This is very irritating. I got my motor put together, and in the car, and cannot crank it because my autometer oil pressure gauge is acting up. Here is what it is doing.
When the ignition is turned on, the gauge jumps to over 100 psi. I have a steel braded line coming off the block that attaches to the sending unit. It is coming straight from the original sending unit location. I tried grounding the sending unit and that did nothing. Here is what I have found:

If I unhook the sending unit wire (coming from the gauge), the needle goes to 0 psi. So I know it has somthing to do with that wire. I replaced the wire, and got the same thing. If I unhook the wire from the sending unit, and ground the wire to the body, the needle jumps to 100psi. I'm guessing that the sending unit is somehow being grounded, and its not supposed to? Has this ever happened to anyone? The guys at autometer aren't very helpful.

 

you follow the instructions?

sounds like you have ignition and sender wires reversed.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by El Pollo Diablo &raquo;</TD></TR><TR><TD CLASS="quote">you follow the instructions?

sounds like you have ignition and sender wires reversed.</TD></TR></TABLE>


Yes I followed the instruction. I've hooked up many gauges on race cars, but this one has just plain stumped me. The gauge was working before I pulled the motor. The only thing different is the way the steel line is ran into the block. Before I pulled the motor, I had the braided line run into a greddy oil filter block adapter. Since I added an oil cooler, I moved the line to the stock sending location.

Could it be possible that a positive charge is running through my block, and into the sending unit?

 

I have an old Pro-Comp oil guage on my desk so I tried a few combinations (w/out the sending unit). I think it will go the other way if he has ignition going to S and sensor wire going to Ign only if the sender wire is grounded. He would get what he's describing if the sender wire is going to ground. I think you (bosco) might want to check that its (the sending wire) not touching something grounded up near the motor ?? Or maybe it does have something to do w/ the steel line (which I am not following you on exactly).

Bosco, for clarification, its not 0 and 100 right? Its like pegged full left or full right (beyond each mark) right? If not, I cannot simulate what you are saying here.

 

So seems like it's a short in the sending wire?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by phat-S &raquo;</TD></TR><TR><TD CLASS="quote">I have an old Pro-Comp oil guage on my desk so I tried a few combinations (w/out the sending unit). I think it will go the other way if he has ignition going to S and sensor wire going to Ign only if the sender wire is grounded. He would get what he's describing if the sender wire is going to ground. I think you (bosco) might want to check that its (the sending wire) not touching something grounded up near the motor ?? Or maybe it does have something to do w/ the steel line (which I am not following you on exactly).

Bosco, for clarification, its not 0 and 100 right? Its like pegged full left or full right (beyond each mark) right? If not, I cannot simulate what you are saying here.</TD></TR></TABLE>

Yes its pegged left or right. I've got a feeling that my block has a positive charge somewhere. The sending wire is not touching any grounds at all. I even replaced the wire with a new one, and it does the same thing. I guess I'll go buy a new sending unit and see if that does the trick.

 

could be just a bad sender too..

 

I think you need to ground the sender body to the chassis...depending on how you mounted it.

Try that before you buy a new sender.

 

1) i've got a bad sender for my water-temp from autometer.
2) i've also experienced crappy customer support from them.
3) when i put my new motor in, i was trying to build oil pressure before i actually started it (which is what i assume you're doing). no matter how many times i cranked it over without starting it, the guage still read 0psi. i decided that by this time i'm sure there is good oil pressure and started it up. as soon as the motor started, the guage went back to normal and read something like 60psi of pressure.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bosco500 &raquo;</TD></TR><TR><TD CLASS="quote">

Yes its pegged left or right. I've got a feeling that my block has a positive charge somewhere. The sending wire is not touching any grounds at all. I even replaced the wire with a new one, and it does the same thing. I guess I'll go buy a new sending unit and see if that does the trick.</TD></TR></TABLE>

I think we are mixing up what we are saying to each other or I am far more electically challenged than I thought (quite possible). FWIW, my test scenario has + to Ign, - to Gnd and all is good. Take additional wire from Snd (or S) and run to + and the guage goes further _left_, take said wire and go to - and it pegs _right_. So it *seems* to me that your sending wire is grounding when it should not (not that your block is positive). Perhaps my test is just bogus however.

 

I'm betting money that the sender is not grounded...

 

I defer, I don't know enough to really discuss it. Just trying to simulate it here w/ what I mentioned.

 

try this:

connect ignition to 12v+, connect ground to 12v-, leave sensor alone (ungrounded, unconnected)

you should get the gauge pegged to max...i think

 

Do you have the ground strap connected from the tranmission to the frame rail?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by El Pollo Diablo &raquo;</TD></TR><TR><TD CLASS="quote">try this:

connect ignition to 12v+, connect ground to 12v-, leave sensor alone (ungrounded, unconnected)

you should get the gauge pegged to max...i think</TD></TR></TABLE>

9v source but fwiw, if I do that, nothing happens. Only when I tie the sending wire to something will the needle move - touch sending wire to (+), moves left (further left0, touch to (-), moves extreme right.

 

the motor is the ground, my autometer is the same and I completely blew off the instructions and did it my way and it works perfectly.

autometer's customer service does suck...

 

thanks for sharing...

 

the sender does not need a a ground (or if it does, it uses the motor). i have this exact same setup on my miata with the sender mounted remotely on the firewall with an adel clamp via braided steel line. from the sender there is the one wire that goes to the guage itself. from the back of the guage there is also the ground wire and the ignition wire. my ground goes to the outside of the transmission tunnel on the passenger side for easy access (make sure the paint is ground off). my ignition wire taps into the harness where the stereo would be.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tnord &raquo;</TD></TR><TR><TD CLASS="quote">the sender does not need a a ground (or if it does, it uses the motor). </TD></TR></TABLE>

It does need to be grounded. Either to the motor (when threaded in) or through the mounting bracket and to the chassis.

Although that no longer seems to be likely cause of his problem. (if it wasn't grounded the gauge wouldn't move at all)

 

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by El Pollo Diablo &raquo;</TD></TR><TR><TD CLASS="quote">I think you need to ground the sender body to the chassis...depending on how you mounted it.

Try that before you buy a new sender.</TD></TR></TABLE>

I've tried it grounded, and not grounded. It does the same thing.

Phat-s -
With the sender wire *not* hooked to the sender, the gauge sits on 0 psi, as it should. When the sender wire is hooked up, it pegs out (over 100 psi). This is what made me think of the positive charge, which I am thinking backwards I believe.

I believe I have a bad sender. I checked the ohms, and it read 278. That is way too high for a sender of this sort. I'm almost positive it should be reading between 70 to 90. If someone could check this, I would appreciate it. I will be buying another regardless though. Hell, I'll probably be buying a cheap mechanical gauge tomorrow just so I can hear my new motor

 

By the way, Mr El Diablo, is that Adam Malley's old car you have?

 

I talked to another tech at autometer today and found out the problem. The sending unit will normally read 230 ohms @ 0 psi, and 270 ohms @ 100 psi. Mine is reading 278 ohms with no running engine. Faulty sender.

The guy was very nice and is sending another unit for free, in the meantime I will be going to autozone and buying a cheap sun-pro gauge so I can start my engine.

 

i bet that support guy is getting suspicious, he send me a water temp sender this morning also.

the guy i talked to this morning was much more reasonable than the last person. i will continue to support autometer.

 

and this thread illustrates why I am using a mechanical oil pressure gauge. I know this is not necessarily helpful, but I feel a lot better having a mechanical gauge even though I know a lot of people feel nervous about bringing a line of hot pressurized oil in the cockpit.