Low Oil pressure, check gauges. Should I change the oil pump? 99 Tahoe 5.7 125k mi

[Goldhawg]

Well, just my luck. I finish my 0411 PCM swap w/efans, and get the engine dyno-tuned, drive it one day and on the way home I get a drop in oil pressure and the light saying "check gauges". The oil pressure @ 50mph was only 20psi, but when I stop to turn w/no gas drops all the way to basically 0 and bounces up as soon as i complete the turn and step on gas. I can hear what sounds like some noise from the engine. I pulled into the driveway, and then the engine dies when I get it right in front of the garage. Needed to back it up and it would fire right up, but as soon as I put it in reverse it would die. Let it roll backwards and parked it. This was last week, and it was still like 15 deg out so I leave it alone. Check online, similar things say I must have low oil; go out and check and I'm almost full. So yesterday it warms up and I go out and start it. Super smooth, no engine noise at all, and 40 psi. So I decide to put some seafoam in it, thinking some sludge may be clogging up the oil pickup, and then I'll change the oil and filter. Go for a drive and as soon as it heats up, my highway psi drops to 20, and when I get back to the driveway it drops all the way down, w/"check gauges" light and it dies. Again I have some engine clattering noise so I don't think its a bad sensor. Shut it down, and several hours later fire it up and same thing--quiet smooth idle w/~30psi (it wasn't completely cold).

So, what could this be? I have 125k miles, and I've only owned it a year, so I don't know the maintenance history although it seems very nice. Was thinking I may have had something get in the oil pump and damage it. Was thinking about just replacing it since they're only $30 at AAP.

Thoughts? Other suggestions?

Thx!

 

[woody31]

put a mechanical gauge on it temporary,monitor it so you can verify the issue is not with electric,gauges,,if you are gonna pull it apart for a oil pump,,i would just go for a basic rebuild,,if your budget allows,,you could order a crate motor from jegs for around 1500/1800 most times delivered no freight with a great warranty,good luck

 

[poncho62]

Being that you had a sudden oil pressure drop and you have just been messing with electrical components, I would say its a gauge, sender, electrical issue...Put a manual gauge on it to verify that its not the engine.

 

[skylark]

Being that you had a sudden oil pressure drop and you have just been messing with electrical components, I would say its a gauge, sender, electrical issue...Put a manual gauge on it to verify that its not the engine.

I would normally agree with you on the gauge issue if it wasn't for the engine noise.
I would agree with the OP that some sludge may be an issue but I wouldn't chance it myself. If this were my ride and I was trying to be frugal I would dump about 2 quarts of diesel fuel on top of the oil and let the engine idle until the engine is good and warm and it starts to make noise. If it would idle for and hour without making noise I would let it. The diesel fuel is essentially a light oil and a mild detergent I would use it to heat the sludge and break it down as much as possible and the drain while its hot. At that point I would yank the engine, pull the pan, pull the valve covers and intake. I would manually clean the sludge, inspect the bearings and plastigauge a few of them. If all looked good then it would get a pump, rear main seal, valve cover gaskets and the Fel Pro ms98000t intake gaskets and call it a day.
If I wasn't looking for two nickels to rub together then I would do the flush above plus hone block, cam bearings, timing chain and gears, rings and bearings for a simple refresh. At 125K I wouldn't be to worried about boring or grinding the crank. Of course you could always do a cam, roller rockers, marine intake, 383.....

 

[IOWNJUNK]

Could just be trash in bottom of pan, once its warm it floats around and clogs screen on pickup. Drop the pan and see whats in there.

 

[Goldhawg]

Well, after reading what a major PIA it is to drop the pan, I'm going to first change the oil and use my HF boroscope to inspect the pickup. I've also heard that, while unlikely, it could be an issue with the oil filter. So I'll gamble $20 on some cheap dyno oil and a new purolator oil filter, check out the screen and try again.