Walbro Intank Fuel pump replacement 99+ f-body
11/7/06
It's been a long time since this was updated and I have noticed a lot of traffic lately so it's time to add a few things since my original install back in early 04. This writeup originally took place back before the Racetronix kit came out for the 99+ bucket fuel pump setups. If you have the extra money for the Racetronix kit I highly recommend going that route as it keeps the factory bucket fill setup in place and fully functional. Otherwise this still works well enough to be an option IMO at around half the price. Also I mentioned in this writeup to get high pressure fuel injection hose, well APE came out with the factory style "straw" looking hose. This is a better option than the rubber fuel injection hose as it will never get soft or have a tendency to split after time. Go to http://www.autoperformanceengineering.com/ to get the factory style flex hose, it's cheap and a better option than the high pressure fuel injection hose. You will have to wrestle to get it on but it's better. For those of you who came here from a direct link you can get back to my site by clicking on this link http://www.gonicd.com
3/29/04 Write-up and pictures by Nicolas DesJardins
When installing an aftermarket in-tank fuel pump for a 99+ f-body there are a few minor things that have to be taken care of for it to work properly. This write up will skim the basics of the required modifications to the pump bucket and general installation for a walbro 255 lph fuel pump. The new fuel line that the walbro kit comes with is too short so you will want to pick up 6 inches of 5/16" high pressure fuel injection rubber hose, fuel injection hose clamps, and a small stainless steel clamp to hold the pump inside the rubber boot. The fuel injection hose clamps are very necessary as to not shred/cut the hose like a standard worm gear clamp would.
I prefer to use the access hole method of installing a fuel pump. This involves cutting out a hole in the car's flat upper trunk area. It literally makes swapping fuel pumps a breeze and if you ever have to delve into it again you will be happy you aren't dropping the tank time after time. Cutting the hole takes around 5 minutes if you use a dremel with an HD cutoff wheel. You must be very careful and not go too far below the surface so you don't cut fuel lines and wires. Before you start making cuts bleed the pressure from the fuel system at the shrader valve up front on the fuel rail and disconnect the battery. Use the two pictures below to see where you have to make your cuts. It measures from the bottom to the top of the cut about 7 inches. You can click on the pictures in this write up for higher resolution versions.
Now to remove the pump disconnect the lines and use a large flathead screwdriver and hammer and pound the retaining ring off counterclockwise. It does take quite a bit of pounding to rotate that ring to the unlocked position. Then just pull the pump out and be careful not to catch the float when you pull it out. After it is out you need to disassemble it. There are two fuel lines that come from the pump and you can just cut them as you won't be reusing them with the new pump. Then just push in the two retainer tabs from the outside bucket and pull it apart being careful not to pull the wires off the fuel level sender. Below is what it should look similar to at this point.
Now cut the existing pump's electrical wires somewhere in the middle since the new walbro pump has it's own connector and pull the pump out of the rubber boot and toss it. Cut open the bottom of the rubber boot so the new walbro barely slides through it and use a stainless steel clamp to hold the new pump in the rubber boot so it sticks down about 3/4" through it. Attach the new section of 5/16" high pressure fuel line that measures approx 5 3/4" long and tighten the new fuel injection hose clamps tightly to prevent it from blowing off. The clamps that come with the standard walbro kit are the worm gear type and will chew up the fuel line. Use the butt connectors that come in the kit to attach the new connector for the pump, black to black and gray to red and plug it in.
Now you have to modify the bucket since the factory fill system no longer functions as designed. With the stock pump it had a pickup directly underneath the bucket which was connected to the pump to fill the bucket so the pump could just draw from the bottom of the always filled bucket to feed the motor. This was designed to keep the pump always in the fuel to keep it cool and keep fuel completely around the pickup so no air could be sucked in around hard corners or acceleration. With the aftermarket pump this design doesn't function anymore so we need to put some cuts in the bucket to keep fuel around the pump and drop the pump pickup below the bottom of the bucket. You will still not want to let the fuel level get very low, especially at the track never run below a 1/4 tank. Below are pictures of how I modified my pump bucket and how the pump fits in the rubber boot.
Now try and put the pump back together carefully squeezing the upper assembly together since it is spring loaded. You will have to bend the fuel line to get it to compress enough to get the upper assembly back into the bucket. You want the bottom of the pump to be resting on the bottom of the bucket and have the pickup of the pump sticking through to the underside of the bucket. There may be a few ridges on the inside of the pump bucket that you can shave down with a dremel so the pump rests flatly on the bottom of the bucket.
If everything measures up correctly and fits nicely you can attach the pump filter sock to the pump from underneath the bucket.
Here is the fuel pump fully assembled ready to drop back into the tank.
Now you just need to drop that back into the fuel tank and tighten the ring clockwise to lock it back into position. Then reconnect all the fuel lines and electrical connections, reconnect the battery, and fire it up! You can make a panel that covers the hole in the rear out of some sheet metal and screw it down, seal it with RTV or whatever you want to do. GM should have put an access panel there from the factory anyways. :)