bouncing oil pressure guage

[Blackened302]

hey guys, got a new one for ya:

the other night i get in my car to head out for a cruise, and all of a sudden i notice my oil pressure guage didn't move--it was at zero.

i freak out.

i can't pull over to immediately check it out, but i notice it's kinda bouncing up as i accelerate, drops as i shift, goes up to normal by itself, then drops a little, then after a while (up to temp?) it stays where it usually was.

no check engine light, runs perfectly fine, no funny noises (other than an exhaust leak and a couple loose rockers), and always seems to bounce around a little but settle down to normal after a while.

bad sending unit/sensor or something?

oh yeah, hehe, i checked my oil level 3 times and it was where it was supposed to be.

thanks for the help
:SNSign:

 

[m0l0]

Well first thing dont start it

Then check with a reliable gauge, in the best case scenario it can be the sensor, on a not so funny and i think is the oil pump pickup because the revs simptoms, on a really sucking worst case is the pump, but first check with a real gauge

 

[95mustang_gt]

Mine has been doing the samething for a month.I have not had a chance to hook a gauge up.?But im pretty sure its a faulty gauge.

 

[Blackened302]

well, before we dropped the new engine in, we replaced the oil pump driveshaft w/ an ARP one, so other than the pump itself (engine had 70k on it w/ about 71xxx now), i don't think it's the shaft.

 

[True 5.0]

Make sure the body ground strap has been connected back to the block. Without a good body ground, the gauges act really weird and give bad readings.

 

[BlownFiveLiter]

+1 on a bad ground. Mine did that before I changed all my cables out with new ones. Same oil pressure sending unit, but on a different engine. I had some funky electrical issues with my old cables prior to the swap which were solved with new cables, and I'm almost positive that was the issue, nothing mechanical. The old engine ran great, just had no power compared to this one.

 

[Blackened302]

ok, cool, i'll look around for some loose grounds.

anyone know where exactly the sending unit is so i can check that connection?

thanks, guys.

 

[BlownFiveLiter]

It's right above the oil filter. The engine ground is also right next to it.

 

[Blackened302]

cool, thanks man, i'll check it out asap (probably not 'til monday).

for curiosity's sake: what would the car run like/act like/etc if there was, in fact, low/no oil pressure? any noises? bucking? burning smell? anything? symptoms?

thanks again, guys.

 

[True 5.0]

Low oil pressure may be hard to hear but NO oil pressure would very obvious. The valve train would clatter, almost clank, like crazy. Your engine bearings would also be toast.

When you're in the engine bay looking for loose grounds, make sure the body to block ground strap is still attached. It is located on the driver side and attaches from the motor mount stud to the frame rail. it is a braided ribbon cable. If it's missing, make a new one. This ground is critical.

 

[Blackened302]

alright, sweet--thanks, guys!

gonna check this out tomorrow and i'll get back to you gents. i appreciate the help!

 

[OrangeMustangGt]

go to autozone and get a mechanical oil pressure gauge. You should read roughly 10 psi per 1,000 rpm when hot and roughly 40-50 psi at idle when cold. My car would read 0 at idle then raise up when i gave it rpms. It was a bad oil pump....i just changed it 2 weeks ago

 

[Blackened302]

thanks, Kyle. geez, i hope it's just a faulty guage/sending unit in my case... i've had enough trouble w/ this new engine already..

 

[Blackened302]

after driving around today, i noticed that the guages goes DOWN as the revs go UP--kinda counters what i figured would be.

also, after 20 minutes or so, the guage seems to act normally.

guess i won't really know 'til i check it out tomorrow, but just wanted to mention that, fwiw.

 

[1TallMF]

I'm gonna bet its just the sending unit (knock on wood). A new one is just $7 or so, but now would be a good time to get a REAL gauge mounted if you can, that will tell you whats really going on with the oil pressure.

 

[Blackened302]

noticed something interesting this morning:

the guage goes down whenever i push the clutch pedal in--at idle and while driving, but only for the first 20 minutes or so.

a while later, the guage reads around 0, but goes UP when i push the clutch in to shift, then goes back down.

a while after that, it'll read normal after it's warm.

i won't be able to scope out the connection and grounds 'til later this afternoon, but i figured that was worth mentioning, too, heh.