2005 Mustang GT cold start, Oil Pressure gauge reporting 0
 

I had originally posted this in a section that was closed so it was suggested i repost it:

Hey All
I did a search but it's a pretty obscure topic and nothing up

here's a strange issue.

When i start my 2005 Mustang GT 5spd, weather i use the Key or Remote start with my compustar 5000 alarm, the car will start as usual but the oil pressure gauge is reporting 0. nothing. this happens ONLY when it's fairly cold outside. when it's warmer this is a non issue.

I took the car to the mechanic and he diagnosed it to be the oil sending unit and i changed that out thinking this was the issue.
the next morning it was fairly cold again, i remote started the car and it was reporting 0 again.

if I get in the car, with it running from the auto start, i put the key in, clutch and turn the key as if i'm starting the car the dash will reset, and all the gauges report normal again.

any ideas.

this issue happens when it's very cold, using the remote start OR the key, either way it's sporadic and trying to diagnose what the issue is

i thought it may be this:
https://mustangforums.com/forum/2005...r-cluster.html

but then i started thinking if the cluster was bad it would always be bad and not sensitive to temparature.....


any tips would be appreciated.

Ignoring what the gauge says for a moment, what does the engine sound like for the first few seconds after it cranks over and the gauge reads '0'? Also, are you using a non-OE oil filter? What brand and weight oil?

Also, note that our oil pressure gauge is really an idiot gauge; the sender is a switch and the gauge only reads that there's pressure or not. It does NOT change with pressure fluctuations. I'm taking a WAG here that when the oil is cold, the switch isn't actuating until the pressure is getting up to a specific value. In other words, you HAVE pressure but just not enough to activiate the switch for a few seconds. It's a cheap system; another area that Ford could have improved on.

Engine starts and sounds fine. I'm running royal Purple 5w20. The filter I don't know but my mechanic uses quality parts.

Thanks for the help

The thing is the gauge will never report unless I clutch. Break. And turn the key as if I'm starting the car again. The starter won't engage because the motor is running. This resets the gauges and then the oil pressure will start reporting.

Try this....just seconds after a cold start...gauge reads "0"....shut car off and restart....does it still read "0?" Sounds like more of a computer issue....not reading the signal properly.

Try setting up an temporary/alternate light from the factory sender and see if it is putting out a good signal when the gauge reads 0. If that works, you know the sender is doing its job...even if previously replaced. Then, track the signal as to where it goes and take readings at any plug it travels thru. Check the wire in and out of the computer....see if the signal is getting thru there. Just keep checking wires and at some point, you will come across the problem.

As with any sporadic problem, you may have to leave a tester/light hooked into the wires to see the reading when it acts up next.

I would suggest you get into a wiring schematic to track this down.

I truly doubt you have an oil pressure problem. It sounds like just an instrument issue. Scroll down to find the wiring for the oil pressure switch to the SJB wiring. You should be able to find the diagram for the wiring from the SJB to the gauge.
http://iihs.net/fsm/?dir=40&viewfile...nt Cluster.pdf

I have an 01 explorer sport that does exactly the same thing in the same conditions for years. I also agree its a dummy switch. It can take minutes when its really cold (below freezing) to come up. But I know I've got oil pressure and there's no difference in the sound of the motor, so for me I just ignore it.

I believe it's your stepper motor within that specific gauge. I had the same issue with my fuel gauge when it was cold then once it was warmer it would work most of the time. I'm banking on a bad stepper motor.

So replace the gauge itself?