How to diagnose a bad oil pump?

2002 V6 Silverado. Replaced the pump about two years ago. There was a bunch of sludge in the pan which I cleaned out. 
 

Truck sat 2 years since I wfh because of a bad cat. Got the cat replaced and started driving it around to burn off the 2 year old gas and reset the sensors to get it inspected. 
 

Oil pressure sat at 20 when warm. Put a bunch of miles on it a few days back. When I started it the next morning, got a zero pressure warning. 
 

Just pulled the pan and the pump. Pump doesn't seem "bad" from what I can tell. Nice and tight, no slop. Pan had sludge again.  
 

not sure if I need to replace the pump again or clean out the sludge again and hope that fixes it. 
 

-Rob

When I replaced the pump before, I just swapped the top that holds the pickup tube. Looking at the top now, you can see a ghost image of the gears. Wondering if it froze up?

-Rob

In reply to rob_lewis :

Its horribly machined. That does not help. Are you sure the pump drive is ok? 
I'd check the driveshaft, blueprint the pump, put a new screen in, and a fresh oil change. Sub a qt of oil for MMM. Run 2-300 miles, do oil change again.

Put the cover back on the pump and it spins ok. No resistance. 
Not sure how I would blueprint it. I assume the gears need to be close to the cover to keep up pressure.  It could be because I used the original cover from the old pump instead of the one that came with it?  
I did that because I didn't have the tools to swap out the pickup and since the pump was the same, it was easier to swap covers. 
 

The screen is incorporated into the pickup, so I'm not sure how I'd swap it out. 
 

-Rob

If you really want to deep clean some sludge (once you get pressure again), put one quart of diesel in it with the normal oil fill.  Start it, but for gosh sakes, don't rev it or drive it.  Just let it idle for 20 minutes.  Change oil and filter.  Drive for 100 miles.  Change again.  Drive like normal.

Complete and instant loss of oil pressure could be a sludge clog, but I'd be more suspect of a busted drive

Yeah, I plan on a flush and oil changes when I get it back together. 

Busted drive?  You mean in the engine itself that drives the pump or a bad pump?

The slot the shaft fits in to in the engine is there, I.e. I assume it'll drive the pump. 

In reply to rob_lewis :

Blueprinting an oil pump requires a 12"x 12" piece of glass and a sheet of wet dry 400 grit paper. Spray paper that's been placed on the glass with some wd40 or similar. Bring your depth of the pump gears to like 10 thousandths or slightly less. IIRC, you need at least 5thou or the gears will bind because they seize. Make the plate smooth. Most pumps ootb are 15-20 thou. Circle pattern the pump body and plate. Clean and put together.

Screen, pickup same thing.

I'd have spun on a fresh oil filter before I dropped the pan.

I've had multiple instances where cheap oil filters (Fram, Im looking in your direction) ballooned a bit which caused the internals of the filter to come loose and cause funky / zero oil pressure readings.

Switched to good filters and the problem went away.

Use WIX, Mahle, Bosch, NAPA, Purolator, Baldwin, ACDelco, anything but the big orange.

Ranger50 said:

In reply to rob_lewis :

Blueprinting an oil pump requires a 12"x 12" piece of glass and a sheet of wet dry 400 grit paper. Spray paper that's been placed on the glass with some wd40 or similar. Bring your depth of the pump gears to like 10 thousandths or slightly less. IIRC, you need at least 5thou or the gears will bind because they seize. Make the plate smooth. Most pumps ootb are 15-20 thou. Circle pattern the pump body and plate. Clean and put together.

Making sure I understand the thinking.  If I take material off of the cover and pump, wouldn't that cause the gears to interfere more?  I would think taking material off of the gears instead of the pump and cover would prevent it from machining the cover.

ShawnG said:

I'd have spun on a fresh oil filter before I dropped the pan.

I've had multiple instances where cheap oil filters (Fram, Im looking in your direction) ballooned a bit which caused the internals of the filter to come loose and cause funky / zero oil pressure readings.

Switched to good filters and the problem went away.

Use WIX, Mahle, Bosch, NAPA, Purolator, Baldwin, ACDelco, anything but the big orange.

It could have been the filter, it was a Wallyworld brand, which is even worse than the Fram ones.....  It could have also been sludge clogging up the filter or the pump or any other place in the oil system.  It's the last weekend of not cold (by Texas standards) weather so I figured I'd just drop the pan and check it all out.  Honestly, I was kinda hoping the pickup had come off as that would have been a simple "duh" fix.

-Rob

Per my plastigauge, the cover is .002 inches from the gears, so that seems within spec. 
 

I'm thinking about putting it all back together with a new filter and oil and see if I have pressure. 

-Rob

That's a very simple gear type of pump and it's driven by a robust steel shaft. Don't start blue printing anything. Those pumps can get hella worn and still supply sufficient pressure to keep the engine happy. A 4.3 V6 is a cockroach and you basically cannot kill one. I really suspect you're chasing your tail down a dead end. I'd be looking at sending unit or oil filter or pretty much anything else before I pointed my finger at the oil pump. 

Did the engine actually lose oil pressure, or did the light/gauge "say" it lost pressure ? What did it sound like ?

If you've had sludge issues, I'd put my money on a clogged oil pressure sending unit/switch. You'd definitely hear the lifters talking if it had zero oil pressure. It doesn't take much sludge to clog up an oil pressure sending unit. I'd screwed a mechanical gauge line into the engine and verify pressure before I cracked the oil pan off.. 

I agree that I'm probably chasing my tail a bit, but was trying to cover all bases before the weekend was out.  It was definitely low/no pressure as the lifters were clattering away.  I let it run for less than a minute so as not to seize it. It might have gotten pressure once the oil warmed up, but I didn't/couldn't afford to risk it.

-Rob

Pick up not sealed, seated or cracked so it is sucking air?  Also could the pickup be to close to the bottom of the pan?  
 

dean1484 said:

Pick up not sealed, seated or cracked so it is sucking air?  Also could the pickup be to close to the bottom of the pan? 

Pickup isn't cracked.  It's wherever it was from the factory with respect to the bottom of the pan.  The slude was 1/4 to 1/2" thick, so it' may have been right in the sludge and clogging it up.

-Rob

What causes sludge?  Blow by the rings?  Pre-ignition?  I dunno.

If the pump is up to spec, I would try some Save-the-Baby like MMOil or Seafoam.

cure it or kill it .....

Pressure relief  valve stuck open?  
 

Pump drive rod issue?  Is this driven off the distributor?  I would look at the distributor and see if that stripped out or broke. 

Low pressure = sloppy bearings.  YMMV.

Oh. Have you tried spinning the pump with a drill with the pump pickup set in oil to see that it is pumping oil?  (Be careful doing this as you can make a big mess fast.). 

rob_lewis said:

I agree that I'm probably chasing my tail a bit, but was trying to cover all bases before the weekend was out.  It was definitely low/no pressure as the lifters were clattering away.  I let it run for less than a minute so as not to seize it. It might have gotten pressure once the oil warmed up, but I didn't/couldn't afford to risk it.

-Rob

I'm North Texas myself so I get where you're at. This has been "beautiful weather work on stuff" weekend for me. 

Truck has 150k miles.  I guarantee the bearings are worn.  I hadn't thought of spinning the pump no a drill.  I may try that before I put it all back together.

The fact that it was fine one day (I probably put 100 miles on it that day) and clattered like crazy with no pressure the next morning made me think the pump had failed.  The cam drives the pump. 

I'm googling where the pressure valve would be.

And, to kinda explain the idea of going big as opposed to just swapping the filter and doing a change (besides the good weather this weekend), I need to get the truck back up and running.  Wife and I both WFH until the 15th when I was laid off.  We only have two cars. I'm going to be interviewing staring in the new year and need to leave her a vehicle while I'm out doing that.  I had planned on doing a bunch of maintenance on the Mazda this weekend until the truck decided to be difficult.

-Rob

rob_lewis said:

....The cam drives the pump....

 

-Rob

Pretty much...

The distributor actually drives the oil pump through the steel shaft. The cam drives the distributor through gears. 

You're dealing with the exact same setup as every small block Chevy. Many of the parts are the same. It's good stuff. Well proven...

In reply to rob_lewis :

I recall the pressure relief valve is held in the side of the pump with a cotter pin.

This sounds ugly but it will work.  Take the oil filter off and spin the motor on the starter.  Of course ignition disabled.  Put a drain pan under where the oil filter goes and check for flow.  Then put a new one on and repeat at the OP sender unit to check for flow.  Pumps rarely fail but sludge will block off lots of stuff.

I see no way that this thing can seal up and pump oil with this surface finish?

Got it back together. Good oil pressure again. Only 22 at idle but up to 40 when revved a bit. 
I still have a noisy lifter, but that's something I've had before and went away as it warmed up a bit. Going to do an engine flush and fresh oil now. 
 

Thanks for talking me through it and helping. 
 

-Rob