Lift Pump Problem - OPS or relay?

[twilson53]

ok checked the crank fuse good checked the ecm-b fuse good i am having no luck locating a fuse on the passenger side firewall for the lp if anyone has a detailed location or a photo of were this fuse for the lp is located it would be of great help

 

[WarWagon]

The 1995's don't have a fuse on the firewall like the older 1993's do.

Start with your OPS harness. Unplug the OPS, key off, and see if you have 12v to any of the pins. They are +12v, lift pump, and oil pressure gauge. If you have +12v at the plug I would then run +12v to the lift pump plug and see if it actually works. Next is hunting down the lift pump ground and cleaning it if the pump works.

If you don't have +12v then you are looking at fuisable links and fuses to the OPS.

With oil pressure and engine off, key off, the lift pump will run till the oil pressure falls off.

 

[twilson53]

ok thanks i will check that when i get a little warm weather here

 

[Dwayne1027]

I've been researching this thread because I have been dealing with the same issues for quite some time. I've replaced the LP, filter in the tank, OPS and added a relay harness from Ried Tekk. Looks like I need to spend some time Thanks for the pics and knowledge. I feel like I understand this unnecessarily complicated fuel system better. I was curious if Tracy and twilson53 figured out what their issue and what the solution was.

 

[JMJNet]

I've been researching this thread because I have been dealing with the same issues for quite some time. I've replaced the LP, filter in the tank, OPS and added a relay harness from Ried Tekk. Looks like I need to spend some time Thanks for the pics and knowledge. I feel like I understand this unnecessarily complicated fuel system better. I was curious if Tracy and twilson53 figured out what their issue and what the solution was.

They have not posted since 2013, so I don't think they will post after your question.

It is not complicated, what year is your truck?
There are subtle differences within the different years.

If you replace OPS, make sure you get ACDelco OPS.
I am not sure what is Ried Tekk, is that a company.

After you do all these, the fuel needs to be able to get to the filter when bleeding the air from the system.
That is the objective.

 

[Dwayne1027]

They have not posted since 2013, so I don't think they will post after your question.

It is not complicated, what year is your truck?
There are subtle differences within the different years.

If you replace OPS, make sure you get ACDelco OPS.
I am not sure what is Ried Tekk, is that a company.

After you do all these, the fuel needs to be able to get to the filter when bleeding the air from the system.
That is the objective.

My truck is a 93'. Reid Tekk is the company that makes the OPS "bypass" relay kit I installed. I thought I had a basic idea of how the system is supposed to work. The problem I am having is power isn't being sent to the fuel pump. Fuel pump does work when wired directly to the battery. I tested the plug to the OPS connector, fuel pump relay connector on the firewall, and the new relay kit I installed. Also checked the crack fuse under the dash and the fuse on the firewall. The fuse on the firewall is the only one not getting power but isn't busted. Everything else is getting 12.6 volts.

When does the fuse on the firewall come into play?

I am also confused on how the glow plug controller fits into the flow of power as well.

I don't understand in what order the power flows to each component, apparently. I've chase every wire I can think of except the ground wire from the fuel pump that runs along the frame rail towards the rear of the truck. Where does it go?

The OPS switch I installed is not ACDelco but I have ordered a replacement. It does read oil pressure and could be the issue. I've bought brand new parts before that simply didn't work.

 

[Jaryd]

My truck is a 93'. Reid Tekk is the company that makes the OPS "bypass" relay kit I installed. I thought I had a basic idea of how the system is supposed to work. The problem I am having is power isn't being sent to the fuel pump. Fuel pump does work when wired directly to the battery. I tested the plug to the OPS connector, fuel pump relay connector on the firewall, and the new relay kit I installed. Also checked the crack fuse under the dash and the fuse on the firewall. The fuse on the firewall is the only one not getting power but isn't busted. Everything else is getting 12.6 volts.

When does the fuse on the firewall come into play?

I am also confused on how the glow plug controller fits into the flow of power as well.

I don't understand in what order the power flows to each component, apparently. I've chase every wire I can think of except the ground wire from the fuel pump that runs along the frame rail towards the rear of the truck. Where does it go?

The OPS switch I installed is not ACDelco but I have ordered a replacement. It does read oil pressure and could be the issue. I've bought brand new parts before that simply didn't work.

I have factory service manuals and wiring diagrams for that truck that I’d sell if you need them

 

[ak diesel driver]

Not sure if 93 is the same as 94-95 but those years only run the lift pump when you have oil pressure. The relay bypass kit takes the load off the contacts in the OPS so it doesn't keep burning them up. Also common is to use the glow plugs system to supply an alternate source to trigger the OPS relay so the LP runs while the glow plugs are on.

 

[JMJNet]

I suspect, the voltage should only be there when engine is running?
You cannot measure anything till engine is running.
If there is no voltage when the engine is running, then the engine would not run.

Then, that is the problem, so we need to diagnose:
Did you hook up the additional relay correctly?
All the relay does is passing on enough and stable amp to the LP as compare to OPS.

Check the thread on adding relay to LP/OPS circuit to learn about this.
IIRC, the Technical Library have a thread on LP/OPS.