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Super strange issue.. stumbling under mild throttle
#1
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!!
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Super strange issue.. stumbling under mild throttle - by Billnot4power! - 12-20-2021, 01:52 PM

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