Primer Timer: eliminate long cranking and hard starting when fuel check valve fails

[Tom, F&L GoR]

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: http://www.homesecuritystore.com/

The enclosure (plastic box) is available from electronic supply stores for about $6. It can be found here: http://parts.digikey.com/1/parts/788...032-black.html

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.

[Tom, F&L GoR]

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.
· The 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.
· The 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 “-“ {picture incorrectly shows “+”}


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 Gen 1 to ’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!

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[Tom, F&L GoR]

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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.

[Tom, F&L GoR]

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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.

[Tom, F&L GoR]

I used to sell these, but posting for anyone to build their own - it's pretty simple and direct plus may apply to other vehicles as well. This is the latest version of the instructions I've sent out, so should be pretty complete. Enjoy.

[smhog]

Tom, thank you for this. I thought the long cranking was something else, mine does the exact thing you describe.

Question for you. In the install instructions the 1st wire you write where to find for a Gen 1. On wire #2, Ground by PCM, only 96 to 99 are listed. Which wire would Gen 1s use for this?

Thanks again,
Tim

[Tom, F&L GoR]

smhog, you can test if this is the case via the key-on/off method or a pressure gauge on the intake manifold fuel rail.

Sorry about leaving off the Gen 1 info; I had one so I'm surprised it's not written down. The 1994 service manual shows the Ground via PCM wire is K51 20 DB/YL* (20 gauge, dark blue with yellow stripe), same as the '96 GTS.

To ensure this, you can verify the wires at the relay itself. There should be a 14RD/WT (12V from battery), 16DG/WT (12V to pump when relay engaged), 14DB (key on power), and 20DB/YL* (ground by PCM.)

Thanks for catching this. I corrected the instructions above.

[72hemi]

Question for you: can the check valve be replaced?

[Tom, F&L GoR]

The answer is yes, but... IIRC, depending on year, it appears the check valve alone is or is not available. And you need a leaky check valve on purpose, not a "real" check valve. I tried a "real" check valve, but the engine heat on a hot shutdown expands the fuel in the rail and the subsequent pressure in the fuel line will push fuel past the o-rings where the injectors are installed in the intake manifold. So the check valve needs to just keep the fuel line full, and not under any more pressure than typical fuel pump pressure.

Also, in a Gen 1 it takes cutting out the trunk wall to remove the tank. Tator had an example where the bonding material from the rear clip dripped and accidentally bonded the tank to the frame and interior panels, so it was extremely difficult to pry out and remove. Not sure if it's any easier in a Gen 2.

[Coloviper]

Tom;

Another question on the check valve replacement. On old 70s Terex loaders I ran in the early 80s, we always had issues with fuel flowing back to the tank and hard starting, just like these Vipers (mine included right now) experience. We would actually add a check valve right in the fuel line just aft the tank to keep it pressured up. Has anyone done this on the Viper. It would have to be spliced into the fuel line and thus modified but seems a whole lot easier than ripping out the back wall to get to the fuel tank. I guess it could also be a good time to just upgrade the entire fuel lines with Aeroquip if we want to keep the old fuel lines in tack as is for future (hanging on the wall).

[Tom, F&L GoR]

Coloviper, been there, done that with the check valve in the fuel line. I put together about a dozen kits when I did mine and about a third of the owners found leaks around the injector-manifold o-ring. As I tried to explain two replies up, I think the hot engine expands the fuel more than some gaskets can handle, so it's not a robust solution. If you use a well-sealing check valve you would also need some kind of pressure bladder tank to give the expansion some where to go. The OEM part is in the tank, so it must bleed back into the tank - not a problem. BTW, even the check valve was a hassle because the fuel line itself is not easy to get to. My idea was to install it in the fuel filter area, and if you have been there, it's not convenient.

[72hemi]

Do you know what part number and availability is for a 96 GTS coupe? How hard is it to replace?

[Tom, F&L GoR]

See if you can find a parts manual online. The 92-96 list has a page of fuel pump module parts, the 97 and up shows only the module.

92-96.jpg

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[72hemi]

Thanks.

[Viper Red]

Sorry to bring back an old thread..

Is the Gen1 fuel pump a generic one shared by other commercial vehicles in the chrysler range? Or specific to the RT/10?
Reason for the question is price related obviously. How much are they sold for in the US?

Parts are ridiculously expensive in this part of the world even though we have no import tax on US products.

[Tom, F&L GoR]

I found an extra plastic box. If anyone wants it, PM an address.

The Digikey link to purchase them changed.

http://www.digikey.com/product-detai...R031B-ND/95387
Manufacturer Serpac
Manufacturer Part Number 031,BK
Description BOX 4.38X3.25X0.90 BLACK

[ellowviper]

Trying to put one of these together....but the dimensions of the 960 timer state: 1.5 x 4 x 7.5 inches and the enclosure you recommend states: 4.38 x 3.25 x .90 inches. So how does THAT work? Your pics look fine, but the math doesn't add up. Before I order it all, I just want to verify sizes.

[ellowviper]

OK...hit several other sites that list the 960....finally found one listing actual dimensions (not what AMAZON lists)....3 x 2.2 x 1 inch. That makes more sense. Shipping or Box size maybe???

[ellowviper]

Assembled, installed, and adjusted over my Thanksgiving break. Works like a CHAMP!!! Finally a easy and effective way to manage fuel pump 'key-on' time adjustments. Thanks Tom for the keys to success.

[John Galt]

Is this for stock PCM or any? Also, any Gen IV?

[ellowviper]

Should work for any year since all it does is intercept the signal wire from the PCM to the relay that controls the pump. As long as you have access to the relay, all you do is tap into the harness (appropriate wires of course).

[Dan Cragin]

Hey Tom,
I have done numerous of these timers, thanks. I also tried the adding a check valve and ran into the same issues you did. The issue is the fuel pressure regulator, which contains the leak back valve. I have been able to get these made, if anyone is interested. You do have to remove the gas tank. The advantage of this correct fix is that you do not need to turn the key on and wait for the pump to prime, just start the car. It does require taking out the tank out, which is about a 4-6 hour job, depending on who does it.

[Tom, F&L GoR]

Good to hear, Dan, I still get requests so will pass them to you!

[ViperVass]

Good to hear, Dan, I still get requests so will pass them to you!

Your timer is a nice solution!
Would be even better if we knew how to reprogram the PCM to run the fuel pump longer. Less weight in the car

My 97 GTS has a hard start issue too, I'm trying to understand what is going on before having a shop replace my fuel pump and saw a hole in my trunk.
If I let the engine crank for about 5 to 6 seconds it will eventually start.
Re-priming the fuel pump seems to be a hit and miss.
It usually takes me two tries before the car starts.
The car is not N/A.

Does anyone know if there is a way to get the PCM to output the fuel pressure sensor value, instead of having to connect gauges?
Does the 97 GTS even have an electronic fuel pressure sensor ?

[KURTSVIPER]

Hello Tom,

I had the same issue on my 1995 Viper R/T 10,so if anyone having any doubts, today is July 4th 2017, and the primer still works.