Relieve Fuel Pressure

Gagliano7 · August 13, 2019

I am going to install a fuel sensor on my 2018 Sierra and I was wondering the best way to release the fuel pressure to disconnect the fuel line?There are a few fuses for fuel pump. I figured I would pull the fuses and start truck to release pressure . Just wanted to make sure this is the best way to do this.

Thanks

1SLOW1500 · August 13, 2019

Depends where you are disconnecting the fuel line. Under truck safety glasses and a rag. But the filter lines are lower pressure anyways.

CamGTP · August 13, 2019

Even if you pull the pump fuse or relay it'll still have pressure in it. Already learned that.

It's going to spray/leak fuel no matter what when you take the plastic line off the metal line near the tank.

Lsgun1 · August 13, 2019

In the old days you'd take the cap off but we don't have them anymore unfortunately. A long screwdriver should reach down the fuel filler neck to push whatever they are sealing the fuel system with.

Gagliano7 · August 14, 2019

I will be disconnecting plastic line to metal line by tank. I know there will still be gas in the line I figured the pressure would be gone. On my swapped LS in my 1992 pickup I just pull fuse and start it and pressure is gone. I guess I gas shower is in my future.

Gagliano7 · August 18, 2019

Well it wasn’t so bad. Removed fuel pump fuse and the truck kept running. So I also pulled the fuse for FPMP and fuel pump relay(probably didn’t have to do that). Still ran for a while but finally shut down. I was surprised how long it ran with the fuel pump off. Disconnected fuel line by tank and some gas came out but it didn’t spray. I couldn’t do what the guy with the reg cab did for the fuel sensor it would’ve hit the driveshaft. I have a SURR fuel kit I used for my 1992 silverado LS swap do used an elbow and looped it around above the tank. Now I am waiting for a plug to connect to fuel sensor since I don’t want to cut my harness. On my dbl cab the plug for the fuel sensor only has about 8in of slack from the harness. Now I have go to hptuners forum and figure out what I need to program.

Gagliano7 · August 18, 2019

Here is a pic but it is kind of dark. I have a short video but this site won’t let it upload because it is to big even though it’s only 27 seconds

Gagliano7 · August 26, 2019

Well I got the plug to connect the wiring for flex fuel sensor. Programmed and filled with e85 and the sensor is working properly. I was surprised how quick the sensor reacts. Seems the truck runs smoother on e85. I had 5 gallons of 93 still in there so my sensor is reading 60%. I will see how much my mpg drops. Here in NY e85 is $1.05 cheaper than 93.

CamGTP · August 26, 2019

I get 10-12 city on E70 right now and I'm not exactly a light foot but not ripping burnouts either.

It's about $2.00-2.15 for E85 and $2.50-2.60 for regular 87 octane, then 91-93 is about $3.00.

Gagliano7 · August 27, 2019

11 hours ago, CamGTP said:

I get 10-12 city on E70 right now and I'm not exactly a light foot but not ripping burnouts either.

It's about $2.00-2.15 for E85 and $2.50-2.60 for regular 87 octane, then 91-93 is about $3.00.

So far on a short run e85 15.8 mpg and on 93 17.4 mpg. This is using the DIC mpg. I will update after a full tank. Just using the stock flex fuel settings the wot is noticeable better.

CamGTP · August 27, 2019

I think my total commute to and from work is about 8 miles total, so I can't really get good mpg lol. I do get about 3 weeks to a tank of fuel though.

Gagliano7 · September 13, 2019

Ok so after 500 miles on E85 going by the dic i am averaging 16 mpg and on 93 i was averaging 17.4. I drive the same routes every week so the mpg is apples to apples. My ride is half highway and half back roads not much stop and go but up and down hills and curvy roads. After doing the math on 500 miles on E85 i saved $16. Also the truck feels way better on E85 power wise.

Here is my tune from Hptuners 2018 sierra 6.2 stock tune flex fuel.hpt

CamGTP · September 13, 2019

You could lean out the alcohol EQ ratio some too if you wanted too. I command right around .87-.89 lambda when I run that fuel. In AFR terms that's about 12.8-13.0ish. Currently it's still a little fat around 12.5 to 12.25 in your calibration.

I'd also lower the rpm delay from 5,000rpm to 2,000rpm or so. As well as lower the pedal enable to 65%.

Then I play around a ton with timing and the spark correction tables. Like the timing adders from gas/E85 and the IAT adder that like to remove a lot of timing when temps are only 70-90 degrees. As well as slightly changing the minimum timing advanced to around -5 to 0 degrees at high rpm so the timing doesn't drop to -20 to -25 on the shifts. It's still pulling it away to help but not as drastic.