To figure out what this is all about, it's probably best to read this thread first. This 'howto' is copied from there in order that it can be made a sticky.
I did this MREL mod yesterday on my rev2 and thought I'd write a quick howto as I believe it is a good thing to do. Having now driven the car, along with the auto to manual resistor change (http://www.twobrutal.co.uk/forum/sho...-on-3VZ-FE-ECU) done in the ECU, I can report that my car no longer tries to stall during 'clutch down' approaches to junctions as it used to. One caveat to mention though is that this was a lot more common during warm up, and it was quite warm out when I test drove it yesterday, so this could be masking the effect somewhat. Fingers crossed, but I'm pretty confident that the combination of both mods will have sorted the problem for good.
My car is a rev2 with 3VZ, originally done by Woodsport. Although I've thinned the loom out to get rid of all the non-used wires I've not changed any wiring from what Paul did during the original conversion, so I'd assume others from the same era are the same.
It's worth mentioning that this mod needs to be done on the car's original loom, not on the engine loom. The MR2 runs the EFI relay straight off the ignition feed and this has to be split and run into the boot so that the ECU has charge over it instead. It's not possible to do it purely by changing the engine loom.
Before you start, identify your 'D' connector on the ECU. It's the far right hand side on with 22 pins. On my car, pins 1, 12 and 13 were black with orange stripe which should help you identify which way around it is. All my pin numbers are on the D plug unless otherwise mentioned.
First off let's check that you're not already wired for MREL. Hook up a multimeter between pin 13 on the D connector and ground. You should see 12v here with the ignition on that goes away when the ignition is switched off. On my car, Paul had fed this from the switched side of the EFI relay which is the way the original MR2 would have been but not the way it's done on the Camry. To confirm that yours is the same pull out your EFI relay (in the engine bay fuse box). If you still have 12v with ignition on and nothing with ignition off you already have this bit wired correctly.
Next step to check is the MREL feed itself. It's on pin 3 of the D connector. On my car it was just taped off so it was obvious that it wasn't connected, but if yours is use a multimeter to check contiunity with pin 1 on the EFI relay socket. If you're standing by the nearside wheel, pin 1 is on the far-right. If you have continuity here you're probably already set up for this mod.
Finally before continuing with the mod itself it would be wise to check a couple of other bits are wired correctly. Pin 2 should have 12v on it regardless of the key position which should disappear if the EFI fuse is pulled. Pin 12 should have 12v on it with the ignition switched on only which should disappear if you pull the EFI relay. If either of things don't happen it's probably best not to carry on unless you know what you're doing!
OK, so assuming you've got this far you'll need to hook up two wires, IGSW and MREL. To do so we need to modify the wiring underneath the engine bay fuse box. Undo the bolts that hold it in, turn it upside down, and remove the bottom cover. Inside you should find a black with orange wire that loops through the ignition relay, to the EFI relay, and then to the fan relay. Of course, before you take anything electrical apart, remove the battery negative lead to be safe. There are high-current feeds to the engine bay fusebox for the starter motor and if these touch the bodywork or engine during your work and you've not taken the negative lead off very bad things will happen!
Now, cut the wires so that the EFI relay is isolated from the other two. Ideally you need to cut them to such a length that the two long ends have sufficient slack to solder back together, but that the two stubs that remain on the EFI relay are also long enough to solder to. If not, you're going to have to do some bodging to get everything to join up, but I'm sure you can figure that out!
Next, take another length of black/orange wire and solder the two long ends together with your new piece. This will become your IGSW feed to tell the ECU when the ignition is switched on.
...and of course use heat shrink to protect it. Note the two stubs left on the EFI relay are unconnected at this point.
Next, take the two stubs left on the EFI relay and twist them together. Solder a length of red-blue wire to this and again protect with heat shrink. It will probably be a bit fiddly as the stubs will be short, but as you can see it's possible if you're careful. This will become your MREL feed back from the ECU to allow it to turn on the EFI relay under it's own command, independant from the ignition switch.
Now you need to put your fusebox back together and run these two wires into the boot near to your ECU. I'll leave you to figure that out for yourself!
Final step is to connect the two wires to your ECU. The red & blue goes to pin 3 'MREL' (this was red/blue on my ECU but the diagram shows it as red/yellow for some reason) and the black & orange to pin 13 'IGSW'.
To test, first of all put the battery -ve back and check for any blown fuses (EFI or IGN fuse most likely) or smoke signals. If all is well, make sure the car starts up as it should. When you switch off you should notice that instead of the EFI relay clicking off straight away it will be 2-3 seconds after the key is turned. You may also hear the ISCV moving back to it's startup position but you may need to disconnect the fan to hear it. Note that this only happens if the engine has run ie if you just switch the ignition on and off again the EFI relay will follow the key.
To really prove it, put your multimeter between pin12 and ground. If you just turn the ignition on and off you should see 12v on this wire in time with your key turns. However, if you start the car up and then switch off the 12v should remain on this pin for 2-3 seconds after the key has been turned off.
Exactly what benefit this will have on the running of the car is uncertain at the moment but we know that at the very least the ECU resets the ISCV position during it's shutdown process so it should aid starting the car the next time. The way I explained it to the Mrs was to compare it to her laptop in that to turn it off you tell it to shutdown first so that it can save all it's settings and be ready for the next startup rather than just pulling the power out which is what the stock installation does. Whatever it does I'm sure that Toyota would have done it this way for a reason so for the ease of doing this mod it's worth doing.
Hopefully that all makes sense. Any questions, just ask!
Chris
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