14CUX running rich

Flyfish

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Oct 29, 2004
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St. Louis
You had mentioned the idle stabilizes when you pull the PCV breather hose off- anywhere at the tee…. That shouldn’t happen. It should almost die.

You should look in to that. Your previous idle and other adjustments may be masking a problem.
 

p m

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Apr 19, 2004
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You had mentioned the idle stabilizes when you pull the PCV breather hose off- anywhere at the tee…. That shouldn’t happen. It should almost die.

You should look in to that. Your previous idle and other adjustments may be masking a problem.
It may well be true. I know that, once the engine is warmed up, after the first touch of gas pedal the short term fuel trims both go rich (and that's why allowing more air stabilized the idle).
Fuel pressure is steady at 30 psi with the engine running - it will shoot up if I pull the vacuum hose off the pressure regulator.
But... it runs nicely. If it passes smog, I'll just roll with it for a while.
 

p m

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Apr 19, 2004
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OK, time to close that chapter - hopefully.
MAF sensor was _not_ an issue - O2 sensors were.
Here are three samples of me warming the truck in the morning, driving to work, and idling for a while. It has highway on- and off-ramps, about 2 miles of freeway speeds, fast hillclimb from standstill, a bunch of stop-and-go driving, and losing all the altitude.
20210803.jpg
Look at short-term fuel trims: they do go down to zero, never below zero, and climb up to +100% whenever they have a chance (at idle).
Two days and even-side new O2 sensor later (I wasn't sure I was ordering a correct sensor, so I only bought one):
20210805.jpg
At the very least, the even-side short-term fuel trims go in both directions.
Two more days later, and O2 sensor purchased at a local Napa store for a 1993 Nissan Maxima (part number NGK/NTK24064), with Nissan-spec connector replaced with Rover-specific one. I also ditched the "new" MAF sensor and reinstalled the original one.
20210809.jpg
Aside from annoying tendency to start at high RPM and keep them for a long time (required a blip of throttle to clear it), things seem to work okay.
The truck passed smog check (with idle HC and both idle and 2500 rpm CO numbers a little on high side), so I can forget about it for another two years.