E46 M3 highway shutdown: tach/speedo drop, DME unreachable afterward

[karter16]

The absence of error codes (edit: actually just noticed you're using a scan tool. Ideally check for codes with INPA, most of the DME low-level operation codes don't have external P-Codes linked to them) related to supply power, OS integrity, memory integrity, etc. make this seem like a very sudden event that is killing the DME immediately with no opportunity for it to log codes. It might be that the issue is happening fast enough that the thresholds aren't met for storage ofr the codes into the EEPROM before it fails completely. What doesn't align with that thinking though is your observation of several minutes of rough running before it fails completely.

I agree with Terra though that it would be worth replacing the DME with a known good unit and retesting, that will for sure tell you whether the issue is inside the DME or out.

[sapote]

So…does anyone know of a MSS54 DME failure? What caused it?

My bet on the power supply to the DME:
* from the ignition sw to DME
* from DME to main relay
* from main relay to DME fuse pack
* from fuse pack back to DME power input pins.

[ATB88]

Holy shit, a new ebox fan is $360..

$122.99 on FCP https://www.fcpeuro.com/products/bmw...46-12907571019

[OldRanger]

So, I told Gemini the whole story…remembering some minor details in the process. Including that I had a fuel pump relay code present before the dyno session, that I assumed was somehow related to the new fuel pump installation process.

That code has been present on both occasions of the car shutting down.

Gemini got very creative…speculative, and suggested:

The new high-draw OEM fuel pump and performance tune are overtaxing your 20-year-old "used" relay, causing it to thermally saturate and arc internally at the one-hour mark. This arcing creates a massive voltage drop that starves the pump of power, causing the engine to stutter and die from a total collapse of fuel pressure. Even with an ignition cycle, the car won't start because the relay contacts remain physically separated by heat, while the resulting electrical noise "jams" the DME’s communication chip into a protective hardware latch-up that takes 45 minutes to thermally reset.

so I ordered a fuel pump relay.

A bit of history here: on my other high mileage M3 a couple years ago I was getting a fuel pump relay code. So I replaced it. A week later, the fuel pump died. My assumption at that time was that the code on the relay was wrong and that it was actually the fuel pump going bad.

I’ll follow up next week after I get the new relay and take a test drive.

Does anyone want a really long, hypothetical, AI explanation on how that fuel pump relay failure sets off this avalanche?

[OldRanger]

My bet on the power supply to the DME:
* from the ignition sw to DME
* from DME to main relay
* from main relay to DME fuse pack
* from fuse pack back to DME power input pins.

In spite of what Gemini gave me as a good story, I still think there’s a DME issue as well, but I can’t figure out why it takes an hour to fail, and the thought of going out for an hour or more to make it fail again on the side of a highway doesn’t appeal to me.

To keep key facts fresh: Between the first occurrence and the second, I replaced the ignition switch (w/new) and the DME relay (w/new), as well as checked the Ebox and main (engine) ground point . I did not check the individual wires for continuity. I took out the fuse pack, the terminals are tight and the wire connections are as well, but I didn’t disassemble it to replace the fuses. (Couldn’t figure out how)

I have a couple options for next step:

1) Get it to fail again. After I put the new fuel pump relay in, take a proper test run and assume the car will fail again at the hour mark. Take everything I need to diagnose the failure and set the conditions, from daylight and warm weather to all the tools and a plan for the first few minutes after it shuts down

2) Pull DME out and send it off for a bench test at ECU Pro. check all the wires in the DME power circuit, and figure out how to replace the fuses in the fuse pack. In parallel use this time to get my GM five repaired at a local repair shop with new relays cause I have problems there too with door locking.

what would you do?

[Slideways]

In spite of what Gemini gave me as a good story, I still think there’s a DME issue as well, but I can’t figure out why it takes an hour to fail, and the thought of going out for an hour or more to make it fail again on the side of a highway doesn’t appeal to me.

To keep key facts fresh: Between the first occurrence and the second, I replaced the ignition switch (w/new) and the DME relay (w/new), as well as checked the Ebox and main (engine) ground point . I did not check the individual wires for continuity. I took out the fuse pack, the terminals are tight and the wire connections are as well, but I didn’t disassemble it to replace the fuses. (Couldn’t figure out how)

I have a couple options for next step:

1) Get it to fail again. After I put the new fuel pump relay in, take a proper test run and assume the car will fail again at the hour mark. Take everything I need to diagnose the failure and set the conditions, from daylight and warm weather to all the tools and a plan for the first few minutes after it shuts down

2) Pull DME out and send it off for a bench test at ECU Pro. check all the wires in the DME power circuit, and figure out how to replace the fuses in the fuse pack. In parallel use this time to get my GM five repaired at a local repair shop with new relays cause I have problems there too with door locking.

what would you do?

If I needed to rule out a DME issue, I'd swap the DME from a friend's M3 and test.

[OldRanger]

If I needed to rule out a DME issue, I'd swap the DME from a friend's M3 and test.

I have a 2005 M3, also with an MSS54, but an Alpha N tune. The friend I have, offered up a spare, but it’s been tuned as well, with an EWS delete. I don’t have knowledge on this, but I’m guessing a DME swap would be problematic.

To your recommendation, which I like, I’ve contemplated buying a spare DME. But they’re going for around $600 right now. So I think I’m gonna wait on that until I road test a new fuel pump relay (that’s already been shipped to me)

[OldRanger]

Fuel Pump Relay:

Pin 5 has an odd stripe on it. Pin 8 has discoloration on one side (in sunlight and shop lights, with naked eye and iPhone camera)

Ground wire tested AOK (Ohms)

[Slideways]

I have a 2005 M3, also with an MSS54, but an Alpha N tune. The friend I have, offered up a spare, but it’s been tuned as well, with an EWS delete. I don’t have knowledge on this, but I’m guessing a DME swap would be problematic.

To your recommendation, which I like, I’ve contemplated buying a spare DME. But they’re going for around $600 right now. So I think I’m gonna wait on that until I road test a new fuel pump relay (that’s already been shipped to me)

As long as the EWS is disabled on the DME, then it is an easy swap. Tune wise, if your friend's DME is setup for MAF, then it can be changed to Alpha-N with Martyn's tool in a couple of minutes. Or if you have the knowhow, putting your tune on their DME is not too difficult.

2005 should have an MSS54HP. MSS54 non-HP can be found for less than 600.

[sapote]

Gemini got very creative…speculative, and suggested:

The new high-draw OEM fuel pump and performance tune are overtaxing your 20-year-old "used" relay, causing it to thermally saturate and arc internally at the one-hour mark. This arcing creates a massive voltage drop that starves the pump of power, causing the engine to stutter and die from a total collapse of fuel pressure. Even with an ignition cycle, the car won't start because the relay contacts remain physically separated by heat, while the resulting electrical noise "jams" the DME’s communication chip into a protective hardware latch-up that takes 45 minutes to thermally reset.

so I ordered a fuel pump relay.

Absolutely there was no arcing ever happened in these relays. US cars have the semiconductor relays using power FET to drive the pump instead of metal contacts in mechanical relays.

What can kill your relay: check if the heavy GND wire (from the ignition coils harness) is bolted tight on the engine head, exhaust side. Loose or bad connection can kill the relay.

[OldRanger]

Absolutely there was no arcing ever happened in these relays. US cars have the semiconductor relays using power FET to drive the pump instead of metal contacts in mechanical relays.

Thanks sapote . You are correct. I learned that contrary to the term “fuel-pump relay”, used by my code reader, the EKP Module uses Power MOSFETs (FETs) to drive the pump. This allows the DME to use Pulse Width Modulation (PWM) to vary the pump speed based on load.

What can kill your relay: check if the heavy GND wire (from the ignition coils harness) is bolted tight on the engine head, exhaust side. Loose or bad connection can kill the relay.

I will check that again. I just did a valve cover gasket, and my recollection was that I torqued it to spec. I will also make sure the wire isn’t damaged.