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I have a '87 and and a '88 pm6 ecu. After reading this thread I was inspired to give it a try and chipped the '88. I followed Longbows diagram and went with the double dip socket. Unfortunately when I flip the switch I get a solid cell. I used a 27SF512 chip with a ng62 rom.

Where is this resistor you speak of? Please share some pics shiftyjonno. Thanks!

Sorry, I've been away on holiday . . .

I will take some pics tonight

Ok, I've finally been able to take some pictures.

I've posted some notes, and taken hi-res pics to try and help decipher any trouble.

Hopefully, the pics can be used somewhat as a very simplified tutorial/guide.
Any comments, amendments are welcome.

I've just realised that the pictures start from finish to start . . . doh!!

Please view the pictures according to the viewing order comment.

Thank you so much! I have already spotted where I made some errors. Thanks again for your help!

No worries, let me know when it works . . . or if you have any problems

I am picking up a 24 pin dip socket then will begin the process. I will report my results when finished. Thanks again!

Using the same method I've shown above, I decided to design a daughterboard type adapter to clean things up a bit.

Using Eagle Freeware, I designed a small board and had it made up by a local company.

It was my first attempt, and it seems to look OK. Has been tested and works mint!

Here's a couple of pics

okay totally noobish questions, but what's with the switches? I was wondering why you had a switch for the EEPROM and another switch for map 1 and map 2? is it not possible to just run off a 28-pin chip? or do you have to keep the stock map on there and you're essentially only switching between your "chip" and the stock?

Pin 31 of the MCU is the external addressing pin. When it is grounded, it will enable data addressing from the EEPROM.
So . . . . The first switch is connected to pin 31 (EA) of the MCU and ground which enables us to now use the 28pin EEPROM.

The second switch is two swap between high and low addresses (2 maps x 32kb) on the external EEPROM itself.

You could just ground pin 31 of the MCU and just use the EEPROM only, but I figured that if you have the option to go back to stock, you might as well keep it as an option should something go wrong. Its like cutting J12 on an OBD1 ECU.

The other thing is that if your using an EEPROM that can store 2 seperate maps, then why not use it. Map1 could be tuned for efficiency, and map2 could be for track days . . . etc

I guess its just handy having additional options available.

In tutorial bout chipping romless ECUs there's a step that we need to bridge pin 1 with pin 28 of our EPROM. Is resistor handling that function instead of soldering a straight wire? I was wondering what will happen, but if it's working for You i'll give it a try as well

THX for the pics bro!

Yes the resistor is used to bridge between pin 1 and 28 only if your using a 512 chip (sst27sf512). If your using a 256 chip, DONT install the resistor, just use a direct connection.

I made this tutorial for the 512 chip, to make use of the map switching function.

Does anyone else experience same problems as me? After switching to external EPROM it's runnin' good. But when i switch over to first bank on 27c512 (0h0000 - 0h7FFF) it throws me a solid CEL. It's not a map issue, cause the same map works flawlessly on the upper half. Could it be caused by me taking source for the ground inside the ECU? I'm not mounting switches on the ECU case. Ground for switching MCU->EPROM is from MCU pin 20. Switching Map1->Map2 is between pin1->pin14 on EPROM. Anyone else experienced such things ever?

There's a couple of things to check:

1. You cant switch maps whilst the car is running. Turn the car completely off when switching.
2. Try re-burning the 64kb file. I once had this problem where I got a solid CEL on the first map. I solved the problemby re-promgramming 64kb bin file to the chip.

See if those 2 things help

Knew about it when i got to switching between maps. I'll try to completly resolder everything, then i'll give You an update I've burned the chips couple of times, but the first bank is always f*cked up...

Try using 4.7k resistor . . . .

Failing that, try using a 2k resistor