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Oil Pressure Gauge not working

S

Steve Diomin

Contributing Member
I have a 1998 Crownline 202br 5.0l carbed mercruiser. 250hrs
My problem is the oil pressure gauge isnt working and im not sure what is left to do, here is a sumary of whats going on.
Baby blue wire goes from sending unit to the gauge on the dash
Gauge reads zero oil pressure ( yes i do actually have real oil pressure)
Got 12 vlts at the gauge, plus tested the gauge on the bench and got deflection. Grounded the wire at the sending unit and get nothing on the gauge. Ohm the sending unit and get 240hms at zero oil pressure, so that checks out.
So the gauge is good and the sending unit sems to be good, i cant see anywhere where there is or would be a problem with the single blue wire........
Im up for some sugestions and some input and I have 1 question. The purple/yellow wire that is connected to the oil pressure switch (not the sender) is not connected at the other end in which is the starter solenoid as the wiring diagram indicates it should be...........Does the oil pressure switch with the yellow/purple wire have anyhting to do with making the baby blue wire and the oil pressure sender work?

ANy input would be awesome.

Thanks
 
re: " i cant see anywhere where there is or would be a problem with the single blue wire........"

Well, there is...

One further check (and procedure) since you apparently have a multimeter.
Remove the blue wire from the sender and measure the voltage between the blue wire going to the dash and ground. It should be 12 volts. If its not, you have to trace it back and see where it disappears. One point to check, if your engine is "connectorized" is the connector.

Re: the oil pressure switch. If you engine has an electric fuel pump, that switch is used to shut down the fuel pump if the oil pressure drops to zero, i.e., the engine stops...or should.
 
The wire connector at the gauge may be corroded internally. Cut it off and see if the wire is blackened. Strip back 1" of insulation and clean the strands of wire w/some 600-800 sand paper by pulling the wire between the folded sandpaper. Twist it tight, flux and solder it to a new shrink wrap connector.
 
1 side to the wire, the other side to a good ground. ign. on should show 12V , if not start tracing back to the dash.
 
it is measuring 7.7volts......i tried wiglling the moldex connector but no change. By moldex pin i mean like the main 10 pin or whatever it is connector.
 
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You need to connect a ohm meter (one lead)from the disconnected signal wire on the back of the oil pressure guage to the diconnected wire at the sending unit. If you have continutity then its either the guage or the sender........If not the there is a break in the wire somewhere
 
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so am i testing for ohms or volts??............i thought i was told to see if ther was 12volts travelling threw that blue wire? when hooking the volt meter to this blue wire i got 7.7volts. On end of the wire was hooked up to the gauge, the other end i took off the post of the oil sending unit. SO i tested between the wire coming of the sending unit and a ground.
 
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OHMS!!!!!!!

do you know how to test a fuse with your meter set to ohms and ~ 1k ohms or 2k ohms????

I am home today if you want to speak about this send me a PM with your phone number........
 
NO,

12 volts is only to power the guage!!!

The sending unit has NO power to it at all. It is strickly a varialble resistor.

The guage needs power to make the needle work. As the resistance changes so does the needle.

The ohms test is not to test the sender or the guage, it is to test the wire from the guage to the sender to see if it is broken!!!!!!!!

Do you understand?
 
this ones got me.
i just ran a new wire from the sending unit to the back of the gauge and still nothing. Nothing meaning the guage isnt even flickering.like the rest of them flicker alittle bit as son as you turn the key to on. But i have 12v at the gauge.
 
You need to remove the sender and apply heat if you are not running the motor to let it warm up.

Also just because a needle jumps when grounded does not mean the guage is good, it only means it jumps!! It is powered up and responds to a direct short to ground. That does not equal it works.......
 
ok, i will try actually running the engine and letting it warm up and see if that changes anything, if that doesnt work les talk. my number is 905-380-7775
i'll come back in about 20mins.
 
I made on error, I said warm up I meant to say let oil pressure build up...........

Also I called and got VOICE MAIL!!
 
ok, well i definatley have readings at the sendor so my question is this and sorry if you tole me this but ifi I put my ohm meter on the gauge, the red on the sendor post of the gauge and the black on the ground post of the gauge should i be getting the same readings as i was at the oil sender unit?............if so i'm not. i'm not getting anything at the gauge when testing there for ohms.
 
NO

remove the sender wire off the back of the guage clip your red lead to that.

Touch the black lead to a ground. you should use the guage ground, if that does not work try another. If the gusge ground does not work then that is a issue.

If you do not get a meter reading then you have a sending unit wire issue.

start the engine and see what readings you get. They should be very close to what the sender readings were.

Remember the wire colors that should be going to the guage are

PURPLE = ingintion on, activates the guage
lite BLUE = sending unit wire
black = ground

dark blue if there is for the lights.

The only red wires will be for things that have power ALL the time such as switches, bildge pump, blower, ignition switch.......
 
ok, red wire went to the sendor post with no sendor wire attached, and black went to the black ground on the gauge, no readings.........engine running
 
not the sender post the sender wire.............

Of course there will be no reading at the post with NO wire on it......
 
Ok here is what we know so far.


Engine running, new sending unit, ohms reading is ~ 110 ohms at the sender.
red lead of meter to sending unit post, no light blue wire attached to sender.
black lead to sending units base.

same reading when black meter lead is toched to any engine ground. ~110 ohms.

This says the sending unit is working correctly.

240 ohms = 0 pressure.
80 ohms = 100+ pressure

so he is at ~ 60 lbs of pressure with a ~110 ohm reading.

Reconnect Light blue wire to sender

go to guage and disconnect light blue from guage.

red meter lead to wire, black to ground, start engine, meter reads ~290 ohms.

this tell me the guage will or should go negative and that is what he is seeing.

Diconnect light blue wire from sending unit, connect new/different wire to sending unit, one long enough to reach the guage. connect red meter lead to the new wire with it NOT connected to the guage. black lead to a ground at guage cluster.

reading ~110 ohms. this is what it should be.

He will do some additional testing and get back,

next tests are,

connect new wire to sender and to guage start engine and see if pressure guage reads.

Yes or no?

If yes the problem is the light blue wire. if no I have no idea at this point......

Anyone else have any suggestions????????
 
ok herers what was done.
new ground wire run from neg battery to black lead of meter
disconnect sender unit wire from gauge
connect red meter to sender unit wire
start engine.
results: 240ohms at no oil pressure (when the engine was off)
100ish and under for running engine
 
If that is the case then you have a ground problem.

I thought you did this when on the phone with me and there was no change in ohms readings????? It stayed at 290 ohms........

If what you just posted is true then it is a bad ground and connecting a good ground to the guage should fix it.

Make sure what you posted is correct.......sounds conflicting.
 
ok well, i guess to confirm whatever i said i will connect this new ground right to the back of the gauge and put the blue sender wire back to where its supposed to go and see if the gauge registers...........back in a few.yes what i posted is what i did.
 
ok when i reconnect the sendor wire to the sendor terminal on the gauge and use the new ground run form the negative battery terminal to the ground post on the gauge, fire the engine, gauge doesnt move, reads zero.
 
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