Priming and lift pump questions

[millsroger]

Question---Priming. Wiring shows the lift pump relay connects the pump to a "priming" circuit when off and to the battery when on during start. Where does that priming circuit end up going???? Also, is there a switch or button somewhere to prime it???

My research so far finds very little:

Reading posts, I found that it runs only when there is oil pressure----makes sense--I noticed that mine keeps running for several seconds after shut down as the oil pressure dropped. It quit running at about 10psi.

I also find that the lift pump goes thru a pressure bypass back to the tank---is this true???


Purpose of the questions---it occurs to me that the lift pump primeing circuit could be hooked to the glow plug controller so that it primes the IP prior to crank. Rationale for this, when they sit for a while the pressure in the lines drops to nil and the input to the IP is not up to pressure when you first crank it. Then it can take a couple of seconds for the pressures to build back up to pop the injectors open. This mod could make for quicker starts by getting the input to the IP up to pressure before you even start to crank it.

 

[matuva]

see post #7 http://www.thetruckstop.us/forum/showthread.php?33383-Lift-pump-actuation-whilst-waiting-to-start

 

[millsroger]

Thanks matuva, I guess, like alot of newbies here, I missed the prior post. I did so a search but it didn't show it. And thanks to ak and buddy too for their 'beentheredonethat' posts and write ups.

 

[matuva]

You're welcome

 

[ak diesel driver]

x2

 

[millsroger]

Thanks to yuse guys I figured it out. In the wiring diagrams it shows a red wire from the fuel pump relay that goes to something called the "priming circuit". No other easily available info without $$$ on factory diagram book. Snooping other forums as well as this one indicates that the only place that red wire goes on a '94 is to the ODB1 connector, pin G. I traced mine and verified that it does do just that.

Sooo, I added a wire to the same pin on the fuel pump relay to the GP side of the controller, 10 amp fuse in line to be safe.

Voila!!! The lift pump now works in the WTS mode, while cranking and after the oil pressure comes up. Now my truck lites up on about the third cylinder with just a puff of black smoke.

For now, the OPS is still wired as original but that is the next step.

Thanks again guys.