So my car broke down during a trip through Germany. No fuel to engine, no working fuelpump, relay broke done (doing 150km/h downhill)
Luckily, I was near SPS Motorsport and they were able to help me out so I could continue my roadtrip to the Alpes. (Great guys, great place, awesome help!)

Anyway, during my Alpes trip I noticed my engine was not running as usual. AFR was quitte low / rich.
First thought of a mechanical issue, checked the vaccuum lines, etc.

The I analyzed the logs, was I making the required amount of pressure? Yeah.
So I started to adjust the tune and car started running better.
Still making adjustments.

But have been breaking my brains over how-come.
The VE map was really good before.

So is it possible that the old relay was partly broke / rusty, and that the fuelpump was running on a lower voltage?
With the new (2nd hand) relay, higher voltage?
And that higher voltage means higher flow means richer ?

(Miata USA 1992, 1.6 turbo, megasquirt)

 

Yes, very likely. I’d also look into your baro corrections to see if the alps had anything to do with it. I’m assuming it’s not running leaner now that you’re out of the mountains?

 

Also now, back at home (where I tuned it to perfection, haha), it is still running too rich.
(the BARO corrections / altitude being the issue also crossed my mind, but couldn't remember issues with my AFR from last year I did a round trip there. But still thinking about adding an external baro sensor to the ms3 basic from Rev)

Great to hear you agree with my hypothesis, thanks!

 

I'd agree with your hypothesis as well. When researching hardwiring and adding a new standalone FP relay I remember reading about people having to retune fuel a bit (leaner) after hardwiring their pump. Makes sense being as a shorter run, heavier gauge wire, or a better connection through the relay means less voltage drop to the pump.