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Assume I have a stock NA S4 motor & I want to start it with only the engine harness & Ignition necessities.
I’ve searched, but I need to be referred to a minimal wiring diagram imagine I’m starting the engine on a metal engine stand.
orrrrrrrr If you have patience & time to help keep reading.
Please don’t tell me search up a wiring diagram & take what I need 😭😭
I have did so already & I have my fuel pump running, 12V to injector wires (All-but 1(it has low voltage) for some reason)
12V to Coil B/Y
No spark & No fuel & my CAS was previously functional so I’m lost & this is about to turn into a wiring nightmare I’m just trying to reset & make sure I’m not too delusional.
FYI I’ve completely deleted the interior harness & the power is switched through fuses & relays as the original stuff was same orientation but for gauges & fuel Pump with a 100A breaker between alternator to power.
Only the connector from the interior harness x15/x16??? Is used with the black & yellow Y spliced into power, for something in the engine harness to get power that I needed I forget but that’s where I get delusional at.
I don’t believe I missed anything, but something where the car connects to the interior harness & possibly powers the ECU or some type of functions etc etc is off.
Facts that might matter:
Engine harness is connected to CAS
all plugs secured.
Emissions is deleted
Power is switched so there’s no (Key)(ignition)) being used.
There’s no Anti-Theft & my car will crank regardless of if clutch is pressed in.
12v to Injectors from ECU & Coils from black & yellow
At least a hiccup would tell me I’m starting, but no misfires bc no spark & fuel won’t get sent I’m telling you the CAS should be fine if it’s that lmk tho.
I'm no expert, but you definitely need the following (aside from what you mentioned):
- Air flow meter (and actually connected to the intake like stock, not just plugged in and hanging)
- Coolant temp sensor on the back of the water pump housing must be plugged in, otherwise you'll get no cold-start enrichment.
- TPS is a good idea, car runs like crap without it. Might not be strictly necessary but it'll help start.
- Resistor pack for the injectors (assuming your engine is 86-87.5 model year). It's a little aluminum box with an integrated bracket, and the connector is very distinctive. In stock cars it sits under the airbox. Without it, you will have no injection.
- Normally you need the main relay, but based on your description it sounds like you've bypassed it.
Also keep in mind that the ECU grounds out through the ring terminal on the harness at the end near the injectors. This means it needs to be connected, it isn't optional.
Others will probably chime in with whatever I have missed. I'm not sure that the wiring diagram you're requesting really exists, so you may have to solve this bit-by-bit. There is however a complete pinout of the ECU connector in the factory service manual, so you could de-pin all the connectors you don't need (AC switch, PS switch, emissions stuff) then peel off the harness wrapping and remove those wires entirely.
I'm no expert, but you definitely need the following (aside from what you mentioned):
- Air flow meter (and actually connected to the intake like stock, not just plugged in and hanging)
- Coolant temp sensor on the back of the water pump housing must be plugged in, otherwise you'll get no cold-start enrichment.
- TPS is a good idea, car runs like crap without it. Might not be strictly necessary but it'll help start.
- Resistor pack for the injectors (assuming your engine is 86-87.5 model year). It's a little aluminum box with an integrated bracket, and the connector is very distinctive. In stock cars it sits under the airbox. Without it, you will have no injection.
- Normally you need the main relay, but based on your description it sounds like you've bypassed it.
Also keep in mind that the ECU grounds out through the ring terminal on the harness at the end near the injectors. This means it needs to be connected, it isn't optional.
Others will probably chime in with whatever I have missed. I'm not sure that the wiring diagram you're requesting really exists, so you may have to solve this bit-by-bit. There is however a complete pinout of the ECU connector in the factory service manual, so you could de-pin all the connectors you don't need (AC switch, PS switch, emissions stuff) then peel off the harness wrapping and remove those wires entirely.
Good luck.
I just wrote a brilliant *** essay agreeing with you & talking it out what I’d learnt like tps & fuel box when I tinkered with the engine harness & that ground under the intake, Regardless. I wasn’t logged in & when I was it was Gone so GG no RE, but thanks. I’m still unsure why no spark & fuel I believe it’s ecu related or something that was on the interior harness needed as crazy as it sounds..
Can’t anyone else chime in? Is there a ground or something missing from the X15/X16 Connectors?? I thought ECU grounded itself just kind of lost.
This is roughly what my harness portrays accept my igniters are built into my coils & I have more stuff linked to the same fuses/relays if they’re supposed to come on together.
I added power from my (Hidden start switch) to 3B on the ECUs, B/L (Black/Blue) wire (3B).
Which should only have power when the car is in the “START” position AKA my start switch sending volts to the starter Sol.
It’s full battery voltage while starting, although I thought it was starter signal?? Apparently it’s just voltage, but still no spark or fuel. Please let me know if this needs to be wired another way.
After messing with 3I & 3G 3J & a couple other we have spark & fuel… Why because for whatever reason the OEM harness is extra complex (complicated) & power to some wires come in from the other side of the FEM plugs.
When I’m done done I’ll make a write up on a STOCK STANDALONE Harness & ask for input.
Since we don’t have one which is quite surprising.
10-13-21, 06:07 PM
