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This is a 92 5.8 Bronco with 179,000 miles.
I can start the engine and let it idle for as long as I want and it will show normal on the oil gauge.
When I put it in gear and drive after warmup, the oil gauge will stay steady for only a few minutes and then start an erratic dance that ultimately has it go to below 0. Once it starts dropping, the oil pressure indicator drops on throttle up, and returns under no load/idle. Once the gauge drops to zero, if I turn the key off, and then immediately restart the engine, the gauge reads normal for a few moments, then the erratic dance to zero starts again. Once back in the driveway in neutral or park the gauge is mainly steady normal. The problem seems to be engine load acceleration, not rpm, related.
I have not let it run without oil pressure indicated to try to hear the lifters, as I don't want to add to any damage unnecessarily.
I have changed oil and filter (10W30). Old filter was not clogged, nothing odd about the oil. I have grounded the sender wire and confirmed that the instrument cluster gauge itself does not have any issues, i.e. known good. I have changed sender switch on the engine with a new one.
I am aware that the oil gauge is really only an idiot light (on/off), so I have to conclude that pressure is in fact dropping below the 6 psi or so that trigger the switch to indicate "pressure".
I am not interested in upping to 10W40 to mask the problem.
To me the perplexing part is that it only occurs under acceleration load and immediately reads normal on re-start within seconds of reading below 6 psi.
Request any thoughts on what the problem could likely be? (oil pump/screen/pickup, main bearings, cam bearings??)

Secondary question - how hard is it to get to the oil pump in this model (working in driveway with ramps/jackstands only?

Thanks in advance for any replies.
 

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First things first verify the accuracy or inaccuracy of the oil pressure gauge. Usually oil pressure related issues show up at idle as low pressure and pressure increases with Rpm. Not always but usually.

Get a mechanical oil pressure
gauge and check the in dash unit against it.
 

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Eric
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2,625 Posts
The oil pump spins faster with RPM increases. I would guess that the shaft is spinning without actuating the pump (pump failure) or has, somehow, rounded off in the distributor snout. This is assuming the gauge tests out okay. If it does, I'd inspect for mechanical failures next.

Eric
 

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Roller rockers are gay
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19,197 Posts
It's not dropping hard until you drive it because simply idling an engine doesn't work the oil hard nor hear it up much, not in comparison to driving the truck.
 

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~*~*~*~*~*~*~
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10,098 Posts
This same event happened to me back in 2007.

Oil pump was at fault and sucked something up. Cost me an entire rebuild.

Put a mechanical gauge on it and verify what you're seeing with the stock gauge. If you're seeing the same results, Don't run it anymore. Then, figure out how you want to put a pump into it before you wipe out your main bearings.
 
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