Pinned Oil pressure Gauge (Page 1/3)
wayne.lockman APR 01, 09:30 AM
Anyone know of a quick fix for an oil pressure gauge pinned to the right?
RWDPLZ APR 01, 09:58 AM
Pinned right = unplugged or bad sending unit (possibly bad gauge). If it was plugged in, and you ground the middle terminal in the plug and the gauge goes to zero, bad sending unit.
Mike Gonzalez APR 01, 10:00 AM
Could be a bad sender, grounded connection, or bad gauge.

Is it always pegged, or only with the key on ? Or is it reading pressure that high, does it go up as oil pressure builds, or immediately when the key is on ? Disconnect the connector from the sender and see what it does.
phonedawgz APR 01, 01:56 PM
But Mike - disconnected from the sender will give a past full oil pressure indication.

Shorted to ground (0 ohms) would be 0 psi

90 ohms to ground would be full scale

Open (infinite ohms to ground) would give an indication of past full scale.

---

So Wayne - first thing to see is what the oil pressure gauge does with the key on (engine off) and then you take and stick a paperclip into the middle pin of the oil pressure sender connector of the engine harness and ground it to the engine. The gauge should go to zero. If it does that would indicate your oil pressure sender is bad. If the gauge remains pegged that would indicate either a bad gauge or bad wiring from the gauge to the sender.

[This message has been edited by phonedawgz (edited 04-01-2011).]

Mike Gonzalez APR 01, 10:06 PM

quote
Originally posted by phonedawgz:

But Mike - disconnected from the sender will give a past full oil pressure indication.




Yup, you're right, I was thinking backwards this morning.
OneSlowFiero APR 25, 04:49 AM
I'm bumping this because I have the same issue. The oil pressure gauge reads full while running and with the key on engine off it reads past full as far as the needle can go. Dies this indicate a bad sending unit?

Thanks

-Josh

[This message has been edited by OneSlowFiero (edited 04-27-2011).]

OneSlowFiero APR 27, 11:27 AM
Bump
phonedawgz APR 27, 01:17 PM
The gauge technology that GM used in the 80's put two electromagnetic fields against each other. They did that instead of an electromagnet against a spring. After time the spring will weaken making a spring/electromagnet gauge inaccurate.

So when the key is off, what happens to the needle has no meaning at all.

A simple test of your oil pressure gauge/sending unit. Unplug the connector from the sending unit. On 85-87 that means squeezing the ring to make it more circular and then pulling up. With the proper squeeze it will pull up fairly easy. Now turn the key on, but leave the engine off. The needle of the oil pressure gauge should read far past high right. Now take a straightened paperclip and insert it into the CENTER pin of the three and hold that against ground. The needle should move to 0 PSI. If you wish to make a third test you can take a 90 ohm 1/4 or 1/2 watt resistor (RadioShack $0.99) and insert it into the middle pin and ground it. With the 90 ohm resistor the needle should read full oil pressure, but not past full.

If your gauge reads what it should for tests 1 & 2, but it doesn't work correctly connected to the sending unit, your most likely problem is a bad sending unit. If your gauge reads low but at some pressure just jumps to full high, your problem most likely is a bad sending unit. That jump-failure is common with the 85-88 sending units.

Rock Auto has some reasonably priced sending units at $12.71 + shipping. Make sure your replacement sending unit looks like the one in your car or it won't fit on the electrical connector. Price check this before buying local. Some stores charge over $50 for this.

Note also - You must use a wrench on the metal part of the base, not that big looking plastic nut thing.

Oil pressure sender/switch for 85-87 Fieros


You can also replace the 85-87 sending unit with an 88 sending unit. You have to also purchase the wire connector and splice it onto your existing engine wiring harness.

[This message has been edited by phonedawgz (edited 04-27-2011).]

OneSlowFiero APR 27, 04:49 PM
Is there any advantage to replacing it with an 88 unit?

Thank you for all the info!
phonedawgz APR 27, 05:03 PM
For a while the only available 85-87 senders were all in that $50 range. It was cheaper to replace the sender AND purchase the connector rather than just replace the old sender. With these lower priced ones on RockAuto that is no longer the case.

The other thing is the 88+ senders do seem to be more reliable than the earlier ones.

You can get and 88 sender and a three pin oil pressure connector from rock auto for a reasonable price also. Make sure the connector you buy is a 3 or 4 pin connector. There are also 1 and 2 pin connectors that don't work for the Fiero.

How long did the original sender work in your Fiero? idk which way is the better way to go. Clearly when you could buy the newer sender and connector for less than the replacement sender then the choice was easier.

Either way will work.