mymustache43

I'm new to the forum...my first post. Did a search but didn't find the answer I was looking for so here it is...my oil pressure has always been 20 psi at idle raises from 40 to 60 when driving depending on my rpms. Well today out of nowhere my pressure dropped looked down to see I was idling under 20 and no matter my rims didn't seem to go above 40 (I believe the middle is 40). I'm one who to watch my gauges closely which is a nightmare of a habit in these cars since everything fluctuates so much. So my question is should I be conserned? I have 125,000 miles just alarmed me cause a week ago when I drove it pressure was high as always. Thanks for any advice

Injuneer

Check the oil level. Check for dilution due to gasoline (it will smell like gasoline).

What grade oil are you running? Last change?

Any strange noises - ticks, knocks?

Is the engine modified in any way?

How far under 20psi at idle? The "Check Gauges" light doesn't come on until the oil pressure drops to 6psi. GM feels that is adequate at idle. Then look for 10psi for every 1,000 RPM.... e.g. 20psi at 2,000; 40psi at 4,000; 50psi at 5,000 RPM.

The real question is why did it change suddenly? It would pay to verify the pressure gauge reading with a mechanical gauge. You can use the plugged port right above the oil filter:

Courtesy of Shoebox

http://shbox.com/1/aux_oil_port.jpg

mymustache43

Oil was changed 1000 miles ago 5w30 I have a slow drip so when It got a bit low I added lucas oil leak fix checked the oil the other day it was surprisingly dark for how recently I changed oil and today it's very diluted smells like gas faintly.ive read 10psi for every 1000 rpm but the car has always idled at 20 psi 900rpm so that's what caught my eye. No check gauges or ses light no knocks or ticks...seems as though it has been running rich though I bought maf cleaner just haven't used it. Thought maybe maf was dirty and making car run rich

Injuneer

Have to figure out where the gasoline is coming from. Quick check - pull the fuel pressure regulator vacuum control hose off the nipple on the passenger side of the intake manifold, and see if it is wet with fuel or smells heavily of fuel.

Courtesy of Shoebox

http://shbox.com/1/fp_reg.jpg

Do you have a habit of overfilling the gas tank? That can saturate the EVAP canister in the drivers side rear fender. Then the fuel gets pulled into the throttle body when the EVAP purge valve opens. Check that connetion of the throttle body for wet fuel. It will normally smell of fuel, because that's where the vapor from the gas tank ends up.

There are two hoses on the passenger side of the throttle body. The lower/smaller hose with the 90-deg elbow is the one for the EVAP purge connection.

http://shbox.com/1/1996_evap.jpg

Could also be a leaking fuel injector. Put a fuel pressure test gauge on the Schrader valve, turn the key to "run". The fuel pump will prime for about 2 seconds. Mentally record the max fuel pressure reached when the pump shuts off, then watch to see if the pressure drops quickly. That could be due to a leaking injector, or the fuel pressure regulator problem.

mymustache43

OK I'll check those thanks...I was suspecting the maf was dirty and giving bad reading making the car run really rich which was just flooding the motor causing some seeping....does that sound like a possibility or am I just making it up in my head? Lol

mymustache43

OK so no fuel in vacuum line on the manifold and no signs of any leakage at the connection on the throttle body. I don't have a fuel pressure tester but I'll pick one up tomorrow and check that. Thanks for your help. I read that if the cars running super rich it can cause too much fuel in cylinders not enough air and cause excess full to run down cylinder walls winds up in the oil. Which again led me to the question if my maf is super dirty could it cause this to happen?

mymustache43

So my buddy and I were just talking and if the injectors are not showing any sign of leakage on the outside of the manifold and there is no smell of gas aside from the faint amount on the dips tick can't I rule out leaking injector? If it was leaking into the manifold I would smell it right?

Injuneer

A leaking injector nozzle drips into the head intake runner. I'm not talking about an external leak, or a leak at the O-ring inserted in the fuel rail. A leaking injector tip, a leaking fuel pressure regulator, or liquid fuel from a saturated EVAP canister all cause excess fuel to run into the cylinder, bypass the rings, wash the lubrication off the cylinder walls, and dilute the oil. So would a "true" rich condition that extends beyond the PCM's ability to correct using the long term fuel corrections (LTFT) and to some extent the short term fuel corrections.

An MAF over-reporting mass air flow would cause a "true" rich condition. Within reason, the PCM can compensate for a "true" rich mixture, using O2 sensor feedback to develop negative LTFT's and reduce the fuel flow. The LTFT's can pull fuel flow down by 15%.

A more severe problem is a "false" LEAN condition. Misfires and exhaust leaks before the O2 sensors cause the sensors to incorrectly report "lean" and the PCM responds by adding fuel the engine doesn't need, causing the engine to actually run rich. A faulty O2 sensor, or O2 sensor wiring can cause a "false" lean. An O2 sensor soaked externally with oil can cause a "false" lean. The sensor requires clean air on the outside of the body, so that the clean air can enter the inside of the sensor thimble. The sensor voltage is developed by the difference in O2 partial pressure, between ambient air and the exhaust gas on the outside of the thimble.

Yes, an MAF sensor reporting 25% more than actual mass air flow can cause the engine to run rich, because it is beyond the system's maximum fuel reduction of 15%. But, the 96/97 OBD-2 diagnostic system includes a rationality check that compares the MAF sensor reported flow to the mass air flow calculated using the speed-density method. When the MAF readings differ significantly from the calculated flow, it sets a trouble code.

A scan for PCM codes is always a good start to solving a problem, and not all codes turn on the SES light.

mymustache43

Scanned it this afternoon no codes no misfires. .. but heated oxygen sensor was ready and second oxygen sensor was not ready I plan to pick up a fuel pressure regulator test as you advised, clean mass airflow and replace second of sensor change oil and see where I get from there
I forgot to mention that the oil level sensor was just replaced but my low oil light has been coming on. I searched some threads and concluded it must be faulty connector which I haven't changed I've been monitoring oil levels at the stick often. But I did read in a thread that someone had discovered putting ignition in run position for a second then off then start makes the low oil light go away which I have been doing last four or five times I drove it. But when in the run position the fuel pump primes and I was wondering if I'm flooding (building too much pressure) in the cylinders and being that I drive the car once a week maybe that excess fuel sitting in the cylinders is just seeping. ..just my uneducated theory. I'll check fuel pressure and update tomorrow thanks again for all the advice. Greatly appreciated

mymustache43

Ok so I did as advised and checked fuel pressure. It went up to 40lbs then dropped to 35 within five seconds then down to thurty and held at 30lbs would that be a sign of a stuck injector?

Injuneer

No. An open injector would probably cause the pressure to drop rapidly to "0". A "drip" would slow the pressure loss, but wouldn't put a lot of fuel in the oil.

I think you get a fuel pulse when you turn the key to "run". But many people with slow starting due to loss of prime pressure will cycle the key several times to help it start quicker. I've never heard anyone indicate they noticed fuel in the oil.

Clean the MAF sensor. Check a plug or two on each bank of the engine for a sooty appearance, indicating a rich mixture.

mymustache43

Thanks I planned on cleaning MAF and changing O2 sensor ...change the oil and see what happens. Appreciate the advice.

mymustache43

So I changed the 02 sensor behind the cat changed oil cleaned maf sensor and cleaned throttle body. Took it for a test drive and going through fuel like crazy. Pulled the dipstick after test drive and still smells like fuel. Oil pressure is still lower than usual as well. I've read that rule of thumb is 10 lbs per 1000 rpm which is what it's at but the car has always idled at 20 lbs at 900rpm and ran about 10 lbs higher than what rule of thumb says so the drop still concerns me. Any thoughts?

Injuneer

You indicate you had a "not ready". The status flags apply to the pre-cat sensors, left and right. But you indicate you replaced an after-cat sensor. The after-cat sensors do not materially affect fuel flow. They are only there to verify the cats are working.

Did I misunderstand what you said was going on with the O2 sensors?

If fuel is still diluting the oil, it would explain the continued low oil pressure.

mymustache43

When I scan the car it comes up H02S ready and 02S not ready. I was under the impression the H02S was the sensor on the manifold which is why I replaced the one behind the cat. This test drive car was guzzling gas almost quarter tank in a ten to fifteen minute drive. It's really confusing cause it's not throwing codes at all and no misfires according to the scanner and honestly she runs like a champ lots of power no bogging down at all. But fuel consumption is through the roof and pressure is down from normal plus fuel in oil. ....loosing my mind over this