66 Oil Pressure gauge-barely reading

MARKDTN

Member
Apr 5, 2019
57
10
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52
Chattanooga, TN
Putting an Explorer 5.0 in my '66-see other post. A problem is the oil pressure gauge. Short story, the first 5.0 I had in there with an original sending unit either barely registered or didn't. I didn't run it long enough to know. Pulled that one out and sold it, guy that bought it says it runs great so I'm sure the oil pressure is decent. So now I put this Explorer 5.0 in. New Melling pump and pickup. New Motorcraft sending unit. My gauges are getting 5V from a modern voltage reducer, not the original style. If I ground the wire at the sending unit, it pegs the gauge (same for fuel level and temperature). When I ran it last night the oil gauge barely moves and it takes 15-20 seconds to move at all. Temperature gauge works fine. Fuel level shows empty when there is at least 3 gallons, but I will add fuel and I think it will read. So my question is on oil pressure gauge. I think it has pressure, I ran it 12-15 minutes and no clattering at all. It idles smooth. I have read that the gauge is not really a true oil pressure gauge, but I expected it to move past the hash line by the "L"-maybe at least towards the middle?
 
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wicked93gs

10 Year Member
Sep 30, 2006
945
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Nashville TN
Its impossible to diagnose without a real reading. Hook up a real gauge so you have a baseline(not a fan of the original "gauges" and never have been, always notoriously inaccurate. You are probably correct in your assumption that its wiring differences though.
 

MARKDTN

Member
Apr 5, 2019
57
10
18
52
Chattanooga, TN
I will hook up a real gauge. I have read a little on this and it seems some people have this issue. Gauge barely moves when pressure is really OK. I want to keep stock gauges if possible (but I already replaced the ammeter with a voltmeter) as I like the look. Anybody else have a gauge that barely moves with OK oil pressure?
 

MARKDTN

Member
Apr 5, 2019
57
10
18
52
Chattanooga, TN
I finally got around to looking at this last night. Oil pressure reads 6K ohms with engine off and 149 ohms running. Obviously way over what it should be (10-70?). I will get a new sending unit.

Added 5 gal of fuel. To check the Gas gauge, I took the sender out of the tank. It works fine. Reading 42 ohms to the wire at the gauge. The gauge in the car reads empty. Have another gauge that reads over 3/4 tank. Should be closer to 1/3, but I know it's not linear. I guess I get another gauge.
 

wicked93gs

10 Year Member
Sep 30, 2006
945
113
73
Nashville TN
Original gauges working as they should....its an area I have never bothered with to be honest because even when they are working they don't actually provide any real relevant information....its one area where I always prefer aftermarket gauges. I plan on re-purposing these I was going to use in another project:

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(Ignore the VDO boost gauge). I really like the Marshall Bluelines...they have a nice classic look, with LED lighting, full sweep, peak recall, and have a warning feature that is user programmable to change backlighting from white to amber at certain readings. I think the entire set cost me a little over $300...but this was years ago that I bought them.

As if that weren't enough....I am using a Megasquirt ECU....which happens to be compatible with an app called Shadow Dash(well, shadow dash was built to display MS information). My plan is to modify the stock speaker grill to accept a small tablet of some type and run Shadow Dash in HUD mode similar to this:

 
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MARKDTN

Member
Apr 5, 2019
57
10
18
52
Chattanooga, TN
I am really torn. I want the classic look. I definitely don't want digital-or white face. Analog kits seem to start at about $390. I have thought really hard about junking the cluster and replacing it with something like a Shelby R. Flat plate with 5 gauges. I could add the lights I want. Could get some SW gauges, but SW isn't the company they were 10-20-30 years ago. Also I would have to change the fuel sending unit unless I go cheap (or unmatching) or Autometer makes a 73-10 ohm gauge (SW does not seem to make a Ford/AMC fuel gauge). So options are $80 for a sending unit and fuel gauge, say $350 for a panel and SW gauges and another sending unit (and I could go tube instead of float style), or $390+ for analog aftermarket. Probably going cheap for now and fix the original-which is the look I really want anyway.
 

wicked93gs

10 Year Member
Sep 30, 2006
945
113
73
Nashville TN
I woulnd't look at SW or Autometer if updating...they are still 10 years behind in gauge technology(except maybe some of their really expensive stuff) Gauges like Speedhut will blow them out of the water. If I look at a "modern" gauge and it isn't even full sweep...that's an indicator its a cheap gauge that the manufacturer is trying to pass off as top-of-the-line. If you upgrade to modern gauages, the features you are looking for are full-sweep, LED, and stepper motor control for the needles....otherwise you are decades behind in accuracy, lighting, and visibility....at which point you are better off retaining your stock gauges and using some type of datalogging computer to get your real info.
 

MARKDTN

Member
Apr 5, 2019
57
10
18
52
Chattanooga, TN
Oil pressure I think I have figured out. Bought a new sending unit. No change. Went from the sending unit to ground with engine running. Like 150 ohms. Then sending unit post to the body of the sending unit. 35 ohms. Ah-ha. The Teflon that the sending units are supplied with do not allow a good ground. I will probably clamp a bare wire to the body of the unit and ground it somewhere nearby. I believe that will fix it (and I have oil pressure).

Fuel level still has be baffled. I bought a new Autometer gauge. Correct resistance for an early Ford. The cluster is unplugged. The battery is in the trunk so I hooked GND to battery -, I to battery +, and S to sending unit. IT STILL READS JUST ABOVE EMPTY! I am reading 42 ohms at the sending unit and 42 ohms at the wire to the gauge in front. I have a new aftermarket wiring harness so there are no connections from the sending unit to a Deutsch plug at the cluster I am measuring at. I have a 10ga ground wire in the trunk direct from battery (in the trunk) that hits the lights in the trunk, fuel sending unit, and fuel pump. That wire shows 0.2 ohms from battery - to sending unit, so I don't think it is a ground issue. I had some resistors so I got a 30 ohm and connected it ground to S on the gauge. It read about 2/3 tank which is rightish. So I suppose that all points to a bad sending unit. But why does it have 42 ohms from the sending unit at the gauge, but the gauge won't read right?