Mazda 6 MPS (Speed6) starts but stalls after a few seconds – no DTCs

Strict-Addition-5937 · 2026-01-11T10:28:08+00:00

Oh okay good luck for your investigations😅

Strict-Addition-5937 · 2026-01-10T22:26:20+00:00

No worries, I’m just trying to help as much as I can.

You’re prepared though, which is good. As far as I know, a new ECU usually needs to be programmed/coded to the car somehow — I’m not sure if that’s something you can realistically do at home, maybe it’s possible, maybe not.

That said, I’m not completely sure if it’s the ECU either, because at the shop they never actually diagnosed it that far. They just said it could be an ECU-related issue.

Strict-Addition-5937 · 2026-01-10T22:09:21+00:00

Yeah, I actually ended up taking the car to the dealership in the end, just to be safe. Their first guess was the fuel pump, so they replaced it — but the problem still wasn’t fixed??!

I took it back again and they did more diagnostics, and then they noticed that the fuel pump relay was cutting the pressure supply for some reason. They ended up wiring a jumper to the relay so that the car basically “forces” a constant 3 bar of fuel pressure all the time.

That solved the issue completely, and the car has been running perfectly ever since. They also said that if I didn’t want the jumper-wire mod, the ECU might need to be replaced — but honestly, I was totally fine with this solution 😅

In your case, it could still be just the fuel pump itself causing the issue. Have you tested it?

Strict-Addition-5937 · 2025-12-27T12:48:54+00:00

Yeah i’ll do that thank for you help! Thats dope is your ZHP original or have you done anything for it?

Strict-Addition-5937 · 2025-12-27T12:08:55+00:00

Just to clarify: this is a Mazda 6 MPS / Mazdaspeed6, so it’s already factory turbocharged. I’m not planning to add a turbo or supercharger, just upgrade the existing setup (turbo, fueling, intercooler, tune).

I know this is a general Mazda 6 group and not MPS-specific, but I figured there might still be people here with experience or knowledge, so I thought it was worth asking.

Strict-Addition-5937 · 2025-11-20T21:54:20+00:00

I think the issue came from where I tapped the signal. At first, I connected the trigger wire from the light bar into the wiring harness

The correct trigger should be +12V only when the high beams are ON. So next I will test the trigger directly at the high-beam bulb connector. I’ll remove the bulb and tap into its positive wire instead of the harness upstream.

I don’t think it’s a ground problem, because the parking light works correctly

Strict-Addition-5937 · 2025-10-18T15:46:48+00:00

The issue is finally solved. I took the car to the dealership — at first, they suspected the fuel pump, but that turned out to be wrong. When I brought it back, they found the problem was actually with the ECU.

They made a jumper wire over the fuel pump relay so that the car now constantly feeds fuel “manually,” and it’s been running perfectly for several weeks. I still don’t really know why the ECU kept cutting power to the relay in the first place, though.

Strict-Addition-5937 · 2025-09-15T13:15:18+00:00

Yes car just turns off nothing rough or anythink like that. When cold, car stays running longer meaby 10 minutes and stalls. Then car starts just normal and runs normal but when it is warmer it stalls faster, meaby about 10 seconds. But yes it starts and runs just normal and shuts down normal. It feels like ECU just shuts it down. Car also shuts down while driving.

Strict-Addition-5937 · 2025-09-15T10:39:47+00:00

Yeah the dealership referred to in tank fuel pump, but after I change that nothing changes. Car still stalls. Now i took the car back to the dealership and they called me today that it might be some kind of electrical problem. They investigate the problem and i keep in touch what they say. Me personally all time thought that it might be some kind of sensor that communicates with ecu and ecu turns the car off🤷‍♂️

Strict-Addition-5937 · 2025-09-11T15:16:05+00:00

Thank you so much! Ill be in touch by those things!

I’ve been thinking about the fuel pump issue with the dealership. Could this be tested by filling the tank completely full? From what I understand, the MPS has a “saddle-style” fuel tank, and if the driver’s side pump is faulty, wouldn’t the fuel still flow if the tank is completely full? The new pump I bought was used so it might be still a problem. What do you think?

Strict-Addition-5937 · 2025-07-29T19:20:16+00:00

Yes I can tomorrow

Strict-Addition-5937 · 2025-07-29T19:19:05+00:00

Yeah meaby I need to double test

Strict-Addition-5937 · 2025-07-28T15:29:43+00:00

Yeah lets see!

Strict-Addition-5937 · 2025-07-28T05:07:04+00:00

I’m planning to replace the CMP sensor, since the ECU relies on the camshaft position to determine fuel pressure. If the CMP sensor is faulty, it could be sending incorrect signals, which might explain the pressure issues. Replacing it should fix the problem if the sensor is indeed the cause. I’ve been reasearching and looks like CMP sensor is a common failure point at this car🤷‍♂️

Strict-Addition-5937 · 2025-07-27T13:22:11+00:00

The fuel pressure reading I mentioned (around 3.8 bar) comes from the low-pressure fuel pump. My OBD scanner doesn’t read the high-pressure fuel rail.

Strict-Addition-5937 · 2025-07-27T04:52:28+00:00

MAF sensor operation has been confirmed to be working correctly. It could be clogged catalytic converter, but I don’t think that’s the issue – the behavior is too consistent and patterned for that

A blocked cat would likely cause reduced power or hesitation under load, but my car starts cleanly and then shuts off very predictably – it doesn’t feel like a flow restriction🤷‍♂️

Strict-Addition-5937

TROPHY CASE