OPS relay install

[Schwind]

The Lift Pump is a solenoid\shuttle type configuration, but the drive is SCR with buffered tickler coil feedback to shut the pump off when operating pressure exceeds flowrate spec,

Word up, dudes.....................

One more question on the things you posted earlier GMCTD. Does adding this relay into the OPS circuit interfere with the above statement.


please explain SCR

 

[vail426]

The wiring diagram for a 94 ( on my all-data ) shows the orange wire as " hot at all times" and the purple wire for the tank sending unit for the fuel gauge. This diagram shows the LP and sender in the tank. It almost looks like you are by-passing the OPS and your pump would run all the time. Some one correct me if I am wrong.

The purple wire is for the sending unit, so why is that in Schwind's mod?

 

[matuva]

Oh I see, I didn't notice the mistake at first look.
You're right, don't mod anything on a purple wire (wich one is it? the wire for indash oil pressure gauge coming from OPS is white). The one connected to pin 87 is the grey cut from the OPS and going to the lift pump---

 

[JMJNet]

It looks like Schwind is using a purple wire from his relay to connect to the grey from LP.

Remember he cut the grey wire, in that cut, there are 2, one coming from the OPS goes to 86 terminal of the relay (his wire is grey) and the other coming from LP goes to 87 terminal of the relay (his wire happened to purple).

Don't mod any purple, just orange and grey.

Actually, on the orange, you can just put a wire tap.

 

[vail426]

" Light purple for the LP: on the cut wire going to the LP I connected the Purple wire"

Thank you, missed that.

 

[gmctd]

Using relay contacts instead of OPS contacts to drive the LP will not create any problems - just a different method of closing the contacts, electrical pressure rather than mechanical pressure

The referenced statement indicates that the contacts are driving an electronic circuit rather than an electrical inductor (coil) circuit = less strain on the contacts, as there is no intense inductive load on the contacts as they close, and no inductive kickback spike across the contacts as they open - 'nuther words: mo' better.........................

 

[Schwind]

Using relay contacts instead of OPS contacts to drive the LP will not create any problems - just a different method of closing the contacts, electrical pressure rather than mechanical pressure

The referenced statement indicates that the contacts are driving an electronic circuit rather than an electrical inductor (coil) circuit = less strain on the contacts, as there is no intense inductive load on the contacts as they close, and no inductive kickback spike across the contacts as they open - 'nuther words: mo' better.........................

Thank you for the clarification GMCTD

 

[Schwind]

" Light purple for the LP: on the cut wire going to the LP I connected the Purple wire"

Thank you, missed that.

Yep, looks like my choice of using a light purple wire to be able to determine my wires at the relay end has been a little confusing. The purple wire was my addition to the OPS wiring not the factory wire color. Just used the light purple to designate the gray going to the LP. The only wires that were used from the factory harness was the orange from OPS (hot) and the gray from OPS to the LP.

 

[gmctd]

Silicon Controlled Rectifier is a diode that can be turned off........and turned back on - it is an electronic switch - unlike a standard rectifier diode, which always passes current in the direction of flow, it can block current flow until triggered 'on' by the control element, and will continue to pass current until triggered 'off' - similar to a transistor but the trigger is either on or off abruptly, much like a switch

 

[vail426]

Schwind, would you please post the part number for the Bosch relay? It would be much appreciated. If you already did, forgive me, as I appear to have gone blind in this post. Thank you.

 

[Schwind]

The bosh relay that I purchased according to GMCTD is the wrong one. The one that he recommends has a resistor included in the relay. I have yet to be able to go and get the proper relay or diode for the truck. It seem to be running fine for now but as soon as I can get to the AP I will be getting the relay GMCTD has recommended. I will probably be going to town tomorrow and be able to get that information for you then.

 

[gmctd]

Suggestion: when I alter circuits or add circuits or accessories, I go to the boneyard and get oem factory relays and the wiring harness from similar-year GM or Dodge trucks - the oem relays are spec'ed for EFI systems and service - if you're adding lights, get the headlamp relay - lift pump, get the lift pump relay - etc, etc - look at the size of that LP relay next to your add-in - you know that sucker will handle the power, plus you can get the connector and wiring harness with it and stay within the stock wiring\color schemes - works for me.........................

 

[treegump]

Ok...i'm getting confused...which I suppose happens when I jump from one topic to another, but are you guys simply relocating the relay? Or are you guys (matuva) bypassing the OPS completely, or what? I'm sorry - just getting confused here. I understand the extension of the harness, and the relocation of the relay, but how do you get the LP to run after the truck is turned off?

 

[JMJNet]

Override the OPS for 95- since 96+ the OPS doesn't matter anymore.

 

[Jess_sr]

The relays I used were the same kind thats already use in the system.
Local auto parts store had them under $20 each.:thumbsup:

 

[Jess_sr]

Ok...i'm getting confused...which I suppose happens when I jump from one topic to another, but are you guys simply relocating the relay? Or are you guys (matuva) bypassing the OPS completely, or what? I'm sorry - just getting confused here. I understand the extension of the harness, and the relocation of the relay, but how do you get the LP to run after the truck is turned off?

The relay is added to the system.
Instead of the OPS feeding the power to the LP it now just turns the relay on.

 

[matuva]

Ok...i'm getting confused...which I suppose happens when I jump from one topic to another, but are you guys simply relocating the relay? Or are you guys (matuva) bypassing the OPS completely, or what? I'm sorry - just getting confused here. I understand the extension of the harness, and the relocation of the relay, but how do you get the LP to run after the truck is turned off?

The goal is to unload the inside circuit of the OPS which is to weak to hold the power needed to feed the LP.
With the relay you can achieve this simply : after the mod, the OPS is here only to trigger the relay. The relay will then feed the LP.
Common relays can hold up to 40 amps which is more than enough.

The LP is running after you shut off the truck simply because the oil pressure remains.
After few seconds (more or less, depending on viscosity and temp) the oil pressure will drop down, the OPS will open, and the LP will shut off too.

 

[dangerousdave]

Ah, techo-talk. so refreshing, stirs up memories.


So, on my 94, the General installed a relay that the other years of 6.5s didn't get?
will my OPS work longer, with less load on the contacts?

Thanx Mucho, gmctd!

 

[Schwind]

The relay is used to reduce the electrical load on the OPS. The pressure switch in the OPS was not properly designed to carry the full electrical load that is required to run the LP. Putting the relay inline where the OPS only switches the relay instead of supplying the power to the LP adds longevity to the OPS. The relay reduces the load on the OPS from amps to milliamps. With the relay inline the amperage required to run the LP is supplied by the relay instead of the OPS pressure switch itself. IIRC the problem was corrected on the 96 and newer through the PCM. I had had problems with the OPS on my truck burning up (aftermarket OPS) before I was advised to only use the factory AC/Delco OPS. I installed the relay to add longevity to the OPS and quit having LP inop issues. I have not had an issue since.

 

[dangerousdave]

The large relay there on the firewall to the left of your addition is the real Lift Pump\OPS relay, replete with clamping\filtering for computerized vehicle circuitry - certainly hope that Bosch aftermarket relay has the same, so inductive kickback spikes don't get into your electrical system - that can really mess with IP operation..............

Not wanting to seem dense, I just want more clarification; If I already have a LP relay, adding another one does what?
If the existing LP relay does not handle the load to the LP, what does it do?

I've never had LP or OPS issues, but I'm not the original owner.