Hacking a N/A V6 7202 to work in a VR-4

[foxdie]

Hi all, crazy thought thread time!

Before all you nay-sayers start saying "this isn't possible!" I ask you to keep an open mind, I've already had a lengthy discussion with Nutter_John who believes there's a chance this may be doable.

History

Yesterday I was handed a MD340289 ECU with a MH7202F chip inside it, serial on the board was JE331B154D, I was told this came from a PFL VR-4, however when we tried to start a VR-4 with it the car started, ran very roughly for a second or two and then died, subsequent attempts to start the car yielded nothing.

I connected EvoScan up, tried to pull fault codes and nothing was listed. I tried logging the ECU and sure enough it was happy to report things like Throttle Position, Battery voltage etc. This ECU will henceforth be referred to as the bad 7202. We swapped this bad 7202 for another 7202 (good 7202 from now on), the car started first time. We replugged the bad 7202 back in, exactly the same problem, car would run roughly for a second or two and then die, no CEL, no errors logged with EvoScan, nothing. I immediately thought "fuelling issue".

I then tried pulling the ROM from the bad 7202, EcuFlash didn't recognise it but I kept a copy of it. I then pulled the ROM from the good 7202 and flashed it onto the bad 7202 without any problems, exactly the same issue as above though, rough running then nada. At this point, I thought the bad 7202 might be toast, so I started to inspect the PCBs;

Bad 7202 Back
Bad 7202 Front
Good 7202 Back
Good 7202 Front

Initially looking over both good and bad, it did indeed look like a VR-4 7202, with no visible signs of blown components or scorched tracks, so I consulted with John

Investigation

I ran through all the above with John, we started bouncing ideas back and forth, comparing pinout diagrams and between the two of us, we came to the conclusion it was most likely a N/A V6 7202 (more on this in a sec), I also passed him a copy of the unknown 7202 ROM image, his EcuFlash didn't recognise it either so he opened it with a hex editor and the ID was a near match to a known-true N/A V6 Auto ECU ROM ID, further reinforcing the idea this was a N/A V6 7202.

Whilst John and I inspected the photos above, I started tracing back both pins related to fuel pump control (Pin 8 and Pin 35, see this post for more info) and noticed the Fuel Pump High / Low circuit was missing a critical component, diode D101, from it's path. I also immediately noticed a couple of other components missing in the same vicinity, diode D103 and an unknown component Q84 (suspected transistor or triac) was also missing, tracing these back to the ECU loom connector identified this circuit as part of Pin 43 (Wastegate Solenoid control), further reinforcing the idea this wasn't a VR-4 7202.

Epiphany

It's common practice in the electronics industry to save money by designing PCBs to be used in multiple devices and then only populating the required components to suit the target, so it's likely Mitsubishi do this with their 7202-equipped ECUs.

My thinking is this, with a bit of soldering, it may be possible to turn a N/A V6 7202 ECU into a fully-fledged VR-4 7202 ECU. We already know that this bad 7202 ECU allowed us to flash a VR-4 7202 ROM Image without any (noticeable) warnings, and that, fuelling issues aside, it seemed to keep a 6A13TT running for a couple of seconds before the fuel in the rails was used up. Speaking with John, he seems to think there's a chance this could be successful, so I figured "why the hell not, for science!"

Moving forward from this, my first task is to identify all the components that have changed, I need to get some high res photographs of a known-good VR-4 7202, the one I took above was taken in haste and is slightly blurred. Once that's done, I guess it's a game of "spot the difference"

[lateshow]

Did you use the definitions I posted in the N/A section? Do you still have a copy of the suspected v6 rom, i could take a look. Was the rom bigger than 128k?

What about ignition, as said before vr4 gets 3 pulses from the ecu as N/A gets 1 for the old fashioned distributor. Boost control isnt important....

[foxdie]

Did you use the definitions I posted in the N/A section? Do you still have a copy of the suspected v6 rom, i could take a look. Was the rom bigger than 128k?

What about ignition, as said before vr4 gets 3 pulses from the ecu as N/A gets 1 for the old fashioned distributor. Boost control isnt important....

The suspect ROM is already linked above as part of the sentence "the unknown 7202 ROM image"

I think ignition pulses are a non-issue because we're running a genuine VR-4 7202 ROM on a N/A V6 ROM, it'll be the ROM code that controls how many pulses get sent, I could be wrong.

Boost control may not be important but it's not the only thing that's bound to be missing, however I'd like to get boost control working so no external boost controller is required.

[lateshow]

http://www.clubvr4.com/forum/attachm...0&d=1313157046 <- As this pinout says the vr4 ecu gives 3 physical outputs to 3 separate coil packs , i dont know about the v6 but as it has ha distributor system there must be only one actual wire that transmits the command "ignite". But since you got it running a little....hmmmm.... strage i would say... ?

[foxdie]

Sorry for delay, pub lunch.. *hic*

Thinking out aloud here, the fuel pump high / low pin was disconnected, one would think that it makes sense that with this disconnected the car wouldn't be able to start (more fuel needed etc), however the car can quite happily idle with a "0" signal being sent (ie. low fuel supply) for idling, so why would it run lumpily for a second or two and then not start at all after that?

This requires more science, and by science, I mean multimeter testing, admittedly I don't have a lot of time to investigate this. I'm going to continue with finding out which components are missing and which differ. I've already found another resistor present on the bad 7202 that's not present on the good 7202.

[scott.mohekey]

I would follow on from what Lauri has said and trace the pins on the bad ecu that equal the three ignition outputs on the good one. I suspect you'll find differences there.

[foxdie]

Updated the above images so they can be overlaid on top of each other, also added a grid to reference where components are / aren't present.

Scott / Lauri, thanks, will start tracing the ignition circuits now.

[foxdie]

I traced back the components for Coil Pack 2 (Pin 23) and Coil Pack 3 (Pin 11), the lines appear to be populated on the bad 7202.

[Nutter_John]

the ecu can control either 1 line or 3 lines and all that will be different is the actual driver code , would not make sense for Mitsi to not use the same ecu across the 6 cyl range

[pbaron]

Taking a quick look at the hex file in a hex editor the internal id of this rom is EM2429, the part number for the ecu it was standard on is one of MD359139 or MD359140, these are listed in ASA General Export version as applicable to EA5A Galant autos and manuals.

Why don't you just put a VR4 rom on it and see if it runs.

[foxdie]

Why don't you just put a VR4 rom on it and see if it runs.

I did say earlier that we tried this, I actually tried a couple of ROMs on it, eventually taking one from another VR-4 7202 that started the car 2 minutes earlier

A general update to progress, I'm going through now playing spot-the-difference highlighting every component that changes between the two PCBS, this may be posted up tomorrow depending on how far I get.

[Nutter_John]

he did and it didn't as both the fuel pump and boost solenoid lines are not connected

[scott.mohekey]

the ecu can control either 1 line or 3 lines and all that will be different is the actual driver code , would not make sense for Mitsi to not use the same ecu across the 6 cyl range

I've got a 96 ST25 here which has a v6 and the 4 speed auto which has an entirely different ECU in it. Instead of having an ECU for the engine and a TCU for the auto, it has them combined into one, physically larger, item.

[crazydriver81]

I've got a 96 ST25 here which has a v6 and the 4 speed auto which has an entirely different ECU in it. Instead of having an ECU for the engine and a TCU for the auto, it has them combined into one, physically larger, item.

can confirm the same for the ST-R25 - only one ECU, combined for engine and auto trans. But I know that the european V6 cars have separate ECU and TCU.

[foxdie]

*Takes a deep breath* 6 hours and literally 2 migraines later, here we go;

Note: Where solder tags are mentioned, these relate exclusively to PCB inter-layer connections (you'll see what I mean when you compare pics)..

Rear

• C2 - Solder tags only on bad 7202
• D2 - Solder tags only on bad 7202
• E2 - Solder tags only on bad 7202
• F2 - Solder tags only on bad 7202
• G2 - Capacitor C135 only present on bad 7202
• I2 - Solder tags only on good 7202
• C3 - Jumpers J7 and J10 only on good 7202, Jumper J9 only on bad 7202
• D3 - Transistor Q53 only on bad 7202
• E3 - Diodes D101 and D103 only on good 7202
• F3 - Resistor R526 only on bad 7202
• G3 - Resistor R335 only on bad 7202
• H3 - Resistor R334 only on bad 7202
• D4 - Resistor R168 only on bad 7202
• E4 - Transistor Q84 and Resistors R226 and R225 only on good 7202, Resistor R392 only on bad 7202
• F4 - Transistor Q202 appears to differ, could be a false positive
• H5 - Transistor Q100 only on bad 7202
• H7 - Resistor R119 only on good 7202
• F8 - Resistors R221 and R222 only on good 7202
• I8 - Capacitor C153 only on bad 7202, Jumper J18 only on good 7202

Front

• F1 - Resistor R167 only on bad 7202
• I2 - Resistor R33 only on bad 7202
• H4 - Resistor R180 and Capacitor C103 only on bad 7202
• I4 - Transistor Q60 only on bad 7202
• H5 - Resistor R191 only on bad 7202
• E6 - Transistor Q82 only on good 7202
• I7 - Resistor R610 only on bad 7202
• C8 - Jumper J8 only on bad 7202
• D8 - Diode D84 only on bad 7202
• E8 - Solder tags only on bad 7202
• G8 - Solder tags only on bad 7202

[GalantOnly]

with a bit of soldering, it may be possible to turn a N/A V6 7202 ECU into a fully-fledged VR-4 7202 ECU.

What about just soldering 7202 chip from N/A V6 into 7201 VR-4 board? Wouldn't it be a flashable VR-4 ECU then?

[foxdie]

What about just soldering 7202 chip from N/A V6 into 7201 VR-4 board? Wouldn't it be a flashable VR-4 ECU then?

I somewhat assumed this wasn't possible, that the boards would be quite significantly different ie. the MPU wouldn't be reflashable later on due to tracks / components not being populated or something...

[scott.mohekey]

The 7201 board is significantly different to the 7202 board. From memory, the chips are so different they even have a different pin count and foot print.

[GalantOnly]

That's makes sense... 7201 is 25x25, but 7202 is 28x28.
There's no easy way out

[wintertidenz]

Has anyone done the same kind of tracing on the 7201 boards to see if there IS in fact a way to flash it without removing chips etc?

There is still that CN102 connector that people have noticed but never really checked out (myself included, but that's because I don't have the tools required to work out what those connectors really do).