Nino1984

I've searched the threads with no luck. I need help with my 3-wire oil pressure switch. The car is a 1984 TA, L69 305 w/ carb. The car is all original. I have an 80 psi electric dash gauge. My oil pressure switch is by the distributor. It has three wires (two orange and one brown with a black or blue stripe) and is the large bell shape one. My gauge is pegged at the highest level with the ignition on, running or not. I can get the gauge to drop to zero if I ground one of the orange wires from the pressure switch (I think it's the one that goes to the gauge, but not sure). I don't know if that means that the pressure switch is bad or not. Does anyone know how I test the switch? I have most test tools including an ohm meter. I don't want to just replace it on the chance that it's bad, those switches are over 50.00. Besides, I can't find one that is 3-wire and made for an 80 psi gauge. All i've found are for the 60 psi gauge. Also, what are the other 2 wires for? I've read about them going to the fuel pump. Well, I have a carb car and mech fuel pump. What else could those two wires go to? With the key on, I get 12 volts from the brown one. That must be the feed in. I assume the other orange one is the line out to whatever it goes to (I get no power there and it is not a ground)? I'd like to get it back to original working condition without having to alter it. Need help big time!

deadbird

Fuel and OP gauges will max if the circuit is open. Grounding causes them to go to zero.
The sending unit works from 0-90 ohm (low-high pressure)

It's been awhile since I've had my 84 but, IIRC, there shouldn't be an oil pressure switch on the early carb'd cars. There should only be a single wire sending unit there with a tan (tan/wht or tan/blk) wire on it. GM used that same bell looking sending unit on my 87TPI a well. It was 88 or 89 when it switch to the 3 wire integrated OP sending/switch unit. The gauge has always used the tan wire for the signal to the gauge as far as I know though. There should be no voltage on it.

I'm also remotely positive that the v6 (maybe 'the duke' too) cars were the ones to get the higher psi gauges. It seems someone may have done some 'custom work'(ie, junkyard upgrade), unless you're the original owner.

The only 84 to have use for a OPS, that I can think of though, would have been the iron duke since it was TBI.
I'm only assuming your part looks like the one I've attached ? (it's for the iron duke, l4) It's $50 as well. The single wire gauge sending unit is roughly $10.

Nino1984

Well, it's definately an 84 car. I am not the original owner, but it's a low milage survivor, so I would doubt that it's been messed with, but it's possible I guess. It's 3 wire, and the brown one zeros the gauge when grounded. no tan wire. My switch looks exactly like your image. When you say 0 to 90 ohm, is that from ground to one of the 3 terminals, with engine running? Any idea what the other two wires would do on a carburated car? Thanks for your help.

Also, the auto parts stores do list a 3-wire unit for the 1984 TA. Just not 80 psi. 60 psi only.

Apeiron

An L69 has an electric pump powered by an oil pressure switch, but I believe it should have been separate from the OPSU for the gauge. The car also would have come with a 60 psi gauge, the 80 was in V6 cars.

Nino1984

i guess it's possible that the gauge was swapped out. The SPID label confirms it'a an L69, carb motor, but I definately have a mechanical fuel pump. So, should I be looking for a OP switch for a V-6 w/ gauge? Assuming mine is bad of course. Still can't determine what the other two wires on the OP switch go to. Could it go to the carb?

Apeiron

Yes on the block, and an electric one in the tank.

Nino1984

Are you saying i have two fuel pumps? I've never seen that. What would be the purpose?

Apeiron

Prevents vapour lock

Nino1984

I did some research on your comment (sorry, I just couldn't imagine two fuel pumps) and apparently that is exactly what they did. it was new for 1984. So I learned something new, again. The research also stated that an 80 psi oil gauge was added in place of the 60 psi in 1984 also. OK, so now i know that I am supposed to have a 3-wire OP switch right? And the other two wires go to the electric fuel pump? So, any idea why I can't find an 80 psi 3-wire OP switch at any of the parts stores? They all only have 3-wire 60 psi, or 1-wire 80 psi. Is there a way to convert it to a 1-wire? What would I do with the other two wires?

Apeiron

In 1984, V8 cars never had an 80 psi gauge, and V6 cars never had the electric pump.

deadbird

I don't believe any of the v8 cars ever got anything but the 60 gauge, did they ?

Nino1984

When I researched wikipedia about the 1984 Firebird, here is what is said... " changes made for the 1984 model year were the deletion of the Trans Am only EFI Crossfire 305, a hydraulic clutch was now used on the T-5 Borg-Warner 5-speed transmission, and on L69 equipped cars, a lightweight flywheel and an aluminum belhousing were employed. L69 equipped Trans Ams also received a 8000 RPM tachometer, an 80 PSI oil pressure gauge, a high output single electric fan, a functional cold-air induction hood, a higher output mechanical fuel pump, and a secondary electric fuel pump to help prevent vapor lock"... So, I am pretty sure it is the way it was made. I still need to know if I can convert to single wire OP switch. Because I cannot find an 80 psi 3-wire switch (yet I have one on my car?).

Apeiron

Hmm... maybe it's yet another oddball Trans Am thing, then?

You could put in the 3-wire 60 PSI sender and just not care that your gauge isn't reading "correctly" (factory gauges are hardly known for their accuracy), or you can use the 80 PSI one-wire sender and a separate fuel pump switch in a different oil port. I'd probably do the former.

Nino1984

Yep, I thought about that. I just wasn't sure how adversely affected the gauge would be, if it worked at all. If it was only off 5 psi or so, I could live with it. I don't intend that it would be as accurate as a mechanical gauge is. but I do want it working so I can use it as a reference for cold oil compared to hot, and high rpm compared to low or idle. Perhaps I can do that for now, then continue to search for the correct one. Thanks for all the help. It's good to know what the other 2 wires do. Still amazed that there are two fuel pumps on that car.

bmorgil

The 1984 oil sender is the same as it always has been on Chevrolet motors. It is a small can style with one wire. The three wire can you found is larger but, if your not that familiar with it it looks just like the oil senders us old guys are used to. It is NOT the oil pressure sender. It is the detonation sensor and is usually on the drivers side lower block in one of the drain holes for the block. It sounds to me like someone indeed worked on the car. They probably got confused as the detonation sensor will screw right into the oil pressure tap next to the distributor. It was a common mistake back in the 80's and 90's (and apparently still) to get them confused as detonation sensors were in their infancy. A lot of mechanics got it wrong when swapping motors. The electric pump was added in 1984 to assist the mechanical pump in preventing vapor lock. In truth it is a great item to have. It definitely helps fuel fuel volume output of the mechanical pump because it helps overcome the high suction required to pull fuel to the mechanical pump. This is an old trick to help fuel delivery. It provides a nice way to create a "Push Pull" fuel system. You should notice that the pump runs as soon as the key is turned to "on". There is only a fuse in its way. It does not route through anything to turn it on or off just the ignition key.

Apeiron

The knock sensor has one wire and looks nothing like an OPSU.

bmorgil

Yep you are right right about that. I have to apologize, sometimes I can't remember which project I was working on. I am so interested in this because it happened to my son's 84. I have an electrical background and I found the factory service manual to be less than needed for effective diagnoses using a circuit diagram. If anyone knows where I can get an actual circuit diagram please let me know.

I went back to my notes on that exact problem. Here is what we found. There is a two wire (one tan) oil switch (small silver can and looks just like they always have right by the distributor). Then on our 84 their was also a three wire OPS switch screwed into the driver side of the block right above the oil filter (larger can style). The oil pressure switch takes you all the way back to the electric fuel pump added in 1984. The OPS routes current through the two wire oil pressure switch (by the distributor) and itself (they are in series). If there there is no oil pressure in either of those switches, the electric fuel pump shuts off instantly. The third wire (I think it's green) feeds back the appropriate signal to set a code in the CPU and sets a check engine light (no oil pressure).

Sorry I messed that up guy's. I think they say the memory is the first to go and.... I can't remember the rest. Sorry again.

Bob

Apeiron

The wiring diagrams in the service manual are the best you could find.

Codes don't get set for low oil pressure, but on an FI car you'd get a code 54 for no fuel pump voltage.

Is your 84 an L69, or an LG4 with the vapour lock recall applied?

bmorgil

I didn't want to ramble much past the the switch and the OPS. I new that some keen mind would pick up on that part however that you did.

It was a great deal. Beautiful low mileage always inside one owner car. Not only that but it is/was a genuine "Recaro" (no kidding). Here is the hurt it part.... Someone skilfully removed those Recaro's and along the way someone blew the motor. At first glance it looked OK. Had the Right intake and so forth. A closer look however reveled the motor had a one piece main seal. It had a 305 something with a manifold and a carb off of a 1984. Love those Chevy's though and I was looking for a potential hot rod.Most of you guy's on this org. are all over it. I love this forum. Stiffen the car, crank up the horses and try to hook it all up!

Got a nice dyno pull on this one. 383 stroker (6" rods). Hit 502 and backed it up with 504 HP. Nice torque. 512 to 525. The HP is all in and flat from 5000 to 6200. Roller motor. Very special heads. Its good to have friends.

Anyway, if you pull that wire harness off the two wire can next to the distributor, and short the two wires together you will hear the fuel pump turn on and off. I am not sure on the sensor portion off the three wire can but I would certainly trust your info. I remember it was a real pain in the butt getting that oil presure gage to work with the new motor!

spencer.24112

Will the mechanical pump do the job alone it did on the old impalas and they were a bit longer. Im doing away with all the old computer and smog wiring harnesses. Do you foresee any problems w/this?

84ws6ta

Yes the mechanical pump will do the job on its own. The electric pump was to help prevent vapor lock. As for the 80 psi gauge, yes they did come on the 1984 V8 cars. I bought my T/A brand new and it has the 80 psi gauge with the 3 prong sender. The middle prong is for the gauge and the other two are to shut the electric pump off in the event of a roll over or crash and the engine has stalled. (fire safety)