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Author Topic: Extremely Low oil pressure at startup while idling  (Read 736 times)

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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #25 on: 03/30/18 12:14 PM »

Just found a pressure test kit on amazon that someone else verified fits my year and engine, guess i have to wait until monday.
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #26 on: 03/30/18 08:49 PM »

If the oil light is coming on its not the servo.  The oil light I'm pretty sure is driven by the PCM based on the pressure sensor...not the servo gauge position.

Oddly enough, it appears the Low Oil Pressure message is activated by the same signal as drives the gauge. From the 2002 FSM:

"The IPC uses the engine oil sensor signal to determine the engine oil pressure. The oil pressure sensor signal circuit is hard-wired to the IPC. The engine oil pressure sensor signal to the IPC is a variable resistance ranging from 0-90 ohms. The sensor resistance is used to drive the engine oil pressure gage. A sensor resistance of 1 ohms will display as 0 kPa (0 psi) and a resistance of 88 ohms will display as 550 kPi (80 psi). The IPC monitors the oil pressure sensor signal circuit in order to decide when the oil pressure is too low. The Check Engine Oil Pressure indicator will be displayed in the message center if the IPC detects a low engine oil pressure."

Note that 0 psi is indicated by low resistance. That means a connection would have to be short-circuited to cause your problem. Poor connections produce high resistance, which would result in a false high oil pressure reading. In my experience, poor connections and broken wires are far more common than intermittent short circuits, but here's a little experiment you can try: Unplug the connector at the sensor. That should peg the oil pressure gauge. Wiggle wires while someone watches the gauge. If it still shows 0, then the problem is definitely electrical. If you can get a low value resistor (eg: 6.8 ohms) from a local Radio Shack or similar, connect it between the tan/white wire at the sensor connector and ground to simulate a low engine oil pressure.
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marzahld

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Re: Extremely Low oil pressure at startup while idling
« Reply #27 on: 03/30/18 09:18 PM »

I wish the best of luck for you, but this was what happened to my '03.  I was first owner and always changed oil immediately when it told me to, but I now think it was not enough.  I read somewhere that GM basically admitted that they revised the newer trucks to count down 20% faster.    My truck always alerted me to change between 5-7k.   Towards the end, I basically had one or two bb sized sludge chunks actually come out when I changed the oil.     I have a theory that sludge build up will be proportional to the amount of oil your truck is burning in between oil changes ( I always had to top off in between changes and had no leaks ).  Towards the end I was adding 2 qts between changes.  You know this has to leave byproducts behind when it happens.  Installing an oil cooler at inception could be a good investment on these trucks.

I only got to 155k miles on that engine, but many here are going to 250k or so, so YMMV.    FWIW my engine never blew up, but I had a lifter ticking, and eventually it reported low oil pressure only when at idle.   I changed the oil pickup tube and screen which was pretty dirty, but it did not help.   I ran a few kinds of snake oil through it for a year or so as well (sea foam, mystery oil, etc).   Might have gotten more out of it, who knows...   it never died on the road on me, but I eventually realized I needed to rebuild that engine or move on....

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robertmee

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Re: Extremely Low oil pressure at startup while idling
« Reply #28 on: 03/31/18 05:08 AM »

Oddly enough, it appears the Low Oil Pressure message is activated by the same signal as drives the gauge. From the 2002 FSM:

"The IPC uses the engine oil sensor signal to determine the engine oil pressure. The oil pressure sensor signal circuit is hard-wired to the IPC. The engine oil pressure sensor signal to the IPC is a variable resistance ranging from 0-90 ohms. The sensor resistance is used to drive the engine oil pressure gage. A sensor resistance of 1 ohms will display as 0 kPa (0 psi) and a resistance of 88 ohms will display as 550 kPi (80 psi). The IPC monitors the oil pressure sensor signal circuit in order to decide when the oil pressure is too low. The Check Engine Oil Pressure indicator will be displayed in the message center if the IPC detects a low engine oil pressure."

Note that 0 psi is indicated by low resistance. That means a connection would have to be short-circuited to cause your problem. Poor connections produce high resistance, which would result in a false high oil pressure reading. In my experience, poor connections and broken wires are far more common than intermittent short circuits, but here's a little experiment you can try: Unplug the connector at the sensor. That should peg the oil pressure gauge. Wiggle wires while someone watches the gauge. If it still shows 0, then the problem is definitely electrical. If you can get a low value resistor (eg: 6.8 ohms) from a local Radio Shack or similar, connect it between the tan/white wire at the sensor connector and ground to simulate a low engine oil pressure.

That's not odd...that's what I was saying.  The message is ultimately driven by the sensor.  Not the position of the gauge.  What I meant by that is there isn't some internal wiper on the servo that based on needle position turns on a light or message.  So we're on the same page.  I maybe wasn't clear enough in the brevity of my message
« Last Edit: 03/31/18 05:12 AM by robertmee »
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #29 on: 03/31/18 09:13 AM »

That's not odd...that's what I was saying.  The message is ultimately driven by the sensor.  Not the position of the gauge.  What I meant by that is there isn't some internal wiper on the servo that based on needle position turns on a light or message.  So we're on the same page.  I maybe wasn't clear enough in the brevity of my message

Yes, I got that, the light is not generated by the physical needle position. But there's a 50% chance that is approximately what is happening -- at least on a 2004 model.

Let me explain: I hooked up my Tech2 to my 2004. I have 3 different oil pressure readings. From the PCM, I get the actual raw data -- a voltage reading (1.67v at idle). From the IPC, I get interpreted values of 244 kpa measured, and 248kpa displayed. In other words, there is a feedback circuit on the needle movement.

So which one triggers the warning display? I personally would pick the PCM signal, but who knows what the GM engineers were thinking sometimes, they might have linked the warning to the feedback circuit.

Now, that's with a 2004, which is all I have here to check. The 2004 uses a 3-wire sensor connected to the PCM. Looking at the schematics I downloaded for the 2002 model, the system shown is somewhat different. Schematics show a single-wire sensor connected directly to the IPC. I don't know if there is a feedback on the 2002 gauge or not.

All that said, I don't know which system he has, because the damn FSM shows both types in the 2002 component locators! Mid-year change? Error in the FSM? Who knows, but the engine component locator shows a 3-wire sensor at the back of the engine (same as my 04):



And the IPC component locator shows a 1 wire sensor under the intake manifold between cylinders 5 and 7:



This is certainly the sensor that matches the 2002 schematic, but I think the OP would have mentioned it if he had to remove the intake manifold to access the sensor! 

So I'm really curious now: acedown13, do you have a 3 wire sensor or a 1 wire sensor, and where is it located?
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robertmee

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Re: Extremely Low oil pressure at startup while idling
« Reply #30 on: 03/31/18 11:42 AM »

Good info...as an Engineer myself I always like the detailed analysis of these systems.  BTW where did you obtain a PDF of the FSM?  I always buy the actual FSMs for my vehicles but the only books I've found for the 2003 AVY is the teal 4 volume set...but it costs $400!!  Haynes and Chilton usually suck in comparison so Im not getting those.  But $400 seems crazy for a FSM.
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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #31 on: 04/01/18 12:52 PM »

It's a 1 wire sensor located in the most awful place behind the engine block, it wasn't as horrible to get to the second time.
So update, i was able to get a reading on the oil pressure with a mechanical gauge i got from amazon, came in 2 days early, thanks amazon!
the readings correlated with my dash gauge unfortunately. 20 psi at start, dropped to 15 for about a min then dropped to 0. When i press the gas it goes up every time.
I also opened my oil filter i pulled the other day, it seemed pretty clean, no metal shavings or anything like that.
Here is the question, my next step, should i attempt my oil pump or the  oil pump pickup screen out of the  the pan? The 02 apparently you can get to the oil pump from the front which seems a lot less evasive than removing the pan which involves removing literally everything  since i have a 4x4. Besides it being the oil pump, screen, or clearance of the bearings, is there anything else it could be? I read some places there is a screen under the pressure sensor which can throw the reading off ,i stuck a pick down there and nothing came out , i also read somewhere they are only in the 04 and up.
it's odd to me that the pressure doesn't seem to be as high after i changed the oil. It stays more at 30-40 after it warms up and idles around 20  instead of 40-60.
« Last Edit: 04/01/18 03:08 PM by acedown13 »
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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #32 on: 04/01/18 03:06 PM »

i'm not sure if this makes a difference but, i completely forgot to add my " change engine oil" light has been coming up lately every time i start the truck
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #33 on: 04/01/18 05:24 PM »

What grade of oil is in there now? What grade was in there before? Thinner oil flows through bearing clearances (etc.) more readily than thick oil, so pressures will typically be lower with thinner oils. Hot oil is thinner than cold oil, so it is not unusual for oil pressure to drop as the engine warms up. True synthetic oils tend to be more temperature stable, and therefore the pressure tends to be more stable as the engine warms up. Finally, oil viscosity tends to change with use, first thinning out, then thickening up. So the change in pressures observed is quite likely related to the oil change.

The "change engine oil" warning system is something that you have to reset every time you change the oil. The system estimates oil life based on the cumulative engine temperatures, loads, hours, etc. If you are really working it (eg: towing a trailer or stop-and-go city traffic) then it will come on after many fewer miles than if you're driving habits consist mainly of cruising gently down the highway. If you didn't reset the system when you changed the oil, then the system thinks you still have the old oil in there.

As for what to do now: That's getting real hard to diagnose over the internet. If there is no bearing noise, then I might try a high quality truly synthetic high-mileage engine oil like Mobile One High Mileage 5w-30 or Amsoil Premium Protection 10W-40, depending on what it was you put in there last week.

The article referenced earlier in this thread is another possibility, especially if you can access the pump and relief valve without dropping the pan (and all the hardware underneath the pan!). Engine oil pumps rarely quit -- they get the best lubrication of all engine parts, after all -- but a leaky o-ring could admit air into the system and air bubbles could account for your "twitching".

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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #34 on: 04/01/18 06:11 PM »

i've only ever put Castrol gtx high mileage 5w 30 in it. I thought maybe if something had of been blocking something i just made it angrier and blocked it up more with the oil decrease since the change.
It's making absolutely no noise from the engine , nothing bad at least , the engine isn't getting above normal operating temp.

I change the oil every 3k miles since i've owned it the past 6 years and it's the second time the change oil light came on. Last time i had to do some weird ungodly turn the truck on for 3 seconds and off like 15 times to get it to shut off.

I've seen a few articles about the 0 rings being bad but then a few about a big chunk of sludge being stuck in the screen too haha, it's going to be a pain whatever it is at this point i'm sure.
« Last Edit: 04/01/18 06:13 PM by acedown13 »
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EXT4ME

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Re: Extremely Low oil pressure at startup while idling
« Reply #35 on: 04/01/18 06:28 PM »

While my post in this spot did contain some good, factual information, I used some terminology that was not exactly correct.

As I reread my post, I realized the point I was making was off track, mainly to me making a poor choice of words.

I still stand by the majority of what I was saying, but I felt it was in the best interest of the group at large that I remove my post in an effort to not add more confusion to an already confusing topic.

The page pointed out in a post below is a very good one and is one I have read many times in the past and I trust.

That series of pages confirms most all of the points I was trying to make, but in other areas of my post, my improper choice of technical wording made other parts of my post appear incorrect.

I apologize if I further confused the issue, but reading the below referred pages should help others understand the topic.

My bad.

Carry on.
« Last Edit: 04/02/18 01:33 AM by EXT4ME »
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #36 on: 04/01/18 07:06 PM »

The multi-grade oils are designed to THICKEN as they heat up to normal operating temperatures.

No, all oils thin as they get warm. Some oils don't thin as much as other oils. I must admit that the language in that quoted article is a mite confusing. I think this article is less confusing (actually, if you have time I recommend reading all the chapters in that series).
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #37 on: 04/01/18 07:14 PM »

Last time i had to do some weird ungodly turn the truck on for 3 seconds and off like 15 times to get it to shut off.

It shouldn't be that bad. Turn the ignition to run (one position before starting engine). Immediately press and release the gas pedal 3 times within 5 seconds. The Change Oil light should flash a few time while the system is resetting, then go out until the system calculates it's time for another change.

How much oil does your engine use between oil changes? I mentioned in an earlier post that doubling the bearing clearance squares the oil flow out of that bearing. In the case of big-end bearings, that can mean as much as 5x increase in consumption as the oil flung from the bearings overwhelms the ability of the oil control rings to scrape it from the cylinder walls.
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enoniam

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Re: Extremely Low oil pressure at startup while idling
« Reply #38 on: 04/01/18 07:33 PM »

Here is the question, my next step, should i attempt my oil pump or the  oil pump pickup screen out of the  the pan? The 02 apparently you can get to the oil pump from the front which seems a lot less evasive than removing the pan which involves removing literally everything  since i have a 4x4.

The problem with replacing the pump is attaching the pickup tube to it.  There's a small bolt that secures the tube to the pump that is quite awkward to get to, particularly if your fingers are not small.  There's also the risk of dropping it into the pan during the attempt to get it started.  If you thought the pressure sensor was bad, well, be prepared for a whole different level of difficulty. 

When I installed an aftermarket adjustable cam timing set requiring the removal of the pump to install a sprocket behind it, the instructions actually included tying fishing line to the bolt so that you could pull it back up out of the pan after dropping it into the pan.  It took me HOURS to get that one little bolt started, and one of my fingers was numb for weeks after due to the pressure I put on it against the hard metal parts trying to get that bolt in the proper starting position.  There's a reason the shop service manual calls for dropping the pan.

I'd suggest if you weren't 100.00% absolutely sure that you put 5w30 oil into the engine, I'd try replacing the oil and filter and see what happens.  That task is immensely easier than what you are contemplating.  You may even consider trying 10w30 oil to see what happens.
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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #39 on: 04/01/18 09:46 PM »

it really doesn't use all that much, just a tick on the dipstick.
I mean i've been known to have to put a quart in it in the past but usually the loss is minimal between changes.

I've seen a few videos about how horrible taking that bottom bolt out is, the fishing wire trick i saw in one of the videos. Your story is making me so excited about trying to tackle this, i'm sure it wont be horrible, maybe. I have this lovely little tool that's been a life saver in small cramped areas for getting bolts loose. I'm not too sure  what it's called, it's a handle with a head that you put the socket on that just bends in any direction but is pretty small so it can get in really hard to get places. It worked wonders when i had to get to my hearter core to replace it.
I'm 1000 percent it was 5w 30 , it's the same stuff i've always gotten and i even went and checked the container afterwards just to double check, I replaced the oil filter as well .
It's fun to think of having to take all this apart and putting it all back together as just a shot in the dark.
Thanks again for all the info and whatnot everyone, i really appreciate all of ya'lls time.
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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #40 on: 04/12/18 08:21 PM »

So today, i pulled the oil pan, what a pain in the ass. Unfortunately the 0 ring seemed to be fine and there were no clogs in the screen. There was no sludge in the bottom of the pan. What else can i check for? Should i go ahead and replace the oil pump for good measures?
Currently at crank it stays around 20 and drops to 0 before it's warmed up, it goes up as soon as a i barely raise the rpms by hitting the gas. Once up to temp it stays around 20 when i'm idling and stays around 40 when i'm driving.
i didn't see any shavings or anything in the oil.
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #41 on: 04/13/18 04:20 AM »

Currently at crank it stays around 20 and drops to 0 before it's warmed up, it goes up as soon as a i barely raise the rpms by hitting the gas. Once up to temp it stays around 20 when i'm idling and stays around 40 when i'm driving.

That description sounds a little different from earlier descriptions of twitching and the mechanical gauge results of dropping to zero after warming up :

Quote
20 psi at start, dropped to 15 for about a min then dropped to 0.


To me, what you are currently describing suggests the pump is losing it's prime. Here is a guess: Possibly the pump makes some pressure at crank because it is still full of oil, but then it sucks in some air and cavitates, losing pressure. Revving the engine raises the suction pressure sufficiently to overcome a leak in the intake and recover prime, so the pump can develop discharge pressure again. As the engine warms, the oil thins; suction pressure is reduced accordingly so the pump is less likely to lose prime. Somewhere in between there could be a period of intermittent operation, causing a gauge to "twitch".

Oil pumps rarely wear out. They are the best lubricated part in the whole engine! I think -- if the above is an accurate hypothesis -- that an o-ring failing to fully seal in the suction path is the most likely culprit. That said, I assume a new pump comes with a new pickup and o-ring? You've already got the old one out, so maybe it's worth it to just replace it with a new one and be done with it. Your call.
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acedown13

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Re: Extremely Low oil pressure at startup while idling
« Reply #42 on: 04/13/18 11:35 AM »

it really doesn't tick as much. I'll crank it, it will hold at 0 for like 2 seconds, jump to 20 then slowly over the course of like 30 seconds dwindle down to 0, if i press the gas it will jump up until i release the gas then go back down. it does this until it's warmed up to where like i said it will stay around 20 at idle and stay at around 35 to 40 while accelerating .
i just think it's odd that this all started happening all of a sudden . Could an O ring be defective in doing it's job even thought it looks brand new?  That's why i figured i'd go ahead and replace the pump as a last ditch effort while i have the pan off to make it easier to get to that bolt at the bottom of the pickup tube. I'd imagine the pickup tube is a pretty basic piece and that if nothing was visually wrong with it i can just reuse it ?
Maybe i could just go ahead and just replace the 0 ring then button up the oil pan and see if that fixes it since i'd have to go in from the top to change the oil pump anyways? 4 dollar 0 ring is better than a 200 dollar oil pump, although i read a few places the oil pump relief could be stuck in the open position. So many decisions to be made.
I was wondering about the bearing clearances being bad, i have no clue how to go about measuring those to see if they are bad or if that's what's wrong.
I'm basically a youtube mechanic, i watch a video online and then do it myself, i'd rather learn how things work anyways than pay someone else to fix my problems.
« Last Edit: 04/13/18 11:42 AM by acedown13 »
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buickwagon

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Re: Extremely Low oil pressure at startup while idling
« Reply #43 on: 04/13/18 12:24 PM »

If the oil pressure relief valve or bearing clearances were at issue, I would expect the oil pressure to drop as the engine warmed up -- thinner oil leaks faster.

As for the o-ring, they can compress and distort over time. And may distort under pressure but relax to a normal shape when the pressure is released.

All that said, I'm not a professional mechanic either, so I could be wrong about any and all of the above.
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RCBearings

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Re: Extremely Low oil pressure at startup while idling
« Reply #44 on: 05/21/18 02:04 PM »

Many years ago I rebuilt a Subaru 1800 engine for a friend.  All went well until the startup.  Pressure was great, idled and ran great until it warmed up and the pressure went to 0.  Lots of headscratching, wrenching, etc ensued.  Finally found out Subaru had sold me the rod bearings for the standard engine but rods and pistons for the BRAT.  Since everything inside the cases was new, I never checked to see if all the part numbers matched up.  Bought everything from Subaru as a kit.  Many apologies later, Subaru admitted their mistake and gave me the right parts.

Seems the viscosity was high enough when cold to generate the right pressure, but clearances were big enough to bleed it off once it warmed up.
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