Code 51 is back months after replacing both fuel injectors?

[UPC78999]

A few months ago my 1988 Nissan Pathfinder XE 3.0L starting going into fail safe mode at 2800 rpm (Code 51) and then a month after that it became completely undriveable. It was idling very rough, jerking and cutting off when accelerating. Both fuel injectors tested below ohm specs. So both injectors were replaced with re-manufactured injectors and the problem was resolved. Or so I thought!! After 3+ months of driving the truck without issue I'm now right back at the beginning of where this whole thing started. The truck is again going into fail safe mode at 2800 rpm with code 51. So what now?

[Slartibartfast]

First thing to do is check the injectors and see if they are in fact out of spec again. If they seem okay, you could unplug the computer and check the resistance of the whole circuit to see if there's a wiring issue. EF&EC 120 of the '89 manual has a circuit diagram and list of checks that I assume is the same for '88, I can send you a link to the PDF if you want.

[UPC78999]

Thanks Slartibarfast,

Ok. The injectors passed (1.5 ohms) but other tests failed. I couldn't get any voltage to read at terminals 101/102 (Injector A) & 114 from the 15-pin ECU connector. Terminals 103/104 were within spec with (12.4V). I then tested resistance between the WL connector and ECU. Terminals 101/102 showed resistance of (14.5 ohms) and terminal 103/104 a resistance of (7.5 ohms). I was surprised 103/104 did not have the correct resistance here? I tested everything multiple times so I am fairly confident in these results.
 

So this tells me there is a wiring issue? So, I will try cleaning the connectors with a brush and vinegar. Then I will inspect all wiring for damage. Maybe something is cutting into the harness. Anything else I should do or look at? Electrical issues are not something I am good at.

Edited January 4, 2021 by UPC78999