Caprice oil pressure issue and sensor

[kevm14]

As my oil pressure issue appears to be getting worse, I may have determined that the sensor is in fact partly to blame.

Quick summary of the issue:
This dates back to 2004 when I converted to the LT1 exhaust manifolds. It's when I first noticed the issue. Essentially what I figured out was that if the sump has no more than 4 quarts or so in it, the oil pressure behaves normally. If the sump has the full 5 quarts, the pressure actually drops at wide open throttle. Even more interestingly, it also requires actual acceleration. I did a test probably 10 years ago by winding out 1st gear but holding it on the brakes to keep from accelerating. The oil pressure stayed stable. Only when I let off the brakes, about a second later, the pressure started dropping. Again, this all only happens with a full 5 quart fill and improves steadily as the level gets down to 4 quarts or so.

Video of the car with around 4 quarts (no issue):
https://www.youtube.com/watch?v=BmU_JEC6aYE

Video after adding a quart:
https://www.youtube.com/watch?v=MEL68eRyx58

The oil pressure gauge is on the right.

Anyway, as the issue appears to be getting worse I finally decided the sending unit may actually be exaggerating the issue. The pressure never gets as high as it used to during a cold start and drops far faster than it used to. But it also appears to be extra sensitive in the middle of the range, possibly showing a slight drop as a big drop. So I probably still have an issue, but instead of dropping like 20 psi, it may only be dropping 10 psi, and the pressure both pre- and post-drop may be higher than indicated.

Rockauto doesn't sell the AC Delco sending unit any more (they may not make it) so I'll do a little research and see which may be the best and try it.

My guess is the pressure will come up to where it should be at all times (it shows under 30psi driving down the highway, in 5 degree weather, after only running for like 10 minutes - there's no way it's that bad), but it will still drop somewhat under the conditions outlined above.

If only I was perma-borrowing someone's mechanical gauge that I could use to compare to the electric gauge...

[kevm14]

Hmm. ACDelco.com pointed me to P/N 10222130.

Rockauto does carry that but it comes up for a 92 Camaro.

http://www.rockauto.com/dbphp/x,carcode ... ensor.html

I would be willing to bet full compatibility. The price is as I remember it. I've actually been through a couple of these but the current one has been on there for forever. I don't think they actually failed...probably part of my aggressive maintenance plan.

[kevm14]

I got my sensor.

Thinking about ordering this to R&R: http://www.amazon.com/Lisle-13250-Press ... B0002SR2RY

Believe it or not the only method I've ever had any success with was channel locks. Regular sockets aren't deep OR large enough.

[kevm14]

My local Napa stocks this particular one:
http://www.napaonline.com/Catalog/Catal ... 0006401129

Not sure if it will fit. Maybe I'll check tomorrow.

[kevm14]

Autozone stocks this one: http://www.autozone.com/test-scan-and-s ... 41490_0_0/

So maybe I don't need to order online.

[kevm14]

Napa had it on their misc rack in the front of the store.

Behold.

WP_001403.jpg

Slides in perfectly.

WP_001404.jpg

Specs:
It is a 1-1/16 socket but with a special thin wall to not interfere with the large plug housing. It also accepts a hex wrench if a ratchet won't work.

Says the applications are 1991 and newer GM oil pressure senders and 1987 and newer Chrysler "combination switches."

Not a bad tool for the toolbox. $10.49 plus tax. Would have been more expensive from Amazon with shipping.

[kevm14]

I couldn't take it anymore. After trying to get the car up on ramps in my driveway, I realized the only option was the street.

DSCF2970.JPG

Apparently I haven't touched this sensor since before I did the dual exhaust conversion back in early 2005. I can't remember but the original sensor location may have been the oil filter adapter. I am running an LT1 oil filter adapter, so it is actually above that in the block. Perhaps more significantly, there's an entire cat in what used to be a total void so sensor access is degraded noticeably.

I almost pulled the plug on this endeavor. Speaking of, the first thing I did was pull the harness off of the sensor. And instantly I broke the retaining clip which I assume was brittle both from age and proximity to the driver's side cat.

But I was able to slip my handy new socket onto the sensor and there was also just enough ratchet swing space.

DSCF2971.JPG

A shot from the other side of the cat.

DSCF2972.JPG

Attempt to show the big picture...but not that helpful really.

DSCF2973.JPG

The broken plug retaining clip.

DSCF2974.JPG

Really not much to this job. One thing that sucks is how much dirt there was around the tapped hole in the block. I probably shoved some crap in there. Luckily I don't see any leaks. I did slip the zip-tie back into the new sensor, which holds the low oil level sensor harness away from the cat. I must have done that 10+ years ago.

DSCF2975.JPG

Results to be continued.

[kevm14]

Results are what I expected. Sensor response seems much more linear and what I would expect the oil pressure to be doing. General notes across the different conditions:
- Pressure was higher on a warm start (showed somewhere in the 50 range)
- Overall I can make the gauge respond more to changes in engine rpm. At hot idle it's at 15 psi but I can rev and see 45 psi. That's more like what I expected it to be doing.
- Hot idle in drive is not as low as it was showing before, and more like what I would expect (a little below 15)
- The oil pressure drop on hard acceleration is still present but I guess less alarming because it drops from like 45 to 30, which is what is shown in the videos I made 10 years ago, as opposed to starting below 30 and dropping from there, which was a bit alarming.

So, great success!

[kevm14]

Look at all that oil pressure!

WP_001412.jpg

Oil pressure wood and bonus mileage wood.