Rep Power: 310

i bought a megan oil pressure gauge.
the replacement(came with gauge) sending unit is mounted on a "T" fitting (turbo feed line is on the "T" also), but its reading incorrectly.
car off it reads 0
turn key on engine off it reads 15
turn car on it reads 100 (pin goes all the way to its limit)

i have two wires on the back of the sending unit, one for the cars computer, one to the gauge.
discuss what it may be please!

p.s. i thought maybe its not grounding or something, so between the sending unit and the "T" fitting i put a grounding wire. but before and after this wire it has the same odd readings.

 
Rep Power: 424

Thats a wiring issue. Might be a finiky connection somewhere between the sensor and the gauge. The sender has to be grounded to something so you got that.
I fought this flicker problem which is what made me ditch the autometers way back when. Check the terminals on the back of the gauge, make sure they're not only correct, but not wiggling around where they may be off the contacts. Pegged to full is usually a sign of infinite resistance.

 
Rep Power: 310

well its not flickering, its just reading incorrectly. i doubt its the connections because i spend alot of time on my wire work to have it done better than factory almost. so it its got infinite resistance than the sending unit is bad?
will the stock sending unit work ok for this?
thx

 
Rep Power: 424

The stock sensor is an idiot switch, its just looking for a trip value to trigger the oil light on the dash. I think its set to 0 PSI, because I know for a fact that dropping to the single digits won't trip it. The gauge won't read anything but 0 and whatever it reads at 5V if you hook it up to the stock sensor. You can check the resistance of the sensor. Measure with the car off, measure with the car idling, then get someone to rev it a little... keep track of the resistance with a multimeter. It should be changing as you go, that sensor is just a potentiometer.
If you tried it with the sensor with the ground wire and ungrounded, then rule that out. just be sure its on a good solid ground. Usually bolting the sensor to the engine block is good enough.
also measure between the terminals in the gauge. If the fuse to whatever circuit its connected to hasn't blown yet, thats a good thing. Also check to make sure there's no **** stuck in the little port on the sensor thats in the oil passage. Something like a little end of the teflon tape can jam that port open and it'll mess it up too.

 
Rep Power: 310

is it possible that the wire from the car(connected to the original sensor) is somehow causing this? maybe it is feeding a 5v+ to the original sensor , then as the resistance changes (oil pressure cahnges) it is measuring the drop or raise in voltage in the circuit, that is why the sensor is grouned???
if so than either, A. i have to put the signal wire for the gauge on the opposite end, in place of the ground, or i have to disconnect the stock wire and see waht that does.
my DMM is at school in my box so i cant use that yet, so 2moro i will just try removing the stock wire, although id like to know what you think of trying the above method.

 
Rep Power: 424

Don't disconnect the stock sensor, you'll throw a CEL for no oil pressure.
Its 2 different wiring sets, they act independent, one will not mess up the other.

 
Rep Power: 310

but if the ecu supplies a 5+volts then it will skip straight to my new gauge. this will cause the gauge to read to its max capacity. and cause no resistance in the circuit for the ecu which would explain i have the oil light on.

 
Rep Power: 424

wait... why the hell is the ECU involved in this at all?
There should be 3 terminals on the back of the gauge (lights excluded). Ground, 12V power and sensor signal.
Ground and 12V come from the car's existing wiring, then there's a direct wire from the gauge sensor to the back of the gauge. The ECU should not be involved with this.

 
Rep Power: 380

I was thinking the same ting.

 
Rep Power: 310

where the wire goes from gauge to sending unit, on the sending unit theres two signal wires. one for gaguge one for ecu. thats why im mentioning the ecu.

today i disconnected the gauge signal wire and it was still at 100psi. so only the ecu signal wire was connected to the sending unit, but the light was still on.

 
Rep Power: 0

i would get this perf installed if ur haveinf this much problem ....the ecu should have nothing to do with this

 
Rep Power: 310

buddy i am a professional. ive done tons of things harder than this (including making my own car alarm systems), in fact im ase certified in electricity and electrical components. the real problem here is that im being lazy and not trying everything i should because im still finishing up a couple other last minute things. i was just hopin someone else had this problem to help me quicker.
and the ecu is involved because my oil lamp is still on, and its wired to the same sending unit. ..... reading posts owns you!

edit: and i found out last night i have to "T" it off again to put stock idiot light on too.....ughh

 
Rep Power: 380

dude this is the never ending problem project for ya, atleast it isn't as bad as the bent valve.

 
Rep Power: 310

hahahha dude tell me about it.
but i can get it tuned and running without the gauge at least, but ill fix it eventually. gonna try a couple things now and if it dont work ill really diagnose it some other time. dont have any more free time.

on a side-note, could be as unlucky as my buddy who spent 5g's on parts for his gtp, then halfway through he noticed a cracked piston so he has to pull the engine and he spend another 3 on more upgrades lol.