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Old 04-03-2012, 01:57 PM   #1
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Question Oil Pressure Sending Unit ?

I have a '89 F150 5.0 Manual .
I have noticed that on idle oil pressure is dropping to zero and or wandering very low , when it was doing this I was listening to the motor and I did not hear any valve noise or bearing noise so I am hoping it is just the sending unit that is going bad , this is a new truck to me and has only 60K miles on it , also I paid attention to the idle when it was doing this and no change in idle either , when it did this ( it did it many times today when I had it out ) , I also noticed I could just touch the accelerator and it would come back up and stay solid , it was doing this intermittently and this is the first time I have seen this in the 300-400 miles I have put on it so far , I am going to change the oil ( have not done that yet since I purchased ) and the sending unit .
I did see the check engine light flash when it got low but I am assuming that the computer is getting its info from the sending unit therefore if the sending unit is bad then that should be expected.
I figured I may as well change the oil and from what I have learned , the sending unit is just above the filter so should be more accessible with filter out of the way , I will buy the sending unit and the socket for it and if I see it is a wiring issue or plug issue while changing the oil then I will just fix the problem and return the parts , otherwise I will go ahead and replace the sending unit if wiring and plug to sending unit are in good repair and connected properly and see if it is still acting up.
It could be a short as well I would imagine but seeing that the truck sat a whole lot in its life I am guessing the sending unit is going bad , any input or other ideas would be appreciated.

Last edited by n4ynu1010; 04-03-2012 at 01:59 PM. Reason: Typo
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Old 04-03-2012, 02:54 PM   #2
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A 27mm 6 point socket should work for the sending unit. Don't buy the high dollar sending unit socket. I know for a fact that the 27mm works perfect on the 94 5.0 and the 95 4.9!
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Old 04-03-2012, 09:09 PM   #3
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Default Oil Pressure Sending Unit ?

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Originally Posted by unit505 View Post
A 27mm 6 point socket should work for the sending unit. Don't buy the high dollar sending unit socket. I know for a fact that the 27mm works perfect on the 94 5.0 and the 95 4.9!
This particular one is 1 1/8" , maybe that is the same as 27mm but I had one at home , I checked it at the store before I left
Also , it seems it was the sending unit , though I have not driven it as much yet , I have not seen the fluctuation at all as of yet , I changed the sending unit after removing the oil filter which made it much easier to get to.
I guess I also need to clear the codes again seeing the sending unit failure was causing the engine light to flash each time it dropped , I will disconnect battery and reset tomorrow morning.
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Old 05-23-2012, 12:53 AM   #4
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I had the same problem in my truck, and after a while it just stayed at nothing, oi replaced the sending unit, and no change, What else could i check?
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Old 05-23-2012, 10:28 AM   #5
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I had the same problem in my truck, and after a while it just stayed at nothing, oi replaced the sending unit, and no change, What else could i check?
I put a manual/analog oil gauge on the truck , I took the sending unit out and put a 6" brass nipple in its place with a Tee on the end , I then put the original sending unit back in the tee and out of the other leg of the tee I ran the oil line for my manual gauge , I found that the pressure is really low , this way I made sure it was not the gauge in the cluster and or wiring , now I am replacing oil pump and pickup screen to rule out pump being bad and or trash/sludge in pan stopping up screen , I had a operation so I to postpone this for a bit , if I do not find trash in the pan or other problem and new pump does not solve pressure problem then it will be clear I need a new motor or maybe I will be able to replace main and rod bearings and solve the problem , I will let you know what I find , it will be a couple of weeks before my incision from the operation heals enough for me to get it done .
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Old 05-23-2012, 01:16 PM   #6
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Before you go thru all that trouble, give the engine a good flush. Gunk motor flush comes in gray quarts. Dump 1 into your oil, when warm, and let the truck idle for 5 minutes, then shut off. Change oil and filter, and see if you notice a difference. I have brought back trucks with absolutely 0psi oil pressure, right back to factory specs. Some take more than one application, but way easier and cheaper than doing an oil pump. Worst case scenario, you still need an oil pump, and you only lost the cost of an oil change.
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Old 05-23-2012, 11:17 PM   #7
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Default Oil Pressure Sending Unit ?

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Before you go thru all that trouble, give the engine a good flush. Gunk motor flush comes in gray quarts. Dump 1 into your oil, when warm, and let the truck idle for 5 minutes, then shut off. Change oil and filter, and see if you notice a difference. I have brought back trucks with absolutely 0psi oil pressure, right back to factory specs. Some take more than one application, but way easier and cheaper than doing an oil pump. Worst case scenario, you still need an oil pump, and you only lost the cost of an oil change.
If the Pan is full of sludge I will do that , I have already used 2 treatments of Sea Foam and changed the oil twice and that did nothing , I have a friend that said he had one that was all sludged up in the base of the pan , I am hoping that is what it is at this point , the truck is a '89 and it was a gift , the people that gave it to me said that it only had 60K original miles , I am thinking it is 160K and just worn out , but hoping that it is just has some junk in the belly of the pan picking it up when warm as it starts circulating , I can start cold and the pressure on the manual gauge is above 55 psi /w 10-30W in it , I have never seen a worn out motor have that kind of pressure cold , plus the truck sat for over 3 years and they did not change the oil before they drove it here , I found some beetle wings in the input side of the oil filter so I think it is worth the effort to replace pump and strainer , it is not that hard anyway , jack motor up and drop pan down and replace without taking pan completely off , it is not that hard of a job on these trucks , you can remove upper intake and jack up further to get pan off completely but I am not going to remove upper intake , just going to replace with pan lowered .
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Old 05-24-2012, 07:30 AM   #8
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Seafoam is nowhere near as effective as the Gunk engine flush. Id try that before you do ANYTHING! At least if it doesnt work, you KNOW you are doing the oil pump.
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Old 05-24-2012, 07:53 AM   #9
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I have used engine flush. It works. Be prepared to develope some major oil leaks if the sludge in your engine is blocking any. I've had good luck with a tripple oil change using 5w30 as my flush. Put it in, run it hard for 15 minutes and repeat several times. A little expensive, but vs. new seals, it was cheap! After several oil changes, go back to your prefered oil and a new filter. Just my 2 cents.
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Old 05-24-2012, 08:11 AM   #10
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Just for info the oil presure sending unit and gauge in Ford products does not messure actual oil presure but is just a simple on off switch. When it senses any presure above about 5 psi it turns on and this caueses the gauge to move to apredetermind point on the dial [about half way] and it reads the same regardless of actual oil presure. so the so called gauge is just an idiot light with a pointer instead of a light bulb. it is comon for these switchs to go bad but before you change it pull the wire off and clean and tighten it the conecter gets oil soaked and loose somtimes all it takes is to put a new end on the wire or squeese the old one tighter
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Old 05-24-2012, 08:11 AM
 
 
 
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