legacycentral bbs

VRG3: "1990-1992 non-turbo models also send the atmospheric pressure signal over to the TCU, which uses it to change shift points at high altitude."

The difference though is that NA models (at least early ones) had the atmospheric pressure sensor INSIDE the ECU.

The difference?

All NA ECUs have internal atmospheric pressure sensors... And all turbo ECUs use the external sensor for both manifold and atmospheric pressure... But only early NA models bring the signal out for the TCU.

Interesting, so a 91 turbo automatic isnt going to send the atmospheric pressure to the TCU? Does that relate to different TCU for Turbo and NA cars?

One more thing Ill have to check when the wiring is done on my project, yay!

That's correct; a turbo ECU doesn't send atmospheric pressure to the TCU. It's quite possible that one difference between NA and turbo TCUs is that turbo ones have internal pressure sensors, but I don't have any information to support or refute that.

Maybe 93-94 NA TCUs also have built-in pressure sensors.

If you need to make a non-turbo TCU work, the simplest way to go might actually be to leave the stock non-turbo ECU wired in (at least to power and ground) and use its pressure output line.

We just had this discussion over the bc-bf list too.

yeah the turbo ecu & tcu don't have that link for the barometric sensor.

Not sure if the turbo tcu has its own sensor in there or not. If someone has a select monitor and a turbo legacy auto, you could hook it up and if the TCU has a barometric reading, you then know that the TCU does have its own sensor.

With my select monitor I can pull barometric readings from both the ECU & TCU.....even though they are off slightly.....which I still don't understand.....

Hmmm. I know someone that has one. I'll see if we can hook it up when he has some free time (rarely).

They're probably just off slightly because the ECU and TCU don't share 5-volt references. The ECU's "5 volts" that it supplies to the TPS and pressure sensor is usually off by around 5%. I'd imagine the TCU's is also off by a little.

that would make sense....damn reference voltages

Dizzy wrote:Cool. Which turbo-back are you going to use?

You can see what I am thinking about here:
http://bbs.legacycentral.org/viewtopic.php?t=14302

Well, turns out my throttle plate seems to be opening properly to 90 degrees as far as I can tell. My boost gauge does show rougly 9 psi of boost being generated pretty much any time I want it above 2500 rpm, so the boost control solenoid is apparently working properly. I suppose I didn't realize how short of a pedal throw I have compared to my old car, and I didn't think it felt like 8 pounds of boost but then again I was used to 4 pounds on a 9.5:1 compression ratio. I just need more boost