The oil pressure switch only has contacts rated at 1 amp while the pump draws about 4 amps, thus short life is a given.
To increase the switch life install a relay across the contacts of the switch. This is done by cutting the gray wire coming off the oil pressure switch. The end of the gray wire from the switch is connected to one side of a relay coil and ground the other side of the coil. The other end of the gray wire goes to the normally open contact of the relay. The common of the relay is spliced to the orange wire leading to the oil pressure switch. When the oil pressure switch sees oil pressure it will close it's contacts and thus supply the relay with voltage which inturn will close the normaly open contacts of the relay and supply voltage to the lift pump via the gray wire leading back into the engine harness. This mode reduces the current across the oil pressure switch contacts to the coil current of the relay, about 300ma.
Would I ground the normally closed curcuit, that opens when the relay is powered? I'm looking at a relay diagram labled ADCEF. A is normally open. C is normally closed. D is going into coil. E is common. and f is out from coil.
Wire it so the coil is energized when ops contact closes, which will close the normal open relay switch , and carry HD power on your common to the lift pump.
If I read above correctly cut wire for normal power from ops to pump and connect to D coil in, F on coil out will go to ground, A will go to lift pump other end of wire cut at ops, and E will come from the new 12v HD source. I'd recommend inl ine fuse from aux terminal in under hood power dist convenience block.
Before cutting OPS wires use a meter and some jumper wires to confirm realy diagram is as you describe, put power on coil in and ground coil out then the 2 relay terminals that have continuity will be the switched ones. (should be A & E if description is correct) these will power the pump from the aux power source, once identified lift power or ground to coil and confirm switched relay goes open, this will save a lot of head scratching later what did I do wrong if relay is bad or diagram is wrong.
If your discription of the relay contacts is correct wire it thisa way.
Gray wire coming up from the OPS goes to, D, the coil, F, the other side of the coil, goes to ground. The other end of the gray wire coming out of the engine harness goes to, E the common of the relay. Terminal, A, is spliced into the orange wire going to the OPS. This keeps Fuse 11, the original fuse for the lift pump, as the fuse operating the pump.
Do not connect, C, to anything as it will have voltage on it during the glow plug cycle and will short out and most likely cause a fire. Depending on were you mount the relay you may want to insulate the terminal for safty.
I got it pumping w/ the relay. First thing I noticed is that the pump no longer pumps during the glowcycle, and doesn't pump for an extended time after I turn it off( like a fraction of a second). The only draw back I can see to this is you have to have the engine running now to bleed the filter bowl.
did you mean that the ops should now draw 300ma, or 300ma less than before?
There is a mistake in your wiring. You have cut the gray wire at the wrong place, between splice S100 and the factory fuel pump relay. That section of circuit 120 is the part of the circuit that supplies voltage to the lift pump during the glow plug cycle. Installing the realy switch contacts in this part of the circuit is way the lift pump is not running during the glow plug cycle and it has not removed any of the current from the OPS.
Remove the plastic shield as it goes down to the OPS and make your cut close to the OPS were there is no chance of another brake out of the gray wire, circuit 120, between your cut and the OPS.
If you send me your e mail address I will send you the drawing.
#300 ma is an approxament currnet drawn by a small relay. This will vary depending on the size of the relay coil.
sorry, not the glowcycle, I mean engine off, ignition turned to run. ( This truck's lift pump previously came on with ign)
I made my splice at the ops connector. I figured it was the ops. when the engine is off, ops doesn't sense oil pressure yet, relay doesn't close the switch, no pump. Also, this is a new ops, installed w/ the relay. thank god for lifetime warranty.
I can live with this.
I have had alot of trouble finding connectors. I tried to buy an accessory relay w/ a connector. not availible.
I also wanted a connector for the splice I'm planning on doing to relocate the pmd out of the engine bay, so far I can't find it. I know I can buy the $100+ wiring form various suppliers, but I only want the connector.Edited by: quantum mechanic
Do a google or other search engine for weather pak several folks carry them, pn for wp is usually on the connector. Sorry on the OPS pwr source connection I had the relay in my hand I am going to use to power my 2nd lift pump in parallel with OEM & was looking at it's schematic and new it needed a source of power, forgot power was already available from OEM source that would work, and goal was to remove load from OPS and not OEM wire/fuse.
Good catch on my bad Howie.
Pump run after shutdown is normal may take a few sec. for oil press on ops to bleed off and stop pump, at least that is what happens on mine.
It will be a bit yet, but I am working on a control circuit/harness to run a lift pump on the Dmax. It will have it's own OPS, and a 4 second "one shot" prime function as well as a manual push button to energize when bleeding filters.
According to the shop manual, the FUEL LIFT PUMP is controlled by the "control module" by way of the fuel pump relay. The OPS is used as a backup system in case the previous system fails. When the oil pressure reaches 4psi, the switch will close to complete the circuit to the fuel lift pump. The OPS is only a backup and the control module/fuel pump relay may be where the real problem lies. If the lift pump is running off the OPS, because of its low electrical rating, it will eventually fail.
My manual says the same thing, BUT it also says only 1 wire feed from OPS to pressure meter, in actuality there are 3 wires coming out of my OPS that per the manual aren't there. I'm inclined to believe Howie's description of how it works is correct, I also believe the manual is also partially right but manual description is missing something, I've been up to my butt in alligators, but I've planning to hand over hand my OPS circuit with my meter and some jumper wires to see what wire does what. I'll post what I find when I get to it.
I'm still leaning towards the fuel pump relay. Its located in the "Underhood Fuse-Relay Center." Relay # 10 which is the front-right (facing foward) most plug-in relay. I wouldn't change anything till this proves faulty. It might even be worth changing just-for-the-heck-of-it. Its a lot easier to plug in a new relay than splice a wireing harness. Keep me informed. If you need any info from the manual, I can scan/email pages to you. I have 136k on my '97 6.5 burb without any OPS failures to date. It has gone thru two lift pumps though.
Did I ever send you the drawing for the OPS mode? Were do you stand on this project?
Sorry about the size but it will not let me post a larger picture.
This is from a GM manual. GM treats ever system independently and will not show wiring from other circuits that may also be connected to the same part. IE the oil pressure guage also goes to the OPS but is shown in the manual as a seperate system. Yes there are 3 wires going to the switch, but only 2 of them have to do with the switch for the lift pump, the other is the guage ground path.
I tested the fuel pump relay and it isn't being powered during the glow cycle. pcm powers the fuel pump during the glow cycle, no?
Progression: OPS, ignition switch, fuel pump relay, and fuel pump and all related fuses replaced at about the same time. everything works for 200 miles or so and then no lift pump at glowclycle, (not tested engine running). OPS replaced, bypass relay installed. lift pump still doesn't come on during the glow cycle, bypass relay tested, lift pump works with engine on. fuel pump relay tested during glow cycle, no power to relay coil, common is powered.
Can the Ign. switch cause this problem? I am willing to try a new one to eleminate it as a potential cause of my particular problem.
I'm finishing up a time belt change on my 01 VW TDI Bug; you think needing a T2 scanner for a 6.5 time set is bad, I just found out on my TDI VW I need a puter tool to check the auto trans fluid level, there is no dip stick for the trans, now that's gone too far.
I'm sure some element of correctness to the manuals description of the OPS circuit, still not 100% in my mind of which comes 1st chicken or egg if you will PCM or OPS, and at what point relay control hands over from PCM to OPS, I know I hear the pump running after shutdown so OPS is in action until pressure bleeds off, but I don't know if it's in partnership with PCM or solo OPS. I was going to experiment with jumpers to the OPS and see what happens to lift pump power at loss of OPS input.
Test for voltage from A3, gray wire, on the underhood fuse/relay to ground. If this is good the relay circuit is OK. If not read on below. If the relay circuit tests good the gray wire is open between your test point and the fuel pump. The first thing I would do is reconnect the gray wire at the point you cut it during the OPS bypass. I think it was cut at the wrong place. If reconnecting the gray wire cause the pump to work during the glow plug cycle you have cut the wire at the wrong place.
If the factor fuel pump relay does not come on during the glow plug cycle, in the test above, locate the green/white wire at D8 on connector C1, a 32 pin brown connector, at the PCM. put a straight pin through the wire and test for voltage during the glow plug cycle. If none its looks like a PCM problem. If you have voltage there go to the other end of the wire, B3, on the under hood fuse/relay block and test for voltage. If none replace the wire from the point were you had voltage at the PCM to the fuse/ relay block. If you have voltage there test from A1 of the fuse/relay block to ground. If no voltage the relay is bad. If you have voltage the wire from A1 to ground is open. This sequence will test the relay circuit from the PMC to ground. It assumes the PCM has voltage because you are seeing other PCM functions work OK. It also assumes the relay if activated at any point during this test has a good connection across it's contacts.
When the ing. switch is turned on the PCM starts the glow plug cycle and sends voltage to the fuel pump relay. The fuel pump relay makes a connection from fuse ECM B fuse to the output side of the OPS and thus starts the fuel pump as long as the relay is held in. At this time there is "FAKENG" signal sent to the PCM telling it that there is oil pressure. Once the oil pressure reachs 5 lbs and the glow plug cycle has stopped, the fuel pump relay had dropped out, the OPS has closed and feed voltage to the fuel pump and the signal to the PCM.
The purpose of the OPS is a safty that shuts the fuel pump down if the engine is stopped, either by shut down or accident.
A forum community dedicated to Chevrolet and GMC diesel truck owners and enthusiasts. Come join the discussion about duramax engines, performance, builds, modifications, classifieds, troubleshooting, maintenance, and more!