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Discussion Starter #1
For the last 10 months Ive been chasinig a "Low oil pressure" message on the DIC. This happens 1-2 times a month and usally its when I come to a quick/short stop. The dealer has test drove the truck with a "real" pressure gauge and has replaced the sender unit. I've used synth oil and dino oil, it doesnt seem to make a difference.

Has anyone experienced this issue? Why only have a quick/short stop?

thx
 

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I had the same problem last year. Mostly in the colder weather.

My dealer replaced the sending unit and it returned and then he replaced it a second time and it still came on one more time after the second unit but has stopped since.

It's been about a year now with no problem but I never actually found out what the problem was either.

Could the dealer reproduce your problem ?
Mine couldn't since there was no pattern to it.

Sorry but that's all I got.

Just make sure you don't have any Real oil problems like a bad oil pump or a loose or cracked pickup tube in the pan that could suck some air in when the oil sloshes to the front of the pan when you stop.

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I have done a lot of research on the lub system, and I have come to the conclusion:

The oil pump relief is occasionally getting stuck, in the open position. A very bad thing if it statys that way for any period of time

If you are seeing what I saw, it is very reduced pressure, and then it just disappears. I could typically rid it, by giving the truck a quick WOT run. In my theory, the pressure relief is being forced free when doing this.
 

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Is your dash gage reading low also?
 

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Discussion Starter #5
Yes, the dash gauge reads low, while the DIC is chimming. Again, only while @ idle and almost always after a quick/short stop. Also sometimes I notice the oil gauge floats between 10-30 lbs while @ idle, dont know if thats normal.
 

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same as I have seen. around 30 psi idle pressure, unless malfunction then around 10, dic chiming, at a stop. Nail it and I can shake her loose.

I did nothing for it, but it only happened a handful of times last summer.

Electric anomoly? Maybe
 

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Discussion Starter #7
Diesel Dragon, the dealer could not reproduce the problem, but I would give them a A+ for effort. They tried for 2 days to find/reproduce the problem. After the second shop visit, the sender unit as replaced, but it didnt fix the problem. I think the low pressure chime happens more often as the weather gets warmer.
 

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sounds like a stuck pressure relief as KB says. crack the throttle once or twice this should jar it loose. if it is persistent try having the dealer keep it overnight ( and leave outside not in garage) so he can start with cold oil as this is about the only time the motor will produce enough pressure to open the valve so that it can stick. >20psi is normal on warm engine on a cold morning <40f you should see 75-90psi cold on realy cold morning it will hit 90 on idle (this is when its up against the relief)
 

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If the dealer will work with you and can't reproduce the problem ask him if you can borrow his Event recorder, it basically plugs into the test port under the dash, there's a recorder box with a hand held start button. When your oil pressure drops you push the button and the recorder records everything on the ECM for a few seconds before you pushed the button and for some more time after you pushed the button. Then the dealer can download it onto his computer and see what's going on.

Even if he can't get much info as to why it happened at least you can prove to him that it Did happen and he may look into it more for you.

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Discussion Starter #10
Well the dealer just called and said GM is aware of this low oil pressure problem and that I'm not the only one reporting this issue. GM engineers think the problem is some where in the dash, but not sure exactly what it might be. As of today, there is no fix or TSB for the issue. I was told not to worry, this issue has been documented 3 times and will be fixed as soon as a fix is available, even if its outside the warranty period.


Anyone ever heard of a problem that couldn't be fixed?
 

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sounds like a stuck pressure relief as KB says. crack the throttle once or twice this should jar it loose. if it is persistent try having the dealer keep it overnight ( and leave outside not in garage) so he can start with cold oil as this is about the only time the motor will produce enough pressure to open the valve so that it can stick. >20psi is normal on warm engine on a cold morning <40f you should see 75-90psi cold on realy cold morning it will hit 90 on idle (this is when its up against the relief)
Just how do you guys think the relief valve is getting stuck? Please help me to understand how this can happen.

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usually sticks in a badly machined cylinder ( excessively rough machined finish with a lose fitting plunger) i have had this happen on high pressure hydraulic systems don't see any reason why it would be isolated to 1800psi systems especially when the spring pressure on a oil pump relief is a lot less.
 

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I guess, its just the reliefs in our engines are not finely machined in the first place to where a little imperfection in the cylinder could snag it.

Its a little different trying to control 1800psi than 30 or 60psi especially in the tolerance of the parts. Tight tolerances = clearance issues.

There is no telling if either of us is right, but my vote is I doubt it.

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I guess, its just the reliefs in our engines are not finely machined in the first place to where a little imperfection in the cylinder could snag it.

Its a little different trying to control 1800psi than 30 or 60psi especially in the tolerance of the parts. Tight tolerances = clearance issues.

There is no telling if either of us is right, but my vote is I doubt it.

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i would think that the possibility of the dic and the gage reading bad would be related to a bad sender or an actual low pressure reading. i had a ford with a bad pressure gage that didn't light the idiot light so that one was easy to fugue out.

gm trys to engineer redundancy into these systems for the ability to diagnosis these problems.

but after re-thinking the problem and as i haven't had a chance to see how the cluster is wired and what circuits operate the dic and the gage it is hard to rule out an electrical problem. and seeing as how the cluster probably runs on class II data like the rest of the truck both the gage and the dic probably read the same bits from the computer. so it is likely to be computer error.
 

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Discussion Starter #15
Well the dealer/GM think its a computer/gauge problem, but I dont. Why would this only happen when its warm outside? Why would this only happen when coming to a stop? This issue happen 8-12 times last summer, disapeared during the winter and came back on the frist 70 degree day this year.

Perhaps the DIC can see the outside temp on the mirror.):h
 

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Well the dealer/GM think its a computer/gauge problem, but I dont. Why would this only happen when its warm outside? Why would this only happen when coming to a stop? This issue happen 8-12 times last summer, disapeared during the winter and came back on the frist 70 degree day this year.

Perhaps the DIC can see the outside temp on the mirror.):h
Electronics are affected by temperature and humidity, especially when there is a bad connection. Warmer weather makes wiring easier to move than cold. Coming to a stop makes the wire or connection move....who knows.

If it were a sticking relief, which I highly doubt, it would be more likely to happen in the cold not the hotter days, which is the reverse of what you say happens.

Hopefully your dealer can actually track it down and then we will know. With all the instrument cluster issues these trucks seem to have though.......I would be looking there first.

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if you had a mechanical gage temporarily mounted (under hood so as not to screw up your interior) the next time it happens you could check the gage just to give your self some peace of mind and your dealer some direction (although they sound as if they already have a direction they would like to explore)
 

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Discussion Starter #19
I think I just got some serious insight to what the problem might be. A friend of a friend, who retired from GM told me that my "pressure regulator valve" is sticking.

He said this will happen more often when the oil gets thin. This explans why using syn makes the problem worst and why it only happens when it gets warmer outside. He also said the the pressure regulator is made of steel and aluminum. The two metal parts heat up and cool down and different speeds. When this happens the regulator can bind/stick.

Killerbee, is the oil pump relief that you meantioned earlier the same as the pressure regulator valve? Does anyone know of any problems or TSB on this part?

thx
 

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Killerbee, is the oil pump relief that you meantioned earlier the same as the pressure regulator valve? Does anyone know of any problems or TSB on this part?

thx
Yes

No

The weather has nothing to do with it, though the temperature of the oil does. In warmer weather the oil is also hotter, resulting in lower pressures yet, in the event of a stuck relief. I believe I have witnessed it happen a number of times over the winter also. Difference is, no dic warning. My feeling is that pressure is staying just over the chime threshold.

First hot day with the malfunction, and it will chime again

The relief is triggered on EVERY cold start, summer or winter. There is no reason to think it can't happen at any time. Synthetic runs a lower pressure, so the dic would be more prevalent, but the problem could exist at other times, though the dic sure makes us take notice if it gets low enough, about 9-10 psi IIRC.
 
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