Fiero GT Oil Pressure Sending Unit Wiring Harness Issues (Page 1/1)
Nghtrain36 AUG 26, 12:23 PM
Hello everyone! I'm new here and an owner of a 1986 Pontiac Fiero GT with the V6 engine in it. Bought it from a guy that, according to him, had the engine rebuilt and had some custom wiring done. I've been unable to start it for quite a while now and have been trying to pin down what's causing it. She does crank and try to start but refuses to turn over. I apologize for the lengthy post but I'd like to post the process for thoroughness. First thing I noticed was I never heard the fuel pump prime at all, so I figured it might be in the fuel system. Checked the fuse, fuse was good and even got the multimeter out to check the contacts. Everything was good on that line, so the next step was to check the relay. Went ahead and replaced the relay and made sure I heard it click when I turned the key. Got the click, checked the lines there with the multimeter and all was good there. Well, when I got done with the relay I noticed that my oil pressure was absolutely gone. Sticking right at zero no matter how much I cranked it. I'd heard before of a lack of oil pressure killing off the power to the fuel pump, so my next avenue was to check the oil. I put in and removed the dipstick three times to be absolutely sure there was proper oil in there. That checked out and the oil I knew was just replaced. Next thought was to check the oil pressure sending unit. This is where things started looking funky to me. I was going to just straight up replace the unit, but when I looked at the wiring harness, I found this attached to it:

Now, I'll be the first to admit wholeheartedly that I am not very savvy with wiring and electrical stuff but, and correct me if I'm wrong, that there don't look stock. I found those three attached to the prongs of the oil pressure sending unit. Most of the people I see with pictures of this thing have a pigtail attached to it, not this. I couldn't find this in the Haynes Maintenance manual either, so I'm a bit lost as to if this is the culprit of my low oil pressure or if I should still replace that sending unit. It does look like the cord connects into where the rest of the wires were taped together so I couldn't trace where this thing was supposed to go. So with that said, if someone could give me some advice on where to proceed from here and how to do it, I would greatly appreciate it. I'm not the most well-oiled mechanic but I'm resourceful enough to try anything to get this beast going again, so any help at all would go a mile for me.
theogre AUG 26, 01:19 PM
Only 1 is OP "out" to dash gauge. OP sender part ground is to the block.
Other 2 are Fuel Pump Power. look for FP wiring.

need a meter or light to see the power...
1 get power any time the key is on.
1 other should be fuel pump. that wire gets power thru FP relay for ~ 2 sec every time turn key on and make ECM to turn on relay w/o starting.
then last other... gauge = 0 short to ground. 80psi is 90Ω to ground.

get 88 sender and plug.
See my Cave, Oil Sensor

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

Nghtrain36 AUG 29, 01:52 PM
Thank you so much for the information! I've got the parts ordered and will give an update once they eventually get here and I can start fixing the issue.
IMSA GT AUG 29, 02:09 PM

quote
Originally posted by Nghtrain36:

Thank you so much for the information! I've got the parts ordered and will give an update once they eventually get here and I can start fixing the issue.



Sent you a PM with a link.