Need answers to using Flex fuel on an Fbody? Come in.
 

Ok so I have been doing a ton of research on the concept of using the Tahoe file in the Fbody. Lots have people have tried and though there is success, many people had issues with airbag lights, service engine lights and passing emissions. I have some answers for you guys. This post will simply focus on getting a file into the ECU that both works and is happy in terms of dash lights. This thread assumes you have hooked up your flex fuel sensor. In my future post I will discuss how I added a flex fuel sensor to my setup.

Tools needed:

HPtuners
PCMHammer
VXDiag Nano (or equivalent tool compatible with PCMHammer)

Lets start with the basics. We are using a P01 ECU (411). We need to use Tahoe Flex Fuel file, which can be found on the tune repository if need be. The OS is 12216125. This OS WILL work on the ECU, no re-pinning or anything. It is different from the stock Fbody OS.

You port ALL the changes over to the Tahoe file from the Fbody file. Do a compare with it vs your Fbody tune, CTRL 5, right click and copy over all differences. In my case i did change the system platform to an Fbody under "system". Once that is done, you save it and write entire to the ECU.

Now you have a Tahoe/Fbody hybrid file in your Fbody, however you will have an airbag light and maybe an oil change light but that eventually goes out on its own. So here lies the issue. When you do a "write entire" your going to flash the Tahoe VIN as well. This is what causes the issue with the airbag. The car just gets confused and can't communicate with the SRS system. Simple fix, you now need to take PCMHammer (thank you everyone who worked on this project) and flash your Fbody VIN into the PCM. This will put the SRS light out and now you are in business. Another thing I noticed is when I ran the emissions check mostly everything was insta-completed. No drive cycle in my case (except the EVAP one, that one was incomplete). I haven't driven it to check cruise control yet, which i heard was another issue. A/C worked fine due to HP tuners havent the ability to switch the AC style now.

How do we flash with PCMHammer? Couple of choices. In my case, I wanted a tech2 for my car. I decided on a Nano off Amazon. It can do everything a Tech2 can (MDI and MDI2 as well), include program with AC Delco SPS. Its very helpful for those issues like bleeding the ABS. Its $125 for a cabled version of it off Amazon.

In my case right now I have a service light because I have no flex fuel sensor hooked up but the car is running like e35 so it defaults to a stoich of 12.4:1 if it sees a failure in the sensor (which mine is seeing) so its fine for now. I will have a sensor hooked up in a few days.

Thank you for everyone who had discovered these solutions in the past. The threads kind of disappeared or are overlooked. I can't take really any credit for finding these solutions. Thank you to everyone who worked on PCMhammer because without it, the simple task of flashing a VIN becomes expensive for us HPtuners users.

can you log flex spark with that OS?

Haven't tried much logging yet. Unfortunately I have a fiancee that is demanding I go to the wedding venue today so I haven't had time to play with it just yet but its a start. Otherwise I logged for a split second and the car looked normal and happy.

btw thank you for those bin files! You played a part in all of this as well!

hey no sweat! if you get to logging flex spark or flex advance let me know...i'm still having problems with mine

What is your setup anyway Doug? I should have the flex sensor tomorrow but I don't have the pins to punch it into the ECU handy so I will have to wait for them.

I'm using that OS on my NA truck. For some reason it does not add any flex spark. The table is there under spark adders, and populated. And the content sensor works and the fueling is right, just no added spark. I can't even see the channel in loggable parameters when I re-poll the computer.

I have another file, same OS from a vin Z engined vehicle that I know for sure came with flex from the factory but I don't have a way to flash bin files yet.

I do have the p59 flex working though thanks to a bunch of other folks on here. So many have helped me I cant even remember them all (and some probably wanna keep a low profile anyways)

Still waiting on the plug at the moment. But here is where I am at so far...

I have it functioning, its defaulting to 12.4:1 with no sensor (and thats pretty close to what is in the tank so it runs fine). My only issue at the moment is the SES light and the TCS light. I pinged all the modules and I get a response back however I am getting the U1000 code. Whats weird is that it complains that while the TCS light is active, I will have no ABS which isn't really true. I can still make it blink the "low traction" light and my ABS INOP light always stays off. I tried re-syncing the ICP and the SRS system to try and get rid of any communication errors that might be present there as well (I was really just playing around with the tech2 program). I am not going to tear my hair out yet until I get the flex sensor hooked up and that code goes away in the ECU. Another thing is that the ECU is set to not report an error with U1000 and to not enable the SES lamp. Unfortunately its just the generic code saying its not receiving the message it expects.

The oil change light would stay on for a little bit then go out but that was an easy fix, i used the tech 2 to reset the oil to 100% and that was gone.

I have been wanting to convert, but does anyone have a guide with part numbers of whats needed to go flex on a f body? I have no issue with the pinning its getting the correct fuel connectors to put the sensor inline, I'm not sure on.

Also have these always been an issue on the f body when running this OS? I have never seen anyone complain about these issues?

The flex sensor is hooked up and functioning. Currently I am running about E55. The transition was pretty seamless, no stumbles or really waiting per say in terms of filling up vs driving. I made some timing tables for it and just let it rip. The car, as it sits at around 5-6psi, is seeing 24 degrees of spark peak with no knock. That up from about the 18.5 I could get out of it with similar intake temps.

The car is an auto car. I have no real issues running the OS other than my TCS and service vehicle light being on. There is DTCs in the abs and IPC modules, both U1000 (communication errors). I tried clearing them but they come right back. Havent really figured out a solution to this yet.

In terms of parts it really depends on your setup but you will need a flex sensor first and foremost. I used the continental one which can be obtained off Amazon for $28 and a 6 foot harness made by boost monkey also off Amazon. You could run the sensor on the feed line if you so desire but I have it on my return line off my rail. The sensor doesn't really cause any kind of restriction per say to the line but I prefer the fuel to pass the sensor on the return and under very little pressure. The senor should be able to hook right into your stock feed line quick disconnect, then you will need a double ended quick disconnect to go from the sensor to the rail. If i was using this setup I would use a Russell fitting number 644123 (3/8 quick disconnect to 6AN male) x2 with a piece of 6AN line between the two fittings.....done. You will also need micro pack 100W ends to feed into the ECU, which can also be obtained from Amazon.

Thanks for the clear instructions. Are you running stock rails?
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Yup stock rail. Running the same return setup from this thread:

https://ls1tech.com/forums/fueling-injection/1882763-how-adjustable-fuel-pressure-regulator-w-stock-ls1-fuel-rail.html

I plumbed my fuel sensor into my retuned line with two of those Russell fittings and female hose ends.

Where do you get pcmhammer

For reference all the info about pcmhammer is located in the opensource thread just above or below this thread. It has been created by the hard workers in that thread so be sure to thank them for their work. It will communicate with the nano that I mentioned in the first thread. Below is a link.

https://github.com/LegacyNsfw/PcmHacks/releases/tag/PcmHammer

and to answer your question Doug no I can not however I will try hooking up torque and finding the address/formula and see if I can add it to hp

A quick update for you guys. Programming wise, I havent had any luck with the TCS light. I have a feeling its because the Tahoe has stabilatrack or whatever, might just not understand our cars tcs vs the tahoes. Not sure. However I have found that plugging in a non-tcs module into the car (at the ABS pump) does remove the light. However it will not bolt onto a tcs cars abs pump.The tcs cars are obviously 4 channel and have 8 abs "pins" on the pump body and the module is physically longer to accommodate this. The non-tcs cars have 4 pins on the pump. The electrical connections are identical though. Maybe someone can figure something out there with that info.

glad to see you're still chipping away at it.

trying when the fiancee allows. I just got finished fighting the dreaded seized rear control arm bolt on the passanger side so my time was consumed in that. Once the car is back together I will see if I can get that flex fuel spark thing working. All in all, no issues. I tested cruise as well, fully functional.

From looking at the pcmhammer page on github it seems like only reading is working/tested, not writing yet, but you were able to use it to change the VIN? That's my main hangup with trying this. My car doesn't have TC so I guess that shouldn't be a problem (?) You still get unexplained comm errors?

I have u1000 codes in the ipc and abs system. Vcm and srs report nothing is wrong. I believe the abs and ipc are reporting errors simply because the tcs and its associated light are not functioning/on. You will probably have zero issues. However I can try another test for you tomorrow. I'll plug the non abs module in and clear the u1000 codes and see if it still reports any problems. If it doesnt, you're golden.

yes pcmhammer will still write a vin no problem.

So a minor update. As far as a solution goes for the TCS light I think i have one, from a mechanical standpoint. If you decide you don't want TCS but want to retain cruise and abs like me, I suggest this. I have a non-tcs abs module/pump.Obviously its for a 3 channel car vs my 4 channel. On the pinouts, pin 4 needs to be moved to pin 3. Other than that, let the car read off the rear left wheel speed sensor as its main sensor (pin 22 and 23). On a non-tcs car this is where the car gets its signal from the diff mounted speed sensor. Run a single line to a splitter at the differential and connect your brake lines. Done. One of my intermediate brake lines burst recently which has prompted me to replace them anyway So i can try this out and see what happens.Should work I would think. This will remove and shut down the tcs and service vehicle light.

Also for those with a blinking check gauges light, use a different file, that's likely the cause. And if you have that annoying change oil light, if you use your tech2, nano or whatever, you can reset the oil life to 100 and eliminate that light as well (it eventually goes off on its own but its takes an annoyingly long time)

https://cimg8.ibsrv.net/gimg/ls1tech...d6660c7bcb.png