Doesn't matter if it's a warm or cold start, my 1994 maxima will start up at 14-15:1 AFR, then dip down to mid-high-11s, then go up to high 12s and finally stabilize at the 14-16 range a few minutes later. I want to avoid this for fuel consumption reasons, is it just because I have my wideband hooked up in place of the stock O2 sensor (without a resistor for the heater circuit so I do have a CEL, I have the resistor just need to solder it) or is it something to do with the MAF or coolant temperature sensor? How can it be avoided?

 

ECU is programmed to add fuel to a cold engine during open loop (no o2 feedback) control. When it warms up it goes into closed loop thus the 14.7ish AFR. Youd have to tune it out, or trick the ECU via the coolant temp sensor or something.

 

I like the signature op

 

omgosh that was my first guess....but 11.6? That just seems stupid rich and as I've said even on a warm start it does it (so I'm thinking it's not something I can "tune out" by replacing the sensor with a resistor).

 

Put the stock sensor back in. It's there to regulate fuel for a reason. Put the wide band in the tail pipe, ( temporarily ) and see what your AFR is then..

 

what is the overall amount of time this takes place in?
does the temp affect how long this whole process takes?

Something to remember, when you start it, all of the injectors are firing, so you're dumping a lot of gas right at start up, and it can take a few moments for the ECU to get that back under control. Most of us wouldn't even notice it without watching a wideband.

I'm trying to remember, you have a pretty decent list of mods don't you? Been a while since I've been over in the green motoring section.
You've got your wideband set up to still send a signal to the ecu, or do you have that bypassed entirely?

there are a few things that can cause this
ranges from coolant tempt sensor, rusty coolant, dirty MAF, poor ignition timing, weak spark, fuel pressure too high, to something really annoying, like a bad/going bad TPS. My Z would just dump gas when the TPS was going bad. Thing is with that though, it would continue to dump gas even after the ECU pulled the timing back to where it should be, and it would run poorly. Notice it running any differently before or after the AFRs balance out?

 

Actually the INITIAL startup is quite lean. Tonight the first few minutes when I started the car and idled it through the parking lot, got out and locked the gate I was running 16-18.4 AFRs at idle, of course by the time I made it to the first stop sign it was doing it's usual 11-13. I'm really leaning towards the car having MAF problems at this point because it doesn't like it when you take a quick stab at the gas, you MUST roll into it or it hesitates (and the wideband hits 10s when I've paid attention to it)

I test my TPS regularly so I know that's not it, coolant I would like to rule out but to be honest I probably haven't popped the cap in a year...I honestly don't even need a radiator fan to keep the engine cool unless I idle it at a drive through or traffic for like 10 minutes so I wouldn't think the coolant is bad in any way (66% water 33% prestone). CTS is good, I've measured resistance from dead cold till the thermostat opened completely and resistance values were EXACTLY what the factory service manual said they would be.

The car doesn't really have a lot of power under 3K rpms until after it warms up and actually will die in gear at idle (due to my slightly lower than stock idle and lack of idle controls, usually settles in the high 600s rpm, specification is 750 +/- 50rpm). As I stated in my first post it's only a couple minutes, sitting at one stoplight for one cycle after it starts doing it usually clears it up. Maybe I'll take a video sometime this week. There really is a night and day difference though in the level of power and smoothness of the engine from cold and rich to warm and lean. Favoring warm and lean.

Can't wait to get Nistune.

 

Some quick thoughts.
- nistune is pretty awesome
- unplug the maf to see what changes. Should go into limp mode, dumping extra fuel, pulling timing, and not revving. "They" like to say that a maf is either good or bad but i've see misfires fixed after swapping a maf. I always take maf stuff with a grain of salt.
- ideas on what your fuel pressure is doing? you said there isn't much power below 3 grand. Pretty sure the maximas have the same fuel pressure controller that the z's have. At 3 grand , they allow full voltage the the fuel pump. Almost seems to go against what your symptoms are suggesting but when I had fuel controller issues, my car seemed to be running rich. Ecu compensating for the lean signals just after start up. Above 3 grand, power came back and it ran beautifully

 

It hasn't run right without the MAF for quite some time....it should limp to 2000rpm if I recall correctly but I get stuck below 1500rpm and it dies if you let off the gas completely - it even did this back when I had working idle controls and what not.

I cleaned the MAF 2 nights ago (along with replacing a ripped strut mount, #$%!) and I haven't really noticed it running RICH RICH on startup, this morning when I glanced over at it it was around 14.0 at the richest and leaned out to at most 15.5 I believe later in the drive. I also borrowed my dad's timing light and I need to get around to checking the timing today, maybe I got it off a tooth in one of the handfuls of times I've had to remove it to get to the valve cover.

 

It was still running rich this morning when I got a chance to glance at it between stop signs. I tried to wire in the resistor today to get rid of the CEL and failed miserably. Adjusted timing...it was around 20 degrees, I set it back to about 17 (which is BARELY within factory spec of 15 +/- 2)