Ok, here's the situation.

With the engine OFF, I turn the key from OFF to IGN and the oil pressure gauge shoots up to 60psi. Again, this is with the engine off. Then when I turn the key back off, it shoots all the way up, pegging the needle, then drifts back to the natural resting place of zero. I don't know what the behavior is with the car on yet, since I've been doing some wiring of new gauges, but the oil pressure gauge worked perfectly the last time the car was on.

Obviously I'm thinking short here, but I'm having a hard time explaining the spike and the *perfect* value of 60psi. Also, when I remove the wire from the sender, the gauge sits at zero. Ok, YES I was doing work in that area, I installed a fuel pressure sender. I just can't figure out the condition that would cause what I'm seeing.

Any help from the geniuses?

 

Stock or aftermarket gauge?

 

Stock

 

I haven't heard of your exact problem, but the stock pressure sender is often noted to be very flaky and to give strange readings. Sometimes it can be repaired with a good (internal and electrical contact) cleaning, but, often, it just needs to be replaced.

 

I know the water will just sit at 0 with the light on if there's nothing connected, so one could assume that you'd get the same response with the oil. Does the stock cluster do anything to indicate a short? If so, is that the proper response?


Oh yeah. With the work you did behind the cluster....I'd look there too other than wiring.

 

Well, it IS connected, but I would expect it to sit at zero with the engine off I don't think the sensor has just "gone bad" by sitting there since the last time i drove it 2 weeks ago.... I think I screwed it up. I just can't even start to think where I would've broken it and how I would've managed to do it so perfectly.

 

Nope, I haven't touched the cluster since before the last time I drove it, and it was working fine then.

 

The jobs you DO do correctly you do very well, so it's easy to see how you can break something with the same quality.

Right, but if there's a short, then you'd get something like what you're seeing I would guess. I had the same thing happen to my EGT. Granted not the same circuitry, but the principal might be the same. With the sensor disconnected, it read as open and read high and the needle bounced. With it shorted, it read low with the needle bouncing. With yours sitting at 60 (smack in the middle) I'd say you have a short somewhere. That's all I can think of. It's just read off the sending unit directly. Doesn't go though the ecu, so I'd say it's all wiring.

Or you shorted it and fried the gauge itself.

 

Agreed, but man...still doesn't make sense. I guess I'll just wait and see what it does with the engine on. Maybe that'll fix it....maybe it just WANTS oil pressure.

 

As we all know the senders are VERY flaky and unreliable. The rest of the circuit is pretty simple.

I have seen FC senders fail where they work OK, then all of a sudden they peg out the gauge, then go completely open circuit.

Try unplugging the sender and see what reading you get. That should tell you if it's the gauge, sender, or wiring.

My experience has been that senders can go bad all of a sudden - it's not necessarily an immediate thing.

Dale

 

So what does that tell ya?

 

Whoops, missed that part - sorry .

If it's sitting at zero with it unplugged, that tells me the wire isn't broken and shorting out somewhere. If it had any continuity to ground or resistance to ground, you'd get a reading. The higher the resistance, the lower the gauge reading - that's why the gauges want to read low as the sensor goes out, the resistance goes up. An open circuit is infinite resistance, which is zero. Shorting the gauge straight to ground with no resistor is a bad idea - the gauge may not be designed to handle a straight short to ground. I've seen FC oil pressure gauges actually *melt*.

Considering how notoriously flaky the FD senders are, I'd go ahead and get a new one coming. I bet that will whup it.

Dale

 

No, I refuse to believe that the sender broke while sitting there not being used for 2 weeks while I did lots of wiring in the area surrounding it and all the engine harnesses I might take it out and give 'er a cleaning and testing with the Ohm-meter (btw- how do i get that ****** out?), but I'm really interested in seeing what it does when I turn the engine on. And can you explain why it jumps to Infinity (straight ground) when I turn the ignition off?

 

I can see your point on it's being too much of a coincidence. However, how about trying grounding the sender wire through a few resistors (or a potentiometer) in the sender's resistance range (I don't remember what the range is - maybe someone else does). That ought to clear up whether anything other than the sender is bad.

 

Its an FD... it has to be haunted...

I would go with a short or very bad connection at the sensor. I had the same problem and it ended up going away when i replaced my wiring harness

 

Holy ****, I think i know the problem.... I'll post again when I get home.

 

 

That sounded like you posted that just after smacking your head...

BTW, to correct an earlier statement - the gauge is NOT at zero with the wire shorted to ground. It's at zero with infinite resistance - ie, open circuit. The gauge is electric, so without power (ie, key off) you'll get no reading.

Dale

 

Eric's comment about haunted cars made me remember something I said about someone going through my car and unplugging wires a few years ago. Then I remembered I unplugged a harness to make room when I was running the sensor wires into the cabin. That was the problem!

 

That was going to be my next guess.

 

what stainless steel line to you having through the cabin?

 

EGT gauge

-Rob

 

Sincerely,
Tom

 

I'm having a similar problem.

Is that picture on the passenger side of the car?

My problem goes so far as to not allow my starter to grab and turn the engine over. It just clicks. (the old one or the new one I bought since I thought my starter was dying)

 

Yep, passenger side. I fixed the oil pressure gauge issue but still have other problems.