96 Suburban 6.5 Wiring Mystery for Lift Pump

[turbopower6]

Hello all,

The adventures never end on this old girl!! What I have is a 1996 Suburban with the 6.5 running a Walbro FRB-5 lift pump replacing the factory frame POS that was a problem from day one. I forget where/who I purchased the upgraded OPS and Lift Pump wiring harness when I installed the Walbro but the harness has a black box I mounted to the firewall that has a red indicator light that is on when the truck is running. Below this box is a momentary switch you can depress to run the lift pump to prime the fuel minder when changing filters.

My situation right now is the lift pump is running even with the key off and truck not running. The red light on the box stays illuminated which did not happen before.

???

The only way to stop the lift pump is to disconnect the weatherpak connector that runs from the little black box to the lift pump. Checking the connection at the lift pump shows hot with a test light on both connectors coming down from the black box. This is odd because i would think one is the ground?

As I get older I swear my ability to process this aggravation is at a lower level. To make matters worse my wife is pulling my chain telling me "that truck is kicking your ass!"

I am going to call John Kennedy and see if I may have purchased that OPS upgrade and lift pump harness from him. I am thinking something fused together inside that plastic black box to make it hot all of the time.

Any help from the awesome folks on the site is appreciated greatly as always!!!!

Regards,
Ted

 

[dbrannon79]

Sounds like the OPS sensor had the contacts welded closed. time for a replacement. only use Delco for this as the auto parts replacements are a hit and miss.

do the relay mod for it and it will save you lots of headaches down the road!

 

[ak diesel driver]

That black box has a relay built into it IIRC. I have one and I got it from Kennedy. It's setting on a shelf now.

 

[Glagulator]

1996 and up (obd2) do not need the LP/OPS relay mod.
The PCM controls the LP with the LP relay and the OPS is “redundant” per GM.
With the key off and the LP running does unplugging the OPS shut it off?

 

[turbopower6]

1996 and up (obd2) do not need the LP/OPS relay mod.
The PCM controls the LP with the LP relay and the OPS is “redundant” per GM.
With the key off and the LP running does unplugging the OPS shut it off?

I need to unplug the harness to the OPS and see if that turns the Walbro off. First I will need to unbolt the Fuel Minder to get my hand in there to unhook the OPS. I remember raising the Fuel Minder up for some reason from where it was originally. It may have been the OPS change when I did the harness. I just cant remember. That makes sense. 96 makes it a OBD 2 so adding the relay is redundant. First things first. should know better since my tech school instructors told us....."check the simple things first before you tear the vehicle apart....." you guys get me back on track...thank you...stay tuned!

 

[dbrannon79]

I was unaware that 96+ used the relay to function the LP. my 95 has a LP relay but it's only used when cranking to power the LP. once the engine has oil pressure the OPS takes over and the relay turns off. that is when it was factory wiring. Now it still uses that function but has a relay that the OPS controls which powers the LP, also tied into the glow plug solenoid so the LP is on when the glows are on to prime before cranking (my ingenues modification).

if your OPS doesn't turn off the LP when unplugged. unplug the relay that powers it and swap with another if that turns it off. I have seen relays fail where the contacts stay closed internally.