I installed an Auto Meter Pro Comp Ultra-Lite Oil Pressure gauge in my Formula using the stock 88 sender, and when I turn the key to "On" position the needle steps immediately to 100 psi and stay there even after engine start.

Do I need a resistance between the gauge and the sender ?

There is one at the back of the stock gauge.

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"I'm not driving too fast, . . . I'm just flying too low."

4.9 ongoing project

I don't know if their is a resistor for the stock gauge. Are you talking about the rally gauges?

I believe the AutoMeter gauge uses a different kind of signal than the stock gauge. In order to get the AM gauge to work correctly, I think you'll need to get an AutoMeter sender.

If I'm not mistaken, the stock oil pressure gauge/sender is a 90 ohm unit. If the aftermarket gauge is not compatible or other than a 90 ohm unit it will not work. Or work correctly.

My 2cents......................

quote Originally posted by 87antuzzi: I don't know if their is a resistor for the stock gauge. Are you talking about the rally gauges?

Yes, on a Formula the Oil pressure Gauge is in the same location as the GT.

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"I'm not driving too fast, . . . I'm just flying too low."

4.9 ongoing project

Do not worry about the resistance on the back of the stock gauge. It's just part of the stock gauge.

If the gauge reads high pressure - it's because of a high resistance to ground.
Two possibilities:

1. Very high pressure (no........)
2. There is a break in the wiring to the gauge. Could be a broken wire, loose connector...

Edit: this would be correct if the Autometer gauge measures the sender's resistance to ground, with high resistance = high pressure, like the stock gauge.

If not, can you show us the wiring diagram?

[This message has been edited by pmbrunelle (edited 12-29-2009).]

quote Originally posted by pmbrunelle: Do not worry about the resistance on the back of the stock gauge. It's just part of the stock gauge. If the gauge reads high pressure - it's because of a high resistance to ground. Two possibilities: 1. Very high pressure (no........) 2. There is a break in the wiring to the gauge. Could be a broken wire, loose connector... Edit: this would be correct if the Autometer gauge measures the sender's resistance to ground, with high resistance = high pressure, like the stock gauge. If not, can you show us the wiring diagram?

For wiring, I connected the "Tan" wire to the "sender" connector on the gauge. Others are "+" an "-".

AutoMeter sender only have one connector.

I have done another test: Without installing it, I grounded the AutoMeter sender, and connect it to the gauge. Needle moves a little bit but stays near "0".
So I beleive "high resistance" means "low pressure" with the AutoMeter sender.

On the ohmmeter, the needle reacts the same under both conditions.

[This message has been edited by falcon_ca (edited 12-29-2009).]

The stock sender is 1/4" NPT.

But you do not need to keep the stock sender.

You would lose the oil pressure switch though, but it's not very important.
The oil pressure switch activates the fuel pump in case the fuel pump relay fails.

If your fuel pump relay ever stops working, you can always stick a paperclip in the relay plug to force the pump on, or use the A/C relay just beside it to get home.

I read a lot of story about the relationship between the oil pressure sender and the fuel pump, butit is the first time I see this one.

The most common is if there is no oil pressure the fuel pump will be shut off.
I also know about jumping 2 pins on the ALDL connector.

Anyway, I will replace the stock oil pressure sender with AutoMeter's one using a 1/8 NPT female to 1/4 NPT male adapter.
I will probably soon have 2 stock senders for sale , I bought a new one for my 4.9 swap.

Thx

[This message has been edited by falcon_ca (edited 12-30-2009).]