Positive wire while engine running

[nick9one1]

Can anyone point me to a wire (any!) that is live ONLY when the car is running, and zero volts when not.

I need to find one to be able to wire the alarm in correctly, the manual says good candidates are tachometer line, oil light, or charging battery line.

Ive been through every wire from the clocks and not found one that is live only when running.

 

[944 man]

The best place will be either a spare switched terminal in the fusebox, or a switched live wire from the ignition switch. Whatever you do though, dont use a Scotchlok or similar bodge. Bare the wires and tightly wrap them around each other and then solder the join. Finish using heat shrink (which you fitted onto the wires before soldering [])


Simon

 

[robwright]

What sort of alarm requires such a feed? They usually only require a permanent live and a switched (ignition) live.

 

[944 man]

Id guess that its a signal wire, rather than a power supply.


Simon

 

[nick9one1]

It's actually for remote start. It attempts to start the engine 4 times while monitoring the live input incase the engine starts before the 4th attempt.
So the live wire I need has to be 0v when the key is turned to run, unless the engine is running.. hence tachometer feed. Does that make sense?!
Like I said I've been through all the clock feeds and not found one!

This is it in action, I have to turn it off quite quickly after it starts. Otherwise it would attempt to engage the starter motor twice more.
http://s430.photobucket.com/albums/qq21/nick9one1/944%20S2/?action=view&current=VIDEO0010.mp4

Just thinking it would also be possible to use a feed that's ground when the engine is running..with a relay, guess Ill have to go through the clock wires again!

 

[944 man]

Id be looking at the DME relay to fuel pump wire. Presuming that your car hasnt been b*stardised by a previous alarm/immobiliser installer; the fuel pump should only be turned on if the engine is turning. If it primes audiably when you turn on the ignition then this wont be the case, rather dangerously...

 

[nick9one1]

Thanks for the suggestion, but not sure if that will work either. As I presume the fuel pump needs to be live before the engine fires?

How about the alternator, do they have the thin wire from them on the 944 that's only live when charging.. so if the belt breaks you get a light on your dash?

 

[robwright]

Exactly the point I was just going to make. The fuel pump is live before the engine fires when the DME sees enough revs from the flywheel. I would defo be looking at the tacho signal. AFAIK the tach and speedo (on oval dash cars) are fed from the DME. If my theory is correct, without studying the diagrams I hasten to add then the DME output to the gauge will be a DC reprensation of the signal it is being fed. It's a simple concept really. The more pulses you see from the flywheel sensor or the greater the output from the hall effect sensor on the final drive then the greater the resulatant DC output to the gauge giving greater deflection. Hence no engine running then no DC output to the tacho. Does the device have a minimum DC threshold for detection?

 

[nick9one1]

It doesnt give voltage required unfortunately. I did attempt to locate the tacho feed by measuring the voltage of each wire when ingnition was at position 2 (not running) and at position 2 when runningn and didnt see any real differences.

Im starting to think the alternator charging feed might be easier?

 

[VanhireBoys]

I wouldnt go with the oil light as it is grounded with no oil pressure and is basically a switch which does not go to 12v with oil pressure present. The only way of doing this is with an interface relay.

Alternator does go from ground engine off giving the ground for the warning light. With the alternator charging this goes to 12v. The ignition warning light then sees 12v each side and goes out... Thats the theory anyway..

This blue wire from the alternator apperars to be bridged near the ECU at the alarm plug. to a yellow/red. This is where I would test if you can find it....! Pin 7 and 8 should be bridged. This is for the factory alarm. I dont know if your car is fitted with it.. On mine its near the ECU but mine is a LHD so I dont know about a RHD,

A word of warning ....make sure as Tony said earlier to do a good solder job as these aftermaket alarms end up causing all sorts of age related issues.. Bad and damp connections and ill fitted electrical items are big achilles heel of the 944.. Test twice and make sure !

 

[nick9one1]

Thanks, I will look for the alternator wire tonight.

Yes I do have the standard alarm, although would like to disable it!

I think I've done a pretty good job with all the wiring. Lead solder used for solid joins and all covered with heat-shrink. It actually looks better than the "professionally fitted" Thatcham Cat 1 alarm that too k me 10 mins to pull out.

 

[944 man]

I still think that the fuel pump supply will work. It will certainly provide the required amperage and its only live when the engine is either running, or in a starting condition ie: the ignition is on, youre turning the key to 'start' and the engine is turning quickly enough for it to fire. This is when the DME relay's second relay is energised and power is provided to the fuel pump.

My understanding is that this is a signal wire whose function is to prevent a further attempt to start when the vehicle is already running; so this appears to be suitable. The only time that the circuit will be energised is when the vehicle is running, or when it is actively being started.

The only circumstance in which it wont work, that I can see, is where power down the signal wire will stop the current starting attempt because the controll unit thinks that the engine is now running; as opposed to stopping further sttempts after successfully starting the engine - which wasnt my understanding...


Simon

 

[nick9one1]

ORIGINAL: 944 man

I still think that the fuel pump supply will work. It will certainly provide the required amperage and its only live when the engine is either running, or in a starting condition ie: the ignition is on, youre turning the key to 'start' and the engine is turning quickly enough for it to fire. This is when the DME relay's second relay is energised and power is provided to the fuel pump.

My understanding is that this is a signal wire whose function is to prevent a further attempt to start when the vehicle is already running; so this appears to be suitable. The only time that the circuit will be energised is when the vehicle is running, or when it is actively being started.

The only circumstance in which it wont work, that I can see, is where power down the signal wire will stop the current starting attempt because the controll unit thinks that the engine is now running; as opposed to stopping further sttempts after successfully starting the engine - which wasnt my understanding...


Simon

I can understand exactly where your coming from, although..

As the 944's aren't great starters it doesn't usually fire on the first attempt, its 2nd or 3rd.
So on the first starting attempt the fuel pump will be live when cranking, even if the alarm doesn't cut the current starting attempt, its possible it wouldn't try again as it had seen 12v (although if it didn't start it would be back at 0v so it may try again).

I will test and report back..

----------
To Test:

DME to fuel pump --- any idea of wire colour?
Alternator charging line ----blue wire near ECU bridged to yellow/red at alarm plug
Oil Pressure light (with relay)

 

[944 man]

Doesnt start first attempt on the key, or first attempt via the remote device? It should start first time off the key, but they take a few rotations before the fuel pump comes on and theyre notoriously lethargic (worse with later RHD cars with their ecessively long cable).

Can you alter the time it allows the car to churn for, because increasing this should make the device more successful?


Simon

 

[nick9one1]

Always starts first time on the key, just takes slightly longer than a modern car.. about 3 seconds or what sounds like 4 rotations of the engine, this is common from what I've read on here (and from what you have just said!).

The remote start only engages the starter for bursts of 2 seconds or about 2 rotations of the engine, which is why it doesn't start first time, it attempts these 2 second bursts 4 times or until it gets the live running feed.
Unfortunately there doesn't seem to be any adjustments for the starter engagement time

 

[944 man]

Four roattions is exactly what Id expect.

 

[VanhireBoys]

Mine is a terrible starter in fairness... The airbag light goes out after 5 seconds.. The engine dosent fire up until about 2 or so seconds after the airbag light goes out ! If teh car is cold it fires up in about 2-3 seconds... I am going to change the DME temp sensor to see if it improves things.

From my memory now Tony and I am open for correction the feed to the DME comes from the alarm.. ! You are 100% right then to go with teh DME relay, pin 86 if im not mistaken... ! []

 

[nick9one1]

Ok, I'll hook up a test lead to terminal 86 on the DME relay and give it a try.

Also going to try the blue charging lead from alternator.

 

[nick9one1]

Done!! Alternator blue wire was the one. Couldn't find it under the dash so spliced into in in the engine bay.

 

[barks944]

You won't find anything ideal for this I don't think. What you need is a signal that indicates that the engine has reached a certain rpm it won't ever reach during cranking.

I could probably make you a bespoke circuit to do just that if you like. It's something I have built in as a feature into my DME project with just this in mind. I would use the tacho signal, feed it into a uP which can measure the engine speed and then generate an ouput that says the speed is over 300 rpm or something. This signal can then block the remote starter from engaging the starter motor again.

Starting can take a while on the 944 because it needs a few rotations to acquire its position. Theres things you can do to speed it up though . It should start within a couple of revolutions even with the standard ECU.