A little feedback for all you that helped me.

[jrsavoie]

Greg, you may still want to consider the lift pump/OPC relay update.

 

[Crankme69]

Greg, you may still want to consider the lift pump/OPC relay update.

I agree Jeff. I also would like for that LP to be on during WTS GP cycle...all in good time my friend.

Thanks!

 

[btfarm]

Uneducated 6.5 preschooller question alert!

Why wouldn't the LP always be on as soon as the key cycle starts (and WTS begins)? Dumping over relief until it's needed.

 

[Crankme69]

Very good question Mike, that is exactly how mine will perform after I get done modding it.

Who knows what GM was thinking...I do believe that the 96 & newer perform the exact way you describe.

 

[Turbine Doc]

Uneducated 6.5 preschooller question alert!

Why wouldn't the LP always be on as soon as the key cycle starts (and WTS begins)? Dumping over relief until it's needed.

Well the LP is self regulating whenever power is available and only will purr/pump when it needs to so no spillover, on OBD-II GM figured out their oopsies of all oad thru OPS wussy contacts only and the lift has 2 power paths one thru the OPS and other thru the PCM have to lose both in OBD-II to lose lift power.

For my dual lift setup I use the signal from OPS/PCM to now act as the control trons for the low amp draw on my now (2) independent relays control coils which is well below what a single lift pump draws, then the independent relays power the lifts directly from aux circuit I put in from the aux power terminals of the under-hood fuse distribution center

 

[Brooklyn Tow]

On my 96 (OBDII) lift works with key on, untill WTS after glow has finished then LP stops.....Normal?

 

[jrsavoie]

Normal and then it should come on with key in the start position

On my 96 (OBDII) lift works with key on, untill WTS after glow has finished then LP stops.....Normal?

 

[Turbine Doc]

On my 96 (OBDII) lift works with key on, untill WTS after glow has finished then LP stops.....Normal?

Yes and if you had the filter mgr drain open it would run a little longer as the pressure sensor in the lift would be trying to run pump long enough to build to cut off pressure, (not so much a pressure sensor, but a current monitor circuit in the pump for how much extra draw the pump sees when pushing against a head as pressure builds when not being used)

Before I put in my manual pump spring loaded run push button next to the under-hood fuse block I would vent the filter manager after a fuel change by key on/off until PCM shut it off or fuel would burp out the vent and I would close the vent cap off the top of the mgr, and it would stop when building to full pressure.

 

[Brooklyn Tow]

Yes and if you had the filter mgr drain open it would run a little longer as the pressure sensor in the lift would be trying to run pump long enough to build to cut off pressure, (not so much a pressure sensor, but a current monitor circuit in the pump for how much extra draw the pump sees when pushing against a head as pressure builds when not being used)

I don't remember that in the Tech Ref (stickys)......But Thank you all the same.........You're like the tip of the sword, Doc.



You're, getting way to smart, like jd (gmctd).......You don't have any plans on moving out to the sticks, do ya?:???:

 

[buddy]

Older trucks like 92 and 93 were supposed to prime during WTS as well. The OPS relay mod is an important one. The reason the LP does not come on with the ignition, to answer that question, is supposed to be for safety reasons. When you are in an accident and a fuel line breaks you may be unconscious or not able to turn ignition off, thrown from the vehicle or whatever and the LP would still be pumping fuel to a potential fire. That and if you ever lose oil pressure you might want the engine to die, even though we know turning off the LP wont do that.

The best solution for OBD1 is something like Kennedy came out with. It is a good idea but too costly. Attached is an alternative I drew up, with a couple relays to do the trick. I havent tried the other single relay method pictured, but the dual relay method has worked great on a few vehicles so far.

edit: I realized this one doesnt have the numbers for the diodes, so when I get home I'll try to replace it with the latest. The diodes in the dual relay method arent really that important anyway, this is not on a computer circuit in OBD1, just battery to the LP, although the LP itself may not like the voltage spiked from relay coils.