Boxer stalling and no start

Is your Boxer completely (euro) stock, or has it had "quasi-Lambda" modification (i.e., a frequency valve added) to be US-legal?

Also, in addition to needing good electrical contact at the terminals holding the fuse ends, the whole riveted plate structure from the male spade where the wire attaches to the metal terminal holding the fuse end on both ends needs good electrical contact -- you might need to solder/improve/replace all of those connections. Bottom line would be to measure the voltage on the wire exiting the fuse(s) at the bottom and going to the fuel pump = should be at least a good +12V relative to ground when the engine (alternator) is running. Alternatively, if you measure the voltage from the female spade terminal of the wire at the top of the fuse to the female spade terminal of the wire at the bottom of the fuse = should be a very low DC voltage (like not even a few tenths of a volt).

 

The frequency valve is a small device with a 2-pin electrical connector that would be added into the control pressure plumbing usually near the fuel distributor(s). However, I should've confirmed just what Boxer model that you have (this wouldn't apply to a BB512 nor 365 Boxer), and, if you aren't in the US, it wouldn't apply -- your Profile isn't accessible. If you have a BB512i, and can post a picture of the engine bay, it should be easy to tell.

Here is an example of an added frequency valve on a BB512i:

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And here's an example of a frequency valve added to a 412:
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You really need a VOM from Home depot and a CIS fuel pressure testing kit to proceed say from Amazon. That is unless you want to guess and throw parts at it. As much as anyone here can tell you it will not replace getting data that can lead to a resolution. https://www.amazon.com/CTA-Tools-3420-Compatible-Injection/dp/B008FJXA3M/ref=sr_1_5?crid=1SIP2PX0BAEJ8&dib=eyJ2IjoiMSJ9.7D5zitcwIWgOoMT308pfcKuzh0BUqkhimAvHY_9oiTHLZmwmwb4HUwZKhNav4k1YiNesun6AF93q0yqdCnQFJhBTRA6U34Zw9AacqM3x2z7NrKEcb3cX5t15k-rZSatJ55o30mCFctEiPhHx5UWRXjUZr6y4rT-7t0ewp_MV8K5rZY7bKdG4bYlfXYtsW3We7d85MTkhZTeaBLDosWLu78ioUg6Z9y9Jrji8Ccb9osA.DEls4_v7wmYQxL0roTdi4jMMuko5ehNDkJ5BCJIBnvg&dib_tag=se&keywords=CIS+pressure+test&qid=1717012427&sprefix=cis+pressure+test+%2Caps%2C136&sr=8-5

 

I would say "no" -- and not having O2 sensor(s) anywhere also indicates "no".

I believe virtually all Boxers did get the FV modification to get into the US originally (and that requires a +12V power source and a separate aftermarket ECU so some extra electrical bits are added), but many have been unmodified -- and some of the (now disused) electrical bits get left behind.

But back to your original problem -- if you don't have the FV modification, an electrical problem there doesn't exist. Have you measured the voltage between the male spade of your fuel pump fuses with the huge red wire at the top and the male spades at the bottom where the beige and beige-black wires go to the fuel pumps? Should be near 0V DC when the engine is running, but there's about 20A coming in the huge red wire, and very common for the plastic to melt up there and loosen the riveted connection (so they are still mechanically OK, but are electrically poor).

 

More where the rivets connect to the metal pieces, but a closer examination of your photo shows this may not be an issue -- typically, the rivets connect to a separate metal piece on the backside of the plastic, but yours looks like there is a direct metal connection between the top pieces on the front side of the plastic (which would be a good improvement). Still doesn't hurt to measure the voltage from the top male spade terminal to the bottom male spade terminals just to confirm things are OK.

 

Have you closely checked the distributor cap for even the slightest hairline cracks? I was experiencing the same exact symptoms that you are describing. Before sending, towing, the car into the shop and as a last resort, I replaced the distributor cap. Now starts and idles perfectly! Once I replaced it, I could see several hairline cracks on the underside of the cap. Makes sense with the exhaust being just below.

 

I also had a equal problem with my carbed car. there it also was the distributor cap. I found this out in the very dark garage. when I started the engine a friend of mien have seen ingintion spraks outside at the cap. after renew this cap no problem anymore.
but I think your problem is somewhere else