Ok, so new motor about 2500 miles ago, and driving it this weekend, i saw the oil pressure drop when on the brakes decently hard, like light turns yellow, and instead of mashing the gas for once, you do a quick stop lol. Also drops turning right at an ok pace. Im pretty sure its the pick up. THis is the one i have:



My question is how would it come off the pump? It was not welded all the way around as i did not see it necessary with the strap bolting to the oil pump, and keeping it from backing out. Any one have this experience with something like this?

 

How high above the bottom of the pan did you set the pickup?

 

Oil control. You don't have enough oil in the pan and/or your oil pan doesn't have a baffle to keep the oil in the sump. When you're on the brakes hard, all the oil in the pan moves to the front away from the pickup. Another possibility is that you have a high volume oil pump and it's sucking the pan dry faster than the oil can get back into the pan (lifter valley screens etc blocking oil flow). When slowing down hard, the oil is still in the top of the engine and what's left in the pan gets pushed forward away from the pickup. One more option is that the oil pump pickup has fallen off for some reason.

A typical street car doesn't normally have that problem but fast drag cars such as mines does when slowing down from high speed quickly. A backup safety feature that I use is a 3 quart oil accumulator to maintain oil pressure if there isn't enough oil in the sump for whatever reason.

 

theres about an 1/8" between the pan and the metal strap, so around 3/8ths" its a 8.25 pan, and a 8.25 pick up. The strap kinda made it difficult to place it anywhere else, and located it where it should have been.
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The oil control has been fine for the last 2500 miles, with harder driving. Then one day it just started doing this after getting off the highway. The pan has a built in windage tray, and a swinging door to keep the oil around the sump/vs sloshing to the front of the pan. Its a 5qt set up with a high pressure pump. Oil pressure is ~65+ at anything above 2500-2800RPMs with 10w30, and ~35 at anything below 1100.

Is it possible the pick up is still attached, but its letting air in around the pump area all of a sudden now? Im pretty focused on checking the gauges in the car quite a bit when driving.

No way this could just be the gauge/wire/sending unit could it? I know that seems a little vague, im just not looking to dropping the pan to not find the issue

 

Any ideas how oil pressure could still drop by only braking/turning right if the pick up is still in place?

 

You have a light and a guage? When the light comes on, does the guage indicate 0psi also? Is it an electrical or mechanical gauge? If it's just the dummy light, then you could have an intermittent short to ground in the wire running to the sender.

 

Those are notorious for getting stuck... not a real good choice of pans IMO. Something designed to be sold to people who are convinced they want it, as opposed to something designed to provide a valuable function.

No it really can't be the wire or sending unit, unless there's some way for the wire to come off the sending unit when you brake hard, touch ground, and then plug itself back on when you let the brakes off. Not bloody likely.

 

All the wire has to do is ground out on a standard dummy light and viola the light comes on. I may be a little behind the times, but all the sending units I ever saw completed the circuit to ground when the pressure was low. The switch opens when pressure comes up. Therefore, a temporary short to ground (such as dummy light wire touching hot engine part intermittently or chafing against firewall passthru) would cause the light to come on intermittently. No magic necessary. A good old mechanical gauge would tell all.

 

No; but a pretty far stretch, just the same.

Ever see a wire do that? Repeatably, reliably, predictably, the same every time? I've occasionally seen one do that intermittently, or maybe even for a little while and then stop, but not an ongoing dependable thing.

See my signature for troubleshooting help.

In this case, the simplest explanation that fits ALL the facts is, the swinging door is sticking open. The most frequent cause of this that I've observed in the past, is damage to the pan; scraping the ground, getting a dent while installing the motor, something flying up off the road and hitting it, etc. It's just not a very robust system. Very very easy to "break" it. Not a good choice for a street-driven car, as it's too fragile and prone to "suffer the slings and arrows of outrageous fortune", as someone once said.

 

I'm sorry, but I didn't see where the OP said it was doing it "Repeatably, reliably, predictably, the same every time". Before pulling the pan, I'd just make sure the pressure really is dropping to 0PSI by using a mechanical gauge.

After carefully reviewing my 1990 FSM, it is clear that (even with a gauge based system) a short to ground anywhere on the wiring between the gauge/light and sending unit will cause the light to come on and/or cause the factory gauge to indicate 0PSI. That is simply how the system works. Checking and verifying the wiring is easier than dropping the pan.

 

Right here:Sounds rather like he's done a certain amount of experimentation to investigate this.

Wire chafing is EVEN LESS LIKELY to occur THE SAME WAY both when braking, AND when turning right. Possible? Sure. Likely? I don't think so. Not too much more likely than the space aliens taking a break in between creating new crop circles and generating Elvis sightings, and sticking their finger in the pickup just to mess with the humans. Again, see my sig for a reminder of how to go about troubleshooting, and avoid getting led astray chasing far-fetched and highly improbable (as opposed to impossible) concocted "explanations".

But yeah, it's always a good idea to get a second indication of some sort, before going directly to yank the motor. Instinct tells me though, that it will turn out to be futile; so don't spend too much time, money or effort on it. I think all it will do is confirm that your oil pressure is indeed going away, and that it will turn out to be because the oil itself is going away.

 

I can see we're getting off to a good start. I hope the OP will read my sig before pulling his motor. As for my "impossible concocted explanations", if you think an intermittent short to ground is so unlikely that you would advise pulling a pan instead of simply verifying the pressure, then I'm speechless.

Do you find that ridiculing opposing viewpoints helps to prove your point? Crop circles? Elvis? Sheez man I offered a viable explanation and you make it sound like I'm some kind of nut.

A couple of other things:
1) The oil pressure sending unit will bypass the fuel-pump relay making for slow starting if the relay is bad.
2) The wire shorting to ground on an oil sending unit (gauge or light only system doesn't matter), will turn the light on and will make a gauge indicate 0PSI.

 

The relative probability is such that I wouldn't spend more than about 60 seconds looking for an intermittent short to ground before I'd start pulling the pan.

 

No; it's not, in and of itself. What IS highly unlikely, is an intermittent short to ground acting like the OP describes. Nealry as unlikely as the joke about the space aliens. (It's a joke, OK? )

If the OP's description of the problem was, I'm driving down the road, and I suddenly see the pressure gauge go to zero; or, I hit a bump, and it flickered to zero for an instant or 2; or something like that, then yeah, an intermittent short to ground sounds likely. HIGHLY likely in fact. If he was proposing yanking the pan to fix it, I'd be talking him out of it; because real oil pressure doesn't act like that, but intermittent wiring shorts do.

OTOH, the OP's description of the behavior sounds like he can duplicate the problem readily by braking hard or by going around right curves. Real oil pressure DOES act like that, but that's MIGHTY TOUGH for an intermittent short in the wiring to duplicate.

In short (please excuse the pun!!), the behavior, AS DESCRIBED, simply does not match the behavior of an electrical problem. Instead, it matches the classic behavior of an oil pressure problem, caused by uncovering the pickup.

You're right though, he should gather more data, before proceeding directly to yanking the pan. However, the mental approach and goal of investigation should be to verify that either the oil pressure is going away, or not; and not, looking for a short in the wiring. If it turns out that the oil pressure really doesn't disappear, but rather that there's a gauge system issue, then yeah, time to look at the wiring. But if I was the odds-laying kind, I'd lay odds of less than 1 in 10,000 that a short in the wiring is at fault. Doesn't make alot of sense to investigate a bizarre and improbable coincidence with 1 in 10,000 odds, but leave the simple 9,999 in 10,000 explanation untouched.

Yes I am familiar with electricity and wiring. I spent MANY years as an electronics tech, troubleshooting and repairing industrial controls and instruments to the component level. So yes, I understand in EXCRUCIATING detail how an oil pressure gauge circuit works. Which is why I feel QUITE sure that this is NOT a gauge system problem, but rather, that the gauge is working properly and telling the truth about the oil pressure.

 

Yep im thinking the pan will be coming off. The only oil sensor hooked up is the factory electric variable pressure one. There is no dummy light. I might try the mech gauge to verify what im seeing on the electric gauge as i have one already laying around.

So, how would a swing door stuck open cause oil to go away when turning right/braking where a normal pan with no baffles at all would be the same design? And it is consistant with the speed/quick the car is slowing down or turning right that the oil pressure will begine to drop, or hit 0. I just hate seeing it go down to keep testing but 1 more time.

I just hope when the pan comes off its easy to see the issue, and not well it might have been this or that.....

 

Normal pans have baffles...

Another real quick thing you can try, is to just add an extra quart of oil. If that reduces the behavior, then you can be pretty sure it's really happening. Cheaper, easier, and quicker than futzing around with adding another gauge.

 

The point being that you would at least check the simple stuff first.

I'll agree that the likelyhood of an intermittent short on a factory install is small, but still likely enough that the manual is chock full of checks for shorts to ground. OTOH, this is not a factory install since the motor was dropped in 2500 miles ago. A perfectly reasonable amount of time IMO to show signs of a wire rubbing thru somewhere.

If the OP had mentioned knocking, tapping or some kind of sign that the oil pressure was actually gone, I wouldn't be making a stink over this.

 

How much does the oil pressure drop? If you're talking 10-15 psi then I wouldn't worry about it, I mean you are off the throttle so pressure will drop.

 

Added an QT of oil to it when i noticed it happening, before adding the level was still good, it did reduce how easily it was happening.

And when i say pressure drop, i mean it goes from 60-70 to near 0, but as soon as the car levels out, the pressure comes right back.

I also tried taping the oil pan with a rubber mallet to see if i could hear the pick up bounce, and didnt hear anything, so its still bolted on, not sure if its sealing or not, I put a tach weld on one part of the neck/pump.

Is it possible all 6qts now are just flowing to the front of the motor and uncovering the pick up on braking? To me it seems like the pickup hole in the pump is uncovering and causing air to be sucked into the system.
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The car nomrally operates at 60+ (verified with mech gauge) at anything above 2500 and idles around 30-35 at 800 RPMs.

Looks like my problem is in the pan, so that will be coming off, and pictures taken if i find the issue to help in the future.

 

The pickup doesn't have to be completely uncovered to start sucking air, it only needs to have the oil level above it reduced substantially. Ever tried drinking a (real, not fast-food) milkshake fast with a straw?

 

Yup, that's pretty much what it is.

I'd suggest a pan with traditional, "passive" baffles, and a windage tray. Those "gadget" ones have caused alot of people alot of trouble over the years.

 

Really? thats crazy sounding, only bad thing, is i could only get this pan to clear the stroker crank. I dont know why it was such a hassle but only the cheap pan had a big enough dent in the rail to clear the crank, and even then i think i had to massage it a bit.

 

Interesting....

I've built no telling how many 400s over the years, and never had any trouble with stock pans...

 

Did you check the crank to pan clearance with the gasket on or off?

 

Checked it with the gasket off first, and then on, about 3-4 times for 4 different pans. A cheap one from the speedshop fit the best. So a trap door stuck open can cause this issue? Ill be honest this is my first stroker motor, and all my others were 350/355's in different fashions, but stock pans/hi press oil pump set ups, and ive never had this issue before. This motor also has trouble spitting oil out the dip stick if i dont run a PCV valve or a free flowing breather, the cheap Mr gasket ones keep too much crankcase pressure in there, and oil will shoot out the dipstick on a WOT pull.