injector constant vs. VE
Thread Starter
Racer
Joined: Sep 2021
Posts: 360
Likes: 59
injector constant vs. VE
Hello everyone,
I've been trying to set up the Power Enrichment to activate at a lower throttle position , 20% after 2000rpm but for some reason It wouldn't activate until the MAP reaches over 88kPA. I even got a knock exactly before it got activated. The engine is a 383 mild cam and would make 420Hp on a carburetor manifold and good flow exhaust. The injectors I have on the car now are Bosch 42lbs. To solve the PE problem I've thought of an alternative, that is to increase VE progressively in the areas I want, >75KPa. I've multiplied the VE with the ratios needed (after the BLM's were zeroed out around 128), for example 14.73/12.5*VE. However, many of the new values exceed 100 so I've heard that you can lower the injector constant and the VE values. The question is, do I lower all VE proportionally with the injector change ratio, for example 36/42*VE? I've already done this but only tested the idle and got AFR Wide Band 17:1 at idle before closed loop. I've increased the rpm by pushing the gas and AFR went down and managed to enter CL. In CL now the engine managed to compensate and give me the 14.7:1. but it seems that all the VE needs to be readjusted
the car is a 1991 TPI stock ECM. and S_AUJP v5 bin file
thank you
I've been trying to set up the Power Enrichment to activate at a lower throttle position , 20% after 2000rpm but for some reason It wouldn't activate until the MAP reaches over 88kPA. I even got a knock exactly before it got activated. The engine is a 383 mild cam and would make 420Hp on a carburetor manifold and good flow exhaust. The injectors I have on the car now are Bosch 42lbs. To solve the PE problem I've thought of an alternative, that is to increase VE progressively in the areas I want, >75KPa. I've multiplied the VE with the ratios needed (after the BLM's were zeroed out around 128), for example 14.73/12.5*VE. However, many of the new values exceed 100 so I've heard that you can lower the injector constant and the VE values. The question is, do I lower all VE proportionally with the injector change ratio, for example 36/42*VE? I've already done this but only tested the idle and got AFR Wide Band 17:1 at idle before closed loop. I've increased the rpm by pushing the gas and AFR went down and managed to enter CL. In CL now the engine managed to compensate and give me the 14.7:1. but it seems that all the VE needs to be readjusted
the car is a 1991 TPI stock ECM. and S_AUJP v5 bin file
thank you
Thread Starter
Racer
Joined: Sep 2021
Posts: 360
Likes: 59
The conversion
vformula as in the original $8D XDF file: conversion: -0.312500 * X + 80.000000. . In the original $8D there is 0.312500 * X + 20.000000 and the stock bin file has 91% in this field. In my SAUJP V5 and V4 the value stored at that address shows me 91% in the original $8D and 8.1kPa in the SAUJP v5, v4. It's possible the conversion formula is wrong in both V5 and V4 I have. I couldn't find any reference about changing that constant. I can try the old formula next time and revert to 42lbs constant and previous VE tables
Thread Starter
Racer
Joined: Sep 2021
Posts: 360
Likes: 59
The with the SAUJP v5 they have changed the code and location of some variables, so it might require a different formula. you probably have the original one:0.312500 * X + 20.000000.
With the original formula 8.1 is exactly 100-8.1=91.9 and 91.9 is 8.1 in the v5. Looks like the ECM reacts to this 8.1 as if it was 91.9
Melting Slicks
Joined: Jul 2005
Posts: 2,221
Likes: 302
I think the v5 SAUP is giving you units of vacuum, not pressure. 100 kPa is atmospheric pressure, so 92 kPa of pressure in the manifold would be 8 kPa of vacuum.
I would upgrade to v7 which is the latest. In v7, the XDF file is in terms of manifold pressure, so you'll see the 91.9 kPa value for the stock 8D.
For reference, I'm running 50kPa there. Also a mild-cammed 383, but with a Miniram intake. Then it takes 60% throttle up to 3200 rpm, after which point I drop to 50%, and then 40% at 4800 rpm. For my set up, its a smoother transition into PE mode.
Also, since you're running a WB and you can actually see your PE AFRs and tune for them, what you want to do is set the flag to avoid the ECM making adjustments to the PE AFR based on the BLM you were at before entering PE. That's a safety feature for the general public that GM put in... but it can make you significantly richer if your BLMs are >128 before going into PE.
Lastly, I also richened up my O2 thresholds at higher maps by about 100mV, and then adjusted the VE tables accordingly. Rather than going from ~14.7:1 straight to ~12.5:1... and particularly for a "slow roll" into PE, I'll get more a of a mid-13-ish AFR at moderate throttle (but not quite PE). Also helps in the smoother transition from non-PE to PE.
I would upgrade to v7 which is the latest. In v7, the XDF file is in terms of manifold pressure, so you'll see the 91.9 kPa value for the stock 8D.
For reference, I'm running 50kPa there. Also a mild-cammed 383, but with a Miniram intake. Then it takes 60% throttle up to 3200 rpm, after which point I drop to 50%, and then 40% at 4800 rpm. For my set up, its a smoother transition into PE mode.
Also, since you're running a WB and you can actually see your PE AFRs and tune for them, what you want to do is set the flag to avoid the ECM making adjustments to the PE AFR based on the BLM you were at before entering PE. That's a safety feature for the general public that GM put in... but it can make you significantly richer if your BLMs are >128 before going into PE.
Lastly, I also richened up my O2 thresholds at higher maps by about 100mV, and then adjusted the VE tables accordingly. Rather than going from ~14.7:1 straight to ~12.5:1... and particularly for a "slow roll" into PE, I'll get more a of a mid-13-ish AFR at moderate throttle (but not quite PE). Also helps in the smoother transition from non-PE to PE.
Last edited by ULTM8Z; Mar 12, 2024 at 04:44 PM.
Thread Starter
Racer
Joined: Sep 2021
Posts: 360
Likes: 59
I think the v5 SAUP is giving you units of vacuum, not pressure. 100 kPa is atmospheric pressure, so 92 kPa of pressure in the manifold would be 8 kPa of vacuum.
I would upgrade to v7 which is the latest. In v7, the XDF file is in terms of manifold pressure, so you'll see the 91.9 kPa value for the stock 8D.
I would upgrade to v7 which is the latest. In v7, the XDF file is in terms of manifold pressure, so you'll see the 91.9 kPa value for the stock 8D.
Thank you
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Thread Starter
Racer
Joined: Sep 2021
Posts: 360
Likes: 59
I've loaded the v7 rev2 XDF with the old PE MAP enable threshold formula and set it to 70%, and PE does activate at that level but now with this version I got a problem with the AFR Wide band logging. I have a 0-5V from my WB that is fed to the ECM U6/F11 and now the ECM reports 64 counts at 5V and 1 count at 0V basically 4x reduced resolution, that is 0.15 AFR accuracy. It also gives random spikes to 1 count (0V or AFR=8.8:1) at about 30s intervals. Not a big problem but I couldn't find reference for these changes, unless I did something wrong.
PS I think it must be this: "Pins F11 and F12 input (ECM A/D counts from sensor voltage), is lag filtered using the Oil Temperature scaling factor:
0x3E8=Oil Temp Filter Coefficient (25%)"
Last edited by Nilak; Mar 15, 2024 at 08:39 AM.