Question
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Followup ToDave Ward
Thank you for your help. I was not able to show any continuity. I assume this leave the gauge or the oil pump? I'm now concerned to drive it even though the engine sounds good. What is your suggestion?
Again, thank you.
Dave in Atlanta
Question -
Good afternoon,
My oil gauge started moving eraticly and it will stay on zero and then move to 15psi and back to zero. I replaced the oil pressure sending unit, no help. The engine has oil and it sounds fine. How do I trouble shoot the gauge? What else could it be?
Thanks so much for your help.
Dave
Answer -
Hi Dave,
If this condition started all of a sudden, and it is very erratic, as you say; the most likely culprit is a wire connection that is loose. This would cause the gauge to sometimes receive all the voltage it is supposed to and other times receive part or none of what it is supposed to.
Since you replaced the sending unit, we'll eliminate that end of the wire as the problem; that connection is secure, right? So, the loose connection has to be at the gauge, or a regulator wired in line with the gauge; and, probably part of the instrument cluster. I'm assuming the gauge is OEM. The other possibility is a short. The most likely culprit here is when the sending wire passes through a firewall hole, for example. Any hole with a sharp edge can wear away the insultation and allow the copper wire inside the insultation to touch the edge of the hole and ground out.
The preliminary testing you can do is this:
Disconnect the sending unit connection. I am assuming there is only one wire. This means the sending unit is "grounded" by being screwed into the engine block. And the block is well-grounded by having its own ground wire running over to the battery itself, or to the well-grounded chassis. If you haven't already guessed, it would be good to re-verify the engine block is very well grounded (read securely).
With the ignition 'Off' and the sending wire disconnected, attach your continuity tester to the negative battery terminal and to the loose wire end. There should be no continuity. Meaning the loose sending unit wire should not be grounded. If there is continuity, it means that wire is touching a grounded chassis part. If there is no continuity try to jiggle the wire and see what happens. If jiggling (or vibrations) creates continuity, then it's a bare wire situation. You'll have to trace the wire from the loose end to the instrument cluster focusing on the edges of holes.
There's still a likelihood the gauge is the problem, but testing it requires some special items. Try the other plan first and write back to let me know what you find. Thanks.
Dave
AnswerHi Dave,
You'll have to make the call as to whether to not to drive the car, but from here, it seems the gauge is the problem...I'd be hard pressed to start pointing at the pump itself. If it was the pump, you'd imagine the gauge would fall to zero and stay there, or show very low pressure all the time, not those weird fluctuations.
Here are two paths to take. Both will deal with the idea that the sending unit varies the voltage signal as it "reads" the actual psi and...as voltage varies the gauge reads different psi's.
1. If you connect the positive probe of your multimeter to the sending unit's wire and the negative probe to the negative battery terminal...you should see varying voltage readings at idle and then in drive (with the parking brake on)... and the voltage readings should, in general, climb and fall smoothly rather than erratically. iF you see these results on the multimeter. the new sending unit is working fine.
2. To simulate the sending unit's signal, you have to get creative. What I'd do is find an old light switch, the kind that when you turn the knob the brightness of the dash lights changes...got it? If you wire the brightness functionality between the battery's positive terminal and the gauge's wire, and you turn the knob, you are varying the voltage to the gauge...if the gauge is working properly, it will register changes in the voltage as the knob is turned...and if you leave the knob unchanged (meaning the voltage is unchanged) the psi reading will remain constant. If so, the gauge is working. Note: to be safest, you should probably wire in a fuse into that line to protect the gauge.
I hope all that makes sense.
Let me know, OK?
Dave
