Reporting back - I fixed the fuel pressure problem. The car now runs mostly fine. There's only one and a half issue bugging me.
The half-issue is unstable idle in closed loop, I've seen tons of threads about this here so I guess I can tackle that on my own.
The biggie is the spark advance: I am trying to re-create my stock dizzy's advance map as a first step and the engine starts having ignition problems as soon as the advance crosses 30°. It's clearly rpm-independent: Wherever I set the advance map to cross 30°, the ignition starts having problems, I even blew my muffler with a violent backfire!
First, I thought I might have an arcing problem so I phased my dizzy correctly. Didn't change a thing. So I connected an engine tester and discovered something really weird:
Yep, somehow, each plug suddenly starts firing twice.
I then moved the P/N wires further away from the coil to rule out any interference from the discharge. Checked the signal with an oscilloscope, it's clean. The oscilloscope also tells me that the coil in fact is triggered two times per plug by the HEI module.
How's that possible? Bad HEI module? Bad ECU? I really need some pointers here...
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