Hey Guys
I bought a truck in July of 2010 knowing it had low oil pressure. The truck has 170 K miles one owner. I got it for a song and figured I would do an engine swap and some upgrades while I'm at it. I can put a GM crate motor in it and still come in under blue book, but I intend to buy a low mileage salvage engine and build it up. Until then, I'm going to drive the original 5.3L till it drops.

My oil pressure stays at a steady 38 lbs while cruising and drops to zero at idle when cold. About 20lbs at idle when hot. I think it will last a long time like this but I have to shut off the ac and put it in neutral at stop lights or the idle drops down to 500 or 600 rpm and the gage bottoms out. If I can get the rpm up to 650 or 700 in gear, the pressure stays at 20 lbs. Can anyone give me a quick fix to increase the idle about 150 to 200 rpm? I am running straight 50w Rotella with a can of STP and it seems to help but not much. I have codes PO420 and 430 on both banks but I know enough about OBD codes to get confused. I think the cats are plugged or I have ring blow-by but haven't got a compression tester yet.

Ant suggestions would be appreciated.

 

if im not mistaken, idle is computer controlled on those trucks and theres no adjustment provided without a tune. your codes are for catalyst efficiency below theshold (bad cats) but that could also be bad o2 sensors (however its unlikely it happened on both banks)

 

Thanks for taking the time to reply Chevy112488,
I took the throttle body off and gave it a good cleaning. Man was it dirty. 170 K and I think this is the first time it's been cleaned. The engine is more responsive but the idle is still 600 rpm. I would like to have 8. What about the new digital technology? Is there anything out there with the chip altering add ons that might help? It's probably alot of $ to be spending on this old power plant, but I want to look into this for the new engine anyway.

At any rate, I erased the cat codes. Haven't driven it yet. Too early to tell if they are going to come back. I don't imagine I'll get that lucky to fix the codes with a $5.00 can of choke cleaner, but it would be nice.

 

A custome tune can adjust idle up or down. The tune costs about $250 average, but they also adjust timing, shift points, fuel, etc. Idle from the factory is usually around 550 RPM's.

 

i would just do a nice little tune up, run some c-foam threw the motor, change the oil to synthetic, ac delco filter, get new ac delco plugs, new wires, pcv valve, get new front o2 sensors, and a new oil preassure sending unit... that will run to about 300-400... i think the oil pressure prob is prob your sending unit just giving you jacked up readings cause my 02 did that, the idle prob is prob in need of a tune up. just giving you some food for thought. good luck.

 

The custom tune might be the most bang for the buck at this point. I'm saving up for a low mi. engine to rebuild and am just babying it till then, but the low oil pressure is really nasty. I wish it were just the sending unit, and I will take your advice and change it, but when the gage reads 0 at 550 rpms cold idle, I can hear bearings running dry. No actual knocks yet but I grit my teeth when I raise the idle and wait to hear the oil pick back up at about 8 or 900. Will synthetic oil help with dry start? I'm thinking about Lucas Oil Treatment.

What I've done:
Delco iridium plugs and wires, 50w Rotella w/ can STP oil treatment, STP oil filter.
I tried the 50w oil and STP oil treatment on advice from a friend. That didn't work! Very little change from the 10w30 that was in it. I cut open and inspected the old filter and found no magnetic shavings but there were a few non magnetic particles large enough to see, along with plenty of carbon grit. The chip dector on the oil plug did have ferrous powder on it when I changed oil. I haven't been inside a V-8 in since '86 but I imagine a plugged pickup screen and a worn out oil pump. the oil pump "up-front" design with the long pick-up tube doesn't help. Do you happen to know if the oil pump is a sliding vane type or gear pump? Just curious.

 

Synthetic oil is thinner so it might make it worse. If you still wanna try it, just try synthetic blend first. But use that Lucas, it works real good at keeping oil on everything it is thrown on, even after sitting for a while.

 

if you're just trying to limp this motor along for a while, my suggestion would be a quart of lucas and a tune for the idle. then just let it ride...

 

Good advice guys, Thanks. I am trying to limp this engine for awhile so I think I'll wait on the synthetic oil. I might get it too clean,(if that's possible), and start getting some blow by. I'm not burning oil yet, I want to "let a sleeping dog lye".
I dumped the 50w and went back to 5w30 with a quart of Lucas. I'll get the custom tune next. I checked out the manual for the overhaul specs on this engine. I was shocked to find such close bearing tolerances. .0008-.0021 oil clearance for crank mains. If the engine is anywhere close to service limit, that 50w is running them dry.

 

I forgot to mention, My $5.00 can of carburetor cleaner on the throttle body took care of the PO420 and PO430 codes for bad cats. I erased the codes and they didn't come back.Yet...