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Oil pressure “gauge” question”

Discussion in 'Stock 1995 - 2001 Explorers' started by Mr. Alligator, July 19, 2019.

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  1. Mr. Alligator

    Mr. Alligator Elite Explorer

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    I am aware that my oil pressure “gauge” is just an idiot light with a needle. Got that.

    Recent problem is that my oil pressure “gauge” does not register anything with the engine running. Zero. And this activates the red “check gauge” light. Super annoying. Dead gauge AND red “check gauge” light on all the time.

    I have replaced the oil pressure sensor with a new Motorcraft unit. That should rule out sensor as the issue. Also did not trust the connection, so I spliced in a new connector. Great connection at the sensor unit. Sadly, nNeither the replacement oil pressure sensor or the improved connection changed anything.

    New oil pressure “gauges” are obsolete... so I got replacement unit from salvage. Same exact problem and still nothing changed. Then I switched out the entire cluster assembly. No change.

    I know that salvage pressure “gauge” and/or salvage cluster could have exactly the same problem as my old units. But seems slightly unlikely.

    QUESTION: is anything else involved in the system that could be causing this? Anything else to check? Could this be main computer? And if I can not resolve this, anything smarter than covering the red “check gauge” light with black tape and putting up with the disfunctional oil pressure gauge?

    Thank you for your consideration.
     
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  3. koda2000

    koda2000 Explorer Addict

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    I'd put a real oil pressure gauge on it (in place of the OE sender) and see what it says. You should see at least 25-30 PSI on a cold startup. The OE gauge will read no pressure if you have less than 5 PSI of pressure and when it sees less than 5 PSI the "CHECK GAGE" light will come on. You've already addressed the typical issues that will cause the needle to not work. IDK if the ECU has anything to do with the OPG working or not. Maybe studying a wiring diagram would answer that question.

    An inexpensive OP gauge can be had for around $20.
     
    Last edited: July 19, 2019
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  4. 974X4BLACKSPORT

    974X4BLACKSPORT Active Member

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    First thing to check would be that the engine is actually building oil pressure, to do this you will need to install a mechanical analog oil pressure gauge (aftermarket) in the engine block oil gallery to get the actual Oil pressure reading from the engine. It is possible that the engine has zero oil pressure, hence your "zero" readings. I have seen sludge build up on the bottom of oil pans restrict oil enough to cause a "zero" reading on the IP gauges, of course there are also other possibilities, but first we need the KNOW the engines actual oil pressure.
     
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  5. 410Fortune

    410Fortune Flood Season 2 Staff Member Moderator

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    these guys have you covered but I will reiterate

    the ecu has nothing to do with this, the wire goes directly from the oil pressure switch to the instrument cluster

    What you can do is check continuity from the engine side of things to the instrument cluster side of things, make sure there is not a break in the wire. Check the ohms also, should be close to 0 ohms if the wire is not damaged or broken

    the FIRST thing you should have done is put a oil pressure gauge on it, manual one from the parts store
    I'm assuming you think it has oil pressure since you did not notice any ticking from the valve train??
     
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  6. koda2000

    koda2000 Explorer Addict

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    Good point about possibly having sludge in the engine. When I first got my POS '01 Sport Trac running and took it around the block it registered zero oil pressure at idle. Turned out sludge was blocking the oil pump pickup screen.
     
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  7. 410Fortune

    410Fortune Flood Season 2 Staff Member Moderator

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    if it is sludge you can clean out the block with diesel oil, some atf or mobil one full synthetic
    I have watched a 5.0L engine go from 0 psi at idle to 30-40 psi at idle just by driving it around with diesel oil and then mobil one for a few weeks...breaks up the sludge and carbon deposits. That truck is still on the road now pushing 300K miles
     
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  8. Mr. Alligator

    Mr. Alligator Elite Explorer

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    Engine is Powertrain rebuild with about 80k miles. Oil changed regularly at 3k. Something (valves?, but does not sound like timing chains/guides)) has clicked since I had the engine installed. I have assumed I had oil pressure because it has run for 80k with its clicking, and just got back from 3k road trip.

    Could an engine keep running like that with zero oil pressure?

    Thank you all for your patience and help. THANKS so much!
     
  9. 96eb96

    96eb96 Well-Known Member

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    At Zero PSI It would sound like a box of marbles.I doubt you would go more than a 1/2 mile or so. Also, you have tensioners in that engine, I can't see any real mileage out of it with that problem.

    The oil creates a bit of a "liquid bushing" around the bearings so things don't bang around.

    Can you hook up a multi meter between the sender terminal and chassis ground when it runs? All the switch does is close when there is 5psi. So it should change from open ckt to short ckt (0 ohms). This should be the case with the new sender. If that don't work something may be blocking flow to the sender.

    This will eliminate any upstream wiring issues. On my 96 I have the older motorcraft variable sender, the needle moves from the bottom to the top of the oil can on the gauge as the RPMs change. I think 96 is the last year you could do that.
     
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  10. koda2000

    koda2000 Explorer Addict

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    "Could an engine keep running like that with zero oil pressure?"

    Not for long.
     
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  11. Mr. Alligator

    Mr. Alligator Elite Explorer

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    @koda2000 how did you resolve the sludge issue?
     
  12. Mr. Alligator

    Mr. Alligator Elite Explorer

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    Ok, I had assumed I had oil pressure because the engine runs and I am able to tow trailers and travel long distances.

    BUT, as usual, the geniuses here are much better mechanics! I checked the signal from the brand new Motorcraft oil pressure sensor ——- the terminal is well grounded, until I start the engine. When I start the engine, the sensor reads no ground, and thus no pressure.

    Maybe this engine has no oil pressure, at least not at the sensor unit.

    Still working on it, and will try to eliminate some assumptions.... Dang.

    And thanks again!
     
  13. koda2000

    koda2000 Explorer Addict

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    I removed the lower oil pan, scooped out at least a 1/2" of of sludge from the pan with a serving spoon, removed the oil pickup, cleaned the screen and reinstalled it, replaced the oil pan and ran engine flush through the engine several times and kept changing the oil and filter every 1000 miles or so 4 times. I've taking the engine apart now and it's not too bad inside. The main issue with the V6 engines is the upper oil pan/engine girdle catches a lot of debris and holds it in it's webbing. I'll be removing the upper pan and giving it a good cleaning before the engine goes back together. Using the diesel oil with some ATF in it is probably a good idea too.
     
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  14. 1998Exp

    1998Exp Well-Known Member

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    Hmm, something is backwards here. With the engine off (zero pressure), the switch should be open (very high resistance from the terminal to ground). When pressure builds up, the switch should close = short to ground. Did you make sure to disconnect the sensor from the wiring before your experiment? Or (no offense), perhaps you are not using your multimeter correctly?

    You can check the gauge and the wiring by disconnecting the sensor. The gauge should read "low" with the wire disconnected from the sensor, and "normal" when you touch it to the block.

    And, as many already said, the first step in a case like this is to measure the actual pressure with a real gauge - they are cheap.
     
    Last edited: July 19, 2019
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  15. donalds

    donalds Elite Explorer

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    When I first got my 99 I used marvel mystery oil to clean the inside my engine
    The reason I say is I have never heard of anyone ever damaging their engine using it

    I still put in a LITTLE in the gas still on just about every tank fill. My grandfather swore by that stuff
     
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  16. Mr. Alligator

    Mr. Alligator Elite Explorer

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    SOLVED.... Finally got it.

    I had assumed I had adequate oil pressure, and that a new Motorcraft pressure sensor would function properly. From there I improved the oil pressure sensor connection, and changed out two used gauges. When all of this failed I could not figure it out.

    The dash pressure gauge would confirm ground and contact through the ignition, until I started the engine, then would immediately shut off and activate the red “check gauge” light. Really, sort of sounds like an issue that several people have had here on the Forum.

    @1998Exp was right, things were reversed.

    To finally resolve this, FIRST I confirmed that I had adequate oil pressure using an ACTUAL gauge hooked to the sensor port. The engine has about 25 pounds of oil pressure at warm idle, which increased to about 50 pounds of pressure at 3000 RPM. Great.

    The ohm meter still showed the oil pressure sensor had a grounded terminal, until I started the engine, then the sensor terminal was no longer grounded. And the gauge and light displayed a lack of even marginal oil pressure under all conditions. Went down to the local auto parts store, and confirmed that the new BWD pressure sensor switch terminal was NOT grounded by default (until there was oil pressure against the sensor!)

    BOTTOM LINE: the new Motorcraft oil pressure sensor was reversed somehow. A properly functioning oil pressure sensor resolved the problem. When I start the engine, the “gauge” now shows I have oil pressure, and the red “check gauge” light is not activated. Perfect.

    And you ALL helped me to trouble shoot this without assumptions. So it made sense.

    Thank you all so much for the help!!!
     
  17. Mr. Alligator

    Mr. Alligator Elite Explorer

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    @koda2000

    ^^^ very very concise and accurate!!!

    Thanks Koda, (and everyone else!)
     
  18. koda2000

    koda2000 Explorer Addict

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    No problem. Glad you got it straightened out and that it was nothing serious. One correction... It's not a oil pressure SENSOR, it's an oil pressure SWITCH (on/off).
     
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  19. 1998Exp

    1998Exp Well-Known Member

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    Glad to help. The first sensor that they sold you was the wrong part. Older vehicles had a warning light, which was connected to battery power on one side, and grounded through the switch. With no pressure, the switch was closed and turned the light on. In my (long gone) '85 LTD the overtemp warning worked the same way and was hooked to the same light. When that light turned on, it was anybody's guess whether it's low pressure or overheating. I finally installed a separate coolant temp gauge in that car.
     
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