[beltrunner]

My '71 Formula 455 HO with the Ralley Gauges has alway displayed between 40 and 60 lbs. oil pressure. The gauge started showing 80 lbs. pressure at idle, and went off the scale above idle. A mechanical gauge check showed the motor actually has between 40 and 60 lbs. pressure.The electrical sending unit shows 88 ohms at idle.I installed a new sender with the same 88 ohm reading.The Ralley gauge shows 80+ lbs. pressure with both the original and new sender.A variable resistance check of the gauge through the existing gauge wires shows normal gauge travel between 10 ohms and 80 ohms (gauge seems to read approx. one pound of pressure for each ohm measured (10 ohms approx 10 lbs...80 ohms approx. 80 lbs.). Is it possible both sending units are faulty? Any ideas on this? Thanks for any help.

[Dens71TA]

According to the service manual, the oil pressure gauge will show 0 PSI at 1 ohm and 80 PSI at 88 ohms. It sounds like you have a faulty sender. The quality and accuracy of aftermarket sending units has been questionable recently. I don't know if they're being outsourced to China or Mexico or what???

[schneidsd455]

What, if anything, have you done to the car recently? With the original and new sensor showing the same thing, I would question another sensor being the solution. Maybe both sensors are bad. Unless you have somewhere around 80+ ohms of resistance between battery negative and carbody? I measure 3.5 ohms between sensor and carbody with the car dead. Has your water temp guage showed anything different recently? Bad parts out of the box really throw a wrench in a guy's troubleshooting.

[beltrunner]

Thanks for the help.To explain further,I had done nothing to the car before the oil gauge went south on me.I am pretty much toward the end of a 4 year resto on the car.It's garaged and has been driveable for almost a year,but has not been driven (registration,insurance,lights not installed yet,etc).But I do run the motor weekly.The oil pressure gauge has always read normal.Last week while I was running the motor and watching the gauges,the oil gauge jumped to 80+ lbs.I did check the ground resistance with engine off as suggested and got less than 2 ohms.It must be (I hope) that the new sender is also bad...I'm taking it back to Classic Industries tomorrow for a swap.I'll let you guys know what happens.

[beltrunner]

And the temp gauge reads normal...

[giles]

Originally Posted by Dens71TA

According to the service manual, the oil pressure gauge will show 0 PSI at 1 ohm and 80 PSI at 88 ohms. It sounds like you have a faulty sender. The quality and accuracy of aftermarket sending units has been questionable recently. I don't know if they're being outsourced to China or Mexico or what???

Dens71TA, Where did you find the chart in the 71 Service Manual that lists the oil pressure guage ohm-to-psi relationship? Is there a similar chart or table for water temp guage? I am trying to resolve a problem with my temp guage and would like to see if my temp sender is right (approx 700 ohms cold and 100 ohms @ 195F).

[70RAlll]

Originally Posted by giles

Dens71TA, Where did you find the chart in the 71 Service Manual that lists the oil pressure guage ohm-to-psi relationship? Is there a similar chart or table for water temp guage? I am trying to resolve a problem with my temp guage and would like to see if my temp sender is right (approx 700 ohms cold and 100 ohms @ 195F).

Giles- if you are having "high" readings from your water temp,and you have the ralley cluster, I too have dealt with this problem.I had one of the newer water temp guages sourced from PY's or Ames,can't recall. Anyway, my car would read 220,when I knew it wasn't that hot. It would get as high (on the dash guage ) as 240.My thermostat was a 180 and my radiator temp readings were 190-200. It drove me crazy. Is this what you are dealing with?? I bought a used temp sending unit from a guy whho pulled it off of a 1971 Formula with guages and wha'la it worked perfect.The newer sending units are junk and don't seem to read correctly with the ralley guages. I had been told by a friend who had experienced similar problems. Try a used ,older sending unit and see if that "cures" the cars ills. my .02C

[RASK]

Temp senders and pressure senders are known to be crap from aftermarket. Get your temp sender from Electric Limited. I believe I got my oil sender from Napa and it was OK but my Napa and other source for temp sender were way off, as much as 20+ degrees. Do a search for more info on these topics in this forum and the electrical forum.

[giles]

Thanks! I had another referral to "lectric limited" as well. I have already ordered one of their senders. I'll let you know what I find.....

FYI, the original sender was reading high, like 230 warmed up, and this was before AND after hot tanking the block and heads, a recore of the rad, new stat and a rebuilt cast impeller water pump. I decided to try a new NAPA sender and it is even worse! Goes to 250 when the stat housing is 195 (with infrared).

[70RAlll]

Giles- I have a feeling you will end up having to get a used original temp sender.That is exactly what mine was doing. I, too, have heard of electric limited,I bought one of their senders for my car. Still have it if you want it. It has a blade instead of a peg like the OEM ones were . I also have two or three aftermarket peg ones, none worked. You see the originals on Ebay every once in a while. I recall the one I bought came off of a GTO. Email lilgto447 on Ebay.Fred is his name. I bet you he has a few originals. He is a nice guy and is always parting out Pontiac engines and has a box full of used senders at all times..
PM me and I can give you his telephone number. I bet he will sell you an original for $15 or so and your problems will be gone.

[thefirebirdm@n]

I'm curious to see if original used units fix the two problems described here. My oil pressure gauge on the '73 went south just after getting the car. Its pegged all the way to the right. I bought a new sending unit from Bulter Performance and was planning on installing it soon. Would like to save myself the hassle of doing it twice if its going to be way off and I have to get a used one.

[Formulabruce]

I have seen a ground issue with the cluster cause more ground than it needed and affect the showing reading