How the ECU knows the gearbox is in 1st/2nd gear or 3rd & up

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How the ECU knows the gearbox is in 1st/2nd gear or 3rd & up

Postby AvivB » Fri Mar 21, 2014 11:31 am

Any idea how the ECU knows if the gearbox is in 1st/2nd gear or 3rd/4th/5th gear?
I know it knows as it limit the boost by keeping the TVSV closed on 1st and 2nd gears.
I already know the ECU pin-out by hart but I went over the diagrams multiple times again and didn't find any signal to indicate it to the ECU.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby underscore » Fri Mar 21, 2014 3:14 pm

I believe it does it based on engine load.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby AvivB » Fri Mar 21, 2014 3:52 pm

Engine load is based on the throttle position and rpm and maybe vacuum...
All of those can be in the same values in 2nd gear (and TVSV will stay shut) and in 3rd gear (and TVSV will open)...
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby polm » Fri Mar 21, 2014 4:02 pm

Maybe speed is also taken into account? Can't remember if the sensor has a wire going to the ecu, but if it does that may also be a variable used. You wouldn't be going 60 mph in 1st so that kind of makes sense. Though speed alone surely isn't good enough to know in which gear the trans is in obviously.

Edit: Speed + rpm works doesn't it? I mean if the engine is running lets say 3000rpm at 30mph, you know it can only be in 3rd gear, right?
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby AvivB » Fri Mar 21, 2014 4:25 pm

ECU indeed knows about the speed but speed+rpm+tps+vacuum won't do the trick...
For example with E151F gear box, 20mph, 4000@1st or 2500@2nd and TVSV closed but 1500@3rd and TVSV is open...
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby AvivB » Fri Mar 21, 2014 4:53 pm

ECU inputs (not all of them valid for all models):
STP - Brakes on.
ELS - Defogger on.
SPD - Speed.
ACT - AC on.
STJ - Cold start.
VTA - Throttle position.
IDL - Throttle is idle (fully closed).
PIM - Vacuum/pressure.
THW - Coolant temperature.
THG - EGR gas temperature.
STA - Clutch on.
G2, G-, NE, G1 - Distributor.
TE1 - Diag1.
TE2 - Diag2.
OX - Oxygen sensor.
THA - Intake air temperature.
VS - Air volume.
KNK - Knock.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby underscore » Fri Mar 21, 2014 6:02 pm

The TVSV shouldn't be open the entire time you're in third, I wouldn't think so anyways. So long as it opens by say 5psi you won't notice. If you hook up an LED to the TVSV signal wire you should be able to figure out when it comes on and then maybe sort out exactly what triggers it.

I'd say air volume + speed though.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby AvivB » Fri Mar 21, 2014 6:39 pm

Yes, I monitor it with a test-light so I can see it while driving...

You're right, throttle should be open more than a bit for TVSV to open...
However, throttle half open can exist in all 3 parts of my previous example...

Air volume is depend on rpm and boost...
Since TVSV is on even in low rpm without boost build up yet, i guess air volume is not a factor.
Throttle position is a factor for sure but it's not enough...
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby alltracman78 » Fri Mar 21, 2014 7:40 pm

Speed and RPM give you what gear you're in.
The ECU sees both.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby polm » Sat Mar 22, 2014 7:35 pm

AvivB wrote:ECU indeed knows about the speed but speed+rpm+tps+vacuum won't do the trick...
For example with E151F gear box, 20mph, 4000@1st or 2500@2nd and TVSV closed but 1500@3rd and TVSV is open...

You don't get my point. If you're going 30mph at 3000rpm it means you can only be in 3rd gear, that specific combination only works in 3rd gear. So the ecu knows you are in 3rd gear and it opens the tvsv. Rpm doesnt matter, its simply used with the speed to know in which gear you're in. Doesn't matter if its 1500rpm or 7000 rpm as long as you have both speed input and rpm input then the ecu can always know in what gear you are.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby polm » Sat Mar 22, 2014 7:36 pm

AvivB wrote:ECU indeed knows about the speed but speed+rpm+tps+vacuum won't do the trick...
For example with E151F gear box, 20mph, 4000@1st or 2500@2nd and TVSV closed but 1500@3rd and TVSV is open...

You don't get my point. If you're going 30mph at 3000rpm it means you can only be in 3rd gear, that specific combination only works in 3rd gear. So the ecu knows you are in 3rd gear and it opens the tvsv. Rpm doesnt matter, its simply used with the speed to know in which gear you're in. Doesn't matter if its 1500rpm or 7000 rpm as long as you have both speed input and rpm input then the ecu can always know in what gear you are.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby underscore » Sun Mar 23, 2014 5:36 am

So when do you see the TVSV light come on? Does it come on when you're still in vacuum?
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby AvivB » Sun Mar 23, 2014 6:20 am

No, TVSV opens on load (which mostly if not only depend on throttle position).
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby MWP » Mon Mar 24, 2014 9:25 am

AvivB wrote:No, TVSV opens on load (which mostly if not only depend on throttle position).


Engine load is measured by air-flow (AFM or MAP), not by the the TPS.
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Re: How the ECU knows the gearbox is in 1st/2nd gear or 3rd

Postby AvivB » Mon Mar 24, 2014 9:35 am

Ok, so do call it engine load... :-)

TVSV open when throttle is open wide enough...
I don't think it related to air volume as it can open on low rpm without boost (low air volume) and it can be closed in high rpm (high air volume).
/Aviv

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