Hey guys, just recently joined because as of a month and a half ago, I bought a ITB’d, megasquirted 1990 Mazda Miata. I had always wanted a Miata but had little to no knowledge on them or any cars at all. About one month and a week into driving it, my car stopped working. The original owner didn’t really care to help me much so I decided to action and learn about the car myself. So I did research, got tunerstudio and found out my KPA wasn’t reading correctly, it was reading around 53-54. Do you guys have any advice or help on what the issue/problem could be? Would really appreciate any feedback

 

No where near enough information. Where is the tune/log? Exactly what megasquirt do you have? What state is the engine in when your reading is 53? How is the MAP reference hose connected to your ITB's?

 

Tune/log? It has an MSPNP2. State of the engine? I have no clue what’s over one how the MAP reference hose is connected to my ITB’s. Heck, I don’t even know what a reference hose is. Ik this prob a pain in your butt trying to explain all this stuff for, but I’m really trying to figure all this stuff out. Would really appreciate if you could explain a little more on how to check all of the things you mention .

 

If it makes it any easier here’s a list of all the things the previous owner put in the car plus pictures of the engine

 

KPA will change drastically with different load/throttle position.
0 KPA is full vacuum
100 KPA is standard atmospheric pressure.
50 KPA is approx 15" of vacuum.
At idle 50KPA is a bit on the high side. Big cams or incorrect cam timing could cause this.
At partial cruise 50 KPA may be fine
At full throttle 50KPA is extremely LOW. (super restrictive, plugged exhaust, wildly incorrect cam timing, plugged air filter)

ITB's will decrease resistance to flow thus slightly raising KPA reading.
At idle each throat will have "pulses" of vacuum followed by "pulses" of pressure (TDC exhaust stroke when both valves are open).
This rapid fluctuation will reap havoc on getting a nice smooth vacuum (KPA) readings...

Adding a separate small plenum with 4 vacuum lines going to all 4 runners can reduce this "flutter".

That's a pretty cool 1st year.
ITB usually are the last thing to do to a wild, high compression, big cam motor to get the final 10 hp.

 

First of all thank you, i was pretty lucky to find a Miata with all these cool aftermarket things and tunes, but at the same time i was cursed since I have no knowledge on any of it. Also, my KPA is acting funny, with the engine off it’s reading 53-54 sometimes, but at other times it’s reading 3-4 KPA. And it needs to be reading 98-100 KPA with the engine off correct? I really appreciate the help btw.

 

So I checked the map sensor port line and sucked on it to see if that would change any of the readings on my computer. It didnt, so now I know that I need to replace the MAP sensor. Could you give me some pointers on how to?