Jumpy oil pressure is now no oil pressure

[460Stanger]

Can anyone help me understand what's going on with this?
The 460 engine was rebuild last summer and I dropped it into my 95 mustang this summer. I took it out a few times and it ran well with a steady 40 to 75 psi oil pressure (it has a high volume oil pump).

After several small trips I noticed the MECHANICAL oil pressure gauge would jump around from high to low quite rapidly just idling. I installed another mechanical oil gauge and it did the same thing. Normally the oil pressure would have been around 50 at idle, but it was now 25 and increasing the rpms would make it go up to about 60, but it still jumped around.

I drove it one more time and now the oil pressure was near zero at idle, and increasing the rpms no longer caused it to increase (no more jumping around).
The oil level was fine at all times.

I changed the oil and the filter and it still had no oil pressure. I've never messed with an oil pump before but I did pull the distributor to see if the shaft was broke or something - it wasn't. I put my electric drill to the shaft and spun it, no oil pressure - turning the shaft by hand did have a smooth resistive feel to it so I'm guessing that means it is turning the mechanism within the pump.

Now what? Pull the pan? If so, what should I be looking for when I do?
For what it's worth, I did hear an odd sounding noise near the end of one of the tire smoking episodes - but I didn't immediately notice anything as far as the gauges or anything else went. Perhaps something broke?

Thanks guys,
runnin' on MT

[SicLinc98]

could be the gauge

[Frankenstein]

Did you happen to hear any odd noises or such when it showed no oil pressure? If you were actually at zero and running, it would cause some problems pretty quick. You said you also increased the RPM while running with the gauge at 0 oil pressure? Doesn't sound right to me.

[Akromix]

could be the gauge

he used two gauges.

[svonasek]

If you pull the oil fill cap can you see any oil making it to the top of the motor?

I'm wondering if there isn't something happening with the pick up tube...

[OffShore]

Is it electrical? if so check your connections, I am having the same problems right now after I put my new heads on and I am sure it is just a connection. when my car idles it goes to 40 psi and when I drive it on the hwy it bounces around and then goes to 5 psi. but car has been fine threw 30 dyno passes like this. Sooner or later ill get it fixed.

[I Tried]

Cut the filter that came off the car apart and look for metal or brass. Poss cam bearing or main rod failure.

[I Tried]

Is it electrical? if so check your connections, I am having the same problems right now after I put my new heads on and I am sure it is just a connection. when my car idles it goes to 40 psi and when I drive it on the hwy it bounces around and then goes to 5 psi. but car has been fine threw 30 dyno passes like this. Sooner or later ill get it fixed.

When it lets go. I would put a mechanical guage on it and see what it actually does.

[OffShore]

When it lets go. I would put a mechanical guage on it and see what it actually does.

When it lets go? please stop being so negative twords my car bud, I dont slam your stuff, please have respect for mine.

[bigblockpaul]

Sounds like a broken oil pump housing....I know this from experience low pressure...Tried two guages same.....Pull dist check shaft..then pull pan>>..

[460Stanger]

Thanks guys, some good stuff I hadn't thought of - I read a bunch of oil pressure problem information before I posted so I knew I'd better point out the fact that I'm only using mechanical oil pressure gages (two different ones). I couldn't get the distributor/oil pump shaft out the top using a magnet - it sort of slops around in the hole and I didn't know if it was secured at the other end or not so I didn't fool around with it too much. It looked normal on the tapered end and turning it by hand with a 1/4 in socket and extension felt smooth and somewhat resistive as I would expect if oil were in the pump - so I don't think the shaft is broke. I'm dropping the pan tomorrow and I'll look for a cracked pump housing . . . anything else I should look for? I hope it will be obvious once I'm inside. I plan on looking inside that oil filter too (if it's still in the garbarge can).
Thanks again gentlemen, you guys are great.
runnin' on MT

[Max Power]

Buy a new pump. When you drop the pan, install it. I really don't think high volume pumps are necessary, but that is your call. Pumps are cheap enough that if you are going through the work of pulling the pan, just replace the pump.

Inspect the oil pump drive shaft while you are at it. They have a clip on them so you can't pull them out the top.

[Pauly]

Check your clearence between pickup and pan bottom if too close that can effect the flow. After a year or so there will be some kind of build up maybe not alot but if your clearence is too close a couple thousants could make a differeance. I know some people who have the pickup too close and were actually sucking the stock pan closer to the pickup key word stock

[I Tried]

Is it electrical? if so check your connections, I am having the same problems right now after I put my new heads on and I am sure it is just a connection. when my car idles it goes to 40 psi and when I drive it on the hwy it bounces around and then goes to 5 psi. but car has been fine threw 30 dyno passes like this. Sooner or later ill get it fixed.

Dan statements like this deserve someone stiring the pot. You are runing a 502 chevy with aluminum heads that would cost a few thousand dollers to replace. I would not run any motor that had a oil psi issue, even if I suspected just a electrical gremlin, much less a moderate to high hp engine before I was positive it was not a connection. It is not worth the risk . Not trying to pick on you but read the statment above. It makes you look bad in my opinion.

Tim

[460Stanger]

I'm still in the "getting it ready to pull" stage - draining fluids, disconnecting everything. My enthusiasm isn't exactly soaring . . . I'll get 'er done one of these days. For the record, I know better than to run an engine with no oil pressure - My post made it sound rather fatal and Frankenstein picked up on that - good point, and I should have chosen my words more carefully. Thanks again to all you gentlemen that are so willing to help - There's one heck of alot of knowledge, experience, and wisdom floating around here - I wish some would rub off on me.
runnin' on MT