Hondata

My s300 will lose its tune and divert back to the stock p28 map after every key cycle.

Will be fine while it is plugged into and adjusting the basemap.

I purchased this s300v3 in June 2023. Installed into a p28 a couple months ago. And have had this problem since start up a few weeks ago

I will post data logs later

What is the serial number that is on the s300 board inside the ECU?

Here it is

Spunkster wrote: Thu May 09, 2024 9:33 am What is the serial number that is on the s300 board inside the ECU?

Also once I put it back in the socket it is holding the file. I wonder if it was not lined up on the socket, or bad connection.

Who did the socketing of the ECU for the s300?

I'm having the exact same issue! I never had this issue with previous updates but I just finished rebuilding my Y8 and I can't get my base map to stay loaded in the ECU. I've tried numerous resets and erases, I've turned live updates off, and I can't for the life of me get this thing going.

1997 Honda Civic Del Sol
D16Y8: Wiseco CP (9.0-1), Skunk Alpha Rods, BC Stage 2 (NA); BC Valvetrain, Stock Y8 IM, Full Skunk Exhaust, AEM Wideband and Oil Pressure, Running on 91 Octane.
HONDATA S300 SN: 64616
Board Socketed by Pro Auto ECU for S300 V3

All purchased a few months ago.

Any assistance would be appreciated.

Spunkster wrote: Fri May 10, 2024 1:32 pm Who did the socketing of the ECU for the s300?

I did, this was my 4th time doing it without any troubles.

Upon further inspection I found one of the socket pins was bent slightly and not in contact with the board.

Ok so I’ve narrowed it down to a battery that won’t hold amps or volts while cranking.

First I put in a bus bar and isolated every 12+ connection on bus bar, battery (from trunk) to bus bar, to starter, to fuse box, to fan relay. S300 is now not losing memory.


Charge battery, I have a battery box in the trunk with a group 58r batter, 580cca. Starts right away.


Now this gets interesting. I have a speed factory obd0 to obd1 jumper. Aem uego wideband is tied into the jumper harness on a 12+ lead they come with. Car starts if I let fuel pump prime for 2 seconds like normal. If I let the wideband sweep, it doesn’t start. Trace positive lead to jumper harness back. Pin a25. Watch display in hondata, drops volts when cranking when wideband is powered up.

So I then put relay in for a25 and b1. With those being the trigger. Is more consistent now. Starts 7 of 10 times without voltage drop.

I am going to get more 10g wire to feed a second relay from bus bar and wire in second relay for wideband tomorrow.

And it will always start no matter what if I have my noco gbx45 on “override” mode feeding the charged battery more.

Going to get a more powerful battery from somewhere this weekend.

ok, relay for wideband added. relay for ecu power added.

tried 3 different main relays, and a main relay conversion harness.

all the same results.


1991 crx
b18b1/type r trans
ebay turbo
tial mvs wastegate
tial blow off valve
alpha dynamic 1000cc injectors
omnipower 4 bar map sensor
hondata 4 valve boost contorller on pin a11
aem uego wideband wired into d10
digidizzy
ngk bkre7e plugs
speedfactory obd0-obd1 harness


any help is appreciated. going to go junkyard hunting for another virgin ecu and get new sockets to transfer s300 into

found these in the ecu also. maybe need to replace some capacitors.