How to build a Primer Timer and cure your Viper Fuel Pump Starting Problem

Tom F&L GoR

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For a time I built and sold these so I am sure they work well. Here are the instructions on how to do it yourself. I hope this is explained well enough to make it into the How-to section.

Vipers may experience prolonged cranking when attempting to start, but once the engine actually fires, it runs fine. Often this issue is caused by a faulty check valve that is supposed to prevent gasoline in the fuel line from draining back into the fuel tank. The long delay to restart is because the fuel pump has to first refill the fuel line before any gasoline can reach the injectors. To make matters worse, the PCM only allows the fuel pump to run for one second if the engine is not running, and then only intermittently during cranking. This is why multiple key-on, key-off actions help- you are refilling the fuel line one second at a time before attempting to crank and start.

The problem can be repaired with a complete fuel pump module replacement, but the Primer Timer provides a less expensive alternative. To operate the fuel pump during cranking, the PCM completes the electrical circuit by making a connection to ground. To extend the fuel pump run time, an ELK960 circuit board acts as a second, longer time period path to ground to keep the fuel pump running longer. The ELK960 is triggered by sensing the 12V power at the fuel pump. After a few seconds (time length is adjustable) of being “active” it becomes dormant for the remainder of your trip. This means it won’t keep running the fuel pump in case of an engine stall or accident and that if the ELK 960 fails, the Viper reverts back to the original, long cranking time condition and does not disable the car.

The ELK960 delay timer circuit board is available from home security stores for about $26. Try this one: Home Security Store | Home Security Camera | Wireless Security Systems

The enclosure (plastic box) is available from electronic supply stores for about $6. It can be found here:BOX 4.38X3.25X1.41 BLK - 032 BLACK

You will need three clip-on wire connectors as used to add trailer lights, a wire cover to bundle the additional wires, and a small rubber grommet with an inside diameter to pass three wires. It should cost you less than $50 to build one.

Setting up the circuit board will look complicated. It isn’t, it just is complicated to describe it in text! The instructions that come with the board will also help explain the function. I am simply stating how I did it and that it worked.



I used double face sponge tape to mount the circuit board into the enclosure. Make the wires at least 12”-18” long so you can position the enclosure wherever you want in the trunk. Drill a hole in the side of the box, install the grommet, and pass the wires through while attaching them to the board. It is highly likely that another wiring setup could be used because the ELK960 is fairly versatile. This worked for me:

From the top,
· Red wire connected to the upper terminal labeled “+” This is the power input.
· Black wire connected to the second terminal labeled “-” This is the ground input.
·T he third “TGR” terminal is not used.
· A jumper black wire connects the second terminal “-“ to the fifth terminal labeled “COM.” This is the common pole of the relay.
·T he green wire is connected to the fourth terminal labeled “N/O.” This is the normally open side of the relay that switches to ground to run the pump.
· The bottom N/C terminal is not used.

On the upper right corner is a blue block with a white wheel. This is the adjustment for how long the pump runs.

There are several jumper settings. (Most of these are the default settings.)
· JP1 set to SEC
· JP2 set to 1-SHOT
· JP3 set to BEGIN
· JP4 set to A
· JP5 set to “-“
· JP6 set to 12V

The assembled unit is mounted in the trunk. It is therefore not exposed to heat, water, or road damage. In an RT/10 it can be mounted in the right forward area of the trunk where the cable bundle enters. The wires that need to be found are in the tape and plastic-covered bundle.

In a GTS it is located at the left wheelhouse, next to the amplifier. The red and green wires connect into the nylon-covered bundle, and the black wire connects in the plastic covered bundle. For ease of installation, the amplifier can be moved by using a 10mm socket to take off the clamp and the bracket.

The installation consists of locating three wires:
1. Power supplied with key-on (zero volts when key-off, 12V when key-on)
a. In a Gen 1, connect red wire to A21 14DB (dark blue)
b. In a Gen 2, connect red wire to F12 18 DB/GY (dark blue/gray stripe)
2. Ground by PCM to complete the circuit (infinite ohms to ground when key-off, cycles to no resistance to ground when key-on.)
a. In a ’96 GTS, connect green wire to K51 20 DB/YL* (dark blue/yellow stripe)
b. In a ’97-99 GTS, connect green to K31 20 BR/VT (brown/violet stripe)
c. In a ’97-99 RT, connect green to K31 20 BR (brown)
3. Any solid black wire ground for the taillights
a. Connect to black wire
b. In a ’97-99 GTS, can use pin 7 ground of rear window defogger relay

The three wires are intercepted with clip-on wire clamps and attached to the timer box with female spade connectors. Use black tape to re-wrap the wires and pliers to squeeze on the wire clips.

Before closing the box, have someone turn the key to the run position. You may hear the fuel pump run, but the red light on the board will also illuminate. Adjust the pump run time to about 6-10 seconds. Close up the box and mount it out of the way. In an RT/10 the box was double-face taped to the trunk wall. In a GTS it was placed behind the carpeting. Make sure you have long enough wires!



In an RT/10, the wires are found as the bundle enters the trunk in the right forward corner. The box was attached to the forward bulkhead with double-sided adhesive tape.



In a GTS, the amplifier and bracket was moved to reach the relays (black-fuel pump and red-heated rear glass.) Two wires are in the nylon covered bundle and one in the plastic bundle. The box was placed behind the carpeting.
 

bvk

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just bumping this to say thanks for the write-up. Been dealing with this very issue for a while now on my 98 GTS. replaced plugs, fuel filter, got the injectors fully serviced and balanced... was just about to start chopping my way into the pump housing area when i found this.

have ordered an ELK-960 and a box, will be giving this a go soon!

thanks again for the innovative solution, seems much easier and cheaper than thousands on a whole new fuel system or even a replacement pump module/housing, which are getting quite hard to find.
 

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