Oil pressure issues

[NDGuy]

Vehicle: 1995 GMC Yukon, 5.7L TBI, all stock



Since I bought my Yukon a while ago, it's had a very slight miss at idle that would happen on and off. Never fixed it because I'm still getting 17-19 mpg on the highway and 10-14 in town.

A few weeks ago my heat shield (or so I thought) started to rattle while sitting at idle, never really gave it much thought. Today I was at a drive through and the miss was a little more noticeable but when I looked at the instrument cluster I noticed my oil pressure going between 20-40 (back and forth) at idle, mainly stayed around 20-30 lbs. The rattle I thought was the heat shield would change in pitch with the fluctuation of the oil pressure (louder when oil pressure dropped). This was with the transmission in drive and my foot on the break. Start up when cold my oil pressure is around 60, when under power (and the engine is warmed up) it stays at 40 or higher. The oil pressure does not fluctuate at idle if the transmission is in Park.


Any ideas?

Vehicle does not use or leak any oil, checked intake gaskets and crap right after I bought it.

 

[BattelWagun]

Sounds like you could have a spun bearing. When the bearing spins and blocks the oil port the pressure shoots up, then when it spins back into place again the pressure drops. That rattling could be your cam (if it's the cam bearings that are bad). This would cause a misfire too as the camshaft would most likely have play, and be grinding down the distributor gear, causing the timing to jump around before the computer can compensate for it.

Or t could be a bad heat shield and a simple misfire

Any other symptoms?

 

[NDGuy]

Sounds like you could have a spun bearing. When the bearing spins and blocks the oil port the pressure shoots up, then when it spins back into place again the pressure drops. That rattling could be your cam (if it's the cam bearings that are bad). This would cause a misfire too as the camshaft would most likely have play, and be grinding down the distributor gear, causing the timing to jump around before the computer can compensate for it.

Or t could be a bad heat shield and a simple misfire

Any other symptoms?

Checked the heat shield and some other bolt-on things, all were tight. Not really any other symptoms but I've been wondering lately if it's losing power. I know these things aren't power houses but I can't even get the tires to squeak if I gun it from a dead stop on concrete (only time I gun it is pulling on the highway if I have to). It just doesn't seem to really have any power.

 

[BattelWagun]

Depends on the gearing. These things don't have tons of power, but they have enough. Rated at 255 horse, and a 300 and some change worth of torque. My truck has more than enough power to be pulling 1000 pounds off the back and still maintain 90-95(very easily) on the highway. My brother's '03 F150 could barely do 75 with the same load a few weeks later. If you're looking to do burnouts with this thing, you're looking in the wrong place. GM made these trucks to be stout but not so powerful that it goes through transmissions, rear ends, and transfer cases like candy.

 

[SunlitComet]

Unless you put on a Whipple supercharger on it.

 

[NDGuy]

Depends on the gearing. These things don't have tons of power, but they have enough. Rated at 255 horse, and a 300 and some change worth of torque. My truck has more than enough power to be pulling 1000 pounds off the back and still maintain 90-95(very easily) on the highway. My brother's '03 F150 could barely do 75 with the same load a few weeks later. If you're looking to do burnouts with this thing, you're looking in the wrong place. GM made these trucks to be stout but not so powerful that it goes through transmissions, rear ends, and transfer cases like candy.

Don't worry, not trying to do burn outs. I'm going to check out some other things, if for some reason it does end up being a bad cam or rod bearing (although there's no knocking or ticking), it just gives me an excuse for a new engine.

 

[retorq]

Since I bought my Yukon a while ago, it's had a very slight miss at idle that would happen on and off. Never fixed it because I'm still getting 17-19 mpg on the highway and 10-14 in town.

Can't say I understand this logic ... These aren't power houses from the factory but if you know what you are doing they will put out some power.

---------- Post added at 06:13 AM ---------- Previous post was at 06:07 AM ----------

Also I doubt it's a cam bearing, if the PSI is fluctuating with the tap it's more then likely a rod. The few spun cam bearings I've seen the block was unusable. I had a 98 Vortec that has a spun cam bearing, it ended up cracking from the main to the cam journal.

To check for a bad rod bearing pull one plug wire, listen for the tap to go away. Replace and move to the next wire, continue till you find it ...

 

[BattelWagun]

[/COLOR]Also I doubt it's a cam bearing, if the PSI is fluctuating with the tap it's more then likely a rod. The few spun cam bearings I've seen the block was unusable. I had a 98 Vortec that has a spun cam bearing, it ended up cracking from the main to the cam journal.

To check for a bad rod bearing pull one plug wire, listen for the tap to go away. Replace and move to the next wire, continue till you find it ...

I would recommend this test as well. I'm not saying for sure it was a cam bearing though, you're right, usually when they go it doesn't last too long. However, I've had about 1/4" of lateral movement in my cam for about 2k miles now with no issues. The mechanic that worked on it when it ate up my dizzy gear said it was ready to die, clearly he has not become one with the vortec.

All that being said, pull the plugs and see what that does and then let us know what happens.

 

[SunlitComet]

To check for a bad rod bearing pull one plug wire, listen for the tap to go away. Replace and move to the next wire, continue till you find it ...

x2

 

[gpracer1]

Depends on the gearing. These things don't have tons of power, but they have enough. Rated at 255 horse, and a 300 and some change worth of torque. My truck has more than enough power to be pulling 1000 pounds off the back and still maintain 90-95(very easily) on the highway. My brother's '03 F150 could barely do 75 with the same load a few weeks later. If you're looking to do burnouts with this thing, you're looking in the wrong place. GM made these trucks to be stout but not so powerful that it goes through transmissions, rear ends, and transfer cases like candy.

He wishes he had 255 hp. Since it's a TBI engine he is lucky to have 200.
I wouldn't worry about the oil pressure fluctuating at idle as long as it is over 10-15. It could be your miss is causing the idle to fluctuate just enough to change the oil pressure swing slightly.