AFR very sensitive to electric load

[louiswun]

S14 SR20DET with type 3 board on 74F00 ecu , non FP version, AFR very sensitive to electric load (voltage does not change much) , in this log, I only turn on front light, and then A/C, the AFR will jump from 16 to 11, any hints to fix this ?
This car had done tuning when the battery located at the trunk, once it return to the engine bay factory location, the whole AFR change a lot, it run richer than usual, wideband had been free air calibration.

[bachig24u]

Earth points need check/clean or Alternator is failing to provide current.

[louiswun]

Download the CSV and open it, you will see how far the AFR jump.
Earth point check twice with no resistant to battery ground (good connection), but found an interesting error on power supply, I think this cause the ECU to act strange behaviour. uploading video to youtube.

[louiswun]

This video is intent to taken for my customer, thats why I speak our own langauge.
The fuse I remove is No.34 fuse in FSM, after checking FSM, it is the power supply for MAIN, MAF, CAS, IGN/SG,
That is power supply for ECCS Relay, MAF, CAS,
If I remove the fuse, the engine should be die at once, but it didn't, someone mess up the ECCS power supply.

https://youtu.be/EM3aPR7MlgU

[Matt]

Incorrect routing of the 12V power supply could definately be causing issues. Also check signal grounds are going to MAF, temp sensor, TPS and not chassis grounds if the car has been rewired, it may be anything causing those issues

[louiswun]

Hi Matt,

Bingo ....
You are totally correct, the signal ground is short with chassis ground.
I have measure the resistant of the sensor ground to the chassis ground, found out it is 0 resistant.
but guess what, it is the 12V ground of the Z32 AFM was connected to signal ground (NOT done by me), so I swap the 12V ground with the signal ground,

I have found that on the S14 engine wiring , the boost sensor ground / TPS ground is 0 resistant to AFM signal ground, I guess that is linked inside the ECU.
And on the Z32 AFM pin C and pin D, the actual pin on the AFM, not the wiring side, it is also 0 resistant, thats mean if connect the 12V ground pin to the chassis,
it will also chassis ground connected to signal ground.

What I have tested:
1)
Z32 AFM pin C 12V ground to chassis
Z32 AFM pin D signal ground to S14 shielded signal ground wire
Idle AFR will change from 16-17:1 to 15:1
Idle with front light and A/C on 12:1 (4 AFR point richer)
remember, both pin c and pin d inside Z32 AFM are 0 reisistant
I have don't all Z32 AFM like this, included my own car.

2)
Z32 AFM pin C 12V ground NOT connected to chassis (hanging),
Z32 AFM pin D signal ground to S14 shielded signal ground wire
Idle AFR will stay 16-17:1
Idle with front light only around 16:1 (less than 1 AFR point richer)
Idle with A/C on around 15.X:1 (around 1 AFR point richer)
Idle with front light + A/C on 15:1 (1 to 2 AFR point richer)

The Z32 AFM pinout (Z32 AFM pin C 12V ground to chassis)
Same pin connection does not show a problem on S13 SR and CA or S15 or R33.
Or .....I was wrong 12V ground pin connected and misunderstanding from the very beginning ?
Or......the S14 engine wiring AFM signal ground somewhere shot to signal ground ?

Another thing, the No.34 Fuse on S14 fuse block.
The fuse that supply 12V to Main (ECU +12 backup power, constant 12V unswitched), AFM, CAS, ECCS relay,
Once I remove the fuse 34, engine still run, ECU draw power from ECU pin 45 (IGN SW)
and the 12v flow backward from ecu to the wire which originally supply power by ECCS relay, even if I remove the ECCS relay, there are 12v live in the wires.

[Matt]

Yes the Z32 MAF will connect chassis and signal grounds together. Just make sure you have signal ground from ECU to MAF and that should be fine

ECCS relay when pulled should cut power to MAF, CAS, coil, injectors and main power in ECU. This may not cause this issue but probably should be fixed

Ignition signal powering up ECU doesnt seem right. Be careful you may be putting extra load on components in ECU if other power removed and damage the diode/resistors inside

[louiswun]

Now, after small adjustment on the latency, car idle fine no matter front light and / or A/C on.
Confirmed that AFM signal ground is connected to sensor ground within the ecu.

[ricardomendes]

i have opened a topic here in last year

viewtopic.php?f=11&t=2838

i had the same problem in this s14, and now i will try to check the maf wiring, because i never have found the solution for this.

thanks louis

[Matt]

I've been told, dot connect the chassis ground to the Z32 chassis ground since it makes a ground loop to signal ground

[raddy]

Hi there. If chassis ground of Z32 AFM is really connected to the chassis,any resistance of it against signal/ECU ground add voltage offset to the AFM output. So,ensure low resistance or rather do not connect it at all...

[STATUS]

you must 100% get the maf wired correct.

its uber common for people to jion the 2 earths on a z32, you cannot do this. one is ground one is sensor ground. if you join them it get mega noise up the sensor ground for the ecu.

[Matt]

Z32 connect these two pins internally. So the chassis ground should not be used when using Z32 in another vehicle. I need to make this more clear in the pinouts which were lifted from SAU