Oil Pressure Gauge not working - except......
06-14-2018, 09:07 AM
#1
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Thread Starter
Oil Pressure Gauge not working - except......
Ok, I'm an electrical guy, and have this half figured out, but wonder if there is a history of this problem in this series of F-150's.
Several years ago, my Oil Pressure gauge quit working. BUT, on interstate trips over 45 minutes, it starts working again. I.e., when the engine and engine bay get good and hot. Easy diagnosis - there is a break in wire somewhere in engine bay. When wire gets hot, it expands, makes connection, OP gauge works fine. When it cools, connection breaks and gauge quits working again.
I put in new sending unit, pulled dash to see if a problem there (even tho I know it has to be in engine bay) but could not identify wire in harness from OP gauge.
Installed new sending unit wire from sending unit to as far as I could go in wiring harness going to dash on top of engine. No change.
Gauge still works fine when engine gets good and hot. Doesn't work if not hot, which is 98% of the time.
Is this a known problem, and is there an easy fix? I don't expect that it is. Is there any connection in the wiring harness between the sending unit and the dash? 99.9% of electrical problems are at connection points. Cannot see one in schematic in my Haynes manual.
Have a real OP gauge with tube to new sending unit, but would rather get the original gauge on dash working, as I know it is fine.
TIA to everyone,
GN
Several years ago, my Oil Pressure gauge quit working. BUT, on interstate trips over 45 minutes, it starts working again. I.e., when the engine and engine bay get good and hot. Easy diagnosis - there is a break in wire somewhere in engine bay. When wire gets hot, it expands, makes connection, OP gauge works fine. When it cools, connection breaks and gauge quits working again.
I put in new sending unit, pulled dash to see if a problem there (even tho I know it has to be in engine bay) but could not identify wire in harness from OP gauge.
Installed new sending unit wire from sending unit to as far as I could go in wiring harness going to dash on top of engine. No change.
Gauge still works fine when engine gets good and hot. Doesn't work if not hot, which is 98% of the time.
Is this a known problem, and is there an easy fix? I don't expect that it is. Is there any connection in the wiring harness between the sending unit and the dash? 99.9% of electrical problems are at connection points. Cannot see one in schematic in my Haynes manual.
Have a real OP gauge with tube to new sending unit, but would rather get the original gauge on dash working, as I know it is fine.
TIA to everyone,
GN
06-14-2018, 11:40 AM
#2
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Location: Memphis, TN, Earth, Milky Way
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A mechanical gauge is a bad idea, for several reasons.
What exactly do you mean by "quit working"? Does the needle simply stop where it is? Or does it swing to one of the pegs? This TSB explains what Ford did to the oil gauge:
(phone app link)
The links in the caption explain how to make it actually work again.
This site has the wiring diagrams:
http://www.bbbind.com/free_tsb.html
What exactly do you mean by "quit working"? Does the needle simply stop where it is? Or does it swing to one of the pegs? This TSB explains what Ford did to the oil gauge:
(phone app link)
The links in the caption explain how to make it actually work again.
This site has the wiring diagrams:
http://www.bbbind.com/free_tsb.html
The following users liked this post:
Gatornapper (06-15-2018)
06-15-2018, 08:07 AM
#3
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Thread Starter
Steve - as always, thsnks.
Gauge swings to zero. As when engine is off. Get engine hot enough (high ambient temp makes it happen quicker), and the gauge functions properly and shows good oil pressure with needle about 2/3 of the way over from zero.
The bad reasons for a mechanical gauge are why I have not yet installed one.........
Will check out the info you sent....you are a living encyclopedia of things re: old F-150's......an incredible resource.
BTW, thanks to you, my sweet '96 is still running like a dream.....
Gauge swings to zero. As when engine is off. Get engine hot enough (high ambient temp makes it happen quicker), and the gauge functions properly and shows good oil pressure with needle about 2/3 of the way over from zero.
The bad reasons for a mechanical gauge are why I have not yet installed one.........
Will check out the info you sent....you are a living encyclopedia of things re: old F-150's......an incredible resource.
BTW, thanks to you, my sweet '96 is still running like a dream.....
A mechanical gauge is a bad idea, for several reasons.
What exactly do you mean by "quit working"? Does the needle simply stop where it is? Or does it swing to one of the pegs? This TSB explains what Ford did to the oil gauge:
(phone app link)
The links in the caption explain how to make it actually work again.
This site has the wiring diagrams:
http://www.bbbind.com/free_tsb.html
What exactly do you mean by "quit working"? Does the needle simply stop where it is? Or does it swing to one of the pegs? This TSB explains what Ford did to the oil gauge:
(phone app link)
The links in the caption explain how to make it actually work again.
This site has the wiring diagrams:
http://www.bbbind.com/free_tsb.html
06-15-2018, 08:18 AM
#4
Member
Thread Starter
Steve -
1. Have replaced sending unit. It works fine without the resister. I had read of this "fix" before - not needed on my truck. When gauge works (hot engine bay), it does not jiggle/wiggle, stays steady at 2/3rd position, lowers a little at idle, but not much. Oil pressure is fine- I've tested it with mechanical gauge. Also tested resistance on new sending unit and it is working properly.
2. The problem is total loss of "signal"/electrical connection (continuity) to the sending unit. High engine bay temp re-establishes the electrical continuity and all is well working as designed.
3. I personally do not believe that the loss of connection is in the instrument cluster connector. The temp inside the truck cabin does not change that much in spring. In winter, it takes a lot longer for the gauge to work, for the engine bay to get hot. In the summer, with higher ambient, it starts working in less time. There is not enough temp change in the cabin to cause this, but there is in the engine bay.
1. Have replaced sending unit. It works fine without the resister. I had read of this "fix" before - not needed on my truck. When gauge works (hot engine bay), it does not jiggle/wiggle, stays steady at 2/3rd position, lowers a little at idle, but not much. Oil pressure is fine- I've tested it with mechanical gauge. Also tested resistance on new sending unit and it is working properly.
2. The problem is total loss of "signal"/electrical connection (continuity) to the sending unit. High engine bay temp re-establishes the electrical continuity and all is well working as designed.
3. I personally do not believe that the loss of connection is in the instrument cluster connector. The temp inside the truck cabin does not change that much in spring. In winter, it takes a lot longer for the gauge to work, for the engine bay to get hot. In the summer, with higher ambient, it starts working in less time. There is not enough temp change in the cabin to cause this, but there is in the engine bay.
A mechanical gauge is a bad idea, for several reasons.
What exactly do you mean by "quit working"? Does the needle simply stop where it is? Or does it swing to one of the pegs? This TSB explains what Ford did to the oil gauge:
(phone app link)
The links in the caption explain how to make it actually work again.
This site has the wiring diagrams:
http://www.bbbind.com/free_tsb.html
What exactly do you mean by "quit working"? Does the needle simply stop where it is? Or does it swing to one of the pegs? This TSB explains what Ford did to the oil gauge:
(phone app link)
The links in the caption explain how to make it actually work again.
This site has the wiring diagrams:
http://www.bbbind.com/free_tsb.html
06-15-2018, 03:33 PM
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Location: Memphis, TN, Earth, Milky Way
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It works fake because of the factory resistor in the cluster.Not if you don't want to see changes in oil pressure.That's strictly electrical - it has nothing at all to do with the engine oil pressure.
I doubt it. The kind of failure you're imagining would be unbelievably rare - I've never observed it or heard of any other technician encountering it, in decades of electrical work on vehicles. The most-likely cause is a bad pressure switch. The next most-likely is corrosion at the pressure switch terminal on the wiring harness. Next is an intermittent open circuit at the instrument cluster connector. Next is low oil pressure.
A break in the circuit that magically fixes itself is off-the-map unlikely. There are only 5 connections in the oil pressure signal circuit: the switch's stud, the engine connector (C101 beside the engine fuse block), the firewall connector (C202), the cluster connector, and the clip that joins the cluster film circuit to the gauge's post. If you run a new temporary wire from the switch to the clip (an overlay), you can see if it's a circuit fault or not.
A break in the circuit that magically fixes itself is off-the-map unlikely. There are only 5 connections in the oil pressure signal circuit: the switch's stud, the engine connector (C101 beside the engine fuse block), the firewall connector (C202), the cluster connector, and the clip that joins the cluster film circuit to the gauge's post. If you run a new temporary wire from the switch to the clip (an overlay), you can see if it's a circuit fault or not.