Lift Pump Pre-Start Timer

[jbplock]

A few months ago Tommy (abear) asked me if I knew of “a 12v fixed or adjustable timer that could be paralleled with our lift pump oil pressure switch which would provide say 5 secs or so of run time when cranking the engine then would fall out of service allowing the oil press switch to take over.” This would allow the LP to fully prime and slightly pressurize the fuel system prior to the oil pressure switch (OPS) kicking in once the engine is running. I suggested the ELK-960 timer (http://www.elkproducts.com/products/elk-960.htm) (found during the early TDP Lift Pump work). Tommy subsequently purchased and installed an ELK-960 timer on his truck. Of course once I heard that his was working I had to have one too… :D So, if anyone is interested here is a summary of the install. (This mod isn’t totally necessary … just cool… :cool: )

The ELK-960 (available from Farifax Electronics (http://www.at-fairfax.com/ConstructionElectronics/Info/ELK960.htm))has several modes. I used it as a simple one-shot timer. When power is applied it will run one cycle and turn on a built in relay for a preset interval. The time is adjustable from 0-60 sec. I set mine for about 15 sec to allow the lift pump to run until the engine is running and the OPS takes over. The timer circuit board was installed inside the lower fuse box cover (http://community.webshots.com/photo/77018086/143154350CzJEWK)
http://thumb0.webshots.com/s/thumb1/5/43/50/143154350CzJEWK_th.jpg
and I also applied a coat of ignition sealer (http://community.webshots.com/photo/77018086/143154439QOGmGG) to protect against condensation. The timer relay is wired in parallel with the OPS and manual LP button.
(see schematic (http://community.webshots.com/photo/77018086/143154393zVJoLp)).
http://thumb3.webshots.com/s/thumb2/5/43/93/143154393zVJoLp_th.jpg
Power for the timer was taken from the input side of the SIR fuse (http://community.webshots.com/photo/77018086/143154529bleUDB) using a Littlefuse “Add-a Circuit” (http://community.webshots.com/photo/77018086/143154203ZUDYIZ) purchased from Autozone.
http://thumb3.webshots.com/s/thumb1/5/42/3/143154203ZUDYIZ_th.jpg
The RUN-START circuit supplies the SIR/Fuse circuit, which is active when the key is in the Run or Start position.
More pics (2 pages) (http://community.webshots.com/album/77018086bLHHHC)

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[Modified]

Thanks for the info.
I still need to install an OPS, but I've been waiting till I decide on a timer circuit. I've been looking at www.amperite.com (http://www.amperite.com) , who sells different timer chips, which are already sealed. The only problem with these, is most are only rated down to about -14 Deg F. I would prefer something rated lower.
I've looked into 555 Timer Chips at Radio Shack, but the chips they sell are only rated down to around 0- Deg F. Not low enough for WI.

Questions:
1). Do you know the temp rating on this ELK-960 circuit board?
2). What type of pipe fitting does the Duramax Oil Pressure sender use? English? Metric? Tapered thread? Straight thread?

I had thoughts of installing a tee at this sender, and install my lift pump OPS at this port also.

Thanks for any help.

[jbplock]

Modified,

Good point on the temp rating. I confess I didn’t really consider it. The ELK-960’s temp range is not specified but my guess is that it will still work over the range of temps we see in the winter and summer. I didn’t study the circuit but I’m guessing it uses an RC time constant to set the delay so the amount of delay could be temperature sensitive. Worst case if the timer fails at temp extremes, the OEM pump will still be able to pump fuel. I also thought about building my own timer with the tried and true “555” but the price of the ELK-960 made it an easy decision. If you wanted to use the 555 it should be available with a MIL spec or automotive temp range, but I would just try the consumer version first. Many High-Rel IC’s are just standard parts which are selected on test to work over the extremes. Also regarding the Amperite timers, they look interesting. They list several automotive applications that sound similar to a LP timer… packaging looks rugged too. Let us know what you find.

Concerning the OP sender threads, I’m not sure… My guess would be 1/8 NPT. Seems like I remember someone added a temp sender with a tee at this port (was it SoCalDmax?) Maybe try a search. The other option is to use one of the ports on the oil filter adapter. (like this one (http://community.webshots.com/photo/65003591/65005642hlJEYv))
http://thumb2.webshots.com/s/thumb1/0/56/42/65005642hlJEYv_th.jpg

[jbplock]

Update on the ELK-960 timer...

I picked up a can of Cold Spray at Radio Shack and sprayed down the Timer so it was VERY cold (the can said -62degF). The timer still worked fine with no noticeable change in the time interval. Not a very controlled test but it gives some confidence that the timer should work OK in the winter. A better test would be to cold soak and test the PC board in an environmental chamber.

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[More Power]

Great job Bill! Have you noticed any change in engine running characteristics or change in trapped air in the fuel filter after the installation of this mod?

The 6.5 uses a lift pump relay, which is energized by the start circuit during the engine starting phase, then the oil pressure switch takes over once the ign key is released and oil pressure has developed.

MP

[jbplock]

MP,

I've noticed is that the engine starts a little quicker with the lift pump running during the glow cycle and it's also nice to hear the pump running (like the 6.5) to confirm it's working. My truck started well without the timer but now it's even quicker. Tommy mentioned that his timer reduced long crank times he was experiencing after adding a power box (Edge/Juice?).

Regarding trapped air, the lift pump alone (without the timer) completely eliminated the vapor build up I saw initially with the Mega Filter.

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[a bear]

Bill,

The ELK960 timer is still working great. After I key up I wait no more than a second or two then fire it right up. I have noticed a large difference in how fast it cranks.(now immediately) No doubt this mod is saving on my starter and batteries. Your suggestion on the ELK960 is appreciated. :D

Tommy