Rx7 FD grounding

[Mekanic Caleb]

Hey guys, 

So I have gone ahead a re-wired my engine harness myself. Being an FD half the harness was dying and the other half was just gross, and what led me to do this was a troubling idle in which the engine would stop pulsing at operating temp.

now I’ve got a plug-in G4x S7-8 ecu, furthermore I re wired each pin and wire individually one by one to ensure they are still correct. So far so good, ECU picks up and sees all sensors and triggers etc, pulses injectors correctly and is reading rpm. One issue though, the damn thing doesn’t start! I believe I’ve narrowed it down to the coils not firing- no spark.

Now there was one bit of confusion point, which were the 5 “Ground” pins from the plug-in ecu, whilst a single “ground signal” which is the sensor ground (I assumed)

Furthermore I wire the 5 normal grounds to the own locations on the engine block, and I wired the sensor ground to a “hub” essentially with all the corresponding sensors grounds including the injectors.

can anyone please point at me and tell me what I’ve done wrong? 
cheers,

caleb.

[hugemikeyd]

FC owner here, I used a wire in ECU but I think it is the same in the end. I have the 2 grounds from the ECU (black) going to each rotor housing separately and the sensor ground (green) is isolated from the other grounds and is a closed loop with only the sensors and the ECU. The sensor ground should never be linked with the other grounds.

With that said, is it possible that one or more of the sensors rely on the engine ground (black)? that would cross the lines which is not what you want.

[Adamw]

Our internal notes list pins L, X, AB, AF & AJ as power grounds.  Ideally these would all go to the same point on the engine somewhere, but if they are currently to separate points its not going to stop it from running.   

3S is the crank sensor ground, and 3AB is the sensor ground for all other sensors.

Do the coils spark in test mode?  

[koracing]

Have you run the car on this ecu before?  Is this a new ecu purchase?  Is the ecu unlocked?  Does a ignition test not pulse the coils?  What about an injector test?  Copy of your tune and a log of cranking as well as a trigger scope?

[Mekanic Caleb]

16 hours ago, hugemikeyd said:

FC owner here, I used a wire in ECU but I think it is the same in the end. I have the 2 grounds from the ECU (black) going to each rotor housing separately and the sensor ground (green) is isolated from the other grounds and is a closed loop with only the sensors and the ECU. The sensor ground should never be linked with the other grounds.

With that said, is it possible that one or more of the sensors rely on the engine ground (black)? that would cross the lines which is not what you want.

So my sensor ground should only have all the sensors ground wires looped in but not grounded to any engine point, only back to the ecu?

16 hours ago, Adamw said:

Our internal notes list pins L, X, AB, AF & AJ as power grounds.  Ideally these would all go to the same point on the engine somewhere, but if they are currently to separate points its not going to stop it from running.   

3S is the crank sensor ground, and 3AB is the sensor ground for all other sensors.

Do the coils spark in test mode?  

So I’m using the pinout on my link software where I do not see a 3S pin, however I routed the CAS grounds back to their original pin from factory loom as it was. See image attached.

 

16 hours ago, koracing said:

Have you run the car on this ecu before?  Is this a new ecu purchase?  Is the ecu unlocked?  Does a ignition test not pulse the coils?  What about an injector test?  Copy of your tune and a log of cranking as well as a trigger scope?

Yea mate been tuned by a reputable Link tuner, engine was tuned as is with the plugin ecu making a reliable 400whp. The idle issue happened about 4 months after the tune, and I’ve had the car back from the tuners originally for 9 or so months now. Ecu was bought brand new at the time, installed by my tuners. Ecu is unlocked yes. I have not tried the ignition test function yet, but on the ecu logging it shows the ecu is sending the pulse signals. Injector test I have not run either, however I can hear and smell the small injectors are definitely pulsing on crank (I held throttle plate open to make sure I could hear it too). I can create a copy and log tomorrow to upload.

[Adamw]

3 hours ago, Mekanic Caleb said:

So my sensor ground should only have all the sensors ground wires looped in but not grounded to any engine point, only back to the ecu?

Correct.

 

3 hours ago, Mekanic Caleb said:

So I’m using the pinout on my link software where I do not see a 3S pin,

Clearer copy below.

[Mekanic Caleb]

13 hours ago, Adamw said:

Correct.

 

Clearer copy below.

Oh beautiful thanks mate, I’ll confirm the pin 3S is going to the CAS ground, and I think I’ve got the sensor ground linked to the block so I’ll disconnect that too.

update you guys once I’ve tested, cheers for the help so far!

[Dean]

On 7/13/2023 at 12:11 PM, Mekanic Caleb said:

 

Furthermore I wire the 5 normal grounds to the own locations on the engine block, and I wired the sensor ground to a “hub” essentially with all the corresponding sensors grounds including the injectors.

Am I reading correctly that you have the sensor ground going to the injectors?

They should only have a switched 12v and the signal to ECU, right?

[koracing]

On 7/15/2023 at 1:08 AM, Dean said:

They should only have a switched 12v and the signal to ECU, right?

This for sure!  I read the same thing and assumed it was a typo.