Hello,

I have a 1983 Firebrid with a 305 engine in it. The kicker is the engine is not the original. The original was a cross fire fuel injected one.

The engine in it now has a Holly 4 barrell carb on it. I was told the engine was either a 1984 or 85 out of some kind of pontiac. The tranny is supposed to be a 700R4. I just got the car about 2 weeks ago and it has finally stopped raining in cloudy central ohio long enough for me to do little work on it.

When I got the car both the water temperature gauge and the oil pressure guage were not working. They are still not working.

I looked for the oil pressure sender unit and found the little dinky one next to the distributor. It has one big male spade connector coming off of it. I just changed my oil and filter but I did not look for the other sender unit above the oil filter yet. That is the next step.

The other problem I have is that there does not seem to be any wires coming out of the harness for the dinky switch sender unit. The Haynes manual indicates that the wire to both the oil switch and the oil guage are tan colored. I did find one tan colored wire that was loose but it has a male spade connector on it. It also did not seem to do anything as I tried grounding it while the engine was running and neither the idiot light nor the oil pressure guage indicated anything. The oil pressure guage is buried all the way counterclockwise and it does not move when the car is running. I did notice the water temperature guage does swing from buried counterclockwise to the lowest reading when you start the car.

I think I am probably going to have to trace the wires from the instrument cluster and just ohm them out until I get everything sorted out.

One question I have is, can I just take out the dinky switch type sending unit by the distributor and replace it with a guage type sending unit? I am not sure about clearence as the disributor is very large and nearby but I think there would be room enough.

The other issue is the water temperature sending unit. The part that you hook the upper radiator hose to that goes over where the thermastat sits has two things that look like sending units for water temperature. Both have one connector coming out of them though one has two wires connected to that one connector. With all that the water temperature guage never moves off of cold except to swing over to cold from the far counterclockwise limit when you have the engine running.

The Haynes manual says there is supposed to be dark green wires going to both the water temperature idiot light and the water temperature gauge. None of the three wires are dark green. two are black and one is yellow. I am guessing someone tried to piece something together but it does not seem to be doing anything.

That is my story. Luckly the car runs great and the transmission works ok for having its kickdown cable all cobbled together. I really would like to get both the oil pressure and the water temperature working as I like to keep an eye on those things in any car I own.

Any suggestions would be welcome. I wish all those fake allen head screws on the dash were real so I could take the guage out and look at its wires by removing 4 screws, haha. I do know how to use and I do have a nice digital multimeter. It looks like it will get some use in the next week or so.

I just posted this as a new thread as I was rightly informed that tacking it on the end of a simular question is not the best way to get it looked at.

dzimmerm

 

I'm not familiar with the CFI setup but your coolant temperature gauge sender should be located in your driver's side head between spark plugs 1 and 3, and it should have only one wire going to it. It's been my experience that it's best to replace that with an AC Delco unit. For the oil pressure sender, get a bell-shaped sending unit. For clearance, I have a 1-inch or so 1/8" NPT pipe (both ends male), and a 45-degree 1/8" NPT elbow (both ends female) on top of that to allow clearance for the sender. Don't forget to use teflon tape on the threads to help keep the oil/coolant in on either sender.

 

It rained all last night, AGAIN, ARGGGG, so I did not work much on the car. I did go out this morning and take a reading on the little oil pressure sending unit near the distributor. It read open both with the car off and with the car running. I am guessing it is broken but that is not too big a deal. I will probably follow flyway190's advice and get a small bit of piping to get the new sending unit where I can reach it easier. I do have teflon tape as I have had to work on the plumbing in my house on and off over the years. I took a reading on that one connector that came out of the wiring harness with a tan wire and it showed no volts nor any connection to ground. I put the multimeter on the 30 volt DC range and hooked one lead to the lead in question and then put the other lead first on the battery negative to check for voltage and then on the positive to see if it was grounded. It was neither so I am guessing it is disconnected somewhere back in the harness.

My next order of business will be to get the plumbing and the sender unit and once that is installed ohm it out to make sure I get a variable reading as the engine rpms go up and down. Once that is done I will start probing wires coming out of the dash area until I find one that makes the oil pressure gauge move. From what I can see from the manual I still need to look for a tan wire. Grounding it should let me know if it is the guage or the warning light. I suppose to be on the safe side I could get a 1000 ohm resister and use that instead of a straight ground so I would limit any current in case a tan wire is somehow coming straight from the 12 volts. That would give me less than 1/4 watt of power across the resister which most of my resisters could handle without going poof.

Ohm law is voltage divided by current = resistance.

Or voltage divided by resistance = current

Picking a common resister value of 1000 ohms I get this.

12volts/1000ohms = .012 amps

Power is voltage times current

.012 amps * 12 volts = .144 watts.

So a 1000 ohm resister of .25 watt will do the job. The only question is whether .012 amps will deflect the gauge.

Yes , I am an electrical engineer, .

Woot, called the parts place and they say they have two different sending units, one for about $14.00 and a different one for about $15.00. I will check it out and see if either of those has just one connector coming out of it when I go over to buy one. Wish me luck.

dzimmerm

 

The oil pressure gauge wire should be dark blue, with a single connector with a big round rubber boot thing over it. The sending unit for the gauge should be pretty big; I'd say about 1½" diameter by 2" long, a round can sort of thing. There should be a brass elbow about 3" tall with a 90° at the end for it. This wire should definitely come out of the main harness at about the same point as the distributor (tach & ignition) wires.

The original motor would have had an additional oil pressure switch involving the fuel pump. You may or may not still have that, or need it; sometimes a block-mounted mechanical fuel pump can draw adequately through an in-tank pump.

 

The fuel pump is a mechanical one. It is on the passenger side up near the front of the engine. In plain sight actually. The sending unit near the distributor is a little thing but I need to replace it anyway so hopefully the parts store has one that will work. I will check for dark blue wires coming out near the distributor. So far I have not been able to spot it yet but there are quite a few wires, cables, and vacuum lines back there. If worst comes to worst I will run a new wire. The tach does work and so does the gasoline guage. I am going into the part of the week where I work 3 twelve hour shifts on the next 3 days so I probably will not be working on this issue until sunday or monday. Thanks for the info!

dzimmerm

 

There was several choices for sender unit at the local autozone. I got the large bell shaped sender unit with the single spade connector on it. I will let you know when I get it installed and how things go. It was only about $15.00 which was good. So many things to replace and repair and so little time, .

dzimmerm

 

I was able to do some testing on what wires went where. The wire to the Oil Pressure guage was indeed a Tan colored wire. After some false leads, (sorry about the bad pun), I found where it ended up. The wire came out in a connector that had 3 wires going to it. This is probably because the original motor was fuel injected and it had a combo sender unit that also would work as an emergency feed to the electric fuel pump.

Well, I don't have an electric fuel pump or fuel injection so I removed the two unneeded wires from the connector and found that it can be used to attach to the spade connector on the sender unit I am going to install. I also located the wire to the water temperature gauge. It was a disconnected single dark green wire with a spade connector on it. I could not find the original location of the water temperature sender but there are TWO sender units of unknown type that are on the metal elbow that covers the thermastat. They look like they have the same thread size as the water temperature sender that I just bought from Autozone for $9.00 .

I need to let the car cool down completely before I remove one of the water temp senders and try this new one with the correct wire connected to it.

I plan on going to Lowes, (a large hardware and building supply place), when they open at 6:00AM. I hope to get a small bit of pipe and an elbow to let me attach my larger bell shaped oil pressure sending unit without trying to squeeze it in under the edge of my huge distributor. I guess the distributor is so large due to the coil being built into the distributor cap.

Another thing I tried was adjusting the float level on the Holley carb. The primary float was set too high. I removed the small port screw and gasoline came running out. After some playing with it I found that turning the large nut after looseing the screw on top of it allowed me to adjust the float level. I had to turn it clockwise to get it to lower the gasoline level in the float bowl so that it would not run out unless I jiggled the car a little. The secondary float bowl as adjusted OK. I adjusted the idle screws leaner a little but I may have to adjust them back up as the engine was pretty hard to keep running when cold. My choke is also not working so I will probably need to research Holley carbs to find out what needs replaced. The lever from the choke to some kind of assembly on the side of the carb is hanging free. It looks like someone disconnected it instead of getting the automatic choke working.

It is almost 6:00AM so it is off to Lowes in my van so I can let the FB stay cool so I can try the new water temp sending unit before I hit the hay.

dzimmerm

 

After much reconfiguring I finally got the oil pressure sending unit piped up to the engine. It works fine, shows about 45 to 50 pounds of pressure and no leaks!

I finally managed to find the old water temperature sending unit right where flyway190 said it would be, between 1 and 3 spark plugs on the drivers side of the engine. The old unit was so caked with grease that I could not see it at first. It also had its connector broken off which did not help in finding it either. Luckly it screwed out ok.

I used teflon tape on all pipe fittings. The water temperature guage is working though I need to actually take the car out and see how warm it gets on the highway.

Thank you to all who gave advice and hints. I ended up using two brass 1/8 inch fittings to get the new oil pressure sending unit positioned so it would fit without hitting the distributor and so the hex nut on the bottom could be reached. It is kinda pointed back towards the firewall but more aimed at the drivers seat, if you know what I mean. I used a 2 and 1/2 inch nipple and a 45 degree elbow at the top of the nipple.

Now I can get a good days sleep.

dzimmerm