Persistent Rich Running Issue � Possible Electrical/Fan Relay Problem?

Hossdies — Tue, 12 May 2026 12:59:59 GMT

Hi everyone,

I have a 1992 Eunos Roadster (Japan import ) 1.6 Turbo with 120.000km and I�ve been fighting a very strange rich-running issue for a long time.

Current setup:

GT2560 turbo
Kraken Top mountbManifold
ECU Master Black ECU
Custom ECU wiring
Bosch EV14 530cc injectors
K24 electronic throttle body
Mazda Demio electronic pedal
AEM fuel pump
Tomei FPR
Bosch 4.9 LSU wideband
Bosch oil pressure sensor
Bosch oil temperature sensor
Bosch coolant temperature sensor
SkidNation radiator + dual fans

The car runs extremely rich most of the time. AFR usually drops to around 9-10, there is a very strong fuel smell from the exhaust, cold starts become inconsistent, and the tune keeps �drifting� richer over time.

The strange part is:
This exact problem already existed when the car was naturally aspirated years ago. Even before turbocharging, the car had a heavy fuel smell from the rear and would randomly start running rich.

When I first turbocharged the car, everything was actually fine for a while. AFRs were stable and the car drove properly. Then after some time, the rich condition slowly started appearing again and became permanent.

The car has been remapped multiple times from scratch, but after 1-2 days it starts running rich again.

One thing I suspect:
After the turbo setup, I replaced the cooling fans. Originally the Miata has one main fan and one A/C fan. With the new setup, both fans are powered from a single connector/trigger source.

Also, sometimes the fan relay sticks ON and the fans continue running permanently even with the car cooling down.

Could this possibly be causing electrical interference, grounding issues, voltage instability, sensor reference problems, or ECU compensation issues that could affect fueling?

At this point almost everything has been changed or checked, so I�m trying to think outside the box.

Has anyone experienced something similar ?

Attached Files

WhatsApp Video 2025-10-13 at 09.22.26.mp4 (2.75 MB)

WhatsApp Video 2026-02-16 at 13.17.04.mp4 (3.51 MB)

Shifter not moving left under braking

triiple — Fri, 03 Apr 2026 00:26:10 GMT

I've got an NB2 6 speed in my 93 coupled to a BP4W and I've started to have an odd problem. Under heavy braking, the shifter will not move left. It will move right just fine and go into 3rd-6th just fine but I physically cannot access the 1st and 2nd gates

Steps to recreate:
Get up to speed
Brake hard
Move shifter to neutral
Try to move shifter left
Problem occurs. Shifter will not move left to be able to access 1st and 2nd gear.

When I let off the brake, even slightly, the problem goes away and the shifter moves left like normal and I can continue my downshift.

Things I've done and checked:
Shifter bushing is only 6 months old and still in very good condition
Shifter itself has no noticeable wear or play
I pulled the shifter out and looked for any debris in the turret. All clean there
I packed the turret with some thick grease to hopefully quiet some rattling (the rattling has reduced)
The transmission only has around 120-150k miles and was allegedly not raced before I owned it
I put XT-M5-QS gear oil in it

Nothing has helped. Any ideas? It almost feels like a selector shaft is moving out of place under the braking force but I don't see how that's possible.

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Persistent Rich Running Issue � Possible Electrical/Fan Relay Problem?

Shifter not moving left under braking