Oil Pressure gauge reading too low & Fuel Gauge too low

[1965GTFB]

Just finished posting this freshly finished project for COTM. Finished it at 2am, did a 3 mile test drive then got up at 4:30am to trailer it to the Mustangs Plus show.

Have a couple bugs to work out. Oil & fuel gauge readings.
Oil Pressure reads barely to the low side.
Fuel gauge doesn't really move.
Have tested both gauges by grounding and they both go all the way up so they should be OK.
Running new style instrument cluster voltage regulator.
Water Temp gauge seems to be working great.
4.9 volts to all 3 sending unit leads with key on.

Oil Pressure Gauge
-Grounded lead at sending unit and gauge will rise all the way up.
-Tested oil pressure while running with an external gauge and pressure is 60 psi.
-Installed a new sending unit tonight, no change. Used correct type for gauge not light.
-Ohms test from stud on sender to body of sender showed no change on both the old and new units but the same test on the sender on my '65(has gauge not light) and on a spare(different thread size) show a change in ohms doing same test although way different numbers for each.
-Should the ohms reading change when checking from the stud to the body?
-Could it be that the new Borg Warner unit I just bought form O'Reillys is bad right out of the box?

Fuel Gauge
-New 22 gal '70 tank with new '70 sending unit.
-Put 5 gallons in for the 30 minute cam break-in run, gauge might have moved a little but honestly our focus was on other things at that time.
- Put in another 10 gallons after the cam break-in, gauge still lays below E.
- Car has only 80 miles on it now so I figure there should still be at least 4-5 gallons still in there even if we burned 3 gallons in during the break-in and 10-11 in the 80 miles(using rate of 10 mpg).
-Grounded lead at sending unit and gauge will rise all the way up.
-Checked with meter from body of sending unit to fuel tank screw, reads there is continuity.

Realizing that the ground test might only prove that the unit is ground to the tank(e.g. the mounting screw might have good contact with the tank but not the body do to strip caulk between them) I checked to the body but didn't get a change and will admit I didn't dig too hard as I hate to scratch all the hard work painting the floor pan. Would testing by running a wire from the body of the sender to the - post on the battery be a good idea?

Don't really just want to put a bunch more gas in to see what happens only to have to drain it to pull the sender to bench check it(which is what I know we may end up having to do any way).

Thoughts and ideas?

 

[Midlife]

Your gauges must match the sending units in terms of ohmage (resistance range). This is a common problem with aftermarket gauges and sending units.

 

[MD69Boss]

Randy, of course is right, I had the same symptoms you're having with your oil pressure gauge with a water temp gauge. Purchased the correct sending unit, Ohms matching from same manufacturer and the gauge has been right as rain since...

 

[1965GTFB]

Your gauges must match the sending units in terms of ohmage (resistance range). This is a common problem with aftermarket gauges and sending units.

-Gauges are the originals.

-The IVR is new from NPD.

-Oil sending unit is a Borg Warner from O'reilly's as mentioned, the Motorcraft unit is 4x the price and was not in stock and only has a 1 yr war. compared to the BW lifetime. So maybe the expensive Motorcraft unit will do it? What about the no change in Ohms reading with the 2 that read way low? I think I'll pull the unit off my original '65 to try on it and see what happens, and maybe try those others on the '65. The '65 usually reads to the higher side of the gauge.

-Fuel sending unit is a new one from NPD. I'm also going to try testing by attaching an extra ground to the unit body with a wire directly to the neg. terminal.

What are the recommended units from which manufacturers that I should get?

 

[Midlife]

Ford sending units are typically 73 to 13 ohms or thereabouts. The high ohm reading is when the gauge is far to the left; the lowest reading is nearly pegged.

Another possibility is that there is excessive resistance in those two lines (fuel, oil pressure) due to corrosion at plugs, pins, etc. since your water temp appears to read fine.

I'm very confused about your readings on the two sending units; can you explain this a bit more? Some oil pressure sending units simply don't change much regardless of oil pressure (I know Midlife's didn't move a bit).

 

[1965GTFB]

I'm very confused about your readings on the two sending units; can you explain this a bit more? Some oil pressure sending units simply don't change much regardless of oil pressure (I know Midlife's didn't move a bit).

I wasn't even sure if this is a legit test of the oil units but thought I'd just do it to see if there was any difference between the 2 that have been on the car so far and the one on my 65 and the additional one(not even sure what car it is from/for) I have laying around that has the different thread size.
The test was:
-senders either on bench or on car with key off
-meter set on Ohms
-Red lead to stud on sender, black lead to body of sender
-the 2 units I've tried on the '67 both show no change/no continuity/meter still reads 1
-unit on my 65 and the extra both show a change from 1/continuity

 

[Midlife]

If you measured things correctly, the two units that showed no change when both leads were connected says that each sending unit has an internal open circuit, so both are bad. The one from your 65 and the extra one seem to work.

What I don't understand is why your meter shows "1" . When it shows continuity, what are the resistance readings? For this test, do not use the setting (if you have one) for continuity (usually a tone): use the actual resistance reading. Those readings are important to better understand what is happening.

 

[1965GTFB]

Confession time. I'm using my cheapo Harbor Freight Cen-Tech meter. I can build a car from the ground up and fab parts with simple tools but understanding using a meter is not a strong suit at all. I need to get better at this and using a test light. But without guys like me you would be bored, right.
What is a good make and model of meter I should invest in?
-If I put my digital meter on the 2000 or 200 setting in the Ohms section it reads 1 when not hooked up to any thing and goes to almost -0- when the leads are touched together.
- On my 65, red to stud black to body reads 59(on 2000 setting) or 58.5(on 200 setting).
- On the extra sender, red to stud black to body reads 247(on 2000 setting) or still 1(on 200 setting).
- On both the senders I've used on the 67 I only get readings of 1 with no change either setting.

How do I make sure the sending units will match the gauges(get the correct sending unit), can you explain that a little more to me? Sounds like it's no as simple as just using the original factory gauges and ordering a electronic IVR and fuel & oil sending units from NPD or trying the O'Reillys BW oil sender. Sounds like I should take the meter with me to the parts store when picking up sending units.

I of course will pull apart whatever I needed to get this fixed but would like to avoid draining fuel or yanking the dash if not necessary.

 

[Midlife]

Wow...I've never heard of a meter that reads "1" when there is no continuity. What you stated makes much more sense. The extra sender is not appropriate for your year/gauge at all. Readings of 59 sound about right. Your two new units are faulty. So yes, it would make sense to go to Oreillys or other parts stores and test what they have in stock and you should readings about 60 to 73 ohms from stud to body.

As for your fuel gauge, I believe the gauges themselves were not changed when the Mustangs enlargened the fuel tanks, so your sending unit must change to accommodate the larger tank. You simply can't use a 16 gallon sending unit in a 20 gallon tank.

Another trick for testing your gauges is to exchange the wires for the oil and water temperature in the engine compartment (if they can reach): the gauges are the same for either sending unit except for the names on the face plates.

 

[1965GTFB]

The 1 on the meter is way off to the left, I figured it's just there to indicate that the battery that powers the meter is not dead when checking resistance.

Sending unit is a '70. Done this before, '69 tank and sender in daughter's '66 and '70 tank and sender in older son's '68. They both worked fine.

I'll try the wire swap trick.

I did go with the cheaper fuel sender from NPD. Just talked to them and they checked the history and did have some go bad in the past. So I just got off the phone from ordering a new fuel(better repo w/ brass float) and oil sending units.

So do you have a better meter recommendation for me instead of the Harbor Freight Tools freebies that I use?

Thanks for the help.

 

[Midlife]

No, I now understand what you're seeing. Your meter is good enough for your purposes. Carry on!

 

[1965GTFB]

Latest test results with Temp & Oil gauge lead switch and Ohms at oil sending unit while running.
Reminder of starting point, temp gauge seemed to be working fine, Oil gauge would only rise to Low hash mark below the low of the bracket between the low and high end.

With car dead cold:
Switched leads and temp gauge came up right away but only to the very low side of cold.
Oil gauge just laid there until the engine warmed up and eventually rose higher than when hooked up correctly.

Also checked Ohms while engine running. Red lead on sender post, black lead to ground(used both body of sender and shock bolt). Meter jumped around the mid 20s(20.1ish to as high as 30).

So as before the oil gauge does move but never gets the needle up between the bracket on the gauge.

 

[1965GTFB]

Another trick for testing your gauges is to exchange the wires for the oil and water temperature in the engine compartment (if they can reach): the gauges are the same for either sending unit except for the names on the face plates.

Randy,
I'm assuming that I could use this same trick by hooking the Temp or Oil lead to the fuel sending unit when it is out of the tank(with it grounded) and move the float arm to check it? Just got a new fuel sending unit from NPD today and want to check it as much as possible before it goes in the tank. Already checked it on the bench for Ohms changing as I move the arm.

Also got a new Oil sending unit. One thing I noticed right away is the size of the hole for the oil to pass through is smaller than was on the car. Even though I haven't put it on the car yet it just seems to make sense, smaller hole more pressure, similar to bore size on a master cylinder.

 

[Midlife]

Yes, and Yes.

 

[Kelly_H]

+1 - the senders are bad. I've been through three oil pressure senders and the only one that worked worth a damn was the Motorcraft one. I believe it's actually fairly cheap through NPD.

Not sure about the best source for a fuel sender, but I've had problems with those too. On my car, when it reads half empty it means it's only down by 5 gallons with 11 left to burn! I have solved this problem by instead opting to just fill up every 200 miles regardless of what the gauge does or doesn't say

 

[1965GTFB]

[QUOTE="Kelly_H, post: 277436, member: 1872been through three oil pressure senders and the only one that worked worth a damn was the Motorcraft one. I believe it's actually fairly cheap through NPD.[/QUOTE]

** Success ** Thanks for the input Randy & Kelly
Well I think I have it all sorted out now.
OIL Pressure sender
Like your experience Kelly it took 3 oil sending units and the Motor craft worked best. Borg Warner(O'Reillys), Standard(NPD, didn't get the right part # to get their Motorcraft), Motorcraft(O'Reillys, quicker than NPD and about the same w/o shipping).
The smaller hole = more pressure theory is out the window. The Motorcraft had the larger size hole.
FWIW did get these Ohm readings when testing each on the work bench with meter set at 200k Ohms, red to post black to body:
Borg Warner - 55.1
Standard - 82.7
Motorcraft - 15.3

So it looks like Motorcraft part # SW1547B is the one to use.
Gauge now reads just below about a 1/4 of the way up from the low side of the bracket on the gauge. Still running break-in oil so that might also contribute to it being a little on the low side.

Fuel gauge
Removed the sending unit(new cheaper "Good Repo" NPD unit) that was in the tank(new). Ran a ground wire to the new("Improved Repo" NPD unit) and dialed it in outside of the tank by bending the arm after at different reading on the gauge. Installed it, added 10 gallons to the 22 gallon tank and it read dead on 1/2. That sound be pretty right on since there may have been 1/2-1 gallon still in the tank, had the nose jacked up to get what was left in the tank away from the sender hole. The 1st sender was probably OK but would have needed major tweaking of the arm since 10+ gallons did even make it register on the gauge and testing it outside the tank and hooked to the gauge it had to be moved way more than 1/2 way to get the gauge to move off of the actual "E". My fault for not dry calibrating it while hooked to the gauge first.

Now only about another half dozen punch list items for it to really be done, done and released to the wild. Charge AC, get spare tire, put jack and wrench in trunk, ground heater/AC fan, etc.

Son now has about 121 mile on the car now after an outing for dinner tonight. Tomorrow he will stretch it's legs a little when he and his girl friend will take his '67FB and my wife and I will take our '65FB out for a few hours for a scenic drive and lunch.

BTW, Kelly you are my hero for your road trip. Just took a quick look at your blog for the first time, very similar to what I've been telling my wife we need to do. I want to make sure I start reading from the beginning, what is the start date and start location of your trip? Also, kind of glanced through some of it and IIRC you have a Viper alarm? How do you like it, would you recommend it?

These should look good together tomorrow.