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Discussion Starter #1
Just wanted to get some opinions before I order the part. I've been reading some of the threads and it sounds like this could be the stepper motor in the insturment cluster. :undecided

This just started today while driving home. When I come to a stop (at Idle) my oil pressure guage drops to zero then goes up again when I start driving. It will also drop at idle in neutral and go up when I accelerate in Neutral. The 'Check Guages' idiot light comes on when the needle drops and goes off when the the oil guage goes back up. None of the other guages are acting funky.

I am not having any difficulties with it bogging down, Idling rough, stalling or accelerating. I cleaned the throttle body 3-4 weeks ago very well and it did not appear that dirty to begin with. Last week I changed the serpentine belt and the battery. The new battery voltage checked out to be normal.

Any opinions would be appreciated
 

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2004 gmc
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I think you have honestly low oil pressure, or a flaky pressure switch.

With those observations I'm certain it's NOT the gauge stepper motor.

It might be the oil pressure switch, but the risk is that you are running under 12 PSI at idle and a good switch is telling you the truth, that you have a real problem. Get the pressure checked at a shop and then decide what to do.
 

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2003 isuzu ascender
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:iagree: Sometimes the gauge AND the idiot light DO their jobs and tell ya something is amiss. Get it checked for faulty sensor or LOW pressure and PEACE OF MIND:yes:
 

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Discussion Starter #4
Wow, sometimes "When it rains, it poors." I had just gone out to check out the oil pressure gauge again and went around the block a couple of times. Everything was working fine. No problems with the oil pressure gauge or any of the gauges for that mater.

So, I was just about home. Doing the speed limit on a 35mph street when a Buck jumped right out in front of me. I had just enough time to start to apply the brakes when he hit me, bounced off my hood and scampered away. The buck seem to have been unharmed.

I wish I could say that for my Trailblazer :hopeless

If you look closely you can still see his hair in my front crossbar.
 

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Discussion Starter #5
OK, I'm back on track. I ordered a new headlamp and front grill from rockauto $120.00 total (includes shipping).

Now back to the problem at hand.

I decided to do what I can can before I take it in to get it evaluated by a shop. So, I changed the oil filter (Just in case it is clogging). I also replaced the spark plugs (they old ones had about 50,000 miles on them). I really wanted to take a look at them since I had a shop replace them last time.

Good thing too, I found that #1 was bent and cracked. When they installed it they must not have taken the time to remove the plastic that impedes access to the retaining nut on the coil cover. Unfortunately, A small amount of the ceramic from the plug got into the hole - I could see it with a flashlight and have no way to remove. From the amount missing on the plug, there is probably more in there that I cannot see.

#5 was fowled with oil although there wasnt any in the seat. All the rest of them looked ok - just normal wear. I labled all of them and bagged them up.

After the plug change I started it up and it ran rough for about 1 minute and then settled down. I took it for a drive and have had no problems. It does seem to accelerate a little better than before. My oil gage is not acting the way it did yesterday.

My concern is that if I take it to a shop and it is not dropping pressure like it did yesterday they are not going to be able to pinpoint a problem and just give me some options for what it might be. I don't want to get into a big guessing game with them replacing random parts.

Until the situation replicates itself I'm going to let it be. If it starts up again I will get a compression gage and check the pressure at the sending unit and the compression at the plugs.

Thanks for everyones input. :)
 

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2002 gmc envoy_slt
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It's the oil pressure switch. I had the exact same problem and my cousin (manager at Firestone) looked into it and found that the switch/gauge had oil around it. Once it was replaced no more problem.
 

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Discussion Starter #7
The problem with my oil pressure guage just started again after a month. Same problem - it even started up in the same place it started last time. On my way home from work at a stop light close to my house.

Thanks for all the advise. I'll be off work for the next 4 days so I'm going to try to find a replacement for the pressure switch here locally and see if that fixes the problem.

I noticed in another post that someone had a problem with a vacuum leak on the manifold that caused this same problem so I will be checking that out as well.
 

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Discussion Starter #8
I thought I would provide an update on this issue. I bought a $35 oil pressure sending unit from auto zone Thursday and just replaced it yesterday.

The one I removed did not 'look' that bad but I have no experience with this part previously. As others have mentioned it seems possible that the hole in the unit had become 'clogged'.

This part was not difficult to remove once I had the right tools. I needed to buy a 27mm deep socket and my 3/4" drive was too long to fit in the space (the part is directly above the oil filter). I could only move my ratchet about 8 degrees either way. It took me a few minutes - got lucky that the old one came out without much difficulty.

I will report back to let people know if the oil pressure guage problem returns.
 

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Did it work?

My 2002 Trailblazer oil pressure is dropping intermittently on idle. This problem started yesterday. Did changing the oil pressure switch/sensor fix the problem for you?

Thanks
 

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Drops to Zero

On idle or stop sign, the oil pressure drops to zero. When I press the gas, it goes back to normal, after a few seconds drops to zero again. Engine sounds fine no fluctuations in idle. This started happening after I cleaned the Throttle body. I cleaned the throttle body before with out this problem. I did add STP Oil Treatment. I'm wondering if the thick treatment caused a problem, but I doubt it. You guys think it's the sensor or oil sending unit?
 

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Discussion Starter #12
My 2002 Trailblazer oil pressure is dropping intermittently on idle. This problem started yesterday. Did changing the oil pressure switch/sensor fix the problem for you?
Well, no. I thought that is was fixed and went through 4 days of my regular drive to work without the problem repeating.

Today I was pulling up into a gas station and it started again. It only happens at Idle and it only happens after I have been driving the vehicle for 20 plus miles. After I shut it down and restart it the problem goes away for awhile - sometimes days at a time. Last time it was almost a month (2 weeks of which I was not driving it).

So, It's back to square 1. Next thing I'm going to look for is a vacuum leak. I remember reading a post here where someone with a similar problem found a vacuum leak on the manifold that caused this same problem.

If that's not it, I might have to take it in. As I mentioned before I'm very reluctant to take it to my mechanic when it is not dropping pressure. I have serious doubts that they could find anything wrong. I don't want to get into situations where they are making guesses and wanting to replace parts that will not necessarily fix the problem. Lord knows, I'm ok doing that on my own and it doesn't cost half as much.
 

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Discussion Starter #13
This started happening after I cleaned the Throttle body.
You know maybe this is just an odd coincidence but I cleaned my throttle body a couple of months ago as well. Hmmm...... Maybe I should take it out again and give it another cleaning.
 

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Solution: Oil Pressure Sending Unit

Hi Everyone,

I found changing the "Oil Pressure Sending Unit" right above the Oil Filter fixed my problem of oil pressure dropping to zero on idle. The Sending Unit cost $35 from AutoZone. I also used an engine flush, changed the oil and filter to make the installation easier and eliminate any sludge build-up.

I've been driving and idling at stop signs without the pressure going to zero. Looks good so far.

Thanks
 

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2004 gmc envoy_slt_xl
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Did either one of these work? I am having the same problem, pressure dropping at idle, except there is a noise coming from under the hood, or possibly under the passenger side dash. Closest thing I can think of to describe the sound is sticking something in the blades of a fan. Not sure if these are related, or 2 completely different problems. Any help would be great. My wife drives this, and don't want this going out on her w/ the 2 kids in the back seat.
 

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Considering that this thread is almost three years old and a lot of these people are gone I would suggest you start a new thread. But I would start with replacing the sending unit and got from there.
 

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I had the same issue on my truck and based on what I read here I changed the oil pressure sending unit. That did nothing to resolve the problem. It seems that everyone that reports this issue indicates that it happens under the same conditions - engine has been running for 10-15 minutes and it occurs when you come to a stop (like at a traffic light). For me, my idle will dip slightly to 400 when oil gauge drops to zero. I press the gas to raise idle to 600-700 and oil pressure goes back up. I take my foot off the gas and gauge will drop to zero again. Temperature gauge doesn't budge so engine isn't heating up due to loss of oil pressure. Needle doesn't stay on zero for longer than a second or two. Start driving again and issue goes away, sometimes for months, sometimes it will occur again in a couple of weeks. It is nerve racking to think your engine is losing oil pressure but I don't think that is the case. I think it is more of a faulty circuit or sensor (but not the oil pressure sensor). It might be sludge in the oil though I always changed my oil on a regular basis. If it happens again to you I suggest you just press the gas to get the idle slightly higher (don't jam it), just a little bit to get the gauge up again.

Over the two years that I have had this issue I have noticed a lot of people writing on this website having the same problem. If anyone has found a cure then they haven't posted it. Keep this thread alive and post your findings as that may help others.
 

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Oil pressure gage fix!!!!

What oil weight are you using? The manufacture recommended 5w30 in my 02 trailblazer. I was having the same problems oil pressure gage bouncing around and dropping to zero but not dieing at stop signs and lights but didn't stall and going back to normal when driving. After lots of research I found a GM mechanics blog that recommended using a heavier weight oil because after time and wear on the engine the gaps get larger inside and the 5w30 is just to thin to hold proper pressure. I had just gotten a oil change so I just drained about a qt and added that thick Lucas stuff for you engine. Worked like a charm!!! Did it 2 months ago instant fix and no problem since. From now on I plan on getting a heavier weight when my oil gets changed. S before you go out and try some expensive fixes maybe try this small but large $13.00 fix. Hope this helps someone. I would love to hear if it helps!:D
 

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Last time I changed the oil I used 10W30. I intended on getting 5W30 but when I got in the store I saw both options and didn't remember which one I was supposed to get. The heavier weight didn't help with the oil pressure issue. How long ago did you add the Lucas? My oil gauge issue only happened periododically so it could happen one day and then not again for three months. I hope you found a solution but it will need to hold up to the test of time.
 

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Last time I changed the oil I used 10W30. I intended on getting 5W30 but when I got in the store I saw both options and didn't remember which one I was supposed to get. The heavier weight didn't help with the oil pressure issue. How long ago did you add the Lucas? My oil gage issue only happened periodically so it could happen one day and then not again for three months. I hope you found a solution but it will need to hold up to the test of time.
Well it has been about 3 months since i did this and it is still doing great. I don't think going up to 10w30 would be enough maybe 10w40 or you could just try what i did drain 1 qt and replace with the Lucas either way i don't think you will be going wrong. A oil change never hurts and the Lucas extends the life of the oil and your engine. My gage was also doing it intimately but honestly has not done it once since. I really hope this helps I know how much it sucks when you just cant figure out a problem.
 
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