Hey guys, I’m sure this has been covered before, but when I’m driving I experience random oil pressure loss, normally down to 0. The car is high mileage (200000) but oil pump worked fine as of 25 miles ago when I rebuilt the top end. The pressure sits at around 33 ish but jumps to a little over 40 with throttle, at idle. When driving much of the same. Some points at running temp, the car will have a drop for 5 or 6 seconds at 0 and then return to normal. I’ve heard it may have been the long replaced nylon cam gear? I’m only driving the car maybe 50 miles a year for another 2 years until I’m further in school and have the money to drop a 350 and th350 in/ strengthen and freshen 700r4. Any ideas/recommendations? Much appreciated
-mike

 

Probably the oil sending unit...

 

I apologize, it’s a mechanical gauge. The electronic control has all been converted and my old oil sensor wire went bad.

 

Not sure exactly what this means... butt, if something about the "cam gear" (whichever one that might be) were to fail, the distributor and/or the cam itself would stop turning, and the engine could then not possibly run. So whatever this drivel you've "heard" is, you can cross it off your list. "It is a tale told by an idiot, full of sound and fury, but signifying nothing" as one of the GOATs in a totally different field once wrote.

A better way to go about diagnosing it would be, correlating it with EXACTLY whatever else is going on when the oil pressure goes away. Does this perhaps involve sudden stops, especially down hills?

 

By cam gear I meant that the old nylon can gear that was in the car til 200k I was told was prone to flaking and chipping, even if it didn’t cause catastrophic failure. The flakes and chips would theoretically be sucked into the oil pump and jam the gears. Just hearsay tho.

As for simultaneous symptoms, (though I haven’t taken it down any seriously steep hills lately) on slight incline the car still seems to run fine. I almost thought my oil line for the gauge came loose or something but it always returns back to normal.

 

If oil pump pickup tube has fallen off,could cause oil pump to suck air and lose pressure at times. Might be able to check through drain plug hole-do not recall if pickup can be seen through drain hole.

 

If you're talking about the cam sprocket,, yes it comes to pieces. When it does the engine quits running because the cam and distributor no longer turn. No, it can't cause the oil pressure to drop to zero. No, little bits of plastic can't "jam the gears" even if they get through the screen; the gears are pretty serious machinery, compared to however-many-year-old nylon. All of that is about as likely as the space aliens getting tired of abducting people and instead getting their rocks off by stealing your oil pressure. IOW, not bloody likely.

THIS is precisely what I was getting at. If the pressure disappears under hard braking, this is the most likely cause. Happens somewhat frequently. And yes sometimes you can see it through the drain hole, or poke something up in there and move it around if it's laying in the pan, or otherwise detect it without pulling the pan to look. Unfortunately however, another thing that can happen is, the pickup can get bent or rotated upwards, perhaps by trauma to the pan which might pop mostly back out and not be obvious, such that the oil sloshes away from it and uncovers it; produces the same basic symptoms. Either failure mode can be confirmed somewhat by adding an extra quart of oil; if the problem goes away or is considerably lessened, then one of those 2 things is probably the cause.

 

Thank you sofa and chev-z that’s exactly what I needed to hear. When I come home from school I’ll do some test driving to see what happens during braking, incline, etc. and probably do the oil. I’ll poke around or try to *gently* snake the pan to check it out. Thanks again for the quick response, I’ll update when the culprits confirmed.

 

Get yourself a cheap borescope, you can drain the oil and stick it in the drain hole and see what's going on in there.

 

Obvious.... but- checked the oil level?
Could be junk getting into the oil pump bypass valve, holding it open.
Nylon / copper oil psi tube getting pinched off?

 

Oil level is good, copper mechanical gauge feed is clear.

forgive me I’m still pretty new, what is the oil bypass valve?

(thank you for response btw)

 

oil bypass valve is built into the oil pump-it is a simple spring loaded plunger that opens to release excessive oil pressure:such as when the oil is cold and thick.

 

(& when something gets stuck in it.)

I once found a piece of wire wheel in a relief valve once, a piece of pretty much anything could get lodged if your unlucky enough.

 

The short block may have reached end-of-life. That 350 swap you mention may be necessary before your planned timeline.

 

Forget about bypass valve and piece of wire and all that for just a minute and go fully Neanderthal. Become logical.

So, does this oil pressure loss miraculously appear when coming to a sudden stop, then return to normal after a few seconds? We still haven't heard.

 

I just got home this afternoon. I go to school a couple hours away so I’m not home to instantly implement suggestions as much as I would like to

hopefully the weathers nice and I can test drive tomorrow to troubleshoot. As soon as results are found I’ll report back. The pressure loss has seemed pretty random in the past; I should be looking for it to disappear during a sudden stop/incline? I’ll try to include a video in the next post. Thanks again for the continued help.

 

YES. Of course.

Are you SERIOUSLY going to tell us you're so ... whatever ... you can't just RANDOMLY STOMP ON THE BRAKES at some point(s) during your coupla hour school commute and see what happens?

At some point you gotta just quit posting crap on the Interwebz and actually OBSERVE what your car is doing. Without that it's all just random guessing. Otherwise, NO "posting" will do you A DAMN BIT of good, because what you'll get (including from me) is all just abuncha "maybe it's this maybe it's that" with no substance behind it. Gotta get some real-world data to back it up.

 

🤦‍♂️ I don’t drive this car to school. I wish. I have a much less cool equinox that takes the trek to campus.

the firebird is kind of a garage princess. It only gets a couple miles a year, quick joy rides, test drives, and the occasional car show. Never in the rain or snow. I don’t abuse it when I drive it either out of aforementioned fear of a bazillion problems coming out of the woodworks. Between the short amount of time I’ve been home because of school and the typically awful upstate weather the firebird really doesn’t see much use unless I’m working on it.

 

Update: I drove the car today. I took a little 15 minute drive down the street, and the car ran well. Good oil pressure for the first half, including during stopping. During light-hard stopping the pressure would dip slightly then return to around 30-35 ish. During the second half (once the car had been fully warm for some time) no oil difference during hard stopping/incline. Pulling up to an intersection (light stopping) oil pressure dipped low to 19-20, and stayed low all the way home, probably only 15 (conservatively) ant its lowest and 23 at its highest (liberally), including hard stopping. Never dipped to 0 during the whole drive, and never returned to idle pressure. Make it make sense guys 🤷‍♂️.

 

Too light of weight oil combined with excessive bearing clearance due to milage.

 

The car is high mileage (200000) but oil pump worked fine as of 25 miles ago when I rebuilt the top end.

Any chance you got over zealous with the Permatex and gobs of it are now blocking the oil drain-back holes?

 

As in the drain holes in the lifter valley? I was (and still am) pretty green but I did have a professional watching when I rebuilt everything especially during the important stuff. My auto teacher taught/explained everything I did to the car as I went, but this is entirely possible and not something I thought of before. Hopefully when I scope it soon I can determine what exactly is going on down under.

 

Which school of thought best matches how you were taught and what you believe and practice in life?

1. Gaskets, seals, and O-rings are what seals things up. I got a fresh new tube of RTV. This will last my entire engine building career.

2. Gaskets, seals, and O-rings are to be slathered with so much RTV you can't even see them and I wonder why we even use them when we have RTV. I got a fresh tube of RTV. This will last me maybe through this engine build.

 

Definitely more the former. All gaskets went on dry with some wonky exceptions. The lifter valley gaskets (intake manifold front and back) I used only silicone; I was told the crappy rubber ones were more likely to leak than just a good line of rtv. The lines weren’t bad for my first time, but probably could have been a little better. The oil pan gasket/timing cover gasket was slightly mangled; the po had ripped the timing cover out without dropping the pan (probably because it’s a major pain in the ***). Out of fear of having to lift the engine to fool around with the pan I applied some rtv to the corners and let her ride. A little while later I slathered a little more in to stop a small oil leak. It’s possible that some got into the pan, but I tend to trust the gaskets more.

 

Yes #1 is the correct answer.

Yes never use the China wall seals provided with the intake manifold gasket kit.

With what little RTV you used on the corners and a small leak it doesn't like you drowned the engine in RTV.

 

So this engine is a stock 200k+ bottom end, with a new timing chain and gear set, and you freshened up the top end of the engine?

What motor oil and weight do you run in the engine?

 

Sorry for the delayed response

As far as I know it’s a stock bottom end. I’m the fifth owner lol. I do know that the engine and tranny are original, and almost certainly the diff. The car was definitely gone through to some extent at some point; there were aftermarket lifters (some were wiped) and springs when I tore the top end off. The lifter valley was also almost spotless and tranny was clean with new fluid under the pan. i cleaned cylinders and checked them for scoring/crosshatching, did valve seals and valve lapped, MEK compression test, polished combustion chamber and gasket surface, ARP studs, new Holley intake manifold, all new gasket set obviously, new summit cam and lifter set, timing chain and gear set, Edelbrock 1406 carb and HEI dizzy. New spark plugs and other maintenance etc.

my go to oil is the Lucas Hot rod high zinc 10/30 but right now it’s got valvoline vr2 high zinc cuz it’s all that was around. The oil has been changed frequently.


edit: I replaced whatever flat tappet cam was in there with a more aggressive flat tappet. I also made sure that all lifters were pumped before reassembling and breaking in.

 

Is what you did to the engine done with the engine in the car?

 

Yes, the engine was in the car.

 

So it had an aftermarket cam, lifters, and valve springs in it when you tore down the top end and did your thing. Some of the lobes and lifters were wiped out. I wonder where all the metal went from these wiped out lobes and lifters. I wonder if the cam and lifters that were in it before someone in the past put the aftermarket ones in were wiped out too and where did all that metal go. I also wonder how much remnants of old hard brittle broken up valve stem seals have made their way down into the oil pan and been sucked up into the pickup and are lodged in the screen in the pickup.

1 thing I haven't notice you mention yet is any valvetrain or other engine noises when this loss of oil pressure happens.

 

Very likely. Hopefully all it takes is a bore scope to really know what’s in there/not in there. I’m home again over Easter so I’ll probably check then.

i can’t seem to hear any other valve train noises when this happens. After some time the car seems to lose power; but it never really seems to have as much power as it should anyways. Pretty sure that’s more of a fuel delivery/tuning/200000 mile engine thing.

thanks again for all the help

 

Took the car for another similar length drive a few days ago. Oil pressure remained above 20 psi the whole time, car ripped through the powerband fine, and did not get hot. Everything seems to be working well but I’ll still be changing the oil to check and likely scoping out the pan this summer. As of right now, the phantom oil drop has magically disappeared.

 

I'm glad to hear that your oil pressure seems to be reading normal now. I think that most of us have a lot more trust in a mechanical oil pressure gauge vs an electronic oil pressure gauge. However, you might have a faulty mechanical oil pressure gauge.

 

Could you explain how the bypass works? I have a 91 firebird and three weeks ago it would sit at 30psi on cold start and after 10 minutes it would drop to 15psi. as of last week and the week before it would cold start at like 15 and drop to about 8-10. if I turned on the radiator fan with the climate control it would drop all the way to 0psi for a sec and then raise back up. would the gradual decrease of pressure be a result of a mechanical fault or does the gauge dropping when electronics are turned on point to electronic failure in the gauge? and how could I test the oil pressure. I took a valve cover off and ran the car and didn't see any oil, except for old oil sitting on the rockers and pooling by a drain hole. I can only give limited history as I've only had the car since Feb 9th and I got it running on feb 20th(fuel pump got clogged), but I believe the oil pressure was decent when I bought it. I added a video of under my valve cover with it running, and a video of my car running, then me flipping teh headlights on and off, and at the end it drops to 0psi when I turned on the engine fan.

 

I think you have bad engine to body ground connection-check the braided copper ground strap that is usually from RT rear of engine to firewall.and there could be other electrical faults as well.If you have very low or missing oil pressure,the rocker arms will start clacking.Factory electric oil gauge is not terrribly accurate or reliable-usually the sender is at fault.

 

My oil pressure switch plug had oil in it so that indicates it failed right? but would it not send consistent oil pressure? cus my gauge fluctuates but never pushes a certain level, a month ago was 30psi max and this week it was almost 10 max

 

It's a little piston with a spring behind it. It normally covers the opening to a passage that can bleed off pressurized oil. When the pressure gets up high enough, it pushes the piston back against the spring, exposing the passage. Dirt simple.

Yeah probably.

Who knows. If it's disintegrated inside, could be doing almost anything. Change it out and see.

 

Could you be more specific about where the ground strap is and what it looks like? I have the engine lifted slightly from pulling the oil pan so the engine and firewall are scarily close right now and I can't get a good view anywhere behind the motor. I looked around and found that the main battery-to-block connection looked worse for wear, as well as some other wires(not all black) stacked on a bolt on the rear of the block that look pretty rusted/corroded that I will be dealing with tmrw at school. I will update and maybe get photos around 3

 

replaced oil pressure switch and high volume oil pump as well as switched to 10w-30 for the warm weather. getting about 50psi now, will probably switch back to 5w-30 next week after the current oil circulates around a bit.

 

Update: car is driving well, put a new fuel pump and supporting elements in and started to lengthen droves to a couple miles to see how the car responds. Everything operates seemingly as it should, but whenever the car has been warm for some time the oil is still slowly decreasing towards 0. No random drops or spikes, just a gradual decline that starts after about 10 minutes of driving. If the car sits for a couple hours and I start it again oil pressure returns to normal. If I try to start it a couple minutes after the problem occurs the gauge will still read low (wherever it was at when the car was shut off). I found someone else that had a similar problem, IROC_BTK posted a thread about it over a decade ago but didnt seem to get a clear cut answer. Any ideas? Mechanical gauge, 14 mile old oil. 86, 305, lg4, 700r4, 200200 miles. I also have a cheap oil filter in it right now, potentially FRAM.

 

So you're using a mechanical gauge now and still get the decreasing oil pressure?

 

Yes, Bosch. It routinely reads 25-30 psi on idle. 10w30 vr2 high zinc oil.

 

I'm just trying to clarify this for myself. You're using a "Bosch" mechanical oil pressure gauge. A mechanical oil pressure gauge with the small diameter, plastic capillary tubing connected on one end to the gauge and on the other end it's plumbed into an oil port on the engine?

 

All good, yes. It’s plumbed to the original “oil sender” port where the old sender wire and connected prong had been mangled. I replaced the plastic with copper tubing of the same diameter. I only included Bosch because I wasn’t sure of the reputation of the brand for qc.

 

Mike, thank you for confirming that you do indeed have a mechanical oil pressure guage.

I had to go back to the beginning of this thread and read again. I was confused because "Firebirds" chimed in on post #34 and I got confused with you and him.

In post #34, I mentioned that it is possible that you have a faulty mechanical oil pressure guage. Probably not likely but possible.

 

Update: I changed the oil and filter to basic car quest and vr1 20w50. Oil pressure bumped up nicely to 35-40 during idle and anywhere from 18 to 30 when warm depending on rpm, consistently. Seems to have solved the problem. Thanks guys

 

You need to pressure tap in multiple places, see what the engine is making before and after the oil filter by plumbing to the port above the oil filter, you should expect to see a pressure drop vs the port above the timing cover which is normal since that’s after the valvetrain but if you have a big difference or drop between the two that’s a huge problem since there’s a blockage. If you have junk floating around in your oil it could clog a drain in the head and cause the 0 oil pressure you’re talking about, I found loose painters tape in my passenger cylinder head one time so who knows what’s in there, also get a roller cam in there before that flat tappet hucks itself like your old one did, if your old one went, your new one certainly will as well and you’ll be back at square one.

don’t run a FRAM at all costs, run the wix without the internal bypass and run a non bypass oil filter adapter housing so that way if a failure happens your motor doesn’t get destroyed, if you notice extremely high pressure before the filter and low pressure after the filter that’s your sign that a failure has happened and you need to replace the filter.

 

Will check.

would love to get a roller cam in it but I’m not sure what I want to do yet, it’s high mileage and ive considered redoing the drivetrain entirely if something serious goes 🤷‍♂️

thanks for the reply

 

my car has two oil pressure gauges because I had a similar problem to you one day, I was cruising and I looked at my oil pressure only to see it at 0, so I plumbed in a mechanical unit and waited until it did it again and when it did, I had perfect pressure on the gauge but none on the electric, the fuse in the dash was the culprit, it was the wrong type and would come loose once in a blue moon, ever since that day I never trusted the electronic gauge and had my mechanical gauge mounted more inconspicuously, also gave me the chance to verify pressures at each tap to check the health of the motor.

I think most GM’s, at least their reman motors calls for 40 psi @ 2000 RPM to be normal, pretty sure that’s the same for their production engines as well

Good luck and let us know how it goes