3500 RPM Lean Spike is hard to tune around : MAFTPRO/7MGTE 1990

CBatstone

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#1
What is the TCCS doing ~3500 RPM that causes a huge lean spike that is extremely hard to tune around? I initially approached the lean area with VE tables, and later with adjusting the Low/Mid User Tunes, Have tried different fuel pressures. I can effectively tune every other RPM/Load range but right at 3500/3600 it spikes lean to 17+ and its a bit scary, even under very low load.

I'm thinking this is the switch from Closed to Open loop, but what is the best way to attack this issue? I started distorting my VE tables to the extreme and was still seeing it. If any supra owners out there have seen this I'd love to hear what you did.

 

JimR

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#2
Yes, this is a regular issue. Your answer lies in the "Enhanced TPS" function of the Maftpro. It will let you set the TPS to 100% at the point you like, making the ECU go into open loop when you want it. Plus it dumps fuel because it sees 100% tps... handy. :)
 

jtamulis

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#3
Do you have your fuel pump 12Volt modded so that it stays at 12V all the time? I had the same problem on my Aristo, and 12V modded the pump, BAM problem solved.
 

suprajztwenty

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#4
i know its an old thread but the topic is the same...any tips to go into open loop early like stated but without maft pro? i was planning on forcing open loop all the time with the coolant temp potentiometer sogi mod. adjust everything on the airflow map where i need and then based on % changed on coolant temp/afm signals ill base that on the stock timing map and remove x amount of timing where i need to (bonus to the emanage blue)

im really struggling with this lean spot. this thread says its common but searching isnt coming up with too much...im a tard when it comes to the exact phrase it takes to get the desired search results. the question i have is, will the ecu stay in open loop and let me tune low/mid by altering just the coolant temp sensor or will it still learn what im feeding it and start this whole battle all over again?

any/all advice is much appreciated.
 

hvyman

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#5
Did you do the 12v mod to the fuel pump. If you didnt you should. That is prolly your issue.
 

IndigoMKII

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#6
Did you do the 12v mod to the fuel pump. If you didnt you should. That is prolly your issue.
This. The fuel pump changes from 9v to 12v near this RPM. This causes a nice hiccup in the fuel system for a blip of a second and makes it a nightmare to tune.
 

emericaskater285

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#7
do you have any gauges or extra things grounded at the ecu harness? I had my gauges grounded into the ecu wire harness, and it was basically untunable because of the noise in the harness. I wired it into a relay that was triggered by the ecu and grounded it on the chassis, and it eliminated all of my problems.
I had the car running okay, but i had these lean spots that i could never get right. I wish I would have known what it was before i went standalone, as I really wanted to see what the 57 trim would do on the 550's and safc.
 

1988ma70supra

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#8
I have the same issue as far as a lean spot but almost exactly in the 2000 rpm. I'm using the HKS set up though (FCON, VPC, GCC, IPM) not the maft pro to tune. I also have a fuel pressure gauge and haven't noticed the jump from 9v to 12v in that spot so i just kinda live with it since its not boosting in that spot anyway and it only leans out to about 16.5-17 on the wideband.
 

hvyman

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#9
I would still do the 12v mod. esp with a ct as they spool so fast.