Oil Gauge 87 gt (Page 1/3)
jon m NOV 05, 09:34 AM
Hi - Its been many years since I posted here and worked on my car so please bear with me as I am a little rusty in the Knowledge Dept.

Right I have got my fiero back on the road all good there - However when I put my key in the ignition the oil pressure gauge pegs straight over to the right.
Quite a few years ago I got a pigtail and a 88 sensor and just looked at that and one of the pins on the sensor is shot - I have diconnected the pigtail from the original 87 plug and the gauge still goes all the way to the right and stays there with the key in the ignition.
So I am thinking there is a ground problem however if anyone has come across this problem then maybe they could give me some pointers ??

Many Thanks in Advance

Jon
pmbrunelle NOV 05, 10:31 AM
The oil pressure sender varies its resistance depending on pressure:
0 Ω 0 psi (0 kPa)
90 Ω 80 psi (550 kPa)

The resistance is measured from the gauge wire (goes towards the instrument cluster) to the threads of the sensor, which is electrically connected to the engine block.

If you just disconnect the oil sender connector and leave it floating in the open, then that is like infinite Ω, which results in a gauge pegged at maximum pressure.
jon m NOV 05, 01:08 PM
Thanks PMBrunelle - So If I have this right because one of the pins broke on the oil sensor that like leaving the plug off would cause the oil gauge needle to go over to the right ?
So when I put a new sensor in and connect it back up all should be good
Jon
theogre NOV 05, 09:09 PM
Gauge "peg" to side means?
Sender not connected or bad
"Wire" to sender is bad. that can be a real wire to several spots in the dash or sender plug.
Gauge is "bad." Actual gauge or parts on it bad, dirty or loose.

New sender may not fix your problem.

Jump Sender Plug Tan Wire to engine. Should see 0 PSI on the gauge.

See my Cave, Oil Sensor
88 sender can break but most cases won't leak oil fast like the old ones and uses a better plug too.

⚠️ Warning:
87 and older used Small SAE 3/8 inch open end wrench. (Think 3/8" but can't find notes.) Do Not use the hex on plastic body.
88 sender uses SAE 1 1/16 inch special socket. Do Not tighten using plastic body when installing using any other tools.
Actual Thread is US NTP Tapper Thread. Do Not Over Tighten or the parts will Break. Look at threads, divide by 3, should be tight somewhere in the middle 3rd.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

jon m NOV 06, 07:05 AM
Thanks Theogre - I have grounded the tan wire and the gauge does go back to zero and the Oil pressure light comes on so the wiring is good just the sensor that is shot - I am going to have a look around the garage to see if my original sensor is lying around and clean it up as suggested in another thread on here - However I have ordered a new 88 one from Rock auto to have to hand.
Thanks again
Jon
jon m NOV 23, 12:02 PM
Hi - As an update I have now put in the new oil pressure sender - What I have found is that when starting from cold is it goes over to 80 but as it start to get warm it does start to drop to 75 but I havent let the car get warm enough yet till tomorrow (something cam up)
However does this sound normal ? The oil is Shell HX7 10w 40

Jon
olejoedad NOV 23, 05:21 PM
That sounds very good.
theogre NOV 23, 07:40 PM
Not Normal or Wanted to read High or Lower then GM Specs.
For V6, VIN-9, oil pressure should be 30-45 PSIG at all RPM and temp in range for oil used...


quote
Originally posted by jon m:
Hi - As an update I have now put in the new oil pressure sender - What I have found is that when starting from cold is it goes over to 80 but as it start to get warm it does start to drop to 75 but I havent let the car get warm enough yet till tomorrow (something cam up)
However does this sound normal ? The oil is Shell HX7 10w 40

What Weather Temp is at start? Because Thick Cold oil will flow poorly and can causing high pressure and not good for the engine. Is why Fiero and many others spec 5W-30 because that oil can run in winter in most places.
See API chart in cave. (or search api.org for current chart covering 0W-20 and 0W-16)

But Can be iffy wiring or gauge reading high pressure.
Is Why next is put mech gauge on engine to read oil pressure but many people already have cheap Ω meter and can reach the sender to check Ω when engine runs.

If can reach safe when engine runs...
Unplug the sender. (Gauge will Peg when disconnect but ignore that.)
Read Ω between 1 pin on sender and engine block.
0Ω = 0 pressure
45Ω = half scale
90Ω = full scale
No read = likely using wrong pin.

So If sender say ~ 45Ω but gauge says ~ 80psi (when connected) then have crap wiring etc adding Ω to sender Ω and gauge is lying.
Sadly often this happens and can be hard to find as each section of wiring can add just 1Ω or less but all iffy parts/sections make gauge say wrong info.
Fuel used exact same setup. Temp is sim to them but way different Ω range and non linear at that. But both get same problems w/ iffy wiring etc.

See my Cave, Oil and Filter & Oil Sensor for pin map/
Fie Ro NOV 24, 09:07 AM
Looks like the sender and gauge at least work, apart from possible wiring issues. Pressure going down when warming up is a good sign.

2 considerations for the high pressure:

- temperatures in Europe are close to freezing this week.
- 10W40 is thicker than the recommended 5W30, especially in these temperatures.
theogre NOV 24, 09:47 AM
Iffy wiring Example: If still used the old type sender, the plug is often "bad."
May seem to work but that plug often have dirt and worse making iffy connection(s) making the gauge to lie and/or iffy power to F-pump.

Sender has a F-pump switch wired parallel to F-pump relay as part backup & part to reduce connect resistance to power the pump.

Is another reason to install 88 sender w/ new plug but new plug pigtail needs "water proof" splices or splices can rot...