Poor running 87 S4 after warm up
 

1987 AT with bad head gasket - all refurbished engine out. Car ran awful before I drove it into the garage for surgery.

Runs great for about a mile and then loses power, throttle response disappears and on uphill curves to the left exhaust popping. It's as if the brain thinks the car is running rich and leans to mixture to the point of popping. S4's don't normally pop. Bad signal to the LH from the O2 sensor? Swapped computers no change. I guess I should test it's LH in another car.

Pretty much everything that can be replaced has been replaced or rebuilt.

It might be easier to list what has not been replaced: Coils, distributor cap/rotor, PS coil wire, fuel pump and filter.

Smoke tested hot and cold - passes except for the tiniest wisp of smoke from the PS throttle bearing.
Dampers and regulator hold vacuum
Vacuum @ idle is 15psi. S/B 20? Clogged cat, maybe?
Spark plug wire Ohm @900-1000
Fuel pressure 60ish cold and hot.
New O2 sensor
New spark plugs.
Refurbished injectors
Rebuilt MAF
Have not verified timing yet, but that is on the list.
Clogged fuel filter? Not a common occurrence. Fuel pump? Car did sit for a few months when failed to start.
Iffy relay?
Clogged cat?

This is first time I've encountered such a difficult problem.

how long was the car sitting before the engine repairs took place?
have you taken a fuel sample?
or removed the tank sender to inspect the in tank filter?.
Are any of the fuel lines crushed on the bottom of the car?
A misplaced jack can easily do this

I'll start there tomorrow,

It does sound like fuel starvation. You could try the fuel flow test : extend the fuel return pipe from the tank top safely into a container. Unplug the LH. Bridge the FP relay contacts for 30 secs, you should collect 1350cc (2.37 pints)

Here's a peek at the intank fuel strainer and what is sitting on the bottom of the tank. I think I should go panning for gold. The strainer is dark, but does not seem clogged. Not sure what the shiny bits are.
https://cimg0.ibsrv.net/gimg/rennlis...d0dac7c62d.jpg

the filter should be white,
it looks dark brown this is from the picture.
If so your fuel rails could also be gummed up,
as well as the dampers and the FPR,
including the freshly cleaned injectors

I'll test following John Speake's instructions next.

So empty the tank, remove the strainer, replace the fuel filter?

Replace fuel and add injector cleaner?

Fuel pressure is clicking away at 60psi even when the engine is runs like crap. Admittedly, I cannot see the fuel pressure driving under load.

Finally had time to do a flow test. Counted to 30 and got way less than was expected.

Assuming a flow issue - where do I go from here?
https://cimg5.ibsrv.net/gimg/rennlis...311621f897.jpg
Cut some AC piping with the correct OD,
https://cimg4.ibsrv.net/gimg/rennlis...2ddc07eaab.jpg
Attached clear hose from AC pipe to gallon jug.
https://cimg8.ibsrv.net/gimg/rennlis...c8f1414923.jpg
Marked the gallon jug at 2.37 pints.

Replace the fuel pump and filter

Figured, New pump and filter in hand.

Should I replace the strainer?
https://cimg7.ibsrv.net/gimg/rennlis...1bcba13655.jpg

now that its out absolutely, it should last another 25 years,
cant say the same for the part you removed

Buttoned up most of it tonight. Waiting until tomorrow to test for leaks.
https://cimg9.ibsrv.net/gimg/rennlis...a293384ff7.jpg
Use a hose clamp to put pressure on the tank to inner collar while tightening the fuel strainer. Read about this in another thread.

https://cimg1.ibsrv.net/gimg/rennlis...d3a6eaaf75.jpg
Bosch pump makes it easy to counter hold it while tightening the fitting.
https://cimg8.ibsrv.net/gimg/rennlis...e417422c6f.jpg
Ready to test

spin that pump clamp so the cover will fit
Same for the filter clamp just reclock it

Here's the before picture I took - I used it as my guide. I guess you are saying it's wrong.

https://cimg9.ibsrv.net/gimg/rennlis...3d36e79fb4.jpg