Oil pressure gauge wiring problem.
 

Alright I hooked up a mech gauge to my car and when it's warm I get 35 psi at 900 rpm idle or so and 85 at about 6k. Everything is working properly. Just bought a new sending unit. and hooked it up. It does the same thing as the last. It just sits at 0 at idle. And crawls to maybe 25 at 6k or so.

So I went to the haynes book and looked up the wiring diagram. It seems there is a line hooked up directly to the signal wire for the oil pressure that goes to the AC compressor? Sure enough I went back to the engine bay and I have that wire just hangin there. I have a reman AC compressor from Victoria british and there is no spot to hook up this wire? (that I can find anyway?) If I touch this wire to ground it pegs out the oil press. gauge.

Does anyone know how to fix this problem? It has to be a problem with resistance value to ground that I'm not getting through the AC compressor. I just dont know what the value is or how to hook it up?


http://i17.photobucket.com/albums/b1...compressor.jpg

I just don't know where to hook it?
Thanks

That is not the ac condenser. You should find a wire with a little black box attached, less than 1" square and 3/8" tall. It bolts to the block for ground. The condenser smooths the signal coming from the op sender.

the condenser is inside the sending unit IIRC. You may need to run new wire from the sender to the cluster gauge. In addition, you may need to change the cluster. Thats what I did in my newly acquired FB. If I were you, I wont worry it since a mechanical gauge is much more accurate than the stocker.

My condensor (another word for capacitor) is bolted to the rear iron using one of the bolts for the flywheel inspection cover. It's a silver cylinder, a little over an inch long and maybe 1/2" in diameter.

Rich

OIC. I never used that thing. My engines along with other installs are just plain block with the usual wirings for alt, oil press and water temp. Never experienced any problem or noticed any negative as far as the stock gauges.

Pictures of this thing? Anyone?

Maybe installing an adjustible pot. inline with ground would work, then I could make my oil pressure what ever I wanted.

Well, actually, you'd be adding resistance if you put a pot in series to ground, and you want less resistance to make it read higher. I thought about adding the appropriate resistance in parallel with the sending unit on mine to make it read higher, but decided to just buy a new cluster...$22 shipped off eBay. If nobody posts a picture by tonight I'll take one and post it.

Rich

Gotcha... I'll try adding a resistor just because I have a million laying around. If you could get that pic I'd appreciate it.

Thanks!

Here is how to test the gauge. Just find some resistors that are close to a couple points in there and connect between the oil pressure sender wire and ground. If the needle moves to the correct position, the gauge is okay.

https://www.rx7club.com/attachment.p...d=150705&stc=1

The condensor isn't really needed. The meter will work correctly without it. The other possibility is the sender or the wiring. Make sure the contacts on the connector/sender are clean. Oil and crap can get on them and mess up the reading. Also, if you used teflon tape on the threads, that will cause problems as well. The sender needs to have a good ground with the block. You can test the sender using the resistances shown in the figure as well. Remove the wire, start the car, and measure the resistance between the sender and ground. Should be around 200 Ohms at idle and about 130-140 Ohms as you rev the engine.

Good luck.

Kent

take the wire off the oil pressure sensor and touch it to a good ground.. if the gauge pegs then your wiring is okay (dont do this for too long, it MAY damage the meter, i dont know... use the two person method).

if the wiring is okay, then its the oil pressure sender, or its ground... did you use teflon tape to install the sender? that may insulate its ground connection. keep in mind the sender must ground through its threads into the engine block.

Everything is leading tword a bum gauge. No teflon tape I replaced the sending unit with new and same thing and yes teh gauge pegs if I ground the wire. Is there any kind of adjustment on the gauge? I know the rx-7 tachs have a little pot to adjust the rpms on the board. I'll try soldering a wire to the case of the sending unit and going to ground but I doubt that will help any.

I'll see if Ihave some resistors so I can ohm check it tonight. Thanks all...

A variable resistor is the easiest way to check the gauge. Either set it to the desired resistance (shown in the diagram that gsl-se addict attached) and connect it in place of the sending unit and see what the gauge reads, or adjust it to give the desired reading (say, half scale), then measure the resistance of the variable resistor with a digital ohmmeter. I'm betting your gauge is bad. I'm in process of tearing my cluster apart to see if there is a way to fix mine, but I'm not too hopefull. Fortunately, as stated previously, I bought a spare cluster off eBay for a very reasonable price.

Rich

I believe you are correct. When I first saw those I thought it was the condenser for the ignition, same size and style. The later ones are the little black box style.

If the gauge is bad, it will show on the fine white wires that are wound around the bar. If there is any browning or blackening of the wires, it's toast. Iirc, it's 4 nuts that hold each side guage, not 2.

Here's the condensor that was on mine...like I said before, it's a little over an inch long and about a half an inch in diameter. It was mounted on the flywheel inspection cover, where I now have three ground wires attached and the empty bullet connector was connected to it.

Rich