Engine keeps cutting off, oil pressure dances?

I was driving my blazer the whole week and today it stalled when I was backing up in Wal-Mart for some reason. I then started it and when I was driving about 30mph, when I give it gas (25K rpm) my oil pressure gauge jumps from 40 to 60, looks like when my tachometer goes up the oil pressure gauge goes up as well?????? When I stopped at a stop light, the thing stalled again on me. I put it into "Parking" and it started again. When I got home, I turned it off. After about 30 minutes I tried to start it the fuel pump didn't make the wyning sound. So I let it stay there for about 10 to 15 min. It started right up after that. I drove to Wal-Mart again and bought new oil and filter. Came home, changed the oil and filter. I started it up but then the oil pressure guage would jump around 40 (35 to about 45). Sort of dance around those numbers ON IDLE!!! When I give it gas, oil pressure guage goes to 60, when I let go of gas, it goes back to 40.

Seems to me, something wrong with the oil pump in the engine (if there is one), and I guess when it reaches low pressure or whatever, it cuts off my fuel pump, right? What could it be?

I'M TIRED OF THIS BLAZER ALREADY, someone help, please??

Any help will be greatly appreciated!!!

Oh, another thing. Could it be the oxygen sensor that I don't have??? My blazer is 97 and should have 4 oxygen sensors, but I have a 2000 year exhaust which has holes for only 3 oxygen sensors. So, basically I have 3 working sensors and 1 dangling plug for the fourth oxygen sensor. Could this cause the problem above that the engine keeps cutting off and oil pressure gauge dancing???????? My "Service Engine Soon" light came on because of that (no duu). But it drove fine before today, the whole last week (with the dangling plug for the O2 sensor)!

Thanks again, in advance!

The lack of the 4th O2 sensor shouldn't have any impact on your oil pressure or your engine dying... At most, it would cause a check engine light and resort to base fuel maps (ignoring the upstream O2 sensors).

I didn't know that any of the OBD2 blazers had 4 sensors... That sucks!

Where is the oil pressure sensor located? Maybe that has a bad connection on the plug and causes the pressure gauge to jump and cuts off my fuel pump?

Thanks swartlkk!!

Oil pressure sensor is on driver's side of the distributor between the distributor and where the head meets the block.

Thanks a lot, do you think it could cause this problem??

Fluctuating oil pressure could cause the PCM to kill the engine (stall). You could check the connection... But... I would do a full oil change with possibly a flush of Seafoam or Marvels Mystery Oil and a new filter before I would get too concerned. You have to try to stabalize the oil pressure if it actually is fluctuating.

When was the last time you changed the oil? And what do you have for an oil filter?

I did change my oil today and I use "Fram" filter. See, my pressure gauge is NOT just fluctuating, it is jumping. Also, my tachometer moves up and down little bit on idle. When the rpms go up the pressure goes up too?????

I start the blazer, drive it for a while. Then when I turn it off, it will not start. The fuel pump doesn't make the noise.

Well, I wouldn't use Fram filters if they were supplied to me free of charge with free oil. I have had bad experiences with Fram as well as have read some serious horror stories about their crappy bypass filters causing severe engine damage.

If the rpms jump around in time with the oil pressure drop, I would be concerned that you aren't getting proper oil pump flow. That is why I recommended an engine flush to clean up the crankcase...

How low is your idle speed? Is it getting down below 500rpm? What is the lowest rpm that it'll dip down to? Also, when was the last time you cleaned your throttle body? It may be that your IAC valve is getting gummed up and cannot adjust the idle speed fast enough and is causing the engine to lope.

Is your engine actualy and simply not running smooth? I mean if rpms go up and down, then the whole motor is either fluctuating or just the gauges.

If the gauges are moving up and down, you have electrical/alternator problems.

Does your motor idle actually go up and down or not?

I mean, before we worry about fluctuations of the gauges, we have to have a smooth running motor.

A simple timing adjustment could be the problem of the idle being wishy washy. Vacuum problems are also a cause.

Just for the record, Ive used fram filters for millions of miles, including at the races and HAVE NEVER had a problem with one.

The topic of filters is for another thread. You want to praise them, please start a new thread on the topic.

Guess you just made my point??

The idle is not THAT bad. It fluctuates just a little bit, my main concern is the oil pressure gauge jumping around. What could go wrong, because my blazer ran excellent last week.

If the oil pressure were to dip too low, you could have oil starvation issues. Now seeing as how it only happens at idle the damage would be minimal, but cumulative. Check your wiring to the oil pressure switch as well as the switch itself as blazingsadle has suggested and see how that goes. If everything checks out fine there, it's possible that something is amiss inside the engine.

How many miles are on the truck?

My concern is simple enough. If your engine happens to have something simple wrong like a small leak in the intake or a bad vacuum hose that makes it idle a little rough. Then all else is a conversation we dont need to have. The oil pressure and even some other gauges might fluctuate.

If on the other hand, you are really worried about oil pressure. Attach a MECHANICAL oil pressure gauge and check it for real. It'll be worth it to know, once and for all. The problem might just as easily be that gauge itself. I'v personally replaced 4 or 5 of them in 85 to 95 vehicles. Easy enough to pull the dash and change it. But check it against a mechanical gauge. Yes you may have to get in some tight spaces, but it can be done and can be remove when you know better.

I have read somewhere, (dont hold me to this) that the oil pressure sending SWITCH not gauge unit, will only shut the motor (fuel) off at 7-8 pound of (oil) pressure. My own that I install are 15 pound ones, and I had always assumed that the factory ones were also. I no longer believe that. I believe they are not really installed to protect the engine, but are there in event of a traffic accident and engine shut off with key still on. With the key still on the pump would continue to run and with the ignition circuit still hot an explosion could result. It is a safety switch and not to keep the engine in one piece.