Hello, need some advice. I have been on this site for years. exclusively in the 2nd gen forum (personal truck) however I also have a 3rd gen (work truck) which brings me to you. truck has 220,000 miles on it. just replaced motor. first motor lost a hardened valve seat which eye browed a piston. Old motor did this oil pressure thing too. with a/c off, in gear, at idle, at operating temps the oil light will come on and gauge drops to 0. I replaced the crusty sending unit with no real change. I checked it with a mechanical gauge and there is a loss of oil pressure. it may read 1 to 3 psi. here's the thing it only does it at about 500 RPM, seems a bit low. with the a/c idle up it doesn't happen. also I have let the truck idle in driveway while doing other things away from truck to get in and see gauge at 0 and probably been there for several minutes with no detectable engine damage. do your trucks idle at 500? should the oil pump still provide pressure at that rpm? is it a throttle body adjustment or a computer deal if the idle is low? new motor is pretty stout, got about 1,200 miles on it so far and this happens at least once a day. the first time it happened I shut it down and had it towed. the shop told me all was good. so I have just been driving it but it does concern me, remember the old motor did this toward the end of it's life. new motor came with new oil pump. Thanks in advance! Jeremey.

 

Oil pressure should be higher at idle. The idle is computer controlled, but you need to indicate which engine you are running. they're different for different displacement

I'm assuming the new engine has a new pump-----really doesn't make sense that its low at idle with all new internals and bearings, the idle can be raised with a programmer or a dealers scanner can adjust it too.

 

FYI, first oil change had minute metal in drain pan, that is why you change oil right off the bat I suspect. subsequent oil changes have been very clean. Shop doing instal was impressed with the cleanliness and build quality of new motor purchased from Rock Auto who was a forum sponsor at the time.

 

sorry Fishin and others.. It's a 2002 quad cab 4x4 with 4.7

 

where do you guys idle at in gear no a/c at temp? more than 500 RPM? just trying to figure out if this engine is eating itself or not. do you think oil pump should produce pressure at 500 RPM? that's just better than 8 revolutions per second. seems like it should but then again there's a lot of oiling to be done. if this thing idled at 575-600 Rpm I wouldn't ever see the oil light. I just want to make sure I am not band-aiding a problem by bumping the idle. The motor is under warranty for 2.5 more years and about 33,500 more miles FYI

 

I'll bet the screen is clogged a bit and at that really low RPM it isn't pulling hard enough to get the oil up to spec. When the RPMs bump a bit then it flows like it should. I'd pull the pan at next change and give it a good look/see...

 

For the cost of an oil pressure sensor, I would replace it and see what you get.

 

from past experience with trucks in general, I would do the following.

Replace Oil Pressure Sensor (inexpensive)
Install Oil Pressure Gauge at Sensor (Check while truck is running at idle)
Check Tension on All Belts
Do Compression and Leak Down Test (Just to make sure the engine is good)
Last Thing to do is pull the oil pan and replace the oil pick-up (might be clogged)

After that point I would be stumped, other than maybe a bad electrical connection.


some info that Might help us is:

Did you reuse any of the parts from the old motor?

If so what parts did you reuse?

 

Strange, I have the same truck, same situation and same problem. Just had the engine rebuilt about 2500 miles ago and yesterday the 'check gages' light came on while idling and oil pressure gage was at zero. I started moving and it would come back up to almost where it should be. As soon as I would get off the accelerator to stop at a light or something the gage would drop to zero again and light would come back on. The engine has had a tick since I brought this truck home from the shop. They already replaced the lifters again as they thought that they were not pumping up and thus causing the tick. Still ticks and now this oil pressure thing. Could pump be clogged/bad and not pumping enough to not have pumped up the lifters causing the tick? (oil pump was replaced with rebuild).