Upgrading to a higher rate of flow fuel sending unit Gen 5

[ViperNC]

I've noticed over the past few months that when I'm hard in the throttle above 4500 RPM's I have a slight spark knock. At first I noticed this late Fall when I had the windows up for the first time driving the car and I thought it was probably just Winter blend gas which created the same issue in my old GT500. By mid Spring when Summer blend was at the pumps the issue went away so I figured it was just a fuel problem to live with. However, the issue persisted this year as we approached the Summer months so I called Prefix and talked with Scot. I've got a Stage II 9.0L build and we checked the build date at Prefix to learn this motor was completed prior to Prefix recommending the use of an aftermarket fuel sending unit which increases the rate of flow by 130 liters per hour. Scot told me they didn't start using this pump until some time after my build had been completed and now they use it on all the Extreme builds. He also shared with me that the 9.0L was installed at Woodhouse Dodge in Nebraska so I called the dealership to see if they had the build information in their database and luckily enough they did. We confirmed the car still has the stock sending unit so the belief is the engine is demanding more fuel at full throttle/higher RPM's than the stock unit can offer. With that said, I ordered the upgraded unit from Scot on Thursday of this week and it arrived today. Looks pretty straight forward:

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Scot gave me a couple of quick tips and I decided to tackle this one myself. To access the fuel sending unit, you first have to remove the side panels just behind the seats and also the carpeted panels in the cargo area. Once removed, there are two 10mm nuts on either side under the rear brake duct hoses you will need to loosen so you can gently lift the carpeted panel directly behind the seats which will allow you to release pressure on the carpet covering the access panel to the sending unit. You can now gently remove the carpet on the shelf by lifting over the tabs on driver and passenger side, then slide out towards the back of the car, and then lay aside. This gives you direct access to the panel:

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There are 4 aluminum rivets that will have to be drilled out:

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[ViperNC]

I used a 9/16 drill bit and carefully drilled out the center of each bit until loose. Then using a small flat head screwdriver, lift and remove each rivet which holds the plate in place. I used a shop vac to vacuum up the aluminum debris before removing the plate and then continued to get the rest of the aluminum shards vacuumed out around the sending unit on the top of the fuel tank. There is a styrofoam cover on top of the sending unit which comes off easily. Afterwards, I took the extra step of cleaning the area thoroughly to avoid getting any dirt in the tank once the factory sending until was removed:

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At this point, you need to depressurize the fuel lines so I removed the electric connector to the unit and attempted to start the car a couple of times. This relieved the system of pressure so I could then remove the fuel line connector and wipe up a slight bit of fuel that leaked out. Unfortunately, I ran out of time to finish the job today. Oh well.... Happy wife, happy life. Will resume in the morning.

[Loud]

Nicely done, Blake. I had Eddie do my install :)

[ViperNC]

On to day 2 and finish this project. I should have known this would take more than an hour so why I started yesterday is beyond me. Before we get going, let me suggest that anyone attempting to do this project needs to have some basic knowledge of mechanical and electrical components and I highly recommend having a friend come help for a second set of hands. The locking ring is VERY tight and I bet there is a specific tool (which I didn't have) to get it loose enough to unscrew by hand. Without the tool, I was forced to improvise, adapt, and overcome... with a hammer and a punch with a flat blunt edge. Yes, I took a hammer to my Viper and can hear the groans as I type this. :slap: Carefully, I used the hammer/punch and went around the locking ring at every tab and it finally began to rotate. Once it was loose enough to be removed by hand I disconnected the electric coupling and fuel line, drained a the fuel out of the line, wiped it up and then removed the fuel sending and gauge assembly:

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Once out of the car, I covered the exposed fuel tank/fuel with a plastic bag to ensure no debris blew in. Next, you have to drain the fuel out of the unit. I took this opportunity to cut my new hardware to use instead of the rivets:

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Once all the fuel is out, its time to take stock of what you're dealing with from an electrical standpoint and I can't stress this enough. The new sending unit has slightly different wiring than the stock unit and you need to pay close attention to where each wire is pinned in the coupling (my friends hands coming in handy). You can take a mini flat head screwdriver and release the pinned wires out of the coupling and put them into the new coupling in the correct order. Make sure you mark which yellow wire is closest to the black wire otherwise your fuel gauge will no longer work properly:

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Now time to take the unit apart. This is where a second set of hands comes in and almost a must. There are three sections to the unit and you'll need to start by removing the top section with 3 connector tabs on the inside which will be a little tough to get. I used a long small flat head screwdriver to move the plastic latch around the tabs and then gently wiggled the top section off. All wires still connected, but now you can also remove the bottom reservoir from the center filter section:

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Its a good idea to clean all the parts at this point and I used some brake cleaner to get some debris out of the bottom reservoir and then cleaned a couple other areas as well. Take note of the resistor on the top which the wire hanging down is going to have to be soldered onto the new sending unit wires later.

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[ViperNC]

Now its time to remove the old sending unit and install the new unit:

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Take the fuel filter off the old unit by using a flat head screwdriver and prying off the filter. This will then allow the locking assembly around the fuel sending unit to come off and then replace with the new unit and install the new fuel filter by pressing onto the inlet of the sending unit:

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This is where you need to look at how the old sending unit is wired into the assembly:

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After talking with Todd at Prefix this AM (he was very gracious to make himself available on a Sunday) I cut the black wire on the new unit and striped/soldered to the existing black ground wire and then heat shrinked the exposed wire to ensure it was completely secure. Then I had to cut the wire going to the resistor so I could begin reassembling the sending unit in the bottom of the unit. This is also the best time to change the green rubber seal and replace with the new black rubber seal.

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[ViperNC]

Now its time to connect the internal fuel lines and use the crimps that came with the new sending unit. Once you have that done, time to re-assemble the rest of the unit:

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Now to re-install in the car. You'll want to use a light amount of grease on the outside of the new black rubber seal which will make it easier to push the assembly back into the fuel tank. Make sure the new seal slides into the tank evenly so it doesn't get pinched. You'll have to work at this for a while making sure the seal seats properly. I used the rubber handle of my hammer to help push while my friend began to turn the lock ring until it grabbed the threads. A few more taps with my punch and hammer to rotate the locking ring to a tight position and then reconnect the fuel line and electric coupling. Time to fire up the car and check for any leaks. Once you have determined everything is good to go, reinstall the carpet and interior panels and you're off and running. I did notice a little knock with the first couple of hard 2nd gear pulls and then it was gone. Problem solved! Hopefully you'll find this helpful and sorry if some of the photos are sideways or didn't load properly.

Time to head to the track or your favorite set of twisties. :drive:

[DZnutz]

Fantastic write up. I also assume that by "sending unit" you actually mean the fuel pump correct?

[ViperNC]

Fantastic write up. I also assume that by "sending unit" you actually mean the fuel pump correct?

Correct. The sending unit/pump is housed in the fuel gauge and sending until assembly. Takes a bit of effort and two sets of hands to get the assembly apart so you can remove the sending unit/pump.

[GTS Dean]

Great write-up!