Once You Go Black, Well You Know The Rest

Silver top out, Black top in.

The JAM ecu was fun and all, but I have used a piggy back on top of a ROM tune before and while you can make small adjustments to dial things in, it’s not worth the time and hassle if you have to make major changes.

I picked up the ECU off of Ebay, and then headed to the Pick N Pull to get the MAP and IAT sensors.

Most of what I’ve read on this swap /conversion said to grab a MAP sensor from a similar era Corolla.  While I think that would probably work, I didn’t necessarily like the made in the USA label on it.  No offense to the hard working people in this country, I just find that the truly hard worker here are few and farther between than the ones in Japan.  I ended up grabbing one from a 95-99 Celica.  A quick check on the EMU instructions showed that to be of the same “type” as the proper one for the AE111, which told me I should be at least close to right.  After checking the voltage to pressure curve in both service manuals the curves match exactly.

The silver top to black top wiring conversion is far easier than then manual vs auto on the silver top.  The car ran pretty well but two things were very apparent.  The first WOT pulls showed we were running extremely rich.  In fact looking at that white line you can see where the sensor blew out from going to rich for too long.  The second problem is that MAP sensor signal.  The stock ECU may have a hell of a filter on that signal, but something tell me it’s not enough to overcome a 30kPa oscillation.



A little bit of research showed that the original installation has what is refereed to as a Gas Filter in line with the MAP sensor.  The part number is 90917-11009 and is available in the states.  At least Lithia was able to source one for me, if you try your local dealer, no promises.



As you can see the filter does some amazing things for that MAP signal.  If you are trying this conversion find at least some sort of filter for that MAP signal.  I pulled one out of the spare parts pile, and I used that to get some rough tuning done while I was waiting for my order to show up.  It worked, but not quite as well as the proper one.

Here’s a better comparison of both signals overlaid.  Once the signal was stable I could keep tuning.  The zero to 2000 RPM range seemed to work quite well with the BT ECU dialing things in.  Above that it looks like it goes into open loop and starts to go pretty rich.  Driving on the freeway was in the 11:1 a/f territory.  Not ideal for economy.  Since a 70 mph cruise speed was already close to atmosphere, I ended up using a combination of injector maps.  One pressure based to do most of the WOT driving and one throttle based that is being used under 50% throttle.  I wasn’t sure how well the this strategy would work with a piggy back on a stock ECU, but it seems to handle things very well.  There is still some fine tuning to do, but it seems to be working very well over all.  You can see in the above “after filter” trace the WOT fuel ratio is pretty close to dialed.  The cruise regions could use a little bit more work to get the economy better, but it’s at least safe and drive able right now.

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