rnln

Recently, when the weather turn cold, I have a new druck press gauge problem. Hope someone can point me to the right direction. And please don't tell me it's my engine, or oil pump is gone, crossing my fingers.

1- at start up and complete stop (idle): if the RPM is 1k or above, the gauge works fine. But if RPM drop to below 1k, the needle pegs to the max (at 5) and stay there. If I touch the gas pedal, the needle come back down at normal position until the RPM drop to below 1k, then it peg again.

2- While driving, the needle works fine except when I shift. When I shift, I usually pause at neutral, which makes RPM drop close to 1k or so, the needle pegs to max and come back down when I hit the gas (RPM raise).

3- If I shift quick, which the RPM down't come down below 2k RPM, the needle sometimes doesn't peg to the max but it still bouces/dances in front of me before it come to the right position.

So the problem is related to the RPM, when it is drop low. The druck press sensor is new. It's only several months old. Before I replaced the sensor, the synptom was different. It either stayed at max top, or at the bottom. It was working perfect for several months.
I checked the wire the pass weekends and it looks ok. Does anyone have this problem?

rusnak

Hi Ron, does the oil pressure look any different once the engine heats up?

Do you know how much oil is in there right now? Did you check the oil level? What brand of filter are you running, and when was the oil changed last?

Russ

srf506

What's the volume gauge showing and have you used the dipstick to verify you have the correct amount of oil in it? Remember it should be hot and on level ground. The symptoms you describe almost sounds like an electrical issue with the guage. Almost like a bad ground or short somewhere. I'd recommend you get an aftermarket one and plumb it in to see what you got.

theiceman

sounds to me like the sender unit is shot .. looks like it needs some pressure to wake it up . usually it pegs when it loses ground ....

it's about 60.00 for a new one but that is where i would start. the fact your oil pressure light is not coming on its pretty indicative you don't have low oil pressure at all. with the ignition on you can try taking the wire off the top of the sender and ground it , it should toggle between 0 and pegged ., this will tell you the guage is okay and you can go after the sender.

rusnak

I agree it sounds like a sender unit, but why would it show correct pressure at higher rpms? It must be a mechanical failure in the unit? The ones I've seen that go bad just peg and stay there.

Ron, was it doing this last time, or was it doing something else? (i.e. what was the history of this failure?)

theiceman

oh it is definitely mechanical inside the sender all right.
I had a oil level sender that did soemthing similar once

rnln

rusnak, srf506,
it happens the same no matter cold or warm, full or not full (oil mark at bottom or top of the dip stick). It happend when the oil level was lowed. I then added some oil to the mid line. Then I change oil on the weekends and filled it close to the max mark. Problem still there.

Last time, several months ago before I replace it, it was dead. It always at max or bottom depend on the engine is running or not. It never works.

You really think Ground/short would affect the gauge base on RPM?

One more question: there is another single wire clips in below the pressure sendor. This thing looke like a pressure switch. This wire come up and goes together with the pressure sendor. Do you know what it is?

theiceman,
I did, and it works ok. I also tried it when it was happing, then nothing happen. Meaning when the engine is idling at low RPM, below 1k, it acts as there is no sendor, but when the engine is off and key is at ON, everything works normal. So, the problem is only when RPM below 1k.

But the sendor is new. It's only couple months old. I am telling myself I am having a defective sendor, and wishing nothing is wrong with my engine. Do you guys think if it's posible that the sendor get stuck. It needs more pressure then nomrla to push it to move?

rusnak

I wonder if there is a break in the wire somewhere or a loose ground connection.

theiceman

yes I think your sender is bad. i think the other wire your talking about is the engine temp wire that goes to the sender below your presure sender. for the rpm to go low and max out the pressure ? has to be a sender or as rusnak said it is a wire and the vibration of the engine is affecting it . M money is on the sender. Too bad there isn't a renlister near you . you can swap it with another car in about 5 seconds.

srf506

I'd check the connections on the sender and the gauge really carefully. Especially the grounds. I think you got an intermittent loss of ground. The fact it isn't just going to peg seems to me its not the sender but something in the electricals. I could be wrong, but usually a sender hard fails, not this "irrational" behavior, but a gauge can certainly exhibit bad behavior.

I remember a long time ago I was barrelling down the runway to take off in an F-4. The left engine's oil guage was all over the map as I went to Mil-power. I was trying to figure out whether I should try and abort (not a real easy task), shut down the suspect motor and press-on single-engine (a better option, but still not optimal) or, believe my own senses which said oil pressure can't really do that in an engine, its gotta be the guage or sender and press on. There were no other warnings or alarms on the motor and all the other gauges were nominal. I pressed and it indeed turned out to be an issue in the gauge and the engine flew beautifully for about two-and-half hours (which was all the flight was scheduled for).

Keep us posted on what you find. It was a good suggestion to try and find another 911 owner and see if you could swap the involved pieces and see what fixes the problem.

rnln

ice, srf506,
swap the pressure sendor in 5 second? You must be a superman. I took 1/2 day to undo mine last time. Oh wait a min, are you saying swapping the wires, with the sendors in place (2 cars running side by side)? Good idea. I search for someone who would like to help. In addition, I will clean connectors and check the gauge.
Thanks for the ideas.

theiceman

er no ...... that sensor just screws in !!!!!! ... how tough could it be ?

but running a long wire with the cars back to back would work too

ahem .. glad I thought of it ahem ....

Barry A. Waters

theiceman,

BRILLIANT! Have the 'Donor' car (with properly working sensor and gauge) source its pressure reading to the problem car's gauge to eliminate a gauge issue with the problem car. Genius! Sheer GENIUS!

Barry