In Europe, this engine was commonly fitted with the Bosch L-Jetronic fuel injection system, married to Ford's EEC-IV engine management.
so ILL ASSUME its USA spec car.
2.9L Cosworth twin cam?
replace the 02, cleaning it, does nothing.
the pump power is bad, this is a very old car and as such
wires and connections fail. that bad ground was the big clue.
good fuel pressure requires a real gauge. its not carb car.
where even gravity feed, or 1psi runs the car, this car is fuel injected
and fuel pressure must be good.
there are 6 or more fuel pressure tests.
sounds like the Fuel system is running lean hot.
it can with a bad 02, the O2 (oxysen) sets fueling at idle. and light easy cruise. so , if the 02 is bad and sticks rich the fueling goes lean.
code 41 means stuck lean.
that new FPreg install is smart buy on such and old car.
the spec, pressure for 2.9L at idle is 35-45PSI, at all times.
it varies by altitude.
this engine and all of the ERA, all hate bad fuel pressure.
the ECU can not measure it. so it MUST be right.
i do all tests in the FSM regarding this parameter (pressure)
leak down tests and if MPI enigne, the balance test.
the Innova 3140 scan tool can scan this engines. ECU. in theory.
OBD1 scan tools are all weak. ( spotty coverage, but i do try)
live data is blessing,
when working any EFI system there are 1st questions,(seen at hood up,glance one... i cant do that)
The V6 EFI is it the TBI or MPI fueling, system.
1 injector (or pair in TBI) or MPI with 6 injectors.
2nd glance, is it MAP based or MAF engine.
speed density or air density, (big time important this......)
its hard for me to look this up because, there are so many engines.
the MAP engine races fast with FULL Power, if there are air leaks.
and has a hyper sensative IAT sensor, replace it if tests bad.
the MAF system(AIR flow actual) goes LEAN (see?) if there
are any air leaks, in this from the MAF actual point all the way to the
head intake valves (daunting huh.?) will cause lean.
and lean misfire.
and bogging, off idle and may be low idle. (if very bad)
some calif engines have the MAF setup.
when the engine is cold the ECU runs huge rich fuel mixtures.
(long injector squirt times) so hides the lean issues.
the ECU has 3 modes, cold, warmup and hot.
all 3 work different, (think of 3 ECUs) and win.
working scan tool free and no live data. is a very very hard job.
done many. old 90s, cars.
The fuel pump needs 12vdc, 13.3 to 15vdc runing
that is at the pump actual across the 2 pins to the pump
if less, then the wires are bad. (connections too) that includes the pesky ground do the pump. inspect every inch, if living in the SALT belt (google that) inspect and test every inch 2 times.
We dont have those issues in Texas. but up north, big time.
posting location ALWAYS helps, (like what STATE)
(if in calif . now is the time to fess up.....)
or car hood sticker shows CALIF words there....(C.A.R.B) certified, bla bla bla.
DO YOU HAVE THIS>?
this is a MAF< the AIR meter. (i look for this first on all engines) ALL!