I just upgraded my 87 v6 to the 88 oil sending unit following the instructions on the Ogre's Cave Fiero site. The Car is running fine, but my gauge which had been bouncing around is now pinned to the far right. This is when the car is running or just key on. I pulled the tan (center) line from the sender and grounded it as described in the post below and my gauge went to zero. Sounds like this is a bad sending unit...but it is a brand new AC Delco part. #1808A.
Update: I noticed that after the key has been off for 10 seconds the gauge slowly returns to zero.
Thanks, Bill
quote Originally posted by phonedawgz:
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. d
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07:23 PM
PFF
System Bot
The Aura Member
Posts: 2290 From: Winnipeg, Manitoba, Canada Registered: Nov 2001
Are you positive that that is the correct sending unit to drive a gauge? It could be that you have one that is only for the low oil pressure light and not the whole gauge.
Just a thought.
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08:05 PM
Aug 5th, 2012
lordbg0205 Member
Posts: 236 From: cincinnati, oh Registered: Nov 2011
i too did this upgrade, i used an AC Delco part from Rockauto, it worked great for about 9 days, then i was driving to work and it pinned to the right, i did the tests like you and the gauge is fine. i did notice that the plug for the sending unit, which is brand new seems to look like it was shorting or not making a great connection to the pins, they were getting that corroded look to them after 9 days. Im just gonna buy one from someone local with a lifetime warranty and just keep swapping it out, AC Delco is garbage, so dissapointed with it.
I installed a 1988 oil pressure sender unit and changed out the pigtail plug to the new style back in 1996 and have had no further issues. I must have had over four of the original types fail from 1986 to 1996. I also have a mechanical oil pressure gauge and it reads almost identical to the factory electric one. Something is amiss somewhere if your's is not working correctly.
