How to wire the ECU/Ignition on a 944 race car
#16
Herr Unmöglich
Rennlist Member
Rennlist Member
This change would not affect the factory DME harness. The DME harness remains untouched. This actually would make it much more obvious to inspect for cheaters as there would be few wires to inspect and trace. I believe that both Cup and Spec make provisions for removing all unused wiring in the car and this falls under that provision in my opinion. It is purely a reliability move and would have no affect on performance except maybe to pull a little weight out.
I've seen several Cup cars with aftermarket fuse boxes.
I've seen several Cup cars with aftermarket fuse boxes.
#17
If you start a car, you can remove the battery and the car will still run. The battery acts like a large filter (capacitor) to the alternator and filters out all the spikes the alternator puts out. Most new cars have a warning label about removing the battery since it can damage the electronics and computers in a car.
Last edited by Bri Bro; 01-14-2010 at 07:03 PM.
#18
Brian, all very good points, thank you.
I see what you mean by using the DME relay ground though I wouldn't re-use the stock DME relay, I could duplicate that safety feature. Basically, you are saying that when the DME realizes the engine is no longer running, it would cut power to the fuel pump in the case of an accident.
I didn't mean to imply that I would necessarily use the DME pin 4 to carry load to the starter, just that the start wire needs to feed back to the DME.
I missed the idle controller in my research but I would have gotten it by default when I put power to T21 Pin 2 for the injectors out of dumb luck.
How is the alternator regulator separately powered? I see connector T24 with two terminals which look like they go to the regulator (I'm assuming these cars don't have a separate regulator). T24 Pin 1 goes to the ignition switch and starter solenoid and would get powered from my momentary switch. I assume that is to "flash the field" to get the alternator to generate electricity. What is T24 Pin 2? Does constant voltage go to the alternator via Pin 2. I'm a little confused here.
I see what you mean by using the DME relay ground though I wouldn't re-use the stock DME relay, I could duplicate that safety feature. Basically, you are saying that when the DME realizes the engine is no longer running, it would cut power to the fuel pump in the case of an accident.
I didn't mean to imply that I would necessarily use the DME pin 4 to carry load to the starter, just that the start wire needs to feed back to the DME.
I missed the idle controller in my research but I would have gotten it by default when I put power to T21 Pin 2 for the injectors out of dumb luck.
How is the alternator regulator separately powered? I see connector T24 with two terminals which look like they go to the regulator (I'm assuming these cars don't have a separate regulator). T24 Pin 1 goes to the ignition switch and starter solenoid and would get powered from my momentary switch. I assume that is to "flash the field" to get the alternator to generate electricity. What is T24 Pin 2? Does constant voltage go to the alternator via Pin 2. I'm a little confused here.
#19
If you start a car, you can remove the battery and the car will still run. The battery acts like a large filter (capacitor) to the alternator and filters out all the spikes the alternator puts out. Most new cars have a warning label about removing the battery since it can damage the electronics and computers in a car.
#20
How is the alternator regulator separately powered? I see connector T24 with two terminals which look like they go to the regulator (I'm assuming these cars don't have a separate regulator). T24 Pin 1 goes to the ignition switch and starter solenoid and would get powered from my momentary switch. I assume that is to "flash the field" to get the alternator to generate electricity. What is T24 Pin 2? Does constant voltage go to the alternator via Pin 2. I'm a little confused here.
#21
Brian,
You are a true wealth of information and I sincerely thank you!
Sorry to belabor this subject but would you supply T24 Pin 2 with battery voltage at all times when the car is running? Also, what is the function of T24 Pin 1 if it is Pin 2 that is flashing the field?
Thank you again and I owe you a beer (or two)!
You are a true wealth of information and I sincerely thank you!
Sorry to belabor this subject but would you supply T24 Pin 2 with battery voltage at all times when the car is running? Also, what is the function of T24 Pin 1 if it is Pin 2 that is flashing the field?
Thank you again and I owe you a beer (or two)!
#22
You don't have to do anything to T24 pin 2 if you are still using the stock dash with the alternator light in it. If you were to remove the stock dash and use an aftermarket dash, you would connect a 68 ohm, 5 watt resistor (or a small light bulb) to 12V on one side and the alternator D+ (T24 pin 2) on the other. Once the car is running, you can leave the D+ pin open because it will generate its own voltage that maintains the field in the alternator. Most auto circuits just keep 12V ( after it goes through a light bulb) on the D+ pin. The connection to the D+ pin should be current limited by using a light bulb or a resistor. When the alternator isn't moving/running, the D+ pin has a very low resistance to ground and it can pull a lot of current so it needs to be current limited. The low resistance to ground is what turns on the alternator light until the alternator starts to generate voltage.
T24 pin 1 connects to the starter solenoid, pin 50. That needs to go to your push to start push-button switch. You really don't need a relay on that push to start switch because a little drop in voltage due to the long wires will not effect the starter solenoid much. Pin 30 of the starter connects directly to the battery.
T24 pin 1 connects to the starter solenoid, pin 50. That needs to go to your push to start push-button switch. You really don't need a relay on that push to start switch because a little drop in voltage due to the long wires will not effect the starter solenoid much. Pin 30 of the starter connects directly to the battery.
Last edited by Bri Bro; 01-14-2010 at 10:17 PM.
#23
If you use a after-market dash with an LED indicator, you might need to add in this circuit to stop the LED from flickering when the alternator is working. The light bulb reacts slowly since it has to heat up to emit light, the LED reacts very fast in comparison. I did this circuit for a rennlister some time ago and it solve the problem of flickering.
#24
OK, today I sketched up what I think the wiring will look like for my race car using a Painless Wiring 8 circuit race car harness. This harness comes with 8 single pole relays and all circuits are fused.
Note that I didn't show the fuses in the diagram.
I didn't draw the lines from the power side of the relays to the non-engine vital circuits as they are pretty self explanatory and would only complicate the diagram.
The DME side of T21 remains stock.
I'm using all aftermarket gauges so there is no need for any of the gauge wiring.
The one part I'm still not fully understanding is the resistor in line with the D+ pole on the alternator but I did draw it in. Is it OK to have this come off the ignition circuit? What happens if you don't have that resistor?
Thanks again for the help!
Note that I didn't show the fuses in the diagram.
I didn't draw the lines from the power side of the relays to the non-engine vital circuits as they are pretty self explanatory and would only complicate the diagram.
The DME side of T21 remains stock.
I'm using all aftermarket gauges so there is no need for any of the gauge wiring.
The one part I'm still not fully understanding is the resistor in line with the D+ pole on the alternator but I did draw it in. Is it OK to have this come off the ignition circuit? What happens if you don't have that resistor?
Thanks again for the help!
#26
Nope, all instruments and dash are gone. I'm using mechanical instruments with dummy lights. There are going to be 7 toggle switches and a momentary switch per the diagram.
Still a little confused on the purpose of the resistor in the alternator circuit. If I used a light bulb in this place, would the bulb go out when the alternator generates? I think what you are saying is that the alternator acts like ground until it generates and then ground goes away and therefore the light goes out when generating. Is that right? I never knew that was how the light worked if that is the case.
Thanks again for the help!
Still a little confused on the purpose of the resistor in the alternator circuit. If I used a light bulb in this place, would the bulb go out when the alternator generates? I think what you are saying is that the alternator acts like ground until it generates and then ground goes away and therefore the light goes out when generating. Is that right? I never knew that was how the light worked if that is the case.
Thanks again for the help!
#27
Intermediate
Join Date: Jan 2010
Location: Naples Florida
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
Im going to be doing all the same thing in the next week or 2, ill be sure to send pics on how i do it, it might help, if not it will help someone who is not technically inclined.
#29
Nope, all instruments and dash are gone. I'm using mechanical instruments with dummy lights. There are going to be 7 toggle switches and a momentary switch per the diagram.
Still a little confused on the purpose of the resistor in the alternator circuit. If I used a light bulb in this place, would the bulb go out when the alternator generates? I think what you are saying is that the alternator acts like ground until it generates and then ground goes away and therefore the light goes out when generating. Is that right? I never knew that was how the light worked if that is the case.
Thanks again for the help!
Still a little confused on the purpose of the resistor in the alternator circuit. If I used a light bulb in this place, would the bulb go out when the alternator generates? I think what you are saying is that the alternator acts like ground until it generates and then ground goes away and therefore the light goes out when generating. Is that right? I never knew that was how the light worked if that is the case.
Thanks again for the help!
The picture below is from the dash, bulb 18 is the alt light bulb and the resistor is marked 68/5 and is in parellel with the light bulb.
Last edited by Bri Bro; 01-20-2010 at 01:58 AM.
#30
I still have my dash and would like to replace my dead ignition switch with a toggle switch and a push button using the wires at the back of the ignition switch. I want to keep my dash. What should I know to keep the fuel pump off when motor not running function?