I posted this question on 2 facebook groups and did not receive a solution so I thought I?d try here.
I have a 5.3 turbo motor with a P59 PCM. I have an in the fuel line E85 sensor on the return line after the regulator. I am logging Alcohol Percent and also Ethanol Fuel % (SAE). The log is reading 82.4% Alcohol, but only 49% Ethanol, even after running for around 15 minutes. Can this be explained? I must be missing something.
Which of these percentages does the PCM rely on to determine:
1. Stoich AFR.
2. injector fueling.
3. Flex fuel timing.
There are 2 choices under Engine>Fuel System>Composition. Alcohol Percent and Ethanol Fuel % (SAE). Do both of these channels read from the in-line flex fuel sensor, correct?
If so, the problem is that the Ethanol Fuel % SAE channel is reading incorrectly, but the PCM reads Alcohol Percent and not Ethanol Fuel % SAE. So even though the SAE channel is not correct, Stoich AFR. injector fueling and flex fuel timing are receiving accurate readings from the in-line flex fuel sensor.
So I should remove the Ethanol Fuel % SAE channel from the VCM Scanner and rely on the Alcohol Percent channel? Correct on the above?
The sensor only outputs a raw voltage. It takes math to turn a voltage into a percent value. The GM PID and SAE PID are using different math to get their value. I trust that GM knows better what math will give the correct conversion from voltage to percent over what the generic universal SAE math will give. You know what they say, 'universal' means it doesn't fit anything.
Don't use SAE channels if there is any way around it, unless it's a raw voltage display like O2 sensors, or something really common like vehicle speed or coolant temp. They too often get it wrong.
Thanks. It makes sense that a formula converts voltage into a percent value. I was unaware that SAE formulas may not be accurate, because they are generic. So, I'll remove the Ethanol Fuel % channel and only log the Alcohol Percent. And, try to avoid SAE when possible. I did not think it would be that simple, but it make sense.
I have a P59 Corvette on flex fuel, the PCM doesn't even report ethanol content via SAE PID for me (0x52). The GM one works correctly. On other (newer) vehicles, SAE PID works just fine.
Also the ethanol sensors output a digital signal (measured in hz) not analog / volts, fwiw.
You should be able to log ethanol sensor hz raw signal as well. That could help you confirm which is correct
Based on the log, it is using the GM alcohol percent, since it is saying lambda of 1 = 9.9x AFR or whatever.
Yeah, of course. I think I made that mistake because I've always thought that sensors that output frequency instead of a normal sensible thing like voltage are dumb and annoying, and my brain has been trying to delete all knowledge of their existence.
How do I go about logging ethanol sensor hz raw data?
I take it that (0x52) meant that Alcohol reading was 52% and ethanol reading was 0%.
This discussion encourages me to analysis all of my channels.
Anyways, use the GM specific "alcohol content", it looks to be good to go. Are do you believe the actual E content was something else?
It looks like the raw ethanol signal output isn't an option to log in VCM scanner for me on my car...it's probably not there for you either, oh well. If you have the ability to define your own PIDs in a different app or tool the address is 0x22139C (at least for my OS, should be same for most P59, I think?)
Might want to verify your %'s. https://revxoil.com/shop/ethanol-super-tester/ You can pick them up on Amazon for about $12 Check your actual content and see what is true and correct. Some E85's can be in the 70's. Some regular gas can be 15% to 5% in my area.
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