Z32 ECU: heavily retarded in low rpm range, why ?

[RomChip200]

I never caught the rationale of having this area heavily retarded on Z32 ECU. Some other ECUs are in 15° range there.
In which driving conditions, such retard is required and what's the effect on AFR in link with values in the fuel map in this area !?

Nistune low rpm retarded.JPG

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[Eric]

if you'll do a maptrace during a long run that has all sorts of driving conditions, you will find that about 25-35% of the fuel/timingmap is never used...especially the areas of low rpm-high TP.
The area in the fuel/timing map with the weird values is one of those areas that is and will never be accessed, unless there's something seriously wrong...

[bachig24u]

Probably an Auto trans would only ever see this with a TPS fault,
but a manual trans vehicle may during;

bump start with TPS 'off',
TPS faults, A vehicle accident, rpm dip in manual trans vehicles during standing start.
the engine doen'st need much advance to start, only really helps it control engine torque to maintain idle speed.
all in all it's probably a failsafe as you are right, under normal conditions it's not accessed.

btw, it's not retard. it's less advance.

[Eric]

During my 'quest' to reprogram the ECU so it can run a MAP sensor instead of MAF, I did a lot of maptracing under all sorts of conditions.
I also maptraced stall, near stall and semi bump start conditions (starting in gear)...none of these conditions made the ECU access these fields.

I didn't test it with weird (or disconnected) TPS behavior though.

NB: I did/tested this on a 300ZX twinturbo (both manual and auto)...not sure if the same is true for other Nissan models.

[unex]

I think on the SR20 these cells are accessed (for a short time) when the MAF is to close to the turbo. Of course in normal conditions this shouldn't be.
When you close throttle, rpm are dropping, but the air goes throw the MAF and ECU thinks that you have load.

[RomChip200]

I got some logs where some near cells (TP= ~30 and rpm <800) to the ones mentioned get accessed.
This is typically when you are starting in 1st gear on a hill: you open a lot the throttle to compensate (so you get an overshoot on TP) ; clutch is still not fully engaged and rpm drops because the engine struggles.

I tested to increase the timing of the 400 rpm line (and btw, 800 too) with these:

Code: Select all

800: 15	41	38	35	32	32	30	28	25	25	25	25	25	20	20	20
400: 15	26	26	25	25	25	25	25	25	25	25	25	25	25	25	25

My car dies from starting in 1st gear most of the time (and when you manage to move, the car struggles)

In my case the "right" values are:

Code: Select all

800: 15	41	36	32	28	26	22	20	15	15	15	15	15	15	15	15
400: 15	25	15	12	10	5	5	5	5	5	5	5	5	5	5	5

Enriching this line is not a good track neither.

[RomChip200]

I don't manage to figure out what are the best timing values in this area in the case of E85, and particularly on a cold start (20°C ambient temp.). I have cold start advance too in dedicated tables.
On a cold start, 1st gear, if I floor a bit too much the pedal, TP> 60 and rpm drops to 400-800, so I reach this area quite easily and often. And the engine bogs down.
My car doesn't like strong change on gas pedal when engine is cold. ECU has routines to process strong changes on gas pedal, but I wouldn't want to modify them, because once 40°C is reached, everything is fine.
If I confine TP in 30-40 (moderate gas pedal), the start is good.

This may be related to cold plugs (NGK LFR7AIX) , E85 difficult to ignite in cold cylinders ....

[Torque]

I have seen my car/ECU dipping into the middle the lower row.
It doesn't happen often thought.

As written here some areas of the map will never be accessed
(for example 100% load and 400rpm)