Sudden dip in oil pressure at idle

[yodaddy4200]

This happened at work today


I just got back from the store and had the truck idling AC on full blast. Im sitting there and i feel the truck idle down so i look down at the cluster in time to see the oil pressure gauge dip down to about 20. Then the CHECK GAUGES light comes on.

I turn the truck off immediately and then restart and it acted totally normal the ride home???

So i called the stealership right away and they said something about possibly the "oil pressure sensor/regulater" i cant remember the exact term he used. he also said it could be the gauge itself but i dont think so because i felt the truck "idle down" didnt get a chance to notice the RPM's while this was happening?

I hope this inst really bad... Im at 69,000 miles if that helps... Thanks guys!!

 

[freddyboy61]

Time for a throttle body cleaning. When the idle goes below 600 RPM or so, the oil pressure switch kicks out and the gauge will go down. This doesn't necessarily mean you are losing oil pressure, it just means the switch is on the verge of changing state (it is only a on/off switch, not an actual pressure sensor). If you have the dealer clean the throttle body, have them check the oil pressure with a mechanical gauge just to be sure.

 

[The_Roadie]

If you're any kind of DIY mechanic, you can clean the throttle body for $5 and the instructions you can find here on the site. Dealers are such goofballs sometimes, since you're talking usually to commission-paid service WRITER, not the mechanics who are supposed to know better. We've read about dealers who have sold unsuspecting owners entire throttle bodies when all they needed was cleaning after a battery swap.

 

[yodaddy4200]

If you're any kind of DIY mechanic, you can clean the throttle body for $5 and the instructions you can find here on the site. Dealers are such goofballs sometimes, since you're talking usually to commission-paid service WRITER, not the mechanics who are supposed to know better. We've read about dealers who have sold unsuspecting owners entire throttle bodies when all they needed was cleaning after a battery swap.

Ok sounds like ill be cleaning the throttle body this week!! Thanks for the replies guys.

 

[yodaddy4200]

Freddyboy and Roadie, thanks guys she was nasty...


View attachment 29323

View attachment 29324

Bling* Bling*

 

[CaptainXL]

To be fair to those that have already cleaned their throttle body. I would like to know how many people have cleaned their throttle body and still get an occasional near stall with the AC on?

The oil pressure gauge is not the actual oil pressure. It is a fabricated signal sent by the PCM. The 4.2 I6 just has an oil pressure switch which is just an on/off signal.

Something tells me there is more too this than just cleaning the throttle because the exact thing happens to me and my throttle is so clean you could eat off it.

 

[yodaddy4200]

My idle was kind of rough i noticed to. That has cleared. Ill keep you posted if it happens again!

 

[yodaddy4200]

To be fair to those that have already cleaned their throttle body. I would like to know how many people have cleaned their throttle body and still get an occasional near stall with the AC on?

The oil pressure gauge is not the actual oil pressure. It is a fabricated signal sent by the PCM. The 4.2 I6 just has an oil pressure switch which is just an on/off signal.

Something tells me there is more too this than just cleaning the throttle because the exact thing happens to me and my throttle is so clean you could eat off it.

Happened again today??? This time i was at a light... There must be another issue.

 

[yodaddy4200]

anything guys? i dont wanna get raped at the stealership!!

 

[djthumper]

When was the last oil change? Have you looked at the oil since this started to happen? What is the condition of the oil?

 

[triz]

Clean your MAF.

Check your airbox and make sure everything is plugged.

A new fuel filter wouldn't be a bad idea.

At that many miles I doubt you would need plugs but I would pull and check them. A bottle of Amsoil PI Performance Improver or send the injectors out to Witchhunter performance for a thorough cleaning.

AMSOIL P.i. Performance Improver Gasoline Additive

 

[djthumper]

Clean your MAF.

Check your airbox and make sure everything is plugged.

A new fuel filter wouldn't be a bad idea.

At that many miles I doubt you would need plugs but I would pull and check them. A bottle of Amsoil PI Performance Improver or send the injectors out to Witchhunter performance for a thorough cleaning.

AMSOIL P.i. Performance Improver Gasoline Additive

He doesn't have a MAF he has a MAP. They switch to the MAF in 06.

 

[CaptainXL]

anything guys? i dont wanna get raped at the stealership!!

The dealership won't do anything unless the problem pops up while doing a test drive or other diagnostic. The most useful thing they can do is put a logger on the truck and have you come back after it does it's thing.

If you have it diagnosed have them check to see if the computer has the latest calibration on it. There were a few updates on the TIS2web to solve poor idle/stall issues around that timeframe. http://tis2web.service.gm.com/tis2web Let me see if I can pull some up.

 

[yodaddy4200]

Thanks for the replies guys. ill take some of these options into consideration!! Im going camping for a week so first thing when i get back ill get into finding the solution.

My oil looks good. Looked at it today. Thanks

 

[Playsinsnow]

On super hot days when driving mostly in city during rush hour, very rare, and only in the summer will my ride do the same thing. The tach will drop to maybe 400 at the very lowest, usually 5-550, when the ac is CRANKED. I have always attributed it to the alternator (a no BS older gal service writer said she has seen alternators go on the tb's) or some aspect of charging because it happens when there is a decent deceleration drop to a stop and occurs very rarely and recovers instantly. Hasn't really happened yet this year and I do not believe I had any gauges light up ever. My .02


Silly question but have you ran a check on your alternator while activating everything (radio, ac, fan, lights, brakes) while keeping a reader on it?

 

[KNBlazer]

To be fair to those that have already cleaned their throttle body. I would like to know how many people have cleaned their throttle body and still get an occasional near stall with the AC on?

The oil pressure gauge is not the actual oil pressure. It is a fabricated signal sent by the PCM. The 4.2 I6 just has an oil pressure switch which is just an on/off signal.

Something tells me there is more too this than just cleaning the throttle because the exact thing happens to me and my throttle is so clean you could eat off it.

you remember to disconnect the battery?

 

[CaptainXL]

you remember to disconnect the battery?

Disconnecting the battery has nothing to do with it for the most part. The problem is an intermittent issue.

I have disconnected the battery many times over the last couple years troubleshooting and upgrading the vehicle. It's just something I like to do for fun as a proof of concept being an engineering tech.

 

[triz]

On super hot days when driving mostly in city during rush hour, very rare, and only in the summer will my ride do the same thing. The tach will drop to maybe 400 at the very lowest, usually 5-550, when the ac is CRANKED. I have always attributed it to the alternator (a no BS older gal service writer said she has seen alternators go on the tb's) or some aspect of charging because it happens when there is a decent deceleration drop to a stop and occurs very rarely and recovers instantly. Hasn't really happened yet this year and I do not believe I had any gauges light up ever. My .02


Silly question but have you ran a check on your alternator while activating everything (radio, ac, fan, lights, brakes) while keeping a reader on it?

I've actually had this happen. Even to the point where it feels the truck wants to shut off. As you say it usually recovers quickly. It has not done it in a while.

 

[yodaddy4200]

So she stalled twice today on the way home. Both times sitting at a light. First time AC on 4. Second time AC on 2??? NO lights or codes.

Ive tried searching about the MAP. Pardon me but i dont even know what it is or does. I need to try and fix this tomorrow because thats when ill have the time.

Im gonna hop on google and see what pops up!!

 

[triz]

Its on the air intake.

 

[yodaddy4200]

So after it stalled those two last times it never did it again.

 

[RayGumm]

So after it stalled those two last times it never did it again.

Did you 'relearn' the PCM after you cleaned the throttle body? This is crucial to avoid running rough/rough idle after a cleaning. The PCM actually needs to relearn how a clean throttle body acts after it's clean. You have to pull a couple fuses under the hood for about half an hour to clear the learned info in the PCM and reset it to factory defaults (clean throttle body). May03lt has a video on youtube showing you which fuses to pull. Search trailblazer throttle body cleaning.

If yours stopped acting funny after a while, the PCM probably just relearned the clean throttle body on its own.