Injector Current Draw

[grimreaper]

In the middle a refurb of the engine body harness and engine harness. The connectors I'm heavily considering for the body to engine harness plugs can take 20 amps. From my research I've concluded that the injectors CAN draw as much as 4-6 amps each. The only hold up is the power to the injector resistor. Stock uses a .250 series with a 14g wire.. Its a rather large terminal and the largest wire in the engine harness.

Is it as simple as multiplying 4-6amp x 6? or is my info bad on the current the injectors require? if its that simple I'll move to a different connector..

I have the tools to measure the current, just not a running car due to a jump start on the harness tear down.. any body with the knowledge care to enlighten me?

---------- Post added at 12:22 AM ---------- Previous post was at 12:18 AM ----------

I know all 6 never fire at once, but the heat build up from the engine cycles + the near constant current draw to the resistor may be enough to warrant a larger connector. I also understand that the initial opening is where the load is at, and current should drop off quickly. Trying to make an evidence based decision, not an assumption.. Jetjock or jdub care to set me straight?

 

[IJ.]

Just checked an old MoTeC PDM file I used last time and I had 8x Inj and 8x Ign on the one 20a output, I had the maximum current set to 14a, this was using 730cc injectors sequential and the LSx Coils in batch fire mode, I would have at the time tested the actual current draw before setting the limit to 14a.

Hope this helps.

 

[Nick M]

The injectors fire in pairs. Each leg of the resistor block is 3 ohms. I had to look it up.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=111

By the book, the injector can draw (2.0-3.8 ohms)3.68-7 amps. That is stock injectors. I don't know what you are using. Add the series portion of the circuit(resistor) to the branches (resistance) to get total current. Voltage divided by resistance is your current draw. How does the injectors not firing at once effect it? You only figure the ones firing. Unless the man says otherwise.

 

[grimreaper]

if I'm picturing this right, the injectors are in parrallel with each other. Common connection points with two paths of flow.
So 4-4.6 amp through the resistor to 2 injectors,assuming 12-14v. the injectors in parrallel provide 1.25ohm for a total of 4.25ohm per injector circuit. Thats 2.8-3.3amps per circuit. Calculated in sereis the current is something around 1.5amps per circuit.

I'm using rc PL8M-550, peak/hold=4/1amp. 2.5ohm res. at 68*. I'll measure their resistance tonight to verify..

Nick, i think I see what your saying. The injectors are fed a constant voltage with the ecu grounding as the control point. My thoughts where that since two fire at a time, the current would not be a constant as if all 6 where firing at once. Meaning the current would never be a total of what all 6 could draw.

IJ, thanks, it does help. EVERYTHING works on paper right? real world experience goes a long way.

 

[CyFi6]

Since you have 1 wire/connector pin for each pair of injectors, your pin/wire/connector only need to be able to flow enough to provide current for one pair of injectors (like you said 2.8-3.3 amps). I think that's exactly what you said but just wanted to verify. Are you talking about a connector going from the engine bay to the firewall? You said body to engine harness connector, but the injectors only go from the engine harness to the ECU

 

[grimreaper]

^ right, the engine harness feeds the resistor power and then it is split 3 ways back out to the engine harness and injectors. I'm replacing that plug and the other engine to harness plugs as well. I just grouped it with the body to engine plugs since its in the same group of wires.

 

[grimreaper]

just some info I found, the injectors are all fired at ounce on starting.. meaning you will see the max current all 6 can draw. 20 amps should be sufficient head room on my setup but depending on the ohms of a stock injector, you could be pushing it depending on the connector. oh and its 12 awg wire or close to 12 awg for the resistor power supply.

Third paragraph down.. http://www.mkiiitech.com/forum/showthread.php?t=842

 

[hvyman]

Efi fuse is like 15 amps.

 

[grimreaper]

Ecu doesn't power the injectors, it comes from the dash harness. After that I'm not sure though, haven't traced it any further. Ecu grounds them for control

 

[Nick M]

Nick, i think I see what your saying. The injectors are fed a constant voltage with the ecu grounding as the control point. My thoughts where that since two fire at a time, the current would not be a constant as if all 6 where firing at once. Meaning the current would never be a total of what all 6 could draw.

I'm not the EE, one of them would tell you about how much to figure when they are not supposed to fire at once. Come to think of it, they do at start up. I just now thought of that. At cranking they are not firing in their order. I think they all pulse a few times, and that will have to be figured in for total draw. The firing order is started after there is Ne and G signals.

---------- Post added at 12:59 PM ---------- Previous post was at 12:57 PM ----------

just some info I found, the injectors are all fired at ounce on starting..

Yeah, I just thought about it.

 

[jetjock]

Right. Asynchronous injection occurs at start up. Iirc it also occurs when the throttle is opened quickly.