Leaking injector

[stevecam1607]

Recently bought 2002 Pathfinder 4WD with 3.5L engine (90,000 miles). New ECU had been installed before I purchased to solve idling problem, but still had a slight miss. I installed new coils, injectors, plugs, and fuel filter. Ran somewhat better, but noticed had to give slight throttle to start, not required before tune-up. Later, SEL activated with P300 and P420 code and started running rich. Changed MAF and then fuel pressure regulator. Progressively running richer with unburned fuel from exhaust. Discovered #6 injector leaking, unplugged injector electrical connection for several days until I could replace injector. Spark plug firing was good. Still dumping fuel with injector unplugged, 4-5 mpg. Replaced #6 injector and fouled plug and then it ran in showroom condition for 4- 5 days (SEL light cleared after 10 minutes), then started running rich again and progressively getting worse and dumping unburned fuel. Same #6 cylinder injector is dumping fuel. Getting ready to replace injector(s) again, but seems suspicious #6 cylinder is culprit again with two different new injectors. Possibly something wrong with injector bore that O-ring is not sealing? I lightly oiled the O-rings before assembly? Any suggestions before I dismantle everything again this weekend and install new injectors?

[atraudes]

Sounds like you're on the right track, unfortunately. What brand and model of injector are you using? One thing to try this time around is bring the bad injector to the store and have them test it. I don't think there's much doubt that it's bad, but it'd be pretty telling if it wasn't.

[atraudes]

Have them test the new one for good measure, too

[stevecam1607]

The injectors are aftermarket. First set are new manufacture, supplier sent me a replacement injector from a different manufacturer which worked well for 4 to 5 days. I've ordered a replacement set of JCS remanufactured injectors as not able to afford set of OEM right now. Seems strange new replacement #6 injector and its replacement both dumping fuel. Odd that injector dumping fuel even when unplugged which means mechanical problem rather than electrical signal. Is there a way a leaking O-ring can result in dumping fuel into cylinder?.

[atraudes]

A leaking injector is caused by the pin that moves up and down to open and close the flow sticking open, either by debris, buildup, mechanical failure, or receiving constant electrical signal to stay open. My guess is that if they worked for a period of time and then didn't, they were just bad. A bad o-ring would mean loss of compression in the cylinder or leaking fuel at the rail, depending on which ring.

One other thing I just remembered: change your oil when you get this sorted out, even if you're only a thousand miles into this last change. A leaking injector will mean the cylinder walls are getting washed with gasoline which will end up in your oil. Gasoline dilutes the oil and reduces lubrication.