First thing is first, a HUGE credit goes out to @aaronc7 for his thread below that made my conversion less of a headache:
https://www.corvetteforum.com/forums...uel-on-c5.html

This thread will act as another confirmation on how to Flex Fuel your early C5 (up to mid 2003). Many of this is also outlined in the thread above.

Hardware:
-Early C5 PCM is known as a P01 version. You need to source a P59 from later C5's or other LS variants. Service #: 12586243 Hardware #: 12583659
-E85 sensor comes in different versions but I used a 13577429 with the shorter/more compact ends
-E85 sensor pigtail I found on Amazon with power/ground/signal wires
-Racetronix RFPK-055-340 fuel pump kit. Comes with everything you need including a billit pump bucket, just have to swap the fuel hat over and do some wiring. Other pumps work as well, just source one up to the task.
-Racetronix FPWH-007 hotwire kit for above pump kit
-DeatschWerks 18U-01-0060-8 60lb injectors or equivalent capable of flowing E85 volumes.
-Holley 12-876 filter/regulator with associated fittings to make it work in the stock location
-PCM Green terminal covers I sourced used from Ebay. P01 PCM is a Red/Blue connectors and we are going to a Green/Blue combination.


Software:
For the OS needed, we ended up with the files created by AaronC7 and made some tweaks. This is the 12587603 OS. The other confirmed one is a 12592425 OS.

***Initially we had issues with what we assume was a bad PCM. We got the car running on a 2005 Avalanche truck OS. While this "works" it causes two issues. 1) The cruise control will not work 2) The PCM will only "see" the DS fuel level sender. So if your tanks are actually full, the gauge will only read 1/2 full. Going to a C5 specific OS solved both of these issues.***

I believe this is due to the trucks having a separate/external CC module and only one tank/sending unit.

Wiring:
-Blue connector: two grounds were added at pins 64/67. These were grounded to the frame above the PCM via standard ring terminals and self-tapper screw.
-Blue Connector: added sensor signal wire to Pin 56
-Green connector: Pin 52 (grey wire) moved to Pin 75
-You will also need to ground E85 sensor and power it to a switched 12V source both of your choosing. Sensor ground also tied into above PCM ground location.

Mechanical install:
-I mounted the Holley filter/regulator in place of the stock unit and used AN fittings to mate to stock feed/return from the pump. A new 6AN line was ran to the motor. I needed to bend the brake lines out/around the new filter, but wasn't a big deal.
-At the motor there are more AN fittings along with the E85 sensor.
-Pump install...it's a pump install. Remember to unclip/unpin the sending unit from the assembly and remove it prior to removing the whole assembly so you don't damage it.
-Swap over the hat assembly to the new bucket/pump...wire accordingly and put it back in.
-Pump wiring harness was straight forward and ran through the DS rocker panel up to the motor/alt. (kept from having to remove the exhaust/tunnel plate).

Pictures:

 

Enjoy!

 

At the time of writing this I am in contact with Holley about some strange noise/vibration coming from their filter/regulator assembly. I don't know if the regulator is bad or it is the combination of fittings used to make this work. So far they have said the install does not look like the issue. Awaiting more answers from them.

 

Good job

 

Filter/regulator noise has been greatly diminished by increasing the return line back to the tank with a 6an line:

 

What issues did you encounter before adding the grounds for those two pins?
I ask because I just started my car with a P59 and the fans aren't coming on, and I wonder if that's why.

The fans and relay were tested in the car, and they work, but the PCM doesn't seem to be sending the signal to the relay.
The tune calls for the fans to turn on at 205 and 210, and the coolant got up to 220, and the fans never came on.

Thanks!

 

Honestly, I couldn't tell you. I found a thread where someone added these grounds so I copied that approach. IMO it's never a bad idea to have more grounds lol.

 

Fair enough. Thanks!

 

Most likely the cause of regulator noise. The restriction is already the 5/16" line in the return, but inside the tank seems to neck down as it is bent around:


This may be 100% fixed going to a simple -6AN bulkhead fitting on the steel hat.

 

I need to get off my *** and add the sensor, I flashed everything else into the PCM using Aaron's thread. I did want to add a point of clarification though: the early C5 PCM was known as the LS1A and has less support than the P01. Both the P01 and P59 are known, at least in some circles as the LS1B PCM. The P01 is in fact a late PCM for the C5 as a whole, with the P59 being the latest.

Here's the early LS1A (monstrosity) PCM.




And the LS1B which could either be the P01 (512kb red/blue) or P59 (1mb blue/green, 2004 only I believe), they're identical in appearance. I forget what the year break is between LS1A and P01.

 

I think 97/98 is LS1A but don't quote me!

 

Another great thread. Sorry the car has been giving you fits lately, but this is all solid info and a great project. I remain eager to see if you decide to add a blower kit to complement to corn.

 

No PD is going on this car, I don't care for added weight and complexity. Car will be done after ported/milled heads.

 

This is an uncorrect statement.

 

Aside from minor things like speaker upgrade etc, the BIG projects will be done. Car already has full suspension/delrin bushings/cam/exhaust/intake so, yes, ~450hp and the car will be done. It's a strict goal to keep this a dual purpose car for autocross and daily driving so I won't let this car go too far down the rabbit hole.

Worst thing about moding cars is not having a "plan". So far, my plan is coming to completion of what I want the car to be like.