Looks like the EEC cannot increase the fuel trim without the "aid" of some fuel through a vacuum line. Now the issue is to ID why. Did the engine show the signs of a too rich A/F during the KOER under those conditions? (black smoke, rough idle, etc)
Things to recheck:
View attachment 271706
Exhaust leaks at the headers?
it's fine
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Fuel pressure over 38-45 psi with vacuum line connected?
FP is at 33 at idle with line connected
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Vacuum leaks? vacuum lines, intake gaskets, no open breathers present, PCV valve operational and sealing, canister purge line connected solenoid/CANP or plugged.
they all check out fine except a little problem with the pcv valve grommet
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HEGO ground wire attached to rear of intake manifold stud or cylinder head bolt? (orange wire)
i took it from the firewall back to the intake bolt a couple days ago
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Correct 19# injectors installed (orange color)?
yes they are orange stock ones
If all the above is OK, leave FP gauge connected, search for a flexible section of the fuel return line, pinch the line with a set of locking pliers, and confirm pressure increases to +45 PSI engine idling. If it does, run the KOER again with the fuel pressure at the new higher pressure setting and LUK what codes show up.