I recently got a 88 f150 xlt lariat 5.0l 4wd automatic with 73xxx miles that was parked for years. It does some weird stuff. Oil pressure will drop only when in gear an coming to a stop. Put it in neutral and it doesn't do it. Heat will work sometimes but rarely.
so far I've replaced, all coolant sensors and therostat, cleared heads of gunk (old oil and valve cover seal reminence) which made it go from unable to go uphill to doing burnouts, redone all fuel pumps from rear tank forward (front is rusted so the previous owner bypassed) and full custom exhaust being it was just headers to start.

My main't question is why would my oil pressure so this? I've replaced filter and sensor both and it'll only do it sometimes I thought it was everything it warmed up but nope just at random! Haven't heard any knocks or taps that sound bad. Does sound like a air tick from exhaust flanges or maybe intake but other then that it's great.

Secondly why would I experience sudden loss of power? Have donefull tune up in the past 30 days i just noticed it last night doing it maybe fuel filter clogged?

Qny advice on what to check would be great!

 

Went to leave this morning sputtered and died in reverse refused to start. Changed fuel filter it started but still little to no power and noticed small bits of white smoke coming from my oil hose running airbox to Dr side valve cover.

 

oil pressure lowers with fan level? you have an issue of power/grounds/ and the sender. i dont remeber what year, but post 1990(maybe earlier) trucks, the oil pressure is not even a sender. its a switch. on/off. Good will point rowards good, and bad (under 8 psi) will show 0

 

An ‘88 does not have a real oil pressure gauge. While grounding out the wire at the sensor, look at the gauge to see if is pegged at the high side. If you had that much oil sludge and cork in the heads them maybe some of made its way to the oil pan and oil pump pickup.

I’m still trying to understand how cleaning some old gasket material out of the heads made it be able to do burnouts.

 

Yeah I was kinda trying to figure that out... i just figured it left untouched would probably make its way back into the convo anyway

 

Pretty normal for an old engine to turn on the oil light when hot idle in gear
You rev it up some or take it out of gear and the light goes out (normal for a old tired engine)
It may just be an indicating issue and the ones with a factory gauge we used to have to put a resistor in the sender wire line
That would up the pressure that the gauge reads and turn off the light
Used to see that issue on new low mile trucks
Install a direct pressure gauge in that sender port and check the actual oil pressure and go from there