Squarebody Adventures

One man's adventures of rebuilding a 1987 GMC R1500 Longbed

E85 Fuel System Upgrade (INWORK)

Below is what’s required for switching to EFI but maintaining the stock TBI setup.

Understandings

Parts

Fuel Tank

Make sure the fuel tank you have has the baffles in the bottom from the 87 R10 Fuel Tank. My 1987 R1500 truck had a new fuel tank installed when I bought it but when I dropped the tank it had the older style non-baffled fuel tank installed. My truck originally came with dual 16-gallon tanks. I chose to convert my truck to a single drivers side 20-gallon tank. Below are the two OEM tank sizes.

Fuel Sending Unit

Option 1: Modify fuel sending unit

Make sure you buy the correct fuel sending unit for the side tank you will be upgrading. You will still need to remove the fuel sending unit(s) and modify the inlet and outlet lines so you can add on the hard line to 6AN fittings. On the fuel sending unit you’ll need to use a hacksaw or cut-off tool to cut the metal flares off the inlet and outlet tubes. Make sure you use some air to blow off any metal shavings.

I ended up buying a cheap TRQ drivers side fuel sending unit on Walmart.com and I would not recommend it. The construction felt flimsy compared to the Herko or Spectra units.

It’s not required and would only be for aesthetics but you can convert the EVAP tube to AN fitting. If you decide to, you’ll need to cut off the flare and would need a connector. Even the pre-fitted fuel sending units don’t convert the EVAP line to AN fittings. I chose to use fuel injection hose clamp to hold the hose on.

Option 2: Buy pre-fitted fuel sending unit

Purchase a fuel sending unit that comes pre-fitted with 6AN fittings built-in. I found this method to be much more expensive than purchasing an OEM fuel sending unit, modifying it, and adding on compression fittings.

Fuel Sending Unit Note

Before you install the fuel sending unit into the tank. You will want to take a multimeter and check to see if the float is reading correctly so the fuel level on the gauge will be correct. The stock ohms are 0 - 90 ohms. The unit I ordered read 1 ohm to 91 ohms so it was off a little but it won’t be noticeable on the fuel gauge.

Fuel Pump

Fuel Filter

Depending on if you want to switch fuel filter styles multiple options will be listed but you need a 10 micron filter. Each option has it’s pros and cons but the option you select should be determined based on the fuel hose kit you purchase.

Option 1: Use stock C-10 fuel filter

This is the simplest option and the option I chose to use. Based on the hose kit I purchased I probably would have done Option 2 if I did it all over again. The stock fuel filter has different threads so you’ll need the 2 adapter fittings listed below.

Option 2: Use newer GM quick connect fuel filter

This is a great choice if you buy a 6AN LS swap hose kit because it will come with fittings for this type of filter allowing you to maximize the use of the fittings you have and not need to purchase additional adapter fittings. The kit I purchased had 2 x 6AN 3/8” quick connect fittings.

Option 3: Use an 6AN fuel filter

This is the more expensive option but allows you to stay with an 6AN filter without having to use any adapters. If you purchase a filter make sure it’s not a filter just using adapters to make it work otherwise you would be better off selecting Option 1. I found the 6AN filters be more of a cost in the long term maintenance since they are more expensive. I also did not like the idea of a reusable filter that could be cleaned. That seemed like more of a mess and aggravation than simply replacing a fuel filter.

Option 4: Use the Corvette Fuel Pressure Regulator/Filter

I don’t recommend this option for use with the stock TBI. The stock TBI has a fuel regulator built in. Understand if you plan to LS swap later you will have to change to this option. You can get these filter/regulators with push connections or 6AN connections.

Fuel Line

For this you will need about 40 feet of PTFE 6AN fuel hose. Depending on the routing and decisions you make can get by with less or you may need more but I found about 40 feet to be enough. I bought a 25 foot LS Swap kit on Amazon and then I bought a smaller 6AN kit on eBay. The kits give you the hose and an assortment of connections. You can buy it all separate but I found buying a kit gave me just about everything I needed. I’ve added notes here where I thought I could have made better decisions for better utilizing the connections I had.

Additional Fittings

TBI

For the connection to the TBI you will need two fittings. I found a kit on eBay that sold both connectors for around $20. Keep in mind that you’ll still need to use the pod adapters connected to the TBI. See the example images for the assembled fittings.

Tank Disconnects

I chose to have a disconnection point between the fuel sending unit and the when the hoses crossed over the frame rail so it would be easier to drop the tank in the future. Here you’ll need two 6AN male to male connectors.

Fuel Filter Disconnect Location

I also chose to have a disconnection point for the return line at the same location as the fuel filter instead of having a long run of hose all the way to the TBI. You will need one 6AN male to male connector.

Dual Tank

If you plan to use the dual tank system then you will need additional connectors to convert the switching valve to 6AN fittings.

Fuel Pressure Gauge

If you want to add a fuel pressure gauge you will need an adapter fitting. I found a 0-100 psi gauge and fitting on Amazon for under $20. Later on you may want to purchase a higher quality gauge or go the route of using a fuel pressure sensor and a remote gauge. If you plan to stay with the TBI then you can get a 0-15 psi gauge but the point of this conversion is to eventually go fuel injection so you will want a 0-100 psi gauge.

Testing

When you build your fuel lines you are going to want to test them with an air compressor. The LS swap kit I purchased came with the fittings needed and then I had some air line quick disconnects left over. I set the pressure on the air compressor to 110 psi and then checked all the fittings with soapy water for bubbles. When building the fittings you’ll want to apply thread tape to the NPT threads but not the AN threads. The AN threads are self sealing but you should apply a drop of lubricant to the AN threads.

Clamps

Most of the clamps you have for the old fuel lines are probably metal and/or 30 years old. You’ll need 1 set of rubber cushioned stainless steel clamps. I ended up buying a pack of 20 on Amazon for under $10. A 20 pack should be enough to replace the old clamps.

Notes

While you have the tanks dropped there will be other things you’ll probably want to replace and/or do.

You may want to purchase new tank support brackets. Mine were very rusted and I ended up snapping the bolt on the front tank bracket strap when I was removing the tank. If I was going to order 1 tank bracket I may as well order both tank brackets. I was able to pick up both tank brackets from Jegs for a decent price. While I was replacing the tank brackets, I also chose to purchase a new bolt set from LMC Truck for mounting the new hangers and the anti squeak kit.

Cleaning up the frame. Depending on how rusty and dirty your truck is you may want to take a wire wheel to the frame to knock off the years of rust and dirt. If you do this then you’ll need to spray on some kind of protecting paint or undercoating.

Understanding Minimum AN Hose Bend Radius