Oil pressure senders failing (Page 1/3)
tmadia FEB 06, 10:33 PM
When I first got my '88 the oil pressure gauge was pegged right whenever the key was on. I replaced the sender with one from Rock Auto and it worked perfectly, for 2 weeks, then it pegged right again.

I then ordered a Delco sender, replaced it, and it lasted 3 days. Ok, I'm thinking I'm just having bad luck? I get one more Delco sender and it just dies after 2 weeks.

Any ideas for what I should check? I don't want to keep throwing sending units at it.

Thanks!
pmbrunelle FEB 06, 10:51 PM
Rather than replacing the sender, try just unplugging and replugging the connector when the problem arises.

Just in case it's oxidation on the connector that's getting scraped off and barely making the connection every time you plug in the connector...
theogre FEB 07, 02:58 AM
Do what he said. might work or not.
The plug could be bad or wires to it and also wreck the sender.

Metripack (and Weather pack) plugs can has problems because isn't "water proof" only "Weather resistance."
Seals won't protect pins etc when soak in polluted water etc. even if dries out later, "rust" and chemicals can still eat metal parts.

If plug is crap then just install new pigtail using weather proof crimps w/ glue inside heat shrink at minimum.

See my Cave, Oil Sensor Sender ground is metal going into engine.

------------------
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

fierofool FEB 07, 09:52 AM
Usually, a bad ground can cause the gauge to peg. To test this, when you have a known good sender, unplug the harness with the ignition on and watch the gauge.
theogre FEB 07, 11:16 AM

quote
Originally posted by fierofool:
Usually, a bad ground can cause the gauge to peg. To test this, when you have a known good sender, unplug the harness with the ignition on and watch the gauge.

Iffy plug or wires can do same. Iffy gauge and resistor can make problems too. Resistor is on the back of gauge hidden inside of dash.
gauge clips holding the bolts and dash "board" on back of dash can cause problems too. The clips may look good but make crap connection between gauge and board.

Can short the gauge to ground for 0 on gauge I think.
But make sure of is sender pin.
Others is Fuel pump and short 1 pin of them to ground blows FP fuse at minimum.

cave page has pin out for 88 plug is why to read even w/o "upgrade" for older cars.

Multiple Senders doesn't fail this way.
Plug/wire w/ problem can wreck them.
Example: If shorts FP switch wires to sender wire can wreck sender and maybe gauge.

Bad sender sender ground is hard to do but possible.

Check sender Ω. 0Ω = 0 pressure, 90Ω = max pressure. 45Ω is half scale.
Should be 0Ω between pin A and engine w/ engine off.
If true use a needle poke thru Tan wire plastic should be same connected to sender.
If true wiggle tan wire watching Ω meter. should stay at 0Ω.

Check other senders pin A to metal bottom for 0Ω.
It all are open, wiring/plug problems are very likely.
Sender part can't handle power on FP switch and fries fast when has plug/wire problems.

Gauge "reads" sender's 0 to 90Ω.
Gauge pegs if sender or wire is disconnected.
Gauge can read off, way off, or even peg if sender wire is iffy or body to engine grounds are iffy.
Temp gauge should read off to way off too when has engine ground problem too. Volt meter in GT cars can have same plus iffy HL lights etc.

Sender wires go thru C500 and more on the way to the gauge. Any plug along the way can have a crap connection cause a peg gauge.

[This message has been edited by theogre (edited 02-07-2020).]

tmadia FEB 07, 06:39 PM
I unplugged it and put a meter on the sender. The center pin reads infinite resistance as soon as I start the car and 0 ohms when off. I'm guessing that means the sender is bad?
theogre FEB 07, 08:20 PM
likely.
But likely something else is wrong causing all to die this way.
olejoedad FEB 07, 09:36 PM
Oil pressure does not go through C500, it goes through the C203.
Check the fingers on the flexible circuit board (dash pod) for delamination and shorting to other circuits.
tmadia FEB 07, 09:44 PM
I'll check the gauge next. I figured something must be causing these to short out unless I am just that lucky and got 3 faulty senders in a row.
tmadia FEB 09, 02:30 PM
Today I got home from a short trip (in a different car) and when I walked by the Fiero I heard the buzzing of the fuel pump. The sender failed in such a way that the fuel pump was running continuously even without the key.

I'm guessing that's not caused by the gauge.

[This message has been edited by tmadia (edited 02-09-2020).]