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DocHolidaySLI
05-10-2009, 10:00 PM
1991 SC 5spd

I probably already know the answer to this question(and don't want to face it), but i'm getting a huge drop of oil pressure on acceleration, a big enough drop to trigger the "Check Gauges" Light

At idle i can hit 5k and hold it and oil pressure goes up and holds just like it's supposed to, everything that i know about typical lubrication systems indicates that i have crank bearings and/or Thrust bearings failing on me

i haven't put a oil pressure gauge on the engine and ran around town with it to see what the numbers are, and it's a 5pd so i cant put a load on it at a standstill so i would have to rig up something and not really necessary as i have done the OP gauge conversion, and replaced the sender with a new one today and the oil pressure gauge goes up at idle so that leads me to believe that the gauge is telling the truth

There is no lower end noise coming from the engine which is weird, no loss of power, one would think that if you lost this kind of oil pressure at 4k+ RPM you would lock it up in a second, hence me tossing this post up, maybe u guys know something i dont about these engines

To those of you that know these engine inside and out, have i missed something?

scxr7
05-10-2009, 10:19 PM
my 5.0 did the same thing. :( its a sad day when that happens. My 5.0 ran fine even though it was losing oil pressure. sometimes the oil pressure went down to 1-4 psi. I took it to the track, I knew it was going to blow. it ran the same as before. mid 14's. eventually I put a new motor in it. when I tore mine down, it turned out to be a bad oil pump along with a spun bearing. Just take it easy on your car while you try to find another motor to put in it. or if you want, rebuild your current motor. sorry to hear that though.:(

Mike8675309
05-10-2009, 10:27 PM
Are you sure it is full of oil? No chance the dip stick is wrong? Are you sure the sensor lead is tight on the pressure sensor?

If you haven't changed the oil lately, you might want to do that and use a good quality filter. Perhaps the old filter is causing some sort of problem?

Unless you want to just take it down and rebuild, you should try and get a mechanical pressure gauge on there to verify things. It's just not easy to get one on.

Duffy Floyd
05-11-2009, 01:04 AM
You might also want to replace the oil pressure sender. It is only a switch and when the contacts are going bad will cause all kinds of screwy readings.

DocHolidaySLI
05-11-2009, 07:03 AM
Are you sure it is full of oil? No chance the dip stick is wrong? Are you sure the sensor lead is tight on the pressure sensor?

If you haven't changed the oil lately, you might want to do that and use a good quality filter. Perhaps the old filter is causing some sort of problem?

Unless you want to just take it down and rebuild, you should try and get a mechanical pressure gauge on there to verify things. It's just not easy to get one on.

Yes it has 5.5qts in it as of 2 days ago and a new motorcraft oil filter, the wire on the sender is as tight as it should be.
i took the wire off, the gauge reads Zero, ground it the gauge reads pegged

91BlackBird
05-11-2009, 07:20 AM
Before you do anything,put a real gauge on it and see what your pressure actually is.
To be on the safe side,replace the oil pump before you blow it up.
It is external and easily replaced.

Duffy Floyd
05-11-2009, 07:21 AM
Like I said...replace the sender....a cheap fix and likely the issue. If that doesn't solve it then check the pressure with a mechanical gage and go from there.

DocHolidaySLI
05-11-2009, 05:48 PM
Before you do anything,put a real gauge on it and see what your pressure actually is.
To be on the safe side,replace the oil pump before you blow it up.
It is external and easily replaced.

what all does a R&R Oil pump involve on these engines? Im used to SB Chev where you have to pull the oil pan to replace a pump

And duffy ill throw a 3rd sender on it just to make sure.

And i cant duplicate the problem unless there is a moderate load on the engine so a mechanical gauge is going to be close to impossible to rig up safely

Thanks for the input so far guys i really appreciate it

Young-SC-Owner
05-11-2009, 07:36 PM
Not another sending unit, an actual mechanical gage

Mike8675309
05-11-2009, 09:12 PM
what all does a R&R Oil pump involve on these engines?

The oil pump is in the same assembly that the oil filter screws to. It's held to the timing cover with 6 or more bolts and seals with a large o-ring. You remove the oil filter, remove the oil cooler plate, unbolt the oil pump and remove the housing which contains the gears and the pressure relief valve.

But that's not likely to be it. If it's not the sender, then it may be a restriction in the pickup, which requires pan removal to get at. It could also be excessive clearance in the bearings.

But verify this with a mechanical gauge before going too far. You can get one with a long lead that you just duct tape to your hood to watch while you're driving.

Duffy Floyd
05-11-2009, 09:31 PM
Oil pumps can be changed without dropping the pan. David Dalke did mine. He might be able to give you some tips. Might as well get the Melling M246 pump if you do change it. Equivalent to the pump used on a 94-95. Higher volume pump.