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924 Carrera GTS replica tach/boost gauge
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Tue Oct 25, 2022 7:18 am    Post subject: Reply with quote

OK, found the right wiring diagram, I see this that way:

Terminal 1 goes to DME / Injector PWM switched to GND.
Terminal 2 hangs in the air
Terminal 3 goes to always hot +12V (same as clock).
Terminal 4 GND
Terminal 5 switched +12V
Terminal 6 goes to the ignition coil



The tach looks like that:


and the PWM-possible-motor:



According to the service manual economiser uses speed sensor (hall) and signal from injectors (PWM to ground). When stationary it shows fuel consumption per hour. So if there is nothing on the Hg, then only by applying PWM'ed signal (switched to GND) on Terminal 1 it should move the needle... In theory.

If that works, then it's just finding the correct PWM signal to drive the needle as needed - that would be nice
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Sun Nov 13, 2022 9:25 am    Post subject: Reply with quote

One step forward:



I have one extra, so if interested PM me.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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morghen  



Joined: 21 Jan 2005
Posts: 8666
Location: Romania

PostPosted: Sun Nov 13, 2022 5:24 pm    Post subject: Reply with quote

Would be cool if you could actually just implement an oldschool boost instrument there instead of some electronic stuff.

I'd take one in green letters matching my S1 931 dials if it used just a vacuum hose as an input.
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Sun Nov 13, 2022 8:11 pm    Post subject: Reply with quote

Morghen it crossed my mind, but I could not find a mechanical boost gauge with the scale as in this gauge (VDO makes though 50mm marnie gauge that is electronic and kind of matches this scale). Most of the mechanical boost gauge do travel like 3/4 of the full turn.

EDIT: And yes, green should be possible as well.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Sun Nov 20, 2022 3:42 am    Post subject: Reply with quote

So it looks like that. Nod bad IMHO.



Wanted to do some bench testing today, but my lab power supply died and I don't have the parts to repair it.

Just managed to see what drives the boost (econo) hand. There are 2 coils, each works the opposite direction. Providing some voltage to any moved the hand (like an oldschool voltmeter). Both directions (polarity) and both coils.

So this seems to be operating same way as 3-wire IAV that is PWM driven.

Need to hook that to my function generator, but first need to repair my lab gear.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Tue Nov 22, 2022 12:56 pm    Post subject: Reply with quote

Well I thought it will be easier, no solution yet, so few notes:

Pin 4 is GND
Pin 5 is VCC (+12V)
Pin 6 is Tacho Signal (48Hz = 1000RPM / 82Hz = 2000RPM / 120Hz = 3000 RPM / 150Hz=4000RPM / 180Hz=5000RPM / 210Hz=6000RPM) - hey it's not linear, at least in lower RPM range.

Pin HG kinda allows to control the "boost" gauge. With frequency getting higher boost goes lower (which makes sense, as it means the faster you drive with same fuel usage, the lower is the fuel usage).

Pin1 kinda allows to control the "boost" gauge, but in much less range than HG. This is odd, as I'd expect this pin (signal from injector opening) would mostly influence the hand of the clock to move, especially when stationary (litres per hour in theory).

The problem with these "kinda" is that the "boost" hand is not that much getting back to a position with boost value at same frequency when changing the signal at generator up and down. it means that "boost" grows i.e. to 1bar at certain frequency, then the frequency drops, but the hand stays same place. it will move in the end, but the frequency needs to be altered more that I'd expect.

Not sure what to do about it yet. Would be easier if I could point two PWM signals at same time to PIN 1 and HG, but that's not possible with my generator.

Not sure, maybe my Econo gauge is faulty (read people had issues with these).

Leaving that for later, unless you have any thoughts?
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Thu Nov 24, 2022 8:06 pm    Post subject: Reply with quote

Well it seems my Econo gauge is faulty. Tried to search the web for a Solution, but usually the answer is „it’s a crap, delete it”
Talked to a friend that is electronics guru and decided to convert the econo gauge to accept a „stock” map sensor from something popular, leaving the factory econo electronics alone. That „stock” map sensor (maybe VW/Audi one by Bosch) will drive the econo gauge hand according to the readings from the Map sensor (adjusted and calibrated).
Therefore I should be able to have a „standalone” MAP driven boost module for those tachos that would easily convert the Econo Gauge to Boost Gauge
Well, that’s the plan.
Need to buy a spare MAP sensor with 0-5V output and measure it properly.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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morghen  



Joined: 21 Jan 2005
Posts: 8666
Location: Romania

PostPosted: Thu Nov 24, 2022 10:00 pm    Post subject: Reply with quote

There are those small diameter pressure gauges, i've only found 10bar ones but there must be one thats small enough to be fitted inside the 924 dial and has a 2bar range.
That would make things so much easier...no electronics, just a vacuum hose.

EDIT:

Scratch that, here it is, just fit this in the box and be done with it.






https://www.ebay.com/itm/254762539941
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kondzi  



Joined: 02 Jul 2018
Posts: 317
Location: Poland/EU

PostPosted: Fri Nov 25, 2022 8:40 am    Post subject: Reply with quote

I want to do it the proper way Ciprian
The gauge hand won't look as it should
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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View user's profile Send private message
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