Stepper Valve - DIYAutoTune.com

6. I would adjust your timing at the lower values. Set it up so you have 500 = 19 and have 17 degrees at 750. this way it will give you a little timing when the electrical load increases to bring the RPM back up. Looking over the idle/accel tab I have more settings available and a 16x16 table to play with. I think this is the limitation on the Microsquirt vs the Megasquirt.

 

 

Open loop vs. closed loop: I have had a stock 280 NA with factory injection and MSX fuel only to start with just the air bleed screw and bi metal IAC valve and it worked and idled fine. When I swapped to a stock turbo 280ZX engine with factory injection. I changed the IAC valve to a Ford 2 wire valve and used open loop then closed loop as I learned the system features. Both worked well but I could get more fuel control with closed loop. You have a lot more temperature swings and intake temps with a turbo engine under the hood that effects idle control. Now with the current stroker turbo engine and the PTZ 75mm throttle body. I spent a lot of time getting the GM 4 wire IAC to work correctly with the large throttle body. Any air leak or incorrect IAC travel setting turned into a higher idle. What I do like about closed loop with this current setup is how it can idle when it's cold or hot, electrical loads high or low, you have finer control over the idle. I also feed the gas tank vapor valve (240z 260z has this valve, I think. The 280z has a charcoal canaster) output and feed that in front of the throttle plate to burn the gas vapor off. When it's hot out the gas vapor would change the idle and AFR by two points. Having closed loop and AFR/EGO control corrects for that swing. Burning the gas vapor off from the tank.

 

Do you need closed loop no, open loop can work just fine. If you want better idle control over different variables then closed loop can help with that, but it takes time to set it up from what I have found. The reason I went to Megasquirt or any modern ECU. I was tired of troubleshooting with a voltmeter and a closed system you could barely modify. Now I can tune at my computer and get real time data and logging to review your results. What a step forward, but it's been a long journey learning these features and how to apply them (incorrectly and correctly). 

 

I included my current tune and a data log. In the middle and end of the log you can see how it idles. 

Hope this helps.

CurrentTune.msq 2025-05-21_16.32.19.mlg

Edited 48 minutes ago by Datsunpowers