NO OIL PRESSURE. HELP NEEDED PLEASE

fiveoho

fiveoho

15 Year Member
Apr 28, 2005
1,958
16
69
TN
#1
decided about 15 min ago i would start my car, after sitting in the garage for a week. started right up but idled very rough for 2-3 seconds then adjusted and smoothed out. i looked down at my gauge and no oil pressure. i quickly cut the car off. the gauge itself i believe is working because with the car off, the needle was bottomed out, with the car on the needle was under the red mark.

its a 2000 gt with 87,000 miles and no mods other than a programmer. had it about 3 weeks and the oil pressure has been just fine ever drive its been on. needle is right in the middle.

could this be the oil pump? if so, isnt it odd to take a dump at 87k?

could it be the oil sending unit? this just controls my gauge, correct? if that be the case, then i actually have oil pressure - correct? but why would the needle move if the sending unit is out?

car ran a total of about 7 seconds. i noticed no motor noise and ticking. did i hurt anything?


other ideas??
 

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#7
Being it a 2000, I doubt it to be a oiling issue, but you never know. Trace down the oil pressure sensor and make sure it's hooked up. I could tell you where it is on a 5.0 Mustang but I have never paid any mind to it on my 4.6L
 
#8
1987stangman said:
Being it a 2000, I doubt it to be a oiling issue, but you never know. Trace down the oil pressure sensor and make sure it's hooked up. I could tell you where it is on a 5.0 Mustang but I have never paid any mind to it on my 4.6L
Click to expand...

from searching a few forums and googling, the oil sending unit seems to be a fairly popular issue. i sure hope thats it rather than the pump.


ive had two people say that it being so cold outside and it not being started in a week that 7 sec was not enough time for the car to make oil pressure. is this true?
 
#9
If the oil pressure gauge in question is the one on your factory dash/speedo cluster, then yes, it is PROBABLY just a bad factory oil pressure switch/sending unit (the little black plug w/ harness that should be threaded into the oil filter housing area; not sure of the exact details on a GT, but it should be pretty similar to the location of my '01 4v engine).

I had the original/factory oil pressure switch/sending unit fail on my '01 snake. Purchased a replacement switch/sending unit for roughly $10 or so.

I sure was glad that I was also running an aftermarket oil pressure gauge at the time because seeing zero oil psi would definitely be a SCARY thing ! :D
 
#10
COBRA90GT said:
If the oil pressure gauge in question is the one on your factory dash/speedo cluster, then yes, it is PROBABLY just a bad factory oil pressure switch/sending unit (the little black plug w/ harness that should be threaded into the oil filter housing area; not sure of the exact details on a GT, but it should be pretty similar to the location of my '01 4v engine).

I had the original/factory oil pressure switch/sending unit fail on my '01 snake. Purchased a replacement switch/sending unit for roughly $10 or so.

I sure was glad that I was also running an aftermarket oil pressure gauge at the time because seeing zero oil psi would definitely be a SCARY thing ! :D
Click to expand...

scary thing is right! im still very nervous not knowing for sure what the problem is. praying it isnt the pump. ive been seeing these sending units getting a bad rap and im hoping thats what the problem is

the rough idle that i got when i initially started it up...its never done that. could that be associated with a oil circulation problem ( if thats what it is ) or is it just most likely coincidence it being pretty cold and damp tonight along with not being started in a week? car is in a garage but not a insulated one. block walls, open rafters and gravel floor
 
#11
Sounds exactly like the sending unit or the wire going to the sending unit. If the engine sounds fine then you have oil pressure. I had a similar problem with my F-150. Going to work one morning I looked down at the guages and oil pressure was on zero. Truck ran fine and sounded fine. I limped it back home and drove my Cobra to work. Turns out it was the sending unit. Bought a new one for about 10 bucks (even had the thread sealant on it) and everything has been fine since.
 
#12
The oil sender is actually a simple on/off circuit. If greater than 6 PSI, the sender is grounded. Less than 6 PSI, open circuit. The position of the neddle has no relationship to the actual oil pressure. It is an analog idiot light.

The wire connection at the sender could be dirty and not making good connection.

The gauge is easily tested by removing the wire from the sender and grounding. If guage reads OK, then the guage is working.

Measure the resistance to ground through the sender. It sould be open with the motor off. Motor running, it should read low resistance. This will narrow down to a wiring problem or sender problem.

The bad thing about the tests, is they can not tell the difference between a true low oil pressure problem and a bad sender. The sender is cheap enough and easy enough to change for diagnostic purposes (that is unless you have an alternate way to measure oil pressure). Recommend to do the tests or just change the sender.
 
#13
with the help of a enlisted friend, will be putting a mechanical gauge on it tonight and see whats up. how much pressure should a stock pi 4.6 make on a cold start with 5w20 ?
 
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