Over the last few weeks after work I’ve been installing the standard upgrades into my 1990 Supra GTE. I’ve installed a Walbro fuel pump, Aeromotive AFPR, RC 660cc injectors and a new turbo. I’ll be running Speed Density with a GM 3Bar MAP and IAT sensor. I’ve wired in a MAFTPRO running version 5.x, powered it up and entered in all of the values from the Supra MK3 Quick Setup 5.0 guide that is floating around the net. I have an AEM 5v Wideband O2 sensor connected up with the MAFTPRO’s Wideband ground connected inches from the unit and the analog signal wire connected to the AEM’s analog output. The main ground for the wideband is connected to the block of the engine. I’m looking at starting the car this weekend. I am confident about how the car ran prior to the upgrades, and I understand that adding mods to a car that has sensor issues would not be smart. Last year installed a new TPS and adjusted it to perfect drivability. I have been running and maintaining the car for the last two years mostly unmodified with an engine rebuild that I did myself that now has about 10k on it.
In my efforts to prepare for this big day of starting the car on the MAFTPRO I have been doing my best to understand the parameters and documenting my configuration. I have a few questions that I need to get cleared up so that I don’t feel like I’m shooting blind this weekend.
Mainscale:
I understand how fuel pressure affects the realized CC rate of an injector, and I understand the mathematics of how the mainscale can be tuned to compensate for the desired AFPR PSI/CC Rate. I have attached an excel spreadsheet that contains the calculations that I can use to easily see which mainscale value I would use at a given desired CC.
* What I do not understand is how I pick this desired CC value, where should I start?
* For the sake of discussion, I bought 660 CC injectors, so with what fuel pressure should I start?
* Will I not have to to re-tune everything if I decide that for whatever reason I want to bump up the fuel pressure a few PSI because I can simply make the mainscale change and only need to tweak a little from there?
* For what reasons would I want to run them at a fuel pressure that would yield them at less than 660cc of flow?
I’m just not clear on why I would pick one fuel pressure over another at this point. Is it simply because the MAFTPRO cannot adjust mainscale effectively into certain max range values? I know this is an issue with an SAFC, and the MAFTPRO uses the same principals in the mode I’ll be initially running in, tuning for the load ranges. So where should I begin?
In the chart below, which was created by assuming the stock supra fuel pressure is 38 (which I can only identify as somewhere between 34 and 40psi from the manuals) and my injectors are 660CC, the fuel pressure would be set to the value in the leftmost column and the mainscale would be adjusted by the negative of the value in the rightmost column.
fuel psi - pressure ratio - cc - mainsale adjustment
25 - 0.657895 - 535 - 22
26 - 0.684211 - 546 - 24
27 - 0.710526 - 556 - 26
28 - 0.736842 - 567 - 29
29 - 0.763158 - 577 - 31
30 - 0.789474 - 586 - 33
31 - 0.815789 - 596 - 35
32 - 0.842105 - 606 - 38
33 - 0.868421 - 615 - 40
34 - 0.894737 - 624 - 42
35 - 0.921053 - 633 - 44
36 - 0.947368 - 642 - 46
37 - 0.973684 - 651 - 48
38 - 1.000000 - 660 - 50
Tuning Approach
Initial Low/Mid Load
I’ll be leaving the stock O2 connector plugged in for the foreseeable future and so I’ll be planning to adjust the Low/Mid/High load tunes. I realize that on my car I need to tune to satisfy vF, which is the car’s stock O2 sensor acting like a wideband meter for the ECU.
* I will plan to tune these LOW & MID load points to keep my vF at 2.5volts which is, for the supra, normal – not rich or lean. Is this the correct approach?
WOT/High Load
I am then anticipating that once I get a car that idles fine and can drive around with low and mid load tunes completed (unsure how long this will take to achieve) I’ll then be looking at tuning for Open-Loop WOT operation. I am unclear on this approach because with the MAFTPRO I can tune for HIGH load and also enabled WOT AFR Tracking, which sounds great. I will verify that the AFR Reported on the MAFTPRO’s sensor monitor page matches my gauge. But how should I approach this part of tuning?
* How much time should I spend with the Open-Loop HIGH load tune before enabling WOT AFR Tracking on the MAFTPRO?
* Other considerations?
Thanks for any help someone could provide on this subject. I’ve been searching the forums high and low and not finding any data that isn’t related to a specific problem someone was having, and even then extrapolating the good information over the bad information can be difficult.
In my efforts to prepare for this big day of starting the car on the MAFTPRO I have been doing my best to understand the parameters and documenting my configuration. I have a few questions that I need to get cleared up so that I don’t feel like I’m shooting blind this weekend.
Mainscale:
I understand how fuel pressure affects the realized CC rate of an injector, and I understand the mathematics of how the mainscale can be tuned to compensate for the desired AFPR PSI/CC Rate. I have attached an excel spreadsheet that contains the calculations that I can use to easily see which mainscale value I would use at a given desired CC.
* What I do not understand is how I pick this desired CC value, where should I start?
* For the sake of discussion, I bought 660 CC injectors, so with what fuel pressure should I start?
* Will I not have to to re-tune everything if I decide that for whatever reason I want to bump up the fuel pressure a few PSI because I can simply make the mainscale change and only need to tweak a little from there?
* For what reasons would I want to run them at a fuel pressure that would yield them at less than 660cc of flow?
I’m just not clear on why I would pick one fuel pressure over another at this point. Is it simply because the MAFTPRO cannot adjust mainscale effectively into certain max range values? I know this is an issue with an SAFC, and the MAFTPRO uses the same principals in the mode I’ll be initially running in, tuning for the load ranges. So where should I begin?
In the chart below, which was created by assuming the stock supra fuel pressure is 38 (which I can only identify as somewhere between 34 and 40psi from the manuals) and my injectors are 660CC, the fuel pressure would be set to the value in the leftmost column and the mainscale would be adjusted by the negative of the value in the rightmost column.
fuel psi - pressure ratio - cc - mainsale adjustment
25 - 0.657895 - 535 - 22
26 - 0.684211 - 546 - 24
27 - 0.710526 - 556 - 26
28 - 0.736842 - 567 - 29
29 - 0.763158 - 577 - 31
30 - 0.789474 - 586 - 33
31 - 0.815789 - 596 - 35
32 - 0.842105 - 606 - 38
33 - 0.868421 - 615 - 40
34 - 0.894737 - 624 - 42
35 - 0.921053 - 633 - 44
36 - 0.947368 - 642 - 46
37 - 0.973684 - 651 - 48
38 - 1.000000 - 660 - 50
Tuning Approach
Initial Low/Mid Load
I’ll be leaving the stock O2 connector plugged in for the foreseeable future and so I’ll be planning to adjust the Low/Mid/High load tunes. I realize that on my car I need to tune to satisfy vF, which is the car’s stock O2 sensor acting like a wideband meter for the ECU.
* I will plan to tune these LOW & MID load points to keep my vF at 2.5volts which is, for the supra, normal – not rich or lean. Is this the correct approach?
WOT/High Load
I am then anticipating that once I get a car that idles fine and can drive around with low and mid load tunes completed (unsure how long this will take to achieve) I’ll then be looking at tuning for Open-Loop WOT operation. I am unclear on this approach because with the MAFTPRO I can tune for HIGH load and also enabled WOT AFR Tracking, which sounds great. I will verify that the AFR Reported on the MAFTPRO’s sensor monitor page matches my gauge. But how should I approach this part of tuning?
* How much time should I spend with the Open-Loop HIGH load tune before enabling WOT AFR Tracking on the MAFTPRO?
* Other considerations?
Thanks for any help someone could provide on this subject. I’ve been searching the forums high and low and not finding any data that isn’t related to a specific problem someone was having, and even then extrapolating the good information over the bad information can be difficult.