Super strange issue.. stumbling under mild throttle

[Billnot4power!]

Hi all!
Im newly registered however have spent about all of the past week scouring the forums for an issue similar to mine.. this is a long post and i apologize in advance, trying to be as thorough as possible. 

91’ samurai 1.3 tbi

The car will start and run and idle up then idle down like it should. Engine will free rev without issue and idle pretty well, altho could be a bit smoother.. Issue comes when i apply throttle and hold it steady. For example i apply throttle to rev the engine to 2,000 rpm and try to hold it steady, the rpm will surge up and down pretty uncontrollably and at some times will nearly cut out and die all together. Strangest part is the problem pretty much goes away when i restrict the return fuel line, idles near perfect and will hold steady rpms. Now i say thats strange considering ive read the fsm front to back 5 times atleast and done every single test and messed with every possibility ?? 

Things i have done 

New fuel pump fpr and filter, no clogged lines no kinks. Tested pressures and flow rates all is good. 
Ecm tested good and is controlling the ignition and fuel timing 
Tps is properly calibrated 
Every single input and output on the ecu tests within range (id assume all sensors are working as they should)
Checked all resistances and functions of all vsv egr valve bsbv and cold idle circuit 
checked atleast 3 times for vacuum leaks with carb cleaner propane and soapy water 
Gapped plugs 
Set timing 8 degrees 
Cleaned cap rotor and distributor
Not to mention a real tuneup when i purchased the car last summer 
Injector tests good and sprays reasonably well 

Im assuming its something stupid that im just over looking.. like mentioned when i up the pressure by restricting the return line i notice a slight change in the injector sound and slight change in pattern of the injector and the issue seems all but resolved. Injector is clean is not leaking tests within range.. not to mention the car ran perfectly not long before this issue developed. 

This issue i believe began about 2 weeks ago when i was driving home under normal conditions and the car cuts out for a second, comes back for maybe 5 seconds then dies completely (at this time i had just installed a new fuel pump tank sender and all that goodness) anyway.. i got out of the car kicked the fuel tank once and the fuel pump came back on. After that the pump died on and off a few times so i replaced it again with a better brand pump. 

Now im stuck. Signs would point towards a dirty injector? It was cleaned not that long ago and still looks to be in great shape. ??‍♂️

Thank you in advance for any help its greatly appreciated!!

[fixkick]

Hi all!
Im newly registered however have spent about all of the past week scouring the forums for an issue similar to mine.. this is a long post and i apologize in advance, trying to be as thorough as possible. 

91’ samurai 1.3 tbi

The car will start and run and idle up then idle down like it should. Engine will free rev without issue and idle pretty well, altho could be a bit smoother.. Issue comes when i apply throttle and hold it steady. For example i apply throttle to rev the engine to 2,000 rpm and try to hold it steady, the rpm will surge up and down pretty uncontrollably and at some times will nearly cut out and die all together. Strangest part is the problem pretty much goes away when i restrict the return fuel line, idles near perfect and will hold steady rpms. Now i say thats strange considering ive read the fsm front to back 5 times atleast and done every single test and messed with every possibility ?? 

Things i have done 

New fuel pump fpr and filter, no clogged lines no kinks. Tested pressures and flow rates all is good. 
Ecm tested good and is controlling the ignition and fuel timing 
Tps is properly calibrated 
Every single input and output on the ecu tests within range (id assume all sensors are working as they should)
Checked all resistances and functions of all vsv egr valve bsbv and cold idle circuit 
checked atleast 3 times for vacuum leaks with carb cleaner propane and soapy water 
Gapped plugs 
Set timing 8 degrees 
Cleaned cap rotor and distributor
Not to mention a real tuneup when i purchased the car last summer 
Injector tests good and sprays reasonably well 

Im assuming its something stupid that im just over looking.. like mentioned when i up the pressure by restricting the return line i notice a slight change in the injector sound and slight change in pattern of the injector and the issue seems all but resolved. Injector is clean is not leaking tests within range.. not to mention the car ran perfectly not long before this issue developed. 

This issue i believe began about 2 weeks ago when i was driving home under normal conditions and the car cuts out for a second, comes back for maybe 5 seconds then dies completely (at this time i had just installed a new fuel pump tank sender and all that goodness) anyway.. i got out of the car kicked the fuel tank once and the fuel pump came back on. After that the pump died on and off a few times so i replaced it again with a better brand pump. ( wiring to pump bad)_

Now im stuck. Signs would point towards a dirty injector? It was cleaned not that long ago and still looks to be in great shape. ??‍♂️

Thank you in advance for any help its greatly appreciated!!

sammi, tbi, 1.3
wide open throttle tests do what? wot/flat ground or up hill. and parked,  all 3 good?
the ling block proves, fuel pressure is too low or injector is clogged, or ecu running the injector too lean due to wrong input to ECU (map is prime input)

if the fuel pressure shows in spec, at idle and wot (and does not change idle to wot then we  know the list  is less at 2 things, clogged injector (1/2 way clogged) or the ecu sees input lies (map)

the injector has 10micron screens (at its rim) and is 4 times small that main filter, so,  is  always a concern if tank had rust or gunk in it ,ever)

the ECU has many inputs.
do you have 19" of vacuum at idle nd steady needle>?
map hoses clean  and both end nipples must be cleaned, and not using wrong manifold nipples to map sure.
ECT reads 300 ohms hot,   UNPUGGED,  = 180F WATER TEMP BUT , this is not wrong, as more ohms makes more fuel rates (colder)
O2 sensor , run with it unplugged see if fueling goes better ,, richer.
DTC errors  does he ECU flash 12  (good)on demand?
IAT can not cause this, it is only a super fine trim.

the map reading to high for reality will do that.  for sure

https://fixkick.com/sensors/my-map.html

see this , if at cruise and 2.0v normal but yours is lower (wrong ) it will go lean.  best is test 3 or more data points on the map,  key on no start.. iidle and wot volts,

the hard part of all  is not easy top measure fuel pump pressure when driving,  what if bad wiring to it fails driving loose rusty connections, I used  remote gauge on mine to find this.

not sure me my 1.6L map above matches 1.3L  but will be close I think.
and 02 is not sick
all old sidekickes.. sammi, tbi, and trackers all have 02 sensors that have top much control so if bad , fuel mix goes straight to hell.  (1996 OBD2 cured that) then.

i feel your pain,  sure do and you will find it.
fuel pump wiring loves to fail, from left side harness all the why to the tank hot and ground both later big time fails.


good luck and happy holidays !

[fixkick]

this is a 1 wire O2 that will not have a heater to Cell shorted failed, as can happen on newer model cars 91+ inside the O2.
that means it loves to fail , dead, 0v, and that sets fueling full rich, (by design (smog less) O2 is designed when bad to make NOX lows and fuel rich (best of 2 evils) and is good to know troubleshooting, if unplugged the O2, the voltage at the ECU there goes to 0.45vdc, this is mid point and fuel mix goes to that. far better than stuck at 0v or 1v.

[Billnot4power!]

this is a 1 wire O2 that will not have a heater to Cell shorted failed,  as can happen on newer model cars 91+ inside the O2.
that means it loves to fail , dead, 0v, and that sets fueling full rich, (by design (smog less) O2 is designed when bad to make NOX lows  and fuel rich (best of 2 evils) and is good to know troubleshooting,  if unplugged the O2, the voltage at the ECU there goes to 0.45vdc, this is mid point and fuel mix goes to that. far better than stuck at 0v or 1v.

i tested the map under 3 conditions. At idle its 1.15 ish or so. I figure thats within range enough? 
i think the smoking gun was the brand new o2 sensor.. must have been bad from the store? On its way to warmup it was going to .45v and doing its closed loop… then just continued to heat up to .9 ish volts oh boy.. anyway i unplugged it and it runs soooo much better. Im assuming the high voltage was causing a lean condition making for weak injector pulsing. Hot the wts was 300 ish ohms.. 315 at 195 degrees.. 

im sure now my issue was the 02 sensor! 

now my question becomes.. will i be able to set my idle duty back to 50% with the 02 in open loop? Right now it seems like my meter jumps around a bit and wont settle. 

also will the car trigger 800rpm idle with the 02 sensor in open loop? 

thank you for your input! I was definitely chasing my tail there for a couple days pulling out my hair lol.

[fixkick]

wrong 02 sensors on this car is easy to do, so many there are but only 1 works.
0v is lean causes ecu to go rich
.45 is unplugged reading default caused by ECU resistor divider inside ECU
.9 is rich, causes ECU to go super lean.

the older the car the (evolution not wear) the the more fuel mix damage is done with bad O2, back then it had too much control. even causing flooding he engine or blackened spark tips.
02 open loop that is a hard question, I'd say yes if rpm is 800 and CEL lamp not stuck on.

this old ECU is super dumb and can be fooled easy
best is all inputs good. to ECU.

even this old car still running is like magic.
good luck to you, on all work and the car, and cheers.

[fixkick]

ECT working and thermostat not missing and not stuck wide open or like those fail safe thermostats now stuck wide open failed. by design
The 02 for your car from BOSCH is best seen in their actual catalog.
and no exhaust cracks near there, or gaskets there bad newer o2 or in front of CAT, element brick.
but those leaks cause false 0v O2 and super rich (leaks/cracks are 20%oxygen leaks from atmosphere and o2 see 20x more oxygen allowed and slams to 0v) and super rich fueling.
.9v is bad 02. or if o2 has heater( not there i think) the heater leaking juice to O2 CELL+ pin puts it to 0.9v and ECU goes SUPER LEAN./

in 1996 the o2 authority was vastly reduced , and way less troublesome.

[fixkick]

one more problem with 02 , the old car had a 1 wire 02 but is not really true (electronics) the casing is a wire that ground to the rusty old intake manifold
so making up a wire from engine block aluminum head to the manifold exhaust some way can make 02 start working.
as you can see a bad ground with 1volt of noise would make 02 useless,
this is why 1 wire 02 were banned later.
and 3 and 4 wire have a heater and 2 good real grounds.
1 wire is a pain ,2wire ok up.
other tricks is exh man bolts or nuts put lock waster (star) under nut to make it bite into the rust. making head studs ,connect past the iron rust.( this seems the most easy)