94 Nissan Sentra Fuel Cut Off

[GasSavers_Anthony]

Does anyone know if a 94 Nissan Sentra (USDM) GXE has a fuel cut off when you're in gear and off the throttle? I google'd but came up with nothing.

[slurp812]

I was coasting downhill in 1st with my 94 accord. I noticed that it would slow down until it hit 1200 rpm, then speed up a bit till it hit 1500. I am assuming this is because it cuts off fuel if the RPMs are above 1200. It just happened to be the right angle of decline. That gives at least some kind of way to test this theory. Has anyone else noticed this behavior? I am going to do some more downhill engine braking tests...

[kamesama980]

find the FSM (full service manual) not the haynes/chiltons garbage substitute. the fuel section should tell you. I have one for a G20 that says "sequential injection normally, simultaneous injection for problem states, and none during decel in gear. I've never noticed the fuel cut in or out while driving. (this is starting in 91) I would guess you sentra does but I can't say with any reliability.

[ffvben]

I don't think the fuel is cut off or you would have to start it back up every coastdown. the fuel pressure drops at idle/coasting- always spraying some fuel.

[kamesama980]

Originally Posted by ffvben

I don't think the fuel is cut off or you would have to start it back up every coastdown. the fuel pressure drops at idle/coasting- always spraying some fuel.

Taken from the G20 FSM: "...uses sequential injection during normal circumstances....uses simultaneous injection during startup and error conditions...does not inject fuel during deceleration until under 1300 rpm or throttle input..."

fuel injectors don't work at less than a certain pressure and getting close to that point, fuel doesn't atomize well at all. plus, that'd require extra electronic switches not on G20s or sentras. everything remains on and functioning but the injectors are not triggered thus fuel is not injected. some engines cut fuel altogether, some alternate disabled cylinders but they DO cease to introduce fuel to the engine.

[ffvben]

right from the 94 sentra Manuel : fuel to each cylinder is cut off during decel or very high speeds.
2 modes of injection: simultaneous multi port= injects all 4 clys 2xs per cycle- mainly start/fail safe mode
and sequential multi port- injects 1 cylinder all other times.
thx for pushing me, lol i learned a bit more.
when using the Nissan consult 2 monitor, the fuel trim is 100% (+30 or -30% rich/lean). when holding the gas it hangs around 120ish, let off the gas and it drops to 100 , I've always thought it would drop 80ish % if leaned out.

[kamesama980]

fuel trim is adjustment to the factory value. during accel, the O2 sensor may have read that it was leaner than desireable (best power is actually richer than 14:1) so it learned that it needed to richen it up on higher throttle but off throttle it hits fuel cut or lean burn which is factory programmed, thus not affecting the fuel trim.

[ffvben]

no 94 sentras available but I tried this on a 05 altima automatic 2.5L. I'm not sure if scanguage shows Inj pulse width but I used Nissan's consult on a long road test. Watching inj pulse width in the data monitor, while cruising at 60mph, I let off gas(still in drive) and coasted down to 40ish - Inj. pulse was .5msec then i went back up to 60mph, plopped it in neutral and coasted the same distance - inj. pulse 2.5msec. The second part of this road test was to check it at a stop sign. In drive at a stop 3.0msec vs neutral stop at 2.3ms. I wonder if this is the same for all injected veh? I've been neutral coasting to a stop in my automatic ford for a long time, i might have to keep it in drive on coast downs then neutral it at stops.