1979 Gbody wagons used a mechanical fuel pump to feed a carburetor. Swapping in an L59 LS based engine with EFI requires an electric fuel pump.
Some Gbodies came with fuel injection and the OEM fuel sending unit uses an electric fuel pump so they can easily be used for this LS EFI swap. However, none of the Gbody wagons came from the factory with fuel injection. Why then can’t we use the EFI sending unit from one of these Gbodies in our wagon conversion? Because the Gbody wagon has a gas tank unique to the Gbody wagons and therefore unique sending units.
There are a few solutions to this issue. I chose using an EFI sending unit from a 1987-1994 Astrovan. It is not an exact bolt-in sending unit. It does require a bit of modification to the locking tabs on the sending unit itself. I chose the FG18B unit which has barbed connection fittings. I modified the barbed ends by removing the barb so I could attach a Dorman steel to nylon compression fitting. FG18A has threaded fittings, which may be more useful to others.
The FG18A sender would be the wise choice for anyone using AN fittings and braided hose. The FG18A has threaded fitting sizes of 14 x 1.5 Inverted Flare and 16 x 1.5 Inverted Flare. You will need adapters from metric to AN. These are readily available thru and vendor selling AN fittings. Examples would be “Earl’s 9894DBJERL” and “Earl’s 9894DBHERL”.
There are 4 connections on these sending units (FG18A and B). They are supply, return, evap and vent. I used the large one for the vent even though there is no check valve for safety in a roll over accident. I had tried the smaller evap line, but had trouble filling the tank because the pressure would continuously shut off the fill nozzle unless I went very slow on fill ups. So, I changed it back to the larger tube. I simply ran the vent hose up the filler neck, zip tied it on and added a vent/filter end to keep bugs and dirt out. The vent hose/tube just needs to terminate higher than the tank. I simply capped the unused evap line.
The wiring colors are typical amongst most GMs, especially of the years 80s, 90s, 00s. Gray is pump power, Purple is sender signal and Black are the grounds for pump and sender. I used the oem Gbody wiring for the sender and just connected it to the original sender wire at the back of the vehicle and grounded it in oem location also. Of course new wiring was ran for the pump since it was non-existent on the ’79 Gbody. A Weather-Pack style connector replaced the new sender connector so I could shorten up the wiring on the unit and still have a connector there at the tank for future remove/replace convenience.
Here’s a comparison of the stock OEM wagon sender (left) and the FG18B Astrovan sender (right).
EFI requires a baffled tank so that fuel starvation does not occur by sloshing away from the pump on extreme acceleration or turns. While the wagon tank does not have EFI baffles, it does have a half-tank baffle. This seems to be sufficient to keep the pump from fuel starvation. At least in my case, I have not had any issues.
I used a Kemso 340LPH pump from Ebay. I have had zero issues with this pump, but I do recommend using the Walbro brand. While the Kemso pump does have good reviews, the Walbro is more of a standard and has many more positive reviews.
For the rest of the system, supply and return, I used Dorman Nylon fuel line and quick connects which was OEM standard on many 90s and 00s GM fuel systems. If using a fuel rail without return line, you can use a Corvette fuel regulator closer to the tank which integrated the return line in it and makes for a shorter return line.
I ran the nylon lines along the frame rail with the brake line. Up the firewall and to the fuel rail.
I used Dorman steel to nylon compression fittings to connect the fuel line to the sender. I cut off the barbed connection end and sanded down the steel tubing a slight bit to allow for the compression fitting to slide on.
This being an L59 (Flex Fuel), I reused the OEM Flex Fuel sensor from the donor 2003 Suburban. After mounting the new filter (Motorcraft FG-986B) and sensor on the frame under the driver area, I made a sheet metal cover to protect them from road debris.
This is the list of the Dorman items I purchased. I did not use all of these items in my build:
Dorman 800-072 ⅜” nylon tubing
Dorman 800-071 5/16″ nylon tubing
Dorman 800-082 ⅜” quick connect
Dorman 800-086 ⅜” 90 quick connect
Dorman 800-323 ⅜” 90 push connect
Dorman 800-080 5/16” quick connect
Dorman 800-081 5/16” 90 ell quick connect
Dorman 800-321 5/16” 90 push connect
Dorman 800-223 ⅜” nylon to steel compression union
Dorman 800-226 ⅜ nylon to nylon compression union
Dorman 800-145 ¼, 5/16 and ⅜ nylon to nylon compression union
Dorman 800-135 ¼, 5/16 and ⅜ nylon to steel compression union
Dorman 800-084 5/16 steel to ⅜” nylon straight connector
Dorman 800-092 90 ell 5/16 steel to ⅜” nylon quick connect