So as the title says, I have a 1987 GT 2.8 and when it starts up i have around 60lbs pressure but then when it warms up the guage kinda flutters and drops down to the red line at idle. So i'm thinking the sending unit may be bad. I've looked into the Haynes book and it doesnt show the sending unit. I looked at the fiero store listing and see the sending unit but heck if i see it on the car. Sooooo i looked in a 1986 fiero book and it doesnt show it, but does give a description of it and calls it a oil transducer and lock. my question is, where the heck it is, can someone post a picture of its location? does anyone have a wiring diagram of it so i can see why it needs 3 wires? if i go to a mechanical gauge will unplugging the wires affect the engine running? Any tips/tricks/thoughts or help would be great.. thanks you all in advance.

its probably got a leaky diaphragm. It should be on the passenger side of the block, on bank 2 (Furthest twords the front) head, on its end, closest to the belts. Kind of underneith the coolant hose

Here is a picture of it. It is on the passenger side as mentioned near the thermostat housing. It is the grey thing pretty much dead center of the first picture.

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When my sending units have failed, the oil guage gets noisy or peg to the high side. Low oil pressure is another problem.

very nice pictures, thank you kindly. and i feel it is bad, the gauge isnt smooth, it bounces a little like 15 lbs +- now and then. yes the pressure seems low at an idle but i just dont feel i can trust that 20 year old gauge and sending unit.

It seems that even if you replace the sending unit, you can't be sure that you're getting a correct reading. Many of the sending units available today are inaccurate. Best thing to do is to get a mechanical gauge and get a reading at operating temperature. Then install your new sending unit and compare reradings. You can get a Sunpro mechanical gauge at AutoZone for about $10 and it comes with the 1/4 NPT threaded adapter that will screw into the sending unit base.

A word of advise. You'll need to remove the battery to get to the sending unit. Use an 8 inch adjustable wrench and use it to hold the aluminum colored base that you see underneath the sender in the second picture. You could possibly break it if the sending unit has never been removed and is stuck solidly. While holding the base with the adjustable, use a 9/16 open end wrench to loosen the sending unit. Though the sending unit is hex-shaped, don't be tempted to use the case to loosen or tighten the unit. You'll break it.

BTW, there is a wiring harness plugged onto the top of the sending unit. 1MohrFiero's illustration already has the harness unplugged.

thanks guys for the help. and yeah I may just goto all mech gauges.. only trouble i see is the water temp ... i know when you buy them kits they only give you like 6 ft of cable for the water temp. i'd love to put the new gauges up where the electric ones are .. above the radio.. but i dont know where to get a nice kit that has a long enough cable on the water temp to run the distance. without going to refinance my house to buy it. its not a show show car, its just something nice i'm trying to make better.

I wasn't suggesting to replace the electric gauge with a mechanical one. Just use the mechanical gauge as a tool to get an accurate reading. The one I have has a chrome mount designed to be mounted underneath the dash. I removed that and threw it away. The gauge has about 6 feet of nylon tubing that's sufficient to remove the grill over the battery, tape the gauge so that it's visible to the driver while you take it for a drive to get an idea of the pressure under operating conditions.

Anytime I have doubts about my oil pressure, I attach the mechanical gauge to verify the true pressure. Just bought an 86 with 210K that was showing about 50 lbs pressure at idle. The mechanical gauge verified that the electric sending unit was incorrect. The actual pressure was about 22 lbs. It took 3 new electric sending units before I found one that read correctly.

I know what you meant though and i thank you for the advice. I was thinking about changing over to mech guages anyways, i trust them more than the electrical ones.

If , by chance, your car is not equipped with AC it will be located underneath the front exhaust manifold next to the oil filter. The ones in the pics are AC equipped cars.

Just as much as you don't trust the 20 year old gauge, don't trust the 20 year old motor / oil pump. I had a similar issue with an 86 - brand new motor - I had a mechanical gauge installed as well. First start, the factory gauge was pegged - mechancal was 65 psi. Ater warm up, the mechanical was 50 and the factory was still pegged. I found a sending unit for an 86 Vette - listed as high pressure 80psi. I had to install a bushing/adapter to get it to fit but it matched the mechanical gauge perfect. After 300 miles on the motor, I had the same problem - cold I had 60 psi - hot it would drop to red and light would flash on. Not sure what the issues is as we have not tore the motor down to see but I suspect it is the Oil Pump.

Stock 86 on the left, old style SBC in the middle and the 86 Vette Hi Pressusre on the right.

Stock gauge with Vette Sending Unit:

Mech Gauge with Vette Sending Unit:

Brand new stock Fiero sneding unit:

quote Originally posted by 2farnorth: If , by chance, your car is not equipped with AC it will be located underneath the front exhaust manifold next to the oil filter. The ones in the pics are AC equipped cars.

There is also a Technical Service Bulletin about the oil pressure tubes. I read the TSB, and it states that the long tube should be removed, and discarded, and a 45 degree fitting installed, and the pressure sending unit installed into it. If you want the full TSB I can post it :P Aparently GM found a problem with those tubes.

im interested in seeing that TSB.

quote Originally posted by Racing_Master: There is also a Technical Service Bulletin about the oil pressure tubes. I read the TSB, and it states that the long tube should be removed, and discarded, and a 45 degree fitting installed, and the pressure sending unit installed into it. If you want the full TSB I can post it :P Aparently GM found a problem with those tubes.

Please post this TSB. It would be greatly appreciated!

Bulletin Number: 88-8-22
Reference Number: 738101R
Publish Date: 8/88
Subject: OIL PRESSURE SENSOR SERVICE (ADD SHIELD OR RELOCATE SENSOR)

Models
Affected: 1985-88 FIERO WITH 2.8L V-6 (VIN CODE 9) AND AIR CONDITIONING
"This bulletin cancels and replaces bulletin 87-8-12, dated 8/87. The title and service procedures have been changed."

1985-87 Models

Whenever an oil presssure sensor is replaced on the above vehicles, a shield should also be added to protect against water intrusion. This shield is part number 10096127.

Parts are currently available from GMSPO.

Use the following procedure to install the shield:
1. Disconnect the wire harness connector to the oil pressure sensor.

2. Push the connector through the small end of the shield, and move the shield up the harness, out of the way.

3. Reconnect the wire harness connector to the oil pressure sensor.

4. Pull the shield over the sensor, so that the large end covers the entire sensor. The shield should fit loosely over the sensor.

5. Use a silicon sealer, such as GM Silicone Sealant (P/N 1052915), inside the small end of the shield. Then, secure the small end of the shield to the wire harness with a plastic tie strap. Tighten the strap as securely as possible, and cut off any excess length.

6. Tape the wire harness and shield with electrical tape, starting at the tie strap on the shield to the first junction in the harness.

Warranty Information

Labor Operation: T1311
Labor Time : .5 Hours - For the installation of the shield
and the oil pressure sensor.
Part Number : 10096127

1988 Model Only

If an oil pressure sensor is replaced on a 1988 model, the sensor should be moved to the oil pump location just above the filter, using the following procedure:
1. Raise hood and remove the right hand louver assembly. Disconnect negative battery cable.

2. Remove the oil pressure sensor using tool number J35748.

3. Remove the main wire harness retaining clip.
FIGURE 1

4. Remove the oil pressure sensor mounting tube retaining bolt (Figure 1), then move the tube out of the way. Reinstall the bolt, and torque to 50 N-m (37 lb. ft.).
5. Remove the screw from the Electronic Vacuum Regulator Valve (EVRV) mounting bracket, and move the EVRV out of the way.

6. Remove the oil pressure sensor connector wire from the conduit, down to the first tape on the conduit (about 9 inches). Tape the wire to the conduit so that the wires are facing down. Route the oil pressure sensor wires near the main harness, just above the A/C compressor. Reinstall the rest of the wires back into the conduit and retape. Reinstall the main harness retaining clip, insuring that the clip does not touch the transmission cooler lines or pinch any wires.

7. Reinstall the EVRV on its mounting bracket.

8. Hoist vehicle.

9. Remove oil filter.
FIGURE 2

10. Using a back-up wrench on the brass fitting (Figure 2), remove oil pressure sensor mounting tube and discard. Remove the brass fitting and discard it also.
11. Obtain the following parts from a hardware or plumbing supply store:

a). 1/8" nipple (1" long)
b). 1/4" to 1/8" reducer (female inside male)
c). 1/4" to 45 degree angle (female both ends)

12. Loosely assemble the nipple into the female end of the reducer, and the angle onto the male end of the reducer, using GM LocTite pipe sealer with teflon, P/N 1052080 on all joints.

NOTICE: This product is a "thread locker" as well as a sealant. Any substitute must have the same qualities.

13. Install the fitting assembly into the block, also using pipe sealer. Tighten the fitting until it is firmly seated, and the angle is correct to locate the oil pressure sensor just below, and not touching, the A/C compressor.

14. Install the oil pressure sensor, again using pipe sealer. Use the special tool to torque to 20 N-m (15 lb. ft.). Install the connector on the oil pressure sensor.
15. Replace the oil filter. Check oil level, and add additional oil if necessary.

16. Lower vehicle, reconnect negative battery cable, start engine, and run for one minute. Check for proper operation of oil pressure gauge. Shut engine off.

17. Raise vehicle, and check for oil leaks.

18. Lower vehicle.

[This message has been edited by Racing_Master (edited 05-11-2009).]

Is it normal for the oil gauge to flutter around? Mine goes +/- about 5 psi constantly when the engine is warmed up.

quote Originally posted by Racing_Master: Bulletin Number: 88-8-22 Reference Number: 738101R Publish Date: 8/88 Subject: OIL PRESSURE SENSOR SERVICE (ADD SHIELD OR RELOCATE SENSOR)

PLUS for you!

quote Originally posted by Racing_Master: There is also a Technical Service Bulletin about the oil pressure tubes. I read the TSB, and it states that the long tube should be removed, and discarded, and a 45 degree fitting installed, and the pressure sending unit installed into it. If you want the full TSB I can post it :P Aparently GM found a problem with those tubes.

Just a guess mind you, but I've often wondered about that long tube from the block to the pressure sending unit.
It seems to me that each time the oil drains down after engine shut off, that there would be air in that tube...compressible air....and when the engine is started and oil comes up behind that air pocket that it could potentially create a problem with accurate oil pressure readings.
Am I thinking of this correctly, or is there some reason that there would *not* be air in the tube?

I did some searching around the forums and this thread most closely matches the problem I am having. I had erratic oil pressure gauge problems so I concluded that the Oil Pressure Sending Unit was likely the culprit. About a month ago I replaced the water pump on my stock '87 2.8L GT and also installed a belt tensionor. This solved my coolant leak and alternator charging problem but it also pegged my long time erratic oil pressure gauge. I checked the 3 blade connector and and decided to replace it when I could. After about a 2 weeks of very rare driving only about 60-120 miles the Oil Pressure Gauge dropped to about a constant 60psi, never varying idle or WOT, so I decided to replace it when I could which was this morning. Pulled the battery, disconnected the OPSU and replaced it with a Borg Warner unit from O'Reilly (the only one I could find today, including dealers). Reconnect and reinstall the battery. Fire the engine and I get nada. Recheck my connection and now my Oil Pressure Gauge reads just about the red zone and barely moves. Although erratic when hot in the past, I was getting fairly constant 40-50psi at highway speed and around 40psi at idle. I am not sure what to check next as I am not an electrical wizard but this seems to be a common problem. From above I assume when you recommend a mechanical gauge to test you are simply replacing the OPSU with a mechanical gauge?

T.I.A.

Will

Edited because I mistyped that I have replaced the base unit, which I did not. I simply threaded the 1/4" fitting on the bottom of the sending unit into the old base unit (which I assume is the threaded aluminum block the old one was mounted to)

[This message has been edited by infinitewill (edited 10-20-2010).]

quote Originally posted by infinitewill: I did some searching around the forums and this thread most closely matches the problem I am having. I had erratic oil pressure gauge problems so I concluded that the Oil Pressure Sending Unit was likely the culprit. About a month ago I replaced the water pump on my stock '87 2.8L GT and also installed a belt tensionor. This solved my coolant leak and alternator charging problem but it also pegged my long time erratic oil pressure gauge. I check 3 blade connector and and decided to replace when I could. After about a 2 week of very rare driving only about 60 miles the Oil Pressure Gauge dropped to about a constant 60psi, never varying so I decided to replace it when I could which was this morning. Pulled the battery, disconnected the OPSU and replaced it , including the base unit with a Borg Warner unit from O'Reilly (the only one I could find today, including dealers). Reconnect and reinstall the battery. Fire the engine and I get nada. Recheck my connection and now my Oil Pressure Gauge reads just about the red zone and barely moves. Although erratic when hot in the past, I was getting fairly constant 40-50psi at highway speed and around 40psi at idle. I am not sure what to check next as I am not an electrical wizard but this seems to be a common problem. From above I assume when you recommend a mechanical gauge to test you are simply replacing the OPSU with a mechanical gauge? T.I.A. Will

You can, or you can install a 1/4" T-fitting with two female ends and use both gauges.


Edit: On second thought, I seem to remember there not being enough length in the oil pressure sensor connector to use an actual t-fitting. You'll need one like this, with the female end on top:

http://www.suspensionconnec...in/suscon/92848.html

[This message has been edited by 8-P (edited 10-20-2010).]

And update sender unit... Never use old type sender or it will leak again in 2-5 years. It an easy fix.
See cave. oil pressure sender

And thank... I don't have that TSB. I'll add it to sender page in cave.

Edit... I do have it, with images. Thank anyway because I never would find it otherwise.

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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 (It's also at the top and bottom of every forum page...)i

[This message has been edited by theogre (edited 10-20-2010).]

Dave, I read your article in the Cave and if I understand correctly you are recommending switching to the '88 sender and upgrading the connector, is that right?

Thanks man!

Will

Yes! Upgrade is more reliable that old sender. I did it on my 87 L4 this spring with one hand. (stroke). I had enough messing around with old style sender and leaking oil...

PDF of TSB is in Sender page now.
Post in Electrical and Engine General now to. (Can't see menu update? see help page)

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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 (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 10-20-2010).]

Further test: I went a got 2 mechanical oil pressure gauges this afternoon an installed them one at a time, in place of the Oil Pressure Sending Unit. Both read a steady 48psi @ idle warm and both read 52 psi at half throttle (approx 3500 rpm). So I know the mechanical gauge is correct (that or they are both wrong by the exact same amount). I then installed another brand new BW replacement unit and got the same reading as I did on the first replacement:bottom of red at idle and top of red at half throttle. So my next question is this: is it possible that while the needle was pegged over the roughly 60-120 miles it was driven that way that I have simply "knocked the needle out of calibration"? I had removed them before when I repainted them last fall.

Further, I am still going to do the upgrade you suggested Dave but unfortunately, I am leaving town tomorrow and won't be back home until Sat. and I will likely have to order the parts either way.

Thanks for the help guys! Another lesson learned

Will

Test dash meter more... Bad meter, bad wiring, or bad new sender...

Use a resistor instead sender. 90 ohm = 80PSI I think

See also https://www.fiero.nl/forum/Forum2/HTML/112030.html

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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 (It's also at the top and bottom of every forum page...)

quote Originally posted by theogre: Test dash meter more... Bad meter, bad wiring, or bad new sender... Use a resistor instead sender. 90 ohm = 80PSI I think See also https://www.fiero.nl/forum/Forum2/HTML/112030.html

Alright, I put a 90 ohm resistor in place of the sender and got just under 38 psi which I would conclude means I did in fact knock my needle out of calibration as it is off by 42psi, which I read at idle on the mechanical oil pressure gauge. Do I have that right? Makes sense to me

Thanks again Dave!

Will

Sound like yes....

------------------
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 (It's also at the top and bottom of every forum page...)