Howto: 89+ ECU HAC mod

[GrimJack]

I should have come back and edited this thread, too - mine has been running for several months now with this mod, and it works fine - many thanks to Dave for the roadmap!

I may be the second guy to ask him how he did it, but most of that was due to it being rather tough to figure out who he was, or at least find an email address.

That offer for dinner still stands - if I ever manage to make it down south, or you manage to make it to Vancouver BC, I'm buying.

 

[americanjebus]

crap, i didnt even know about this mod. nor that i had an internal HAC sensor in my ecu.

what are the consequences of me not doing this to my 89+ ecu, and what are the benefits of it.

im still learnding super nintendo chalmers.

 

[boltz]

the mod is only necessary for your MAFT pro (If you have one)

 

[Daves2JZGTE]

http://www.fullthrottletech.com/showthread.php?t=832

I told everyone that I fixed it. No one seemed to care. Maft pro or maft needs this mod if you have an 89+ ecu. If you don’t do this your ecu will get a corrected signal from the maft/pro only to have the ecu correct it again.

Lets say the maft/pro tells the ecu +1 is right. Then the ecu takes the +1 not knowing its +1 and adds +1 to that so now your @ +2 over correcting the single buy 1. Cutting out the ecu Hac you remove the redundant correction for altitude or whether change.

Hope that helped

If i can i will take you up on that dinner

 

[SLO-MK3]

Damn Grim, that sure is a tight squeeze to cut that trace. What did you use? I don't think I have anything small enough to fit in there.

 

[Daves2JZGTE]

exacto blade will do just fine

 

[boltz]

I have done testing on this mod myself and it seems to function

Car runs fine with HAC mod wires looped
Car runs fine maft pro hooked up to the proper wire
car wont run after warm up with Mod wires un looped and not connected to T-Pro.

ECU throws HAC code un looped with no MAFT input
ECU has no HAC code when wires looped.
ECU has HAC code with maft pro signal hooked up, but no issues running the car.

 

[drjonez]

the HAC code (along w/the IAT code) w/the MAFT pro properly connected has to do with how fast the ECU checks for each on key on. a clever way around it would be to wire the MAFT pro to ACC and pause w/the key @ acc for 1 sec or so.

 

[Daves2JZGTE]

^^ What he said. I have my maft this way and never throw a HAC code....


Grims pics are seem to be dead so hear is a link that works

http://forums.celicasupra.com/showthread.php?t=32695

 

[scubajtw]

Thank you to all who figured this out and put the great pictures up. (grimjack) Sticky?!?