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Need a little bit of help setting up my GM FlexFuel sensor on my ‘95 w/ MS3x from DIY Autotune.
Got my sensor installed today. It’s the larger GM FlexFuel sensor with three bolt holes for mounting. I’ve got power going to “VCC”, ground to “GND” and the signal wire going to “OUT” on the sensor. I hit a standstill when I went to run the signal wire to the ECU. My ecu doesn’t have a wire labeled as a flex input. For some reason, I thought I’d read/heard multiple times that you’re supposed to run the signal wire to the “launch” pin on the MS3x, so I wired it there.
Checked and confirmed continuity on the signal wire to launch pin and went into Megasquirt, where none of the FlexFuel input options indicated that the launch pin could be used. I tried them all anyway, all gave me a FlexFuel fault message in TS and a CEL.
Ok, back to square one. Did some reading and reviewed the TruboKitty wiring diagram for my ECU a handful more times, and tried to find my issue on any other thread I could. It looks like the FlexFuel input is generally located on pin 5 of the MS3x, where mine would have the knock sensor input wired? Only issue is I couldn’t find an orange/red wire in my MS3x harness. Also, my ecu has two separate connectors as opposed to the single DB37 connector pictured below.
My harness is almost identical to the TruboKitty photo, but upon closer inspection I found outputs for Spark C and D (wow, I should’ve checked closer before, didn’t know this thing was wired for sequential).
The available sensor ports that show up under the FlexFuel settings in TS are “PE0/JS7” “JS11” “Flex Input” and “PT4”. Can anyone nudge me in the right direction regarding where the sensor output wire needs to go and which input to use in TS?
This is what bugs the **** out of me on Megasquirt. They call all their input pins by a specific name, rather than just what they are, either digital (on/off) or analog (variable) inputs. Then you can't find a specific wiring diagram for your ecu, and once you do, the menu drop downs don't match.
The ethanol sensor requires a sensor ground at GND, aka directly to the ECU rather than the chassis. It also requires 12v (at VCC), so make sure you haven't wired it to a 5v source. Sounds like you've got those two figured out. The signal from the ethanol sensor needs to go to a digital input, the frequency is the eth %, duty cycle is temp, or vise versa I forget.
So any digital input should work, like launch, flex, etc. So according to the diagram above, you should be able to use 1V, 1Q, or 1M, which should be launch, datalog, and tableswitch respectively. Check your firmware version, updating to the latest may change the available pins in the flex menu. Why the pin names don't match the menu drop down options is another amazing megasquirt feature.
Yep, glad to know this debacle isn't ENTIRELY due to me being ignorant for once lol.
So you answered a question I didn't yet know I had. I didn't know all the input pins on the MS are either analog or digital, and it sounds like they don't have any further differentiation (I.E. the clutch input can read frequency/PW even though, if used for the clutch switch, it wouldn't need to). For a bit, I thought maybe the clutch input didn't possess the ability to read frequency or something like that.
Yes, I was going to use voltage as well from the EGR position sensor but found 5v at the connector, so I didn't. Pulled 12v from my ckp/cmp harness, used the ground from the EGR position sensor, used the position sensor signal wire to deliver signal to the ECU. It was already there and I'm lazy and didn't want to route a new wire through the firewall.
With key on, I'm getting 12.5v between the VCC and GND pins at the flexfuel connector, so all good there. I also pulled up one of the input test menus in TS (can't remember what it was called) and saw that the clutch input was cycling erratically between 0 and 5 volts with the sensor connected, meaning its receiving a signal from the flexfuel sensor as far as I can tell.
I don't have the car with me at work today. When I get home later, I'll pop open TS and see if there's a firmware update. My tuner updated my MS3 firmware the first time I put the car on the dyno a year ago but I have no idea what calibration it's currently at. Sounds like if the option to use launch control doesn't appear on TS, I'll just have to splice the signal wire into 1M or 1Q and see if those correlate to one of the options in the drop down menu. I'll report my findings when I get there.
The clutch switch is just a switch to ground, it may need a pull up resistor jumpered in the case, and since your flex sensor has 12v and gnd, it won't need it. Try opening the case and see if there's a physical clutch switch jumper you can remove.
Edit: I'd look it up, but I'm still not fully sure what model you have. Is it the MSpropnp model for a 94-97?
Mine looks just like that, but I believe is a trubokitty unit. I didn't look at the diagram, I just looked at the harness and noticed all the wires were colored/labeled. There was a wire called FLEX in that bundle, it went to the connector but no output from there. I just clipped it and wired straight into that and it worked like a charm.
My car was a '90 with no knock sensor circuit in the factory wiring though, this could be part of the difference? Did you find the wire labeled FLEX in that bundle to see where it actually goes?
So I poked around for a bit last night and couldn't find a wire labeled "flex" in the harness. The only wires I found not listed on the trubokitty diagram were outputs for spark C and D. That being said, I was probing around in my work parking lot after dark with a phone flashlight, so its not impossible I missed one. Do you remember which connector your Flex input went to and/or what color the wire was?
Mine also had no knock sensor circuit in the factory wiring, and I don't see an orange/red wire in my harness for a knock sensor as the Trubokitty diagram suggests.
My ECU harness is wrapped in electrical tape and fastened to the rear bulkhead in multiple places, making it hard to get a look at each individual wire. I'll detach it and cut the tape tonight and attempt to read each wire.
Got it figured out. The Flex input was wired into 1R on the MS harness, via an unmarked orange wire. The Trubokitty diagram insinuates that a yellow wire goes to the corresponding pin on the factory connector side. A look at the factory wiring diagram shows that the grounding wire to the factory EGR vacuum regulator solenoid is yellow, and this connector is pretty close to the fuel hardlines. I'm willing to bet the MS is wired so the Flex input goes directly to the signal wire for that solenoid. I'll check and confirm tomorrow.
As I was saying before, with the signal wire spliced into the launch circuit, the voltage indicator would flash erratically between 0 and 5v. I just cut the datalog and flex wires (although I didn't know one was flex at the time), tied the FlexFuel sensor signal wire to each individually, and checked to see which input flickered between 0 and 5v in this menu.
Side note, JS11 shows up in this menu as an output instead of an input, even though it's listed as an input for the flex sensor in the menu. Don't know what that's about.
Fuel temp reads accurately and ethanol percentage shows 0.1% instead of defaulting to 1.0% and flashing "flex fault" after a minute or so of the key being on. I should clarify, I don't have my fuel lines run to the sensor yet. The adapters come in the mail tomorrow.
Confirmed with fuel lines run to the sensor, ethanol content and fuel temp both read accurately. Getting 8.0% after filling up with 91 octane.
Also confirmed the yellow wire corresponding to the flex pin on my MS3x does not go to the EGR solenoid. Not gonna chase that any further as my wiring is already run.
Sounds good, I’ll post it in a bit. The fuel temp and ethanol content gauges on my dash were temporary for whatever that’s worth lol. Just wanted to make sure they worked.
12-27-2023, 09:25 PM
‘95 MS3x FlexFuel Input Trouble
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