GM Volt Forum banner

Gen 1 Volt Flex Fuel

5687 Views 20 Replies 12 Participants Last post by  lohmatij
Hey guys. Ill be honest I haven't really been active on these forums but this is a bit more permanent than facebook where this started. Speaking of which. There was a post on the Chevy Volt DIY repair and modding group regarding flex fuel since some of us are lucky enough to have e85 cheap enough to offset the economy loss. I am a small tuning business owner and have done many flex fuel conversions on customer cars. I am aware of an article from 2013 and the "Volterado" efforts that happened with this but I havent seen much since. Maybe there are a ton of these I dont know about! But probably not. I also wasn't a huge fan of the direction the "Volterado" tune went so I figured I would give it my own spin.

Anyways E85 is now cheaper than premium AND regular gas even when factoring in a worst case of a 30% fuel economy loss where I am at. If it isnt where you are im sorry but this isnt a debate on if it will save money in your area. Plus I have the sensors, wiring, and tools on hand... and the volt was designed to be flex fuel originally so why not?

So lets start with the parts list. This is to put a real flex sensor in. There is simply no way the virtual flex system will work well on a car that cycles the engine on and off at every opportunity. Sure the volt always runs in closed loop but its asking for errors and drivability problems.

Flex fuel sensor. Any of the 3 or 4 variants will work. I chose the one with short lines and no mounting tabs.
Sensor plug.
Fuel rail 5/16 to barb disconnect.
Sensor 3/8 to barb disconnects.
Firewall 3/8 to barb disconnect.
Pins for the ecu. Molex MX64. You can find these pre terminated. I do this all the time so I buy them loose and crimp them myself.
Add a fuse tap. Available at every parts store. Grab wire loom while you are there.
Fuel line. I had some 6an or 3/8ths braided line from a customer cars left overs and some high pressure hose clamps. You could also use nylon fuel line like factory.
Hptuners or efi live for tuning.
2001 Corvette with a flex conversion. More on this in a bit.

So. Lets start. This isnt going to be hyper detailed. If you cant fill in the blanks you shouldn't be doing this.

Step 1. Jack up the drivers side front of the car. Pop the wheel off or turn it in hard right. Remove the star bit screws holding the bumper cover to the wheel well. Follow the trail of screws under the car and remove the 7mm screws until you reach the lower air duct of the front bumper. Theres a flat plastic bracket thing with 4 plastic push clips. Remove them. Move to the top. Take everything out of the beauty cover that covers the radiator cradle and has the washer fluid fill neck coming through. Lots of those wonderful push clips. Toss that out of the way. Now you have 4 more screws holding the bumper on. Wait. Pop the washer fluid fill neck out first. Now pull those screws. Go to the seam behind the drivers headlight and POP the bumper loose. Woo.

Wheel Tire Car Vehicle Automotive tire

Car Vehicle Tire Wheel Vehicle registration plate

Now go disconnect the negative battery cable in the rear. We are going to do some stuff.

Tire Automotive tire Motor vehicle Automotive lighting Hood

Thats the engine computer. Pop at least the far left plug off. We are modifying the grey one. Snip the zip tie and unclip the back. Go to the front and gently pry up on the shorter two edges. It WILL break if you are not careful. In fact this whole connector sucks. Use a tiny phillips head screwdriver to pop out pin 20 and pin 34 blanks. 20 is ground. 34 is flex input. Pull your wire through and crimp your pins on. Pull them in. Dont break the locking clips. Reassemble. Its an E78 if you wanna google more.

Bicycle tire Leg Automotive tire Automotive lighting Bicycle part

Finger Line Electrical wiring Circuit component Wrist

If you want. Plug it back in. Reconnect battery ground. Turn the car on. With your multimeter check for 5v to ground on the flex pin and 12v to positive on the ground pin. Disconnect again.

Finger Office equipment Gadget Font Wrist

Run your wires into the engine bay. Reinstall the bumper. Open your fuse box. Tap the injector fuse since it turns on and off with the engine main relay. Use a 5 amp or less fuse here. It draws effectively nothing. I found a 3 in the box. Run wire out of box. I let it get pinched in the cover. You can drill a hole if you want. I didnt want.

Circuit component Electronic engineering Gadget Audio equipment Electronic component

Here is where the corvette comes in. I wanted to test stuff before finalizing. My corvette already has a flex sensor submerged in e85. Figured I would borrow it.

Tire Car Wheel Vehicle Automotive tire

Wheel Car Tire Land vehicle Vehicle

So anyways. Pop the engine cover off. Two hose clamps. Two screws. Fuel line can be removed. Connector clips are NOT a single piece. They have a ribbed lock that you pop up THEN you press down on the rounded tab while wiggling. I broke one. Start cobbling your connectors together. You could use AN fittings. I thought it was overkill for this. But I also hate nylon line. So I clamped braided line on with high pressure clamps. If you dont like it keep it to yourself. :)

Motor vehicle Hood Vehicle Automotive tire Automotive design

Connect your wires to your sensor plug. CHECK THE PINOUT. The pigtails are pinned wrong all the time. Red is usually 12v. Black ground. White flex signal. Reconnect your battery. Turn the car on. Check for leaks. I had none. But I do stuff like this daily.

Tuning wise ill go into more detail if there is interest. You enable flex diag in your fuel system tab. Under engine and flex you enable it with a physical sensor. Set your default, delay, transition, and threshold values to sane numbers. Under spark make sure you copy over the cat overtemp spark table into the flex cat overtemp table. Go to engine torque model. Copy EVERY SINGLE AIRMASS AND MAP TABLE into the flex airmass and flex map tables or it will sound awful and be really unhappy. Burn it in. Test. You should see ethanol content in your scanner now! Woo.
See less See more
  • Like
Reactions: 4
21 - 21 of 21 Posts
Ill keep working on this as time goes on.
How is it performing so far? I'd like to do this conversion, sensor install doesn't look too hard from what I see.
But I know nothing about tuning. Do I understand you need to tweak it over time, because there are no stock parameters? How do you tune it so it performs better?
21 - 21 of 21 Posts