hlh0501

iTrader: (1)

I read messing with our MAF signal, messes with ignition bc our ECU tunes timing using MAF as one of the inputs. So if Z32 is registering different voltage for same amount of air as before... ECU is translating to different timing as same airflow as before?

I know very little on the subject of ECU timing as a function of MAF voltage, and don't have a dif MAF so I'm not real concerned... but would Z32 MAF be advancing or retarding timing - or neither?

IceY2K1

iTrader: (3)

Retarding....

What happens is that timing is calculated/based off RPM and injector pulse width. With the larger MAF, the ECU is "seeing" less air then the the ECU measures with a stock MAF, therefore a shorter pulse width will be used. Less pulse width, means less advance. However, for boosted people that run stock ECUs that can help reduce tendency to detonate and for people with larger injectors that can help lean out the AFR ratio.

MardiGrasMax

iTrader: (14)

Actually I thought it would advance because at a given CFM flowand TPS voltage the ecu would get lower voltage from a Z32 maf.

IceY2K1

iTrader: (3)

Your guys ECU may be different then 5th gens, but I doubt it.

On ours, the higher the MAF voltage the more fuel added, thus larger pulse-width. The Z32 MAF produces less voltage at XXXcfm then the A32 does, so the ECU will see less air and adjust the pulse-width shorter to match. Then the ECU uses RPM and the shorter pulse width on the WOT timing map to find advance.

hlh0501

iTrader: (1)

Just curious, how do you know that?

IceY2K1

iTrader: (3)

Several places I've read. I'll see if I can dig one up.

Bags

iTrader: (3)

Let me see if I am following... Your saying the less air that is flowing past the MAF, the less voltage it sees, thus the less fuel you get , thus the timing is retarded?

I thought it was the other way around.

Like when you use a SAFC to pull ful, your adding timing?

And when you use the SAFC to add fuel, your pulling timing?

The only reason I use the SAFC as an exapmle is it "basicly" changes the voltage the ecu sees from the MAF.

If I am way off base let me know.

IceY2K1

iTrader: (3)

YES, this is how I understand it and from Stephen Max's example with the Z32 MAF equaling out the 370cc, it agrees.

The A32 MAF peaks out at 5V@350bhp, but the Z32 MAF peaks out at 5V@420bhp. So, assuming a linear(it's not) and using BHP instead of cfm for simplicity, at 250bhp the Z32 MAF would output 3V vs. the A32 3.5V:



The SAFC adds more fuel by fooling the ECU into thinking there is more air then actual by conditioning(read increasing voltage in this case) the output, so it increases pulse-width to compensate, which using what I've read, injector pulse-width is directly related to ignition timing, therefore the ECU increases advance. And vice versa.

So, at the same cfm airflow or BHP, the Z32 MAF(or larger MAF) will output a lower voltage to the ECU, which the ECU will use along with RPM to lookup in the timing map and calculate advance.

IceY2K1

iTrader: (3)

Also, I didn't want to muddy the water, but I know someone will point this out. Hot-wire MAFs don't actually "output" voltage. The ECU outputs current to the "hot wire" inside the MAF sensor to heat it up to a known value/resistance. As the air rushes past the wire, it cools it, which changes the resistance of the wire, so the ECU adjusts the output voltage to keep the same resistance. The adjustments positive or negative is what the ECU uses to determine how much air is passing through the MAF. An SAFC just intercepts this and conditions it up/down to add/subtract fuel.

At least, that's what I understand.

IceY2K1

iTrader: (3)

Increasing fuel pressure above what's needed, using a larger MAF, and adding larger injectors will *ALL* decrease injector-pulse width, which has the side-effect of retarding timing.

A good benefit when working with a stock ECUs timing curve/map for preventing detonation, however with a TS/JWT ECU, this additional retard could be unnecessary and hurt performance somewhat.

Bags

iTrader: (3)

Hmm maybe I can get with dixit and verify this

nateplaysbass

From my experience with the SAFCII, when we added fuel at peak tourque, the computer advanced the timing.... I don't think this is for the same reasoning though, I think the computer added timing, because there was a rich condition. I don't know if this will help at all though. if this makes sense with the stuff you guys are saying, please explain it to me. I get what you're saying so far, but what other variables will the ECU be reading to determine advance. I guess I'm just curious to see how heavily the ecu relies on the knock sensor... And what about the O2 sensors? when do they come into play in all this mess?

I know, but I'm a student of automobiles. I'd like to know

Nate

IceY2K1

iTrader: (3)

MAF voltage determines injector pulse-width. IPW and RPM determine timing advance.

During open-loop/WOT, the ECU doesn't use the 02-sensors and per Mardi the knock sensor either.

Stephen Max

iTrader: (59)

You won't find many people over in the 4th gen forum that believe this last part. It's like a different world over there.

Stephen Max

iTrader: (59)

Hmmm, that's interesting. So you could indirectly adjust timing (the amount of retard, at least) by adjusting fuel pressure.

Are you speaking in general terms, Icey, or does this actually apply to Maximas?

I have seen Z32 timing maps, and the timing is based on engine load and rpm. Now whether engine load is determined by maf voltage or TPS position, I don't know. I always assumed it was the TPS, but it could just as well be the maf signal. Actually, it may be better to use the maf signal, since that is more of a direct measure of engine load, whereas with the TPS there is a lag between opening the throttle and engine response.

IceY2K1

iTrader: (3)

I'd say it applies to all cars or at least all MAF equipped cars. However, when I say fuel pressure/larger injectors, I'm assuming you've tuned back fuel to compensate, which shortens pulse-width over OEM. You could add injectors AND boost and end up increasing IPW and thus timing over OEM. I should have said any modification thats end result shortens IPW, indirectly retards timing.

You answered your own question..LOL. MAF is how the ECU determines load. Great minds think alike.

Engine load and VE are what the ECU designers use to build fuel/timing maps. As these fluctuate, so will the IPW and timing throughout the powerband.

TPS is used, but probably more so as a secondary factor or possibly to determine when to switch to back and forth between open-loop/closed-loop.

IceY2K1

iTrader: (3)

Also, please don't take this as 100% "the truth".

This is just what I've read/learned from many different sources. If I'm wrong, I'd like to know, so please investigate and show me.

Bernardd

I've tuned a few nissan ecu's. Engine load is determined by maf voltage and rpm. It is corrected for engine temp, o2 when in closed loop and a host of other things. The load value is called the theoretical time of pulse or tp. Viewing a binfile in a nissan romeditor will show the tp scales at the bottom of the fuel/ignition maps. This is what is changed by reducing the maf voltage. The engine thinks it's under less load so looks up timing into the lower load areas of ignition/fuel maps which usually have a higher advance than the higher load areas. All the nissan rom's I've seen would cause a higher advance by reducing the maf output. I've never seen the obd 2 maps tho.
Bernard

IceY2K1

iTrader: (3)

Interesting, since the FSM sample Ignition Timing map uses Tp(msec) as the Y-axis for Injection pulse width. It uses Engine Speed(rpm) on the X-axis.

You're probably correct about the advance being higher in the lower load portion of the map, since timing would ramp up to peak load/VE.