I'm trying to sort out my guages and idiot lights. 1986 GT Auto.
During the bulb test, my oil pressure gauge in the GT/Aux pod pegs then settles at 80. The light does not come on.
My Temp gauge does not peg. It just goes to actual temp. (when cold, goes to 100) The light does not come on.
I'm trying to figure out if the temp light wiring problem has been done already and maybe the bulb is burned out since the guage doesn't peg.
QUESTIONS: (1) Should the oil pressure gauge peg and read high? (2) Should the oil pressure light come on with bulb test? Probably burned out? (3) Does the water temp gauge read correctly during the bulb test even before the wiring correction?
Correction: the temp gauge DOES peg when turning PAST on going into the Start position. That confirms that the temp gage wiring fix has NOT been done. I'll do that.
I also checked the bulbs in the Aux pod's Oil Pressure gauge. Both bulbs on that side are good. What is wrong with my oil light?
Most likely? Temp gauge was fix to stop pegged and temp light left alone. Is a common fix...
------------------ 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)
Most likely? Temp gauge was fix to stop pegged and temp light left alone. Is a common fix...
No, it was my bad. The temp gauge doesn't peg in the "on" position. It pegs when I turn past "on" going toward "start". That's the original problem. It's not been changed in any way from factory. I'll have to make the change.
I'm still stumped on the oil pressure light, though.
On this topic, I've just gotten my '85 GT running after sitting for almost 10 years. All of the gauges work, but some of the idiot lights do not come on with the bulb test. I get Check Engine and Battery, and the Parking Brake and Hi Beam lights work when I use them. Also the Shift light works. The Ajar light works when it wants to. The left hand blinker light does not work, although I have some burned out turn signal bulbs. Other than checking and replacing bulbs, what else should I look for?
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10:43 AM
Boostdreamer Member
Posts: 7175 From: Kingsport, Tennessee USA Registered: Jun 2007
On this topic, I've just gotten my '85 GT running after sitting for almost 10 years. All of the gauges work, but some of the idiot lights do not come on with the bulb test. I get Check Engine and Battery, and the Parking Brake and Hi Beam lights work when I use them. Also the Shift light works. The Ajar light works when it wants to. The left hand blinker light does not work, although I have some burned out turn signal bulbs. Other than checking and replacing bulbs, what else should I look for?
Bad blinker bulbs will stop the dash flasher from working. It is set up that way to let you know that you have a turn signal bulb out. Replace the bulbs in the turn signals and your dash should work again.
Yep, tan wire, ground it and the gauge should go to zero and the light should come on. Conversly, unplugging it should cause the light to turn off and the gauge to be pegged to the right.
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11:45 AM
PFF
System Bot
Boostdreamer Member
Posts: 7175 From: Kingsport, Tennessee USA Registered: Jun 2007
Another "feature" of the oil pressure sensor (all years) is it contains contacts which supply power to the fuel pump after oil pressure has been established. However these contacts are in parallel with two contacts in the fuel pump relay which also provides power to the fuel pump. If the fuel pump relay fails all the power for the pump goes through the contacts in the oil pressure sensor. Apparently these contacts are not rated for the full pump load. This can cause the contacts to overheat and damage the pressure-sensing portion of the sensor. We believe GM erred in this application. The sensor as described by AC Delco (the sensor manufacurer) is for "oil pressure w/light". It appears the contacts within the switch were intended for an "idiot light" on the dash, not as current-carrying components for the fuel pump. Therefore, running fuel pump power through the sensor seems to be a design error, but that's the way it is (unless you change it).
The oil pressure sensor in the '88 Fiero is a different design (no vent hole) but still has the contacts for the fuel pump. If your oil pressure gauge always reads maximum pressure the culprit is likely (a) the fuel pump relay has failed and therefore all current for the fuel pump is going through the oil pressure sensor, and (b) the oil pressure sensor has subsequently overheated and the pressure-sensing portion of the unit has short-circuited, thus giving a high gauge reading. It is wise to check the fuel pump relay when the oil pressure sensor is replaced.
It sounds like my main fuel pump relay could be bad. My oil pressure gauge behaves as described above. Jumpy and high.
Got this from another thread:
quote
The location of the fuel pump relay is in the engine compartment, on the firewall, right behind the drivers seat.
You can't go by the location of the relay since they are easily moved. The fuel pump relay will have wires that are Green/White, Black, Tan/White and Orange/Black
I need to confirm that my fuel pump relay is good before I change the Oil Pressure Sending Unit and subject it to possible frying, too. Gotta search for a relay test. I guess if I pulled the wiring connector off the sending unit, the relay would be forced to work (or not). Is that right?
After that is straightened out, I have a Formula parts car so I'll pull the OPSU from it along with the connector and try them out on the GT.
I pulled the harness from the sending unit. I was able to hear the fuel pump prime and the car started right up with no hesitation. Looks like the fuel pump relay is fine. Now I'll go ahead and change over to the 88 oil pressure sending unit.
I made the change to the 88 Oil Pressure Sending Unit. It was a pretty simple and straight forward swap. Unscrew the old one, screw in the new one. Cut the old connector off, splice the new one on. Both have three wires and they are arranged like an arc ( . The wire colors are not exactly the same but they are similar so they are easy to match. Or just keep in mind what wire came from what point on the arc. Not difficult at all. Also, my Formula had a big rubber boot/sleeve on it that covered the connector and the sending unit. I re-used that as well.
Now the pressure reads very steadily. It rises when I give it gas and drops again when I let off. It doesn't jerk and bounce anymore. The idiot light also worked temporarily. It worked during testing and a couple of times while starting. Now it doesn't work. I thought that maybe the sender was holding pressure in it after having started several times. This morning it did not come on. I'll have to re-check the bulb.
Also when the engine is off and the key is at ON, the oil pressure gauge jumps to full high pressure and stays there until the car is started. Is that normal?
Drove it again today. Gauge is far from perfect. It still does jump some but nothing like before. The bulb is fine but it won't light during the bulb check. I guess the only solution is a new sending unit. The one I put on is probably 26 years old.
I did the water temperature light/gauge wiring swap today. I did it per the Fierosails website and I did not have to cut or splice any wires. Worked just as posted. The instructiosn there state they are for the '88 but mine is an '86 and everything was exactly the same. The hardest part of the whole process was getting the wires released from the connectors. Now the bulb test works as it should.
My Oil Pressure light came back to life again, too. I wonder if there's any relation?
Now the oil pressure gauge is reading low and the light is coming on while the engine is on. I'm going to suspect the sending unit. It is 25 years old and hasn't been in use in who knows how long.
Is this a GM parts counter thing or are the ones at O'Reilly, etc, safe?
When I've had oil sending units go, the gauge has either been erratic or has pegged. May be oil pump??
I sure hope not! This is an unmolested original car with 64K miles on it. I have to hope it is the old '88 sender that I pulled off my junk Formula. Besides, it will be much easier and cheaper to buy and swap a new sending unit vs. a new oil pump.
The car starts and runs fine. I don't feel any power problems even when the gauge was in the red and the light came on. The light never came on before the swap and now suddenly there's a problem.
Is a 2.8 oil pump failure common? Especially with these few miles?
I sure hope not! This is an unmolested original car with 64K miles on it. I have to hope it is the old '88 sender that I pulled off my junk Formula. Besides, it will be much easier and cheaper to buy and swap a new sending unit vs. a new oil pump.
The car starts and runs fine. I don't feel any power problems even when the gauge was in the red and the light came on. The light never came on before the swap and now suddenly there's a problem.
Is a 2.8 oil pump failure common? Especially with these few miles?
An oil pump failure is very, very rare. Have you tapped the gauge to see if you have a loose or intermittent bulb in the cluster?
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10:46 AM
PFF
System Bot
Boostdreamer Member
Posts: 7175 From: Kingsport, Tennessee USA Registered: Jun 2007
An oil pump failure is very, very rare. Have you tapped the gauge to see if you have a loose or intermittent bulb in the cluster?
The bulb and the gauge are in the red at the same time. When the gauge stops jumping and lands in the red, no pressure zone, the light comes on. Then it will jump back up and show a constant pressure again.
When an oil pump fails, does it do it sporadically like that, does it build less and less pressure until it dies, or does it just konk out all at once?
According to the gauge, it works for a while then stops for a while. That doesn't sound possible to me. That gives me hope that it's electrical and internal in the sending unit.
I changed the Oil Pressure Sending Unit today. I got the AC Delco one.
I also took my IAC out and cleaned it with throttle body cleaner spray. Do you think it needed it?
The IAC was not difficult to get out. I just unplugged the connectors for it and the TPS then I used channel locks to loosen the IAC. Not too difficult. After cleaning and part swapping, I put everything back where it was supposed to be and connected the battery again. I wanted to take a test drive so I got in and fired it up. The oil light came on where it should and the engine started immediately but the pressure was barely showing. I tried to put it in gear to back out into the street but that caused it to die. I did that several times. I finally used two feet. One on the gas and one on the brake. I had to keep giving it gas to keep it running. This was worse than before I "fixed" it! Well, after several tries, I got the car out to the street and I got it going. It died again at the first stop sign. Got it going again and I had to drive up a steep hill. It made it but there was no power. The oil pressure was showing very low and the light was coming on. I thought I had just confirmed that I had a bad oil pump.
No sooner than I thought I was in big trouble that the road leveled out again and I was able to get the car up into the 20's and 30 mph. I guess that is what it needed to re-set everything because after that, it started getting better and better. The idle smoothed out and the oil pressure built up. It stopped dying at stop signs and red lights. The oil light stopped coming on. The pressure was reading just below and just above 40 on the gauge depending on whether or not I was on the gas. The needle was very steady from then on. Not a single jump after that.
Now all the lights and gauges work correctly and the car starts easily and it idles smoothly and putting it in gear doesn't kill it. I guess I did it right!
Drove it again today. The pressure keeps dropping. Goes into the red zone and the light comes on. Turn it off, start it again and it's fine. I'm going to swap gauges and see if that helps.
What are the chances that an oil passage is clogged?
if you want to know for sure I would use a mechanical guage for testing. and see where your oil pressure actually is... could you have a connection where you soldered the new harness in to the old?
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87 GT series 1 3800sc (7.597 @88.53 1.579 60ft) (series II swap in progress) 85GT Northstar 86GT 3800 n/a
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02:18 AM
Boostdreamer Member
Posts: 7175 From: Kingsport, Tennessee USA Registered: Jun 2007
if you want to know for sure I would use a mechanical guage for testing. and see where your oil pressure actually is... could you have a connection where you soldered the new harness in to the old?
Do you mean a mechanical gauge that screws into place where the sending unit is? Take the sending unit off and put on mechanical? Would I also be able to connect the Fiero gauge electrically while the mechanical gauge is on? I'd like to be able to see accurate readings while driving.
I did solder the connections where I spliced the new connector on. What was the question about it?
U can attach it and leave stock functioning and see if it drops like stock guage.. If itdoes u have issues if not could be bad new sending unit or guage
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87 GT series 1 3800sc (7.597 @88.53 1.579 60ft) (series II swap in progress) 85GT Northstar 86GT 3800 n/a
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04:10 PM
Boostdreamer Member
Posts: 7175 From: Kingsport, Tennessee USA Registered: Jun 2007
I bought a mechanical gauge from Advance Auto. It's a Sun Pro which is owned by Snap-on Tools. It was about $18. It had everything I needed in the kit.
I took the oil pressure sending unit off and screwed the hose into the oil pressure hole.
I ran the plastic hose over the sail panel and in through the passenger window.
Down to my passenger seat.
Then I zip-tied the gauge to the seatbelt so I could look over and see it while I was driving.
Then I went for a drive. I was out for about 30 minutes and I stopped for gas in the middle. I did some curvy roads, some in-town driving, some interstate, up hills and down hills. From the time I started the car with the new gauge, it worked correctly and consistantly. It showed about 15-20 psi at idle then jumped up to just over 40 psi when getting on the gas hard. It never went to zero. It never went into red. I was very relieved to confirm that my oil pump was working and my main bearings were fine.
So, that leaves the possibliities of wiring problems, factory original gauge problems, grounding problems, or loss of pressure from the sending unit being loose.
The first thing I did was to remove the thread dope from the sending unit. Then I put some teflon tape on the upper threads. That would allow a good ground and provide some leak protection.
I put it in like that and the old problem came back. I tried to improve the ground by running a wire from the sending unit's hex area to a ground by the battery. That didn't help. It's not a weak ground.
Next I decided to swap gauge pods. BING!! That was it. This gauge pod showed constant oil pressure but it was showing low. I pulled the needle off and re-set it so that it showed the pressures that the mechanical gauge did. All done!
Well, not quite all done. I ended up having a terrible leak. It leaked so bad that the oil ran down to the bottom of the engine, across the cradle, crossed to the base of the trunk and got blown back up onto my deck lid while I was driving! In fact, that's how I found out it was leaking. I saw oil droplets on my rear bumper when I was getting in the trunk.
Anyway, I had to fix all of that mess today. I took the sending unit back out and re-taped the threads and only left one and a half threads bare. I put it back in and wiped everything down with a rag then I cleaned everything with Super Clean degreaser. I think it is made by Castrol. Got it from Walmart and it is in a purple spray bottle. It worked very well and I used it exactly by the directions. Spray on cool surfaces, allow to work, rinse before it dries. I used a brush to work the thicker gunk off.
Then I had to wash the car and go for a test drive. NOW everything seems to be fine!
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