89 Ranger oil pressure gauge problem

[marshall-matt]

Hi guys
I just bought an 89 4x4 ranger from craigslist. Got a good deal on it because the pre owners thought the rear main seal was gone because it started blowing oil. I figured id just put a rebuilt motor and bought it because body and interior was in good shape and it is a 5 speed manual which I wanted. Didnt even look under it while it ran till I got it home.
Well I started it up after hauling it an hour to home and crawled under. Immediately I saw the oil leak wasnt a seal but a leaking oil pressure sending unit. Got one from autozone, no leaks and runs incredibly smooth and quiet. No tapping at all.
My problem is this.

I turn the key on...idiot oil gauge goes up. Start it up..oil gauge goes negative of its key-off position.
I dont think oil pump is bad because before I changed the oil sending unit it shot oil out regularly while running. Im gonna go get a mechanical gauge and put it in but any of you guys ran into this before?
I love the truck..plan on driving It for work but I gotta make sure oil pressure is ok.
p.s. will post pics of truck later

 

[kimcrwbr1]

Is it a idiot light on the dash or a guage? You probably just got the wrong sending unit. The idiot light is just a switch that opens when oil pressure is present and the sender is a variable resistor the higher the pressure the less the resistance.

 

[marshall-matt]

Is it a idiot light on the dash or a guage? You probably just got the wrong sending unit. The idiot light is just a switch that opens when oil pressure is present and the sender is a variable resistor the higher the pressure the less the resistance.

Thanks for input.

its a gauge that has L-normal-H on it.
you are probably right its the wrong gauge. I know ive got oil pressure. Runs smooth as silk, no knocks or taps or anything. Needle just goes negative immediately its started. Ill take my old unit in and see if ig can be matched when I go get my mechanical gauge.
gosh im loving this truck so far. Even has working A.C. Great for these hot N. Carolina days

 

[kimcrwbr1]

Call the part store and tell them you need one for a guage not the light! My book shows oil pressure guage with tach only I take it you have a tach?

 

[marshall-matt]

QUOTE=kimcrwbr1;1529404]Call the part store and tell them you need one for a guage not the light! My book shows oil pressure guage with tach only I take it you have a tach?[/QUOTE]

Ive been gone since I posted last so I just saw your suggestion. I actually went back to parts store (autozone) and the guy there spent 20 minutes or so searching the book as well as on the website for a match to my old sending unit. He couldnt find one. Finally he suggested I try looking for a short between the switch and gauge. Im gonna try that but I really think its something else.

odd thing is that soon as I start the truck the needle goes backward (negative) on the dial. Doesnt stay dead or unresponsive...goes past the normal stop at (L). Almost like the switch is set up backwards.
I did get a mechanical gauge im gonna put in as soon as I get a minute. Long day of work tomorrow. But Ive driven this truck about 70 miles since I licensed it today and its doing very well. Seems low-geared tho. Ive gotta check the rearend and see what gear ratio ive got.


Link to picture of my truck (havnt figured out how to post pics yet)

http://www.image-share.com/ijpg-3010-86.html

 

[marshall-matt]

Call the part store and tell them you need one for a guage not the light! My book shows oil pressure guage with tach only I take it you have a tach?

forgot to add...yep it has tach gauge

 

[marshall-matt]

http://www.therangerstation.com/forums/attachment.php?attachmentid=18800&stc=1&d=1437449341

Ah figured it out somewhat. My truck. Not sure tho if this is the right place on forum for me to share it

 

[enjr44]

The oil pressure sending unit is nothing but a switch. Did the gauge work correctly with the old sending unit? If so take an ohm meter and measure from the wire terminal to the base of the unit. Write down the numbers you get. Now do the same with the new unit. You should get about the same numbers. If not - wrong sending unit.

There are two types of sending units. One type grounds the gauge with no oil pressure and then opens when the oil pressure goes above 6/8 pounds. The other type is open and then closes when the oil pressure gets above those 6/8 pounds.

Take the wire off the sending unit and then turn the key to run. The gauge needle should stay at the bottom of its range. Now ground the wire to the block. The needle should go up. IF it does the gauge and wiring is good.

If the oil pressure gauge goes up when you turn on the key and then drops when the oil pressure comes up you have the wrong sending unit. Doesn't matter what the parts guy is telling you. Wrong sending unit!!!!

 

[marshall-matt]

The oil pressure sending unit is nothing but a switch. Did the gauge work correctly with the old sending unit? If so take an ohm meter and measure from the wire terminal to the base of the unit. Write down the numbers you get. Now do the same with the new unit. You should get about the same numbers. If not - wrong sending unit.

There are two types of sending units. One type grounds the gauge with no oil pressure and then opens when the oil pressure goes above 6/8 pounds. The other type is open and then closes when the oil pressure gets above those 6/8 pounds.

Take the wire off the sending unit and then turn the key to run. The gauge needle should stay at the bottom of its range. Now ground the wire to the block. The needle should go up. IF it does the gauge and wiring is good.

If the oil pressure gauge goes up when you turn on the key and then drops when the oil pressure comes up you have the wrong sending unit. Doesn't matter what the parts guy is telling you. Wrong sending unit!!!!

yep I figure its wrong sending unit. Long day at work for me so didnt have chance to do anything with truck but ill get to it soon as I can.

Old sending unit gushed so much oil I never really got a chance to see what it did but I knos the new one they gave me works on opposite principle of what its supposed too. Ill get one that opens when there's pressure and I'll be fine. (Looking at guts of old unit I already figured out thats how it worked.

thanks guys for all your suggestions and sharing knowledge