I have a DIY fix for hard starting (fuel pump check valve) Vipers; now need a Gen 2 volunteer to try it

[Tom, F&L GoR]

Many have heard of or experienced prolonged cranking to start your Viper, yet when it actually fires, it runs fine. The problem is cured with a fuel pump replacement, which for the RT guys, includes a lot of labor. The repair replaces the entire fuel pump module, which includes the electric pump, the fuel gauge sending unit, the pump intake screen, the rollover valve, and the check valve. As has been explained, the hard starting is due to the check valve not keeping the fuel line filled with fuel and the gasoline drains back into the gas tank. When you re-start the car, the pump has to first refill the fuel line before any gas reaches the engine.

What greatly delays your start is a safety feature - the PCM only allows the fuel pump to run for one second if the engine is not running. This is for two reasons: first if you drive, hit tree, engine stalls, fuel line ruptures, gasoline is pumped out. PCM knows engine is off and shuts down fuel pump relay after one second. Second reason is not to flood the engine if the key is on, engine not cranking, and a fuel injector is leaking.

The safety features are good, but means to start you have to crank and crank and it's a looooong time to get it going. It's because the fuel pump is only intermittenly running, so it takes far longer than it really needs to get started. One "cure" is to repeatedly turn the key to run, let the pump run, then off, then run again to run the pump again, then off to prime the fuel line.

The fix - a delay timer relay to extend the initial key-on fuel pump power. This will run the pump for ~10 seconds only upon initial "key-on." Therefore it will refill the fuel line (whether you are cranking or not) allowing for a more immediate start, but for safety will not extend the pump run time should you have an incident later.

The unit is 3.25" x 4.4" x 1.4" and in this shot is mounted in a Gen 1 trunk. It doesn't take up much space.


The skills? All you need is to be able to find three color coded wires in the bundle in the trunk area and use pliers to clip on the wire connectors. The wires are in the bundle coming through the trunk wall in an RT:
* A21 14DB (dark blue; Gen 1) or F12 18 DB/GY (dark blue with gray stripe; Gen 2)
* K51 20 DB/YL* (dark blue with yellow stripe)
* any black wire (ground) used for the taillights

The kit will include the wire connectors, box with the relay inside, wire wrap and instructions (to be written). I figure it will take about 15 minutes to install. If you replace the pump later, the unit can be removed without any damage or sign it was there. If the unit fails, it fails to the original condition of not having the pump run. The first prototype cured a Gen 1; I would like someone with a Gen 2 to try it and take a picture. I'll have parts to complete the next ones arrive on Friday and would ship over the weekend. Assuming the Gen 2 works and no other changes are needed, I expect to sell this for just under $100.

Comments, questions, and volunteers please!

[Matt]

Cool idea. I think I had that issue with my previous '96 RT/10. I just did the key-on prime thing before starting and that fixed it. I'd add this box though if I still had it. My current '97 GTS has no problem starting or I'd give it a try.

Didn't you also have a replacement in-line check valve? Scrapped that idea for this box?

[Tom, F&L GoR]

The check valve became too complicated; it really should have been a pressure limiting valve. It needed to maintain fuel in the line after shutdown, but then also needed to bleed down because the hot engine would boil fuel and increase the line pressure. Without bleeding down, it caused some fuel line or injector o-ring leaks. Fuel is pretty low viscosity and so 100% consistent performance was beyond my garage machine shop capability. The electronic box idea took a little homework, but running the pump longer is something other models of cars do, so it made sense to figure out how to do it.

[Tom, F&L GoR]

Any volunteers? If you are near the 12590 zip code, I'll deliver or help install. Thanks.