Oil Pressure Problems, 92 Ford F-150 5.0 liter

  • 1992 FORD F-150
Hello, Sorry this might be long winded.
Last year my sister through a rod in this 92 ford 5.0 Liter F150. As we could not afford a new engine, I found a 86 5.0 liter engine that had been in a Thunderbird. It had a lot of miles on it, so I rebuilt it with new bearings, rings, gaskets, oil pump, etc. The only things I used from the old motor was the intake/induction, oil pan, oil sump pickup, and distributor. I got the engine installed, got it running fairly smooth, and turned her loose with it. About the only problem it had was transmission related, the transmission would not shift into overdrive (it's an AOD that I have already replaced once in the life time of this truck), and the transmission would not always down shift to first when you stopped at a stop sign. Anyway, she went on a trip of about 20 miles in it, and for some reason, the shift cable popped loose from the transmission, resulting in her making the trip in first gear apparently. She had also overfilled the oil by about three quarts, I have no idea why, she said she was used to adding oil before going anywhere, and never really checked the dipstick. Anyway, when she called me, it was overheated, and when I started it, there was no oil pressure. I had it towed home. I am trying to fix this truck again now. I replaced the transmission shift cable first thing. I dropped the oil pan, it was full of extremely sludgy oil. I cleaned it out, took the sump off and cleaned it out, put a new oil pan gasket on it, refilled it with oil and coolant. I started it up, sounded real bad. I pulled the plugs out, found that number four cylinder spark plug was covered in oil. I pulled the valve cover off, found the push rod had popped clean out from under the rocker and the rocker nut was loose. I put it back in, tightened the nut, the cylinder now fires. Then I fire the engine up, after about 7 minutes, after it warms up a tad, the oil pressure drops to zero, just drops, doesn't fade. I drain the oil again, fill it with new oil, engine flush, and flush it out. After putting new oil in it again, I try it again. It starts right up, runs a little rough, but runs. After seven minutes, as the temperature guage just gets in the normal range, the oil pressure goes away again, instantly, not fading. If I watch it for a few seconds, it will go away, then pop right back up. If I put a distributor in the engine with no drive gears, and turn it with my drill, the oil pressure is rock steady. If I put the original distributor back in, then the oil pressure just poofs out again. I have absolutely no idea where to go from here. There is obviously no overheating in that seven minute period. There is no smoke whatsoever from the exhaust, though there was blue smoke when I first started bringing it back to life. Other than the distributor, the intake, and one sensor mounted on the top of the engine behind the intake that the old engine had, the new one didn't. I bought a new sensor and made a metal pipe tee and mounted that sensor in the heater hose as I was led to believe it was a water temp sensor. Anyway, the engine always bogs a tad right when the oil pressure drops to zero, so I shut it right off. And the bottom line, I don't know what is broke, so how do I go about fixing this. This is 100% repeatable, cold engine, start engine, seven minutes, poof on the oil pressure.
Do you
have the same problem?
Monday, July 9th, 2007 AT 4:50 PM

1 Reply

  • 416 POSTS
The sensor that screws into the block behind the intake is the knock sensor.

Have you hooked a mechanical oil pressure guage up to the engine and monitored oil pressure while the engine is warming up? That will give you a true oil pressure reading, and an indication of whether or not it is actually bad oil pressure, or a bad sending/guage unit.
Was this
Wednesday, July 11th, 2007 AT 10:56 AM

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