I have this problem for some time in a while, 1996 year, 5.7 V8 LT1 A4, 50k mileage, after a couple of minutes since I start the engine and my car warmup, the oil pressure needle go​es in the red zone and Check Gauges light come on when I stop on lights and in heavy traffic, always when warm while idling, RPMs about 650-700 +/- 50 difference.

At first I thought the dash gauge is inaccurate or the oil pressure sending unit is defective, so I checked these two things with my electrician, everything correct, put new Standard Motor Products oil pressure sensor anyway, the same happens with new one. What is more interesting, when I turned off the car in that situations the needle always come off from the red zone above and come a little forward closer, about on half way to 1/4 mark (20 PSI is the first one)

After that change, I get worried and anxious and put the mechanical gauge on the place where is the oil sensor on the back, rear of intake manifold, where the shoebox Rob's picture shows it and get the low readings about 0.2-0.3 bar which is 4-5 PSI which I know is insufficient

The oil pressure rises after I rev the engine and the needle jumps to 20 PSI on about 2000 RPM and above on higher RPMs while driving and the engine sound is very quiet without any noise, groan, chatter, and anything else similar, absolutely normal, strong in acceleration, no stalling or anything else, maybe the MPG is the only thing I am not satisfied with 10-12 and 11-13 heavy city traffic

The oil which is always filled is 5W30 GM or Mobil 1, oil type and gradation as stated in owner's manual, the oil filter which I used last couple of times is Wix 51069. Last time I changed the oil and filter I saw the small increase, better pressure on gauge, after oil and filter change, but not the obvious one, it's a couple of PSI, but the same situation with dropping down like with the used one, maybe a couple of minutes later this occurs

What is the best possible chronology for steps to do at this situation now, because I don't know the cause of this problem, I was thinking about the dropping the pan and inspect if oil pick up tube get loose and fell of the pump and something similar stupid nonsense, don't want to believe yet that there is some more serious problem with main or cam bearings and at first don't want to take the whole engine out and make a big mess in advance

One note, a couple a months ago during the hot days my water pump gaskets leaked because of cooling fans didn't come on at higher speed and my engine was overheated, temp went in red zone for about 3 minutes in a heavy traffic in a city downtown tunnel and immediately after I could it, I put the vehicle beside the road and turned it off. Don't know if this is what triggered this problem, but just to say that, if that helps in resolving an issue

Thanks in advance,

Nikola

 

it sounds like you have confirmed OP gauge is accurate.

low oil pressure is typically due to excessive bearing wear. At 50k mi on motor that should not have happened unless the motor was abused (overly reved a bunch). Your overheating "may" have contributed if coolant and oil mixed.

I would suggest you drain your oil while warm and send sample to Blackstone Labs. They will send you collection kit for free. You pay, IIRC $25, on the free postage return sample. They will advise what contaminants are in the oil, especially metal from bearings.

At this point refill with 10-40 conventional oil like Castrol or Valvoline. Before that though get one of those snorkel cams that work off your iphone or have their own screen, They are fairly cheap. Go through your oil pan drain plug before refilling with oil to see if the oil pick-up did fall off. Pulling the pan with engine in car is a huge job so the snorkel cam is way easier and faster.

You may just wind up needing to use the thicker oil, even 20-50 if the bearings have worn that much. Obviously if you start seeing glitter in oil and in filter you take apart you know the engines lifespan is about done and needs a rebuild.

 

Unfortunately the gauge and sending unit are accurate in this case

I hoped so that would be different scenario I hope so that I didn't destroy a 50k engine with this overheating what happened as I described in first post

Okay, I'll try to find the lab which can do that operation for me, since I'm not in US unfortunately, I am in Southeast Europe, Serbia, so I'll try find out the adequate lab for that action

Great idea, this will be done with snorkel cam before anything serious done just in case to see if I have a little luck and the problem occured with pick up tube fall off and also will give a shot with the other oil 10w40

I'll check it and inspect for glitter in my used oil and filter and see what is the situation then

 

Does the oil smell of gasoline?

Poor fuel mileage may be due to leaky injectors, excessive fuel pressure, leaking fuel pressure regulator, faulty engine coolant sensor, etc. The excess fuel can bypass the piston rings, wash the lubrication off the cylinder walls, and dilute the oil to the point the viscosity is significantly reduced, lowering oil pressure, and providing inadequate engine lubrication.

 

IDK what Serbia has for oil analysis. This is the link to Blackstone. I assume postage would be on you if international mail can ship a small oil sample

About Us | Blackstone Laboratories (blackstone-labs.com)

Injuneer makes some very good points on leaking injectors contaminating the oil with gas

Typically a short overheat won't cause engine damage. Oil analysis will also advise if coolant is in the oil as well as various metal and also what the viscosity level is. Your nose should tell you by smelling your oil if gas is in it

 

Thanks a lot Fred for your reply and participating, I checked now in garage when I pulled off dipstick. Yes, I can confirm definitely that I can smell gasoline on oil.

One note, the last oil and filter change was done in June last year, then in August two months later when I put set of new Standard Motor Products injectors, because in that time I was in doubt about some extented cranking after car get warm and sit for more than 15 minutes, it can take a little longer to fire, so because or previous car experience I had with other car, I bought the new set of injectors, but unfortunately that didn't cure the problem with extended warm cranking after sitting

It's interesting that I didn't fix the extended warm cranking after sitting with the new set of injectors then, so I put that at hold for a while, although I assume that the problem is maybe with bad check valve in a pump assembly, since I have changed the fuel pressure regulator, put the new ACDelco and there is no fuel leak in diaphragm, just the vacuum hiss when I remove the vacuum line from regulator. Measured the pressure, it has about 40's PSI on priming and at idle, rise for 5-7 PSI with vacuum disconnected, but once I shut off the engine, in about 15 minutes a pressure drops on 10-15 PSI and after that doesn't move anymore, so I assume that the new injectors can't leak so fast as stuck bad check valve in open position

 

Thanks Chim, I found some labs which are specialists for oil testing here in my city, so I will contact them in the working hours tomorrow and arrange with them about the details and time when to deliver the oil sample for analysis

Yes, I confirm the Fred question about the gasoline in my oil, I smelled it very easily when I pulled off the dipstick in garage a couple a minutes ago

I hope so your claims are true in my case, hope not to damaged my engine when I had that short-term overheating. That last about 3-4 minutes max, maybe a little shorter, there wasn't any noise from engine, just the coolant underneath the water pump hoses in front of the car close under the hamonic balancer

 

Are you sure the replacement injectors are the correct size?

 

Yes, I checked the part numbers, the OE was 17121068 it's Rochester manufacturer, I put in the replacement Standard Motor Products FJ164 and every other measures and specs are ok

I put them because of the previous mentioned extented warm cranking, but that didn't solved it unfortunately. The car started cold immediately after the installation in the rail and put back in intake, don't think anything did wrong in instalation process, there are no external visible leaks or something else, everything fine, smoother idle and cruising with new injectors, but still the engine runs excessively rich, I can smell it on exhaust, when I put the pedal on the gas and activate the clear flood mode the engine fires immediately without extended cranking and the MPG is bad, pretty worse than the factory stated

Forgot to wrote in previous posts, also changed the engine coolant temperature sensor, put the new GM ACDelco, but nothing changed. Also the new PCV valve is there and the new O2 injectors, also the GM ACDelco, because had the P0153 code earlier and the code went away after the replacement of oxygen sensors

Since the injectors replacement was 2 months after the oil replacement and the oxygen sensors also changed after that, is there any sense to change the oil and filter now?

 

Since you smell gas in oil, yes change it. But you need to find out "why" gas is getting into oil

When you do change oil, regardless of source of gas entering it, you should see improved oil pressure due to the normal viscosity of the oil which is now diluted because of gas. If so than your motor is OK but you need to find why its running so rich.

If you ever pull the fuel rails off with injectors, turn key on and see if any leak

Exhaust leaks pre 02 will cause PCM to add fuel. Same with intake manifold leak so confirm that isn't going on. If you have a scan tool read your short and long term fuel trims. If high on one bank than check that side of motor for exhaust leaks, especially anything with air pump if you have one.

 

Thanks, I'll do like you said, change the oil and filter and after that inspect for exhaust leaks pre O2 sensors and intake manifold for leaks

I"ll pull the injector rails up to see if anything leak, but I doubt it, since I have all new injectors, but check it anyway, not a problem at all

Also, I will inspect with scan tool for value of trims and write it then back here

I have air pump, the strange thing about it that when I start the car i hear the air pump sound a little longer than before and at the moment I shut off the engine I hear a short vacuum suck in which lasts maybe second, don't know if that's normal

Everything is stock on the car except the cats, they are on the vehicle, but somebody remove the precious metals from inside of them, don't know why

 

If the catalytic converters have the precious metal containing substrate internals removed, you should have code for the missing cats. Is it possible that someone has substituted "O2 sims" to fool the PCM into thinking the cats are still there? Or, possibly using a spark plug "extender" to space the after-cat sensors out of the main exhaust flow of the pipe?

Some people feel the cats reduce engine performance significantly, but they do not. The HP loss is very small.

The AIR system connections on the exhaust manifolds have a rubber elbow connecting the tubing to the check valve. If the check valve is leaking, the rubber parts may melt. That would allow air to be pulled into the exhaust stream, causing the O2 sensors to report "lean" and the PCM to add extra fuel the engine doesn't need. Any air leaks before the pre-cat O2 sensor can cause the engine to run rich.

http://shbox.com/1/diverters.jpg (1996 configuration may be slightly different)

While the new coolant temperature sensor may "good" (you did change the one in the water pump housing, and not the one in the driver side head?), did you check the reference voltage supplied by the PCM?

4th Gen LT1 F-body Tech Articles

 

As far as I am concerned, from what I can see underneath my vehicle, everything looks at its place like it should be on 100% stock car, I don't have any codes when I changed the pre cat O2 sensors on both sides and also don't see the plug extenders, after-cat sensors are on their stock places

Maybe the people removed that in that order to increase hp, but I don't see they got anything, since I have run the car and measure acceleration times 0-100 km/h, the best time achieved was 6.3s, except awful mileage with bad mpg results, although I have a heavy foot on the gas pedal so often

Okay, I will look carefully at connections and rubber parts and check valves of AIR system connections on both sides

Yes, of course changed the appropriate one, I am defintitely not the Fred almighty specialist but didn't make such a mistake, I replaced the black one in the water pump, ACDelco 213-928 part number, not the grey one on the head. Reference voltage checked also, it's in stock measures

 

I'm not attempting to insult you with my questions. I am not trying to appear “almighty” (that's a new one). I am trying to help you.

I am simply keeping in mind what I have seen happen and go wrong on this forum in the 24+ years I have been helping people sort out issues with the 4th Gen LT1’s.

 

Of course, I am proud that I found a people like you here, that was the meaning when I said almighty in positive way absolutely, little ashamed how a little I know exactly

And thanks again on everything so far, as I said I'm not such a great specialist like you and couple of people here, but I'm dedicated and tireless so I"ll do whatever needed to resolve an issue with this problem and any other