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Hey all, I experienced an omp pump failure. More specifically, the position sensor. This is the 0-5 volt sensor that relays pump position. On the sensor check screen from the power fc commander it would read 0.00 and jump sometimes to .95, .101 ect. Very erratic. I tested it per the fms and it’s bad. I have a few spare omp’s. Unfortunately, one has a bad stepper motor, one has a bad position sensors, etc. etc. i’ve taken a couple different pumps, and been able to assemble one good one. The issue I’m running into is the position sensor ( small rectangular three wire box ) has a set of different size shims to adjust the depth. This changes the initial voltage reading. I’ve gone thru every thread relating to this and the fms. But this info would be the initial calibration done when assembled. The book states around 1.1 volt at idle. Unfortunately, I would have to put the car completely back together to test this. Then take apart again if it’s wrong. If you’ve ever changed one you know this is a No go.
What I need ~ if someone with a power fc and commander with a working omp would be kind enough to check their sensor screen, it will have a voltage number next to the “ VMOP” with the key on and engine off. This would allow me to set the initial voltage of the positioning sensor. Thanks in advance!
VMOP is 1.17 for me with the engine off. It's the same value at idle I'm pretty sure, for what that's worth. And I think 1.1x is a pretty typical value. I've seen people reference 1.17 and 1.19 on here.
Not sure I follow what you're up to, but you sound like you know what you're doing. Good luck! Did you confirm that the wiring was intact? Mine had been rubbing and the wires were nearly worn through. I only noticed when I was taking the engine out, and I had to strip and repair the harness before I replaced it.
^^ That’s extremely helpful. Thanks for that. My general consensus about the voltage number is I believe they target 1.1 V when assembling the pumps. When I hooked up the position switch it would read .14 with the plunger all the way out and the number would be highlighted. As I depressed the plunger it sweeps thru to a max of 4.97 volts and the number becomes highlighted. From .24 thru 4.73 the number is not highlighted by the commander. I’m assuming the area thats not highlighted is the acceptable range by the power FC.
As to what I’m doing….. I’ve never seen a omp mechanically fail, I’m sure there are cases though. But I have seen stepper motors go bad and positioning switches. A new pump is pretty expensive, a used one is a crap shoot and I prefer not to have to remove the top half of the engine bay to get to it right after I just finished it up. I have a few pumps laying around so I tested each harness, stepper motor and position switch. I’m installing a position switch into a housing it was not originally in. Upon disassembly, I realized there are different sized shims to adjust the plunger depth ( see photo). The shim sets from each housing are different. Say 20-30 thousands different which greatly changes the initial voltage. Since mine was bad, I didn’t know where it should be initially other than what I have read.
I found the ohms resistance scale on the chart starts at the 1.1v. So that coupled with your info and a locals info ( theirs is 1.09 ) I have establish that is a safe bet for initial set up.
One thing I do want to note is that the Power fc does not have a trouble code feature as we know. You will not get an individual code for the stepper motor or the positioning sensor. What I have found In reference to the vmop, if you have a bad positioning sensor it will normally read a max or min value. You could still have a bad stepper motor after fixing the positioning sensor. If your voltage is 1.1 or higher and does not vary with RPM and load you have a bad stepper motor or wiring issue. Hope this helps.
Just wanted to circle back and update for future searchers. I set the omp position switch voltage to 1.1v with a combination of different shins from other pumps. I did this before install by just plugging it in and viewing the voltage with the key on engine off. It worked out well, and all is back to normal.
Just wanted to circle back and update for future searchers. I set the omp position switch voltage to 1.1v with a combination of different shins from other pumps. I did this before install by just plugging it in and viewing the voltage with the key on engine off. It worked out well, and all is back to normal.
~ GW
That voltage seems to be the correct "parked" voltage for the OMP with key on, not running. FWIW, my FD is on a Link G4+ ECU, which manages the OMP exactly the same way as the OEM ECU - it's a unipolar drive, with the 4x OMP stepper motor coils all wired to a common +12V (with ignition ON), and each of the 4 coils circuits return to ground through the ECU (4 outputs used). When I first went through the OMP position sensor calibration procedure with my Link, it was reading right about 1.0~1.1V IIRC in the key on/non-running state.
Thanks for that. I don’t believe it matters what ecu it is, they should all be set to around 1.1v as a starting point. The flow rate below that voltage doesn’t reduce any further, so it makes sense that they would start there. Your ecu being a more modern unit with the four outputs ( I think some ECUs only used two outputs ) would give you better control over thing like flow rate vs voltage and load. I’m not super familiar with link unfortunately but it may give you direct control with a 3-D table. The power FC, not so much .
Thanks for that. I don’t believe it matters what ecu it is, they should all be set to around 1.1v as a starting point. The flow rate below that voltage doesn’t reduce any further, so it makes sense that they would start there. Your ecu being a more modern unit with the four outputs ( I think some ECUs only used two outputs ) would give you better control over thing like flow rate vs voltage and load. I’m not super familiar with link unfortunately but it may give you direct control with a 3-D table. The power FC, not so much .
~ GW
The Link G4+ (and newer G4X) does a full 3D control mapping for the OMP, just like OEM - % oil delivered (0 - 100%) vs. RPM and Load (Load = MAP or MGP typically, but you could choose to use TPS for load if you wanted to - generally not a wise choice for a boosted motor). It also has built-in protections to detect OMP failures that can put the car in limp home mode like OEM (e.g., if the OMP position sensor reading doesn't match where the stepper is being commanded to go, with some +/- error tolerance)
My S5T2 FC is running on an AEM Infinity, and that one drives the OMP steppers differently (2 wire, bi-polar arrangement), but it has the same kind of 3D OMP control & fail safes as the Link. But when I was calibrating my OMP map on the AEM to verify average oil delivery/consumption rates (I'm using the RA adapter & separate pre-mix lube tank), I found that I had to increase the oil delivery %'s in the idle and low load/low RPM regions as compared to what I have in my Link map to get the same kind of average OMP oil consumption rates for street driving (~1 oz pre-mix oil consumed per gallon of gas burned). So the OMP maps between the two ECUs look different and what you would think should be interchangeable mapping that could be hand-jammed into any ECU isn't - the Link's 3D curve wants to be more linear from zero load/RPM up to full load/max RPM, while the AEM has more of a curve to it.
That’s what I’d imagine from a modern ecu. I like the ability to program safeguards in the event of a failure. Do you think the difference of your map between the two is the scaling the different ECUs use? Or do you think it’s the aem only having the two outputs?
03-27-23, 08:20 PM
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