Possible relay problem - major driveability issues

[cmac2012]

I'm trying to get my older E30 up and running. My newer E30 of a few years ago just got totaled by an SUV rear ender. Waiting for money, I've already shed the tears. About 6 months ago it showed what I thought were symptoms of a bad fuel pump. I had just had rotator cuff surgery (well healed now, knock on wood) so I drove my newer car. The older one has over 400K, on some level I feel foolish for persisting but it still runs pretty well, I hate to junk it.

I replaced the pump with a tested spare, also put in a Swedish in-tank pump into the stock pump frame. Started up, seemed to be going great, I drove to a job (50 mile round trip). No complaint during that trip.

The next morning I was pulling away and it suddenly lurched hard. Would not get up to speed w/o doing it. I limped home.

In brief: I've since replaced the CPS and the coil. Found a rap on signs of a dying coil that sounded promising, one was stalling during acceleration.

So what does the main relay do? I have a Siemens 5 prong fuel pump relay (I gather that my car only needs the 4 prong) best I can tell it's the same configuration as the Hungarian relay in the 'main' slot, I put it in, no change.

I've been reading the Bentley chapter on engine management - driveability with some devotion. I checked all the ground connections - they look good, no looseness, no corrosion, a bit dirty on the outside. I guess it wouldn't hurt to loosen them and spray with electric cleaner.

I thought I'd found a smoking gun, in the wire cluster in the vicinity of the ground connection cluster above the fuel pump, under the rear seat was a green with lavender stripe wire attached to two others, same color, with a crimped brass sleeve. What caught my eye was the green wad of corrosion around the connection. I did a search: fuel pump circuit. I thought I'd found it - the single wire was barely holding on and broke off as I was handling it. I cleaned it up and soldered in a splice, and holy crestfallen blues Batman, wasn't it.

I finally borrowed a fuel pressure tester from O'Reilly's, it checked out good when I jumped the pump, was erratic after I replaced the pump relay (I've tried a couple of previously tested spare relays) and started it up. Pressure jumped around with the missing and when it stalled out (common now after maybe a minute of running) the pressure went down immediately. I was under the impression that the fuel pump would continue running for 2 seconds after engine shut down. Point being, some direction from the ECU caused the pressure drop, my guess anyway.

Speaking of which, I tried a different ECU that I tested after I got it from a boneyard some years back - no change.