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Hi,
I was thinking of a modifying parameters in ePROM to slightly reduce rev-hang, not sure if this is even possible this way, anyway, before that I wanted to see if any of the previous owners did anything to the ecm. Can this be a stock EPROM? As far as I know it was supposed to be a PROM erasable only through Uv light and temperature set points are popular with aftermarket chips. If aftermarket, any idea of what it does other than triggering fans earlier?
Thank you
As pictured.
1991 PROM. axcn, definition $8D
Modified with a soldered in dip socket.
Gently rub across the label. If you feel a recess area dead center. That is a UV window eprom.
**Do NOT peel the sticker off.
The conversion, favorably, indicates an EEprom was installed.
The eprom tables, control the engine/fuel/ sensors/ fans/ emissions.
No PROM/ chip. NO start.
the temperatures are in C so possibly it was bought from Europe, not imported from US.
I’ll buy a reader and try to see what the maps and settings look like.
I suspect that its simply a copy of AXCN with reduced fan on/off temps as indicated by the label.
Regarding the rev-hang, there is not much that you can do about it since the IAC only contributes about 10 gm/sec (maximum) to the total airflow. Of course, you can limit this and/or increase the throttle following rate or reduce the minimum throttle opening, but only to limited effect.
I'm not suggesting that it is not worth trying, only pointing out that the effect will be somewhat limited by the hardware capabilities.
I suspect that its simply a copy of AXCN with reduced fan on/off temps as indicated by the label.
Regarding the rev-hang, there is not much that you can do about it since the IAC only contributes about 10 gm/sec (maximum) to the total airflow. Of course, you can limit this and/or increase the throttle following rate or reduce the minimum throttle opening, but only to limited effect.
I'm not suggesting that it is not worth trying, only pointing out that the effect will be somewhat limited by the hardware capabilities.
thank you
I will first test how quickly the rpm drops when I cut the ignition. I’ve seen an article that talks about reducing rev-hang by modifying timing advance table.
The car has an aluminum FW revs up quickly then drops normally. I like the sound of the engine whem it reacts quickly plus you can change gears faster if it drops down fast. Anyway, the rev-up can be faster since it’s according to power while rpm drop is caused by friction and air compression. For emission control the manufacturers program it to inject a bit of fuel while the rpm drops so it can burned completely by the CATs.
You can also use aggressive DFCO (or deceleration fuel cut off) and/or fuel cut rev-limiting with wide hysteresis in order to maximize the rate at which rpm will drop, if you really want a digital on/off throttle feel/response. Sorry, forgot about mentioning DFCO the first time. This is probably the best bet, but every little bit can help including IAC and ignition timing in an attempt to kill light load torque.
I read the chip and got the chip code mask AD instead of $8D. Any idea why?
chat gpt says:custom code masks to prevent unauthorized reprogramming of the chip I guess it is right
l just uploaded a modified axcn bit to a new 512kB chip and it works well, I’ll use my own from now on.
I did some changes to reduce rev hang and it worked but while in gear it act quite a bit harder it can potentially be dangerous if you forget to release the throttle gently.
memcal eprom identification
I guess it is right 
