No oil pressure at idle

LawnRanger

Original poster
Member
Jul 26, 2012
7
Hello. I have a 2002 trailblazer LS with the I6 4.2 engine ( 128k miles). I just drove for about an hour and as I was on my way home I was stopped/idle at a traffic light near my house I noticed that the oil pressure gauge dropped all the way to the left indicating no pressure ( the check gauges light came on too) . Light turned green, I hit the gas and it shot back up to its normal position ( around 12 o'clock). I couldn't really find anything here about this issue, so I was hoping someone might now what I am dealing with here? Maybe a bad oil pressure switch?

Also, I let the car sit for about 40 minutes while I tried researching this and I just went and started it up, and the pressure gauge is reading in its normal idle position now. Any help would be appreciated :biggrin:

On a side note-I was planning on changing the oil on Monday, so the current oil has quite a few miles on it. I use Mobil 1 synthetic
 

McGMT

Member
Jun 17, 2012
621
The oil pressure switch is probably leakin around the threads or gone bad, *The oil pressure guage is a GUESS and not the real oil pressure which is around 12-15 PSI at idle.... The PCM guesses what the oil pressure is and flat out lies to you through the gauge so people don't get scared by the low low pressure this engine runs at.
 

LawnRanger

Original poster
Member
Jul 26, 2012
7
Wooluf1952 said:
:tiphat: Welcome:tiphat:

In case you haven't heard:
http://gmtnation.com/f5/welcome-gmtnation-com-heres-story-226/

Did you have the AC on?
Have you ever cleaned the throttle body?
What was the tach reading when the oil pressure read "0"?


The AC wasn't on- It doesn't work. I just replaced the condenser and getting it evacuated and charged on Mon/Tues.
I cleaned the throttle body about 6 months ago. I may do that again when I do the oil on Monday.
I didn't look at the tach as this was happening, but it didn't appear to be running too low - it didn't seem like it was going to stall or anything.

I appreciate the quick responses guys :thumbsup:
 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON
I'm also voting for a bad oil pressure switch. I just wish we could hook up a real gauge.:frown:
 

McGMT

Member
Jun 17, 2012
621
Mooseman said:
I'm also voting for a bad oil pressure switch. I just wish we could hook up a real gauge.:frown:

I (eventually) am going to hook up a real guage. Nothing super accurate, just a nice cheap oil psi guage. Leaning toward a sensor type so I do not have a pressurized oil line running anywhere just asking to leak.
 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON

LawnRanger

Original poster
Member
Jul 26, 2012
7
Ok, so I am changing the oil and the oil pressure switch. I pulled the wire off of the old pressure switch and oil was dripping out of it. I don't think that should be happening, so I wonder if that was the culprit. I don't know if there is a special socket or anything to get the switch out, but there isn't much room to maneuver in there. I will post back shortly , hopefully with some good news.

Also, the pressure hasn't dropped at all today, but I have only driven it about 10 miles this morning.
 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON
OK, just so you really understand, the oil pressure gauge is FAKE. The only time it is true is when it is ZERO. The PCM gives these fake readings just to make you feel good. It changes with RPM, no matter the temperature, viscosity or anything except when it is ZERO psi. It is just an on/off switch. When it is off (ZERO psi), the PCM will show zero on the gauge and give the warning message.

Yes, the switch is defective.
 

McGMT

Member
Jun 17, 2012
621
LawnRanger said:
Ok, so I am changing the oil and the oil pressure switch. I pulled the wire off of the old pressure switch and oil was dripping out of it. I don't think that should be happening, so I wonder if that was the culprit. I don't know if there is a special socket or anything to get the switch out, but there isn't much room to maneuver in there. I will post back shortly , hopefully with some good news.

Also, the pressure hasn't dropped at all today, but I have only driven it about 10 miles this morning.

I think that is switch number four I have seen leak out like that. So, from now on first diag of oil pressure dropping off is gonna be a bad switch... HEY! This can be MY "check the ground" or "Clean your TB" YAY! hahahaha
 

LawnRanger

Original poster
Member
Jul 26, 2012
7
Mooseman said:
OK, just so you really understand, the oil pressure gauge is FAKE.


I completely understand that . I was just a little concerned because I have owned this vehicle for 7 years and this is the first time that this has ever happened. Fake or not, I do not like seeing my gauges lighting up telling me that there is a problem :undecided:

I got the switch replaced and everything seems to be back to normal, although I have only driven for about a 20 minutes stretch down to my brother's house and back after watching the Jets game.
 

McGMT

Member
Jun 17, 2012
621
LawnRanger said:
I completely understand that . I was just a little concerned because I have owned this vehicle for 7 years and this is the first time that this has ever happened. Fake or not, I do not like seeing my gauges lighting up telling me that there is a problem :undecided:

I got the switch replaced and everything seems to be back to normal, although I have only driven for about a 20 minutes stretch down to my brother's house and back after watching the Jets game.

Its gonna be fine now, the seal inside them seems to wear over time from the in and out everytime you start and shut it down then they leak internally but very slow since the oil has to work its way through the switch. Once the seal goes there pressure goes past the switch instead of pushing on it...

Your all good now, enjoy your ride...
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
McGMT said:
... HEY! This can be MY "check the ground" or "Clean your TB" YAY! hahahaha
It's good to have a mission. :raspberry:
 

joee

Member
Sep 3, 2012
7
My wife was driving the TB one day and came home saying the oil pressure gauge went to zero when she stopped at a red light. But, it went back to normal went she took off and started driving. It happened only one time while she was driving during that day. The next day, I was driving the TB and noticed the oil pressure gauge started going to zero every time I stopped. The Check Gauges light would also come on while the gauge was at zero. The gauge would go back to normal when I took off and started driving. As long as the RPM's would stay high (forgot at exactly which RPM the gauge would go to zero), the oil pressure gauge would show normal.

When I got home, I inspected the oil pressure switch (located above the oil filter) and saw it was leaking oil. I replaced the switch with a new one and the problem was solved.

I've attached a picture of the leaking switch.
 

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atron-ward

Member
Aug 20, 2013
8
I have an 08 I6 and had the problem, come to light and as soon as engien dropes below 700 rpm oil pressure drops . I have chk eng light on and its for the purge vent selinoid. It turned out to be a good size vacume leak. I disconnect the battery and did the followingI replaced purge vent with new one,I cleaned the throttel body witch i clean every 6 months, I replaced the oil pressure sending unit. Reconnect the batt and start. Its been two days no problem..
part two. check this out, before I restarted the truck i disconnected the oil pressure swith, on top of oil filter housing with batt disconnected. reconnect batt then start the truck with no oil pressure sendind unit. engien running now and there the neddle moves like the gauge is hooked up. the gauge is a complete lie. THE ONLY THING THAT IS TRUE 0 OIL PRESSURE WHEN ENGIEN IS OFF. I called GM and they said it could be the inst cluster tripping I told him "He's full of s**t".
My conclusion is this system is completly comp controled so and vacume leak of any size, any build up on throttle plate,any thing that can idle speed will trip this system to do werird things. iam putting a mechanical gauge in tommorow.
This hole thing pissed me off at chevy
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
atron-ward said:
...the gauge is a complete lie. ...
Welcome. This is a well-known design choice by GM. The V8 spent the dollar to put in a real sensor. The PCM even tries to convince the driver it isn't a lie by slightly moving the needle as the engine RPM changes.

There are other stupid things. I've posted a list of a dozen of them in the past. Doesn't mean other vehicles aren't worse. Most of us still think it's a great platform overall. Or else we wouldn't have them and talk about them so much. :wink:
 

atron-ward

Member
Aug 20, 2013
8
the roadie said:
Welcome. This is a well-known design choice by GM. The V8 spent the dollar to put in a real sensor. The PCM even tries to convince the driver it isn't a lie by slightly moving the needle as the engine RPM changes.

There are other stupid things. I've posted a list of a dozen of them in the past. Doesn't mean other vehicles aren't worse. Most of us still think it's a great platform overall. Or else we wouldn't have them and talk about them so much. :wink:

I like this platform and when its time for new motor I am rebuild the one I have
 

jstrut

Member
Jul 31, 2013
87
My Oil Pressure Gauge HAs Been Acting Up Lately. In The Morning It Works Like Normal But After Work And Only When Its Over About 80° The Gauge Stays At 0 But No Warning Lights Come On And No Difference In The Way The Engine Runs Just StAys At 0. InThe Morning Back To Normal. Any Ideas?
 

The_Roadie

Lifetime VIP Donor
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Nov 19, 2011
9,957
Portland, OR
jstrut said:
My Oil Pressure Gauge HAs Been Acting Up Lately. In The Morning It Works Like Normal But After Work And Only When Its Over About 80° The Gauge Stays At 0 But No Warning Lights Come On And No Difference In The Way The Engine Runs Just StAys At 0. InThe Morning Back To Normal. Any Ideas?
Welcome, but without a filled-in vehicle profile, we can't guess if you have the I6 or V8. How many miles do you have, and what's your oil change history?

I assume you checked the level and it's OK?

May be a pump getting old, or (if the I6) a flaky pressure switch.
 

jstrut

Member
Jul 31, 2013
87
the roadie said:
Welcome, but without a filled-in vehicle profile, we can't guess if you have the I6 or V8. How many miles do you have, and what's your oil change history?

I assume you checked the level and it's OK?

May be a pump getting old, or (if the I6) a flaky pressure switch.

Yes Sorry About That. I Do Have The I6 And Will Be Checking The Pressure Switch Today. YeS The Oil Level Is Good And I'm About 1000 Out From My Next Oil Change. It Just Seemed A Little Different Than The Pressure Switch Issue And Was Wondering If There Was Another Common Issue With The Oil Pressure Gauge.
 

atron-ward

Member
Aug 20, 2013
8
jstrut said:
Yes Sorry About That. I Do Have The I6 And Will Be Checking The Pressure Switch Today. YeS The Oil Level Is Good And I'm About 1000 Out From My Next Oil Change. It Just Seemed A Little Different Than The Pressure Switch Issue And Was Wondering If There Was Another Common Issue With The Oil Pressure Gauge.

So As I said I installed a mechanical gauge and it was at 50 psi. Well sorry its 50 only when motor not warmed completely. I have new pressure switch and cleaned the throttle. So it runs great. The oil pressure does drop to glove to 10 to 12 at idle. Its so low I am looking for a finer gauge dial send pics. Chevy says the pump test is 12 psi at 1200 rpm nothing for lower rmp stats. I run 5w30 synthetic oil and Chang it 7000 miles
 

Kathy Hidden

Member
Apr 24, 2017
5
New York
Hi all, I know this is an old thread, but I have the same issue in my 2002 trailblazer, not only that but if it idles without keeping the RPMs above 1000 it will start to knock after a few minutes, not terribly loud, but noticable..
Any ideas?
Thank you in advance..
 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON
The noise is definitely not a good sign. You would need to hook up a real oil pressure gauge to get some readings. Could be an issue with the pump, the pressure relief valve, plugged pickup screen or a bad o-ring at the pickup tube or the pump outlet. Either way, getting to the pump is a tough job:

Basically the same as this minus the chain and tensioner:
How to replace I6 timing chain and tensioner
 
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Kathy Hidden

Member
Apr 24, 2017
5
New York
The noise is definitely not a good sign. You would need to hook up a real oil pressure gauge to get some readings. Could be an issue with the pump, the pressure relief valve, plugged pickup screen or a bad o-ring at the pickup tube or the pump outlet. Either way, getting to the pump is a tough job:

Basically the same as this minus the chain and tensioner:
How to replace I6 timing chain and tensioner
 

mrrsm

Lifetime VIP Donor
Supporting Donor
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Oct 22, 2015
7,721
Tampa Bay Area
Old Chinese Proverb:

"If you are trying to climb out of a hole that you have been digging... The first thing to do to make progress... is to put down the shovel..."

Avoid running this engine until you are prepared to investigate the problem. Right now... those two symptoms are very bad signs and indicators of any or all of the following causes that only the Bravest and Most Skilled Mechanics will attempt to repair... but not before first placing an Analog Oil Pressure Gauge into the Oil Galley Port near the Oil Filter and measure the ACTUAL oil pressure at idle :

(1) The 2002 inaugural Trailblazer with the GM 4.2L LL8 Engine suffered from rare catastrophic engine failure when the Oil Pump Pick Up Tube "0" Rings failed and the suction vacuum needed to draw oil upwards and into the Gerotor Pump becomes impossible. The second generation of Gerotor Oil Pumps and Oil Pick Up Tubes remedies this problem.

(2) Failure to keep the engine serviced to the point of having the Pump Pick Up Tube glaze over with thick,black carbon Muck and Mung thereby blocking the suction of whatever oil is available in the Crankcase causes catastrophic Engine Failure from low or no Oil Pressure.

(3) If the Head Gasket failed or the Water Jacket cracks and anti-freeze/coolant enters into the crankcase and mixes with Motor Oil .. the result will be a massive engine failure when the Brown Pudding mix fails to sustain the proper lubricity and the engine bearings seize and the piston rings seize inside the cylinder bores. The result is catastrophic engine failure.
 
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Tiggerr

Member
Jun 6, 2013
1,324
Perrysburg, OH
Hi all, I know this is an old thread, but I have the same issue in my 2002 trailblazer, not only that but if it idles without keeping the RPMs above 1000 it will start to knock after a few minutes, not terribly loud, but noticable..
Any ideas?
Thank you in advance..

If you have a low end knock at normal idle that's a very bad sign... I don't think replacing the oil pump is going to cure it.
The damage has been done.
Only a matter of time...
Not the news you want I'm sure but there it is....
If it was me I'd be looking for a used low mileage motor, or a remanufactured long block...

:twocents:
 
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Kathy Hidden

Member
Apr 24, 2017
5
New York
Thanks all for the replies,I gotta say, I have two trailblazers, this one is the ltz and it's wonderful to drive,I just love it!..
I was getting poo14 code too, they narrowed it down to needing a timing chain and guides.. oye..
Long story short I tossed in some additive to the oil, and a gas additive.. Service light is off now and it passed inspection..
The knock I hear isn't very loud when I'm idling,I'm sure it will get worse sadly over time, but I've been driving it all over the place the past year this way and it hasn't gotten worse,I guess I'll milk this ride for as long as possible..
Such a beautiful truck..
OH the head gasket hasn't blown.. So that's good!
 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON
I doubt very much the P0014 is caused by the timing chain but rather the CPAS that could need a cleaning or replacement. Quite possible that the additive you put in the oil cleaned it up as well as the oil pump pickup. I'd recommend cleaning the CPAS manually and running an oil flush to try and clear the possible gunk in the pickup.
 
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zephyr429

Member
Mar 7, 2013
29
Hello. I have a 2002 trailblazer LS with the I6 4.2 engine ( 128k miles). I just drove for about an hour and as I was on my way home I was stopped/idle at a traffic light near my house I noticed that the oil pressure gauge dropped all the way to the left indicating no pressure ( the check gauges light came on too) . Light turned green, I hit the gas and it shot back up to its normal position ( around 12 o'clock). I couldn't really find anything here about this issue, so I was hoping someone might now what I am dealing with here? Maybe a bad oil pressure switch?

Also, I let the car sit for about 40 minutes while I tried researching this and I just went and started it up, and the pressure gauge is reading in its normal idle position now. Any help would be appreciated :biggrin:

On a side note-I was planning on changing the oil on Monday, so the current oil has quite a few miles on it. I use Mobil 1 synthetic

My 2003 TB LT 4x4 was doing this a while back. I tried changing the oil, changing the sending unit, even changing the oil pressure stepper motor. No luck. Turns out the cause of mine was the oil filter. I had switched from ACDelco to Fram for a few oil changes and realized this is when it started. As a last ditch effort I switched back to ACDelco, and haven’t had the issue since. It’s been over a year.
 

mrrsm

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Oct 22, 2015
7,721
Tampa Bay Area
Its great to see people following up over time... and what you mentioned is Good News, FWIW… These two Videos from @MAY03LT will provide the means to see definitive proof of what the ACTUAL DYNAMIC Oil Pressure is inside the GM 4.2L Engine using an Analog Oil Pressure Gauge (in the Second Video). These are for Adults Only...So Play these when the “Tender Ears” of your Kids are not around:

These Videos will put an end to the Question of "What is the REAL Oil Pressure inside of the GM LL8 Engine?" and qualify the integrity of the Oil Pump and whether or not it is pressurizing properly… For All Time:


 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON
And it also serves as hard proof that Fram oil filters are complete junk. Something to remember when others come asking with the same issue.
 
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