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chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

I have this problem, when I 'm still with engine on the temperature increase and electric fan don't start, they start automatically only when I turn off engine.

I noticed that under the distributor there is a sensor not wired, it's possibile this component is thermo switch?

This sensor is lied to electric fan?
_________________
Porsche 924 2.0 na 125hp (1979) euro
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Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Wed Dec 28, 2016 4:00 am Post subject:

There are two temp sensors below the distributor on the head... one has a single-wire connection, and is for the temp gauge. The other, with multiple wires, is for the thermo-time switch (for cold start valve).

The temp switch to operate the fans is on the radiator, on the top left-hand side.

If the fans start when you turn off the engine, that seems to tell me the temp switch for the fans is OK; rather, they're not getting power from the circuit that should power them with ignition on.

You should be able to test this by shorting the temp switch (a screwdriver across the terminals will work, watch for sparks) with the ignition on.

More to the point, you should have 12V at one of the terminals to the switch with the ignition on. If you don't, odds are something upstream is wrong... I think maybe the next item is the fan relay? Don't have the wiring diagram in front of me, that's from memory...

Might try also jumping the fan relay in the fuse box, see if that gives power to the fans.

Also, when the ignition is off, the fans will get power through a heavy resistor (usually located on the firewall, inside, behind the tach), to step down the voltage to avoid draining the battery...

Hope that helps...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
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chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

Yes, this helps much, then is correct that one of thwoo sensors under distributor have only one wire connected and another disconnected?
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Wed Dec 28, 2016 5:53 am Post subject:

No!

So you're saying the two-wire plug (looks like a modern EFI fuel injector connector) has one wire pulled out? This should not be the case, and should keep your cold-start injector from working... maybe if you completely remove the plug, you will be able to reinsert the one wire, if the terminal is still on the end, and reconnect?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

Not cold start valve and not air valve, but another sensor, that have thwoo simple wire (like in photo), located under distributor, One wire is connected, another cutted.

https://www.google.it/search?q=radiator+fan+switch&tbm=isch&tbs=simg:CAQSlwEJST6ypMqTqVsaiwELEKjU2AQaBAgKCAsMCxCwjKcIGmIKYAgDEiioB_1QSqgfWBqkH9hLgBvcSrwKmB-00oCipNLYoqjSYIPM2-zOFNJknGjAeHif88-kWpihoqp6EaHMBC1R_1mNjiGX6ewxQPq8sQr6n0HqoJAxGTz9bBth08GBEgBAwLEI6u_1ggaCgoICAESBMp_1W-kM&sa=X&ved=0ahUKEwjKp8m4l5XRAhXMFsAKHSveAZIQwg4IFygA&biw=360&bih=511#imgrc=MM8VfHVYVscHLM%3A
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Thu Dec 29, 2016 12:12 am Post subject:

Oh, OK - maybe you're talking not about those installed in the head, but rather in the coolant transfer tube?

I wanna say that's for the fuel injection, to identify warm-running condition...

Here's a pic of the ones in the coolant transfer tube:

From here:
http://www.924board.org/viewtopic.php?p=361393
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

I have to see and today I link a photo of this sensor on my engine.
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Thu Dec 29, 2016 1:47 am Post subject:

Ok, but again if you're talking about trying to get the rad fans to turn on, this page describes where the switch is located, complete with diagram (even though it's talking about a 944 - same answer):
http://www.justanswer.com/porsche/6jsg3-porsche-944-fing-thermal-switch-controls.html

As I said, since you have the fans coming on when you turn the key off, the switch is OK - more likely the relay.

Here's the wiring diagram...

V7 is the fan motor, and F18 is the temp switch in the rad.

Sounds to me like you're getting power through the resistor N39, but when ignition's on, the relay J26 should be powered through fuse S18 (may be actually on the relay? I forget), and then to the fan(s).

So you need to trace back to that relay, if your fans are not running with the ignition on.

Don't get distracted by other components not in the circuit.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

Yes, the component disconnected is the one in the coolant tube that exit from head, only one wire is connected, another is truncated, I don't know the reason.
Do you think is useful to restore this sensor?
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Thu Dec 29, 2016 8:53 am Post subject:

It may or may not be... what is the problem you're trying to solve right now?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

When car is still with engine on the temperature increase a lot and electric fan don't start.
Last weekend before trackday I warm up the engine for 10 minutes and temperature was in red zone, but if control of fan is the component wired on coolant system it's possibile that wd40 is enough. I remember some time ago that electric fan start when I turn off engine.
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Thu Dec 29, 2016 11:22 pm Post subject:

Then no, in my opinion the switch you're looking at below the distributor is irrelevant.

You need to trace out the wiring for the power supply to the fans, as I've described.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

I have another problem, only with engine warm I have to try long time for start engine, and only if car turn off by at least 15 minutes.
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

924RACR · Posted: Fri Dec 30, 2016 1:59 am Post subject:

OK - but unrelated to the fans.

There are a few other causes of that for some years vs. others, so those with '80 EU cars may have to chime in - but your first test will be to see if the fuel system pressure is maintained after the engine's shut off. This is critical for a proper hot start; if it does not, either the fuel injector(s) are leaking down, or the fuel accumulator(s) are.

You'll need access to a CIS pressure tester for this test...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

I have pressure tester always connected on cis, there are always problema in this car

Then I already found the cause, control pressure go zero after only 2 minutes.

Now, the injectors and all injection components are new and setted properly, then the cause can be only accumulator or leaking valve of fuel pump.

But I don't understand why if Il start engine after 5 minutes and zero control pressure I have no problems.
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro