Mystery ECU pressure sensor...?

Heads, valves, pistons, rods, crankshaft, etc...

Moderators: Helpinators, Moderators

Post Reply
free5ty1e
Fifth Gear
Posts: 2268
Joined: Wed Nov 12, 2003 12:26 am
Location: USA: Central FL
Contact:

Mystery ECU pressure sensor...?

Post by free5ty1e »

Hey hey.

Just got a pair of what are supposed to be N/A ECUs for their connectors and am puzzled upon taking the first one apart:

Image

What the fork is that?? There's a hole on the back of this ECU where this thing is aimed. The entire circuitboard's sole purpose appears to be driving this thing, which I suspect is some sort of pressure sensor.

Did some Legacy ECUs use a board-mounted atmospheric sensor instead of sharing the MAP sensor under the hood? The other N/A ECU I have here does not appear to have this strange piece of aircraft-grade technology.

The sensor itself is a thick film hybrid microcircuit - on the exposed thick film (on the top) I can see laser-trimmed resistors. Highly accurate stuff. Overkill, in fact - which does agree with Subaru's engineering practices.

Anyone know for sure what this is and what it's for?
-Chris
91SS 4EAT stock, 200k mi
91SS 5MT rebuilt engine waiting for a shell
93TW 4EAT, Forester lift, 3" TBE, 11psi, 200k mi
94SS 5MT4.11+rLSD 311k km: RobTune550,TD05-16g @ 18psi,FMIC,3"TBE,Forester lift
vrg3
Vikash
Posts: 12517
Joined: Sun Nov 03, 2002 2:13 am
Location: USA, OH, Cleveland (sometimes visiting DC though)
Contact:

Post by vrg3 »

Non-turbos up through 92 had that kind of onboard barometric pressure sensor.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
rallysam
Fourth Gear
Posts: 1162
Joined: Tue Oct 15, 2002 3:49 pm
Location: London (originally from Wash DC)
Contact:

Post by rallysam »

Never seen inside the ECU before. Pretty cool. That's not too complicated - we design stuff more complicated than that all the time. But, it is surprising to see so many surface-mount chips from what's basically an 80's design.
'00 Impr RS - sold
'91 Legacy Turbo 5MT - mothballed
13psi, TurboXS TBE, WRX IC, Hallman MBC, TurboXS FCD, KYB AGX, Phil's STI seat, SPT short shifter, David Carter hood, Zeitronix widebandO2, Kuhmo rally tires, STI IC spray, thanks:gearboxtech.com
vrg3
Vikash
Posts: 12517
Joined: Sun Nov 03, 2002 2:13 am
Location: USA, OH, Cleveland (sometimes visiting DC though)
Contact:

Post by vrg3 »

Well, JECS ECUs like this one are of a newer design than the 80s-ish Hitachi ones. It's more of a 90s design. This same basic ECU was used up through like 96 or something overseas.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
rallysam
Fourth Gear
Posts: 1162
Joined: Tue Oct 15, 2002 3:49 pm
Location: London (originally from Wash DC)
Contact:

Post by rallysam »

Hey Freestyle -

You're just poaching connectors, right? Mind sending me the circuit board when you're done abusing it?
'00 Impr RS - sold
'91 Legacy Turbo 5MT - mothballed
13psi, TurboXS TBE, WRX IC, Hallman MBC, TurboXS FCD, KYB AGX, Phil's STI seat, SPT short shifter, David Carter hood, Zeitronix widebandO2, Kuhmo rally tires, STI IC spray, thanks:gearboxtech.com
free5ty1e
Fifth Gear
Posts: 2268
Joined: Wed Nov 12, 2003 12:26 am
Location: USA: Central FL
Contact:

Post by free5ty1e »

Thanks - I couldn't imagine what else that thing could have been used for. So pre-facelift N/A ECUs have this onboard sensor? Interesting.

All turbos had the under-hood atmospheric pressure sense, correct?

Rallysam - I am mostly poaching connectors, yes. Not sure if I will end up using or experimenting with any other parts of the ECU, but if I don't you'd be welcome to the internals. It may be a couple months though, because of the move. Right now I'm just planning for the next LegacEBC circuitboard while I've got a little breathing room with my paid work.
-Chris
91SS 4EAT stock, 200k mi
91SS 5MT rebuilt engine waiting for a shell
93TW 4EAT, Forester lift, 3" TBE, 11psi, 200k mi
94SS 5MT4.11+rLSD 311k km: RobTune550,TD05-16g @ 18psi,FMIC,3"TBE,Forester lift
vrg3
Vikash
Posts: 12517
Joined: Sun Nov 03, 2002 2:13 am
Location: USA, OH, Cleveland (sometimes visiting DC though)
Contact:

Post by vrg3 »

Not just pre-facelifts -- 92 models also.

Yes, all turbos used the pressure exchange solenoid to allow the underhood pressure sensor to measure both manifold pressure and atmospheric pressure.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
free5ty1e
Fifth Gear
Posts: 2268
Joined: Wed Nov 12, 2003 12:26 am
Location: USA: Central FL
Contact:

Post by free5ty1e »

By the by, there were so many high-quality useful components on the ECU boards, I'm not sure you'd want what's left... we stripped the hell out of them.
-Chris
91SS 4EAT stock, 200k mi
91SS 5MT rebuilt engine waiting for a shell
93TW 4EAT, Forester lift, 3" TBE, 11psi, 200k mi
94SS 5MT4.11+rLSD 311k km: RobTune550,TD05-16g @ 18psi,FMIC,3"TBE,Forester lift
Post Reply