I need some help here. Tonight I was driving on the interstate, been cruising along for about an hour when I look down and see the oil pressure light on. It was only on for a couple seconds, but it caught my attention. So, I started watching the factory oil pressure gauge - not good.

A little bit of throttle would cause the factory oil pressure gauge to drop. It never fell out of the "normal" range on the gauge, but it was at the bottom of it during heavy throttle. I also pulled off onto a back road, to do some further investigation. From a dead stop, I could floor it to 70 and the oil pressure would not drop. Strange. Only after a minute or so of driving at around 70 MPH would the oil pressure drop with throttle input. When I was out of the throttle, the pressure would read like there was no problem.

I know the pressure is taken from the HPOP resivoir, and that's probably why it only happens with throttle, and after a bit of highway driving has drained the resivoir. I also topped off the oil just a few days ago, so it shouldn't be from low oil level.

So, any advice here? Possibly a bad pressure sensor, or do you think it's actually the oil pump going out? I looked at the repair manual on replacing the oil pump, and it doesn't look to be the easiest job. Radiator out & crank pulley off? That's no fun.

I've parked the truck for the time being. If it really is the oil pump, I don't want to risk damage from low oil pressure. I'm wanted to get some input from you guys before I go buying new parts tomorrow.

 

JT, I'm probably not going to be much help but it is wise to park it until you resolve it. Like I posted the other day, I don't believe the stock/factory gauges are direct wired to the sender. Rather, they recieve input from the PCM which interprets data and tells the gauge to go normal, or oops, and too late. In this case the PCM may have reacted quickly enough with the idiot light.

We will now await the really smart folks.

 

man that sucks jeremy. probably that big oil setup taking too much oil, and starving the engine.. lol, sorry.

but seriously, my only guess would be to hook up some sort of actual mechanical oil pressure gauge and tie it to your mirror, so it is outside the cab yet you can see it while driving. hopefully it is only an electrical gremlin that makes the needle move up and down but youre not losing oil pressure.

 

you deffinatley want to put a mechanical gauge in there to check it out.... because the factor guage is hooded up to the sender which might be bad... and the sender isnt really sensitve to presure it will read the same no matter what... all the sender does is makes a ground and turns the light off and the needle will read normal... some of you might not belive me but try it for youself ... 1) start the truck 2) unhook the wire from the sender 3) ground it out with a test lead or a wire 4) read the guage and it will read just like you goin down the road (and its not even hoooked up to the sender) so i would definatly not trust that guage because it could be a loose conection or a bad sender and it might jiggle loose from the torque when accelerating from time to time

 

Just was wondering, when was the last time you changed your oil? Filter? Could your oil filter be clogged?

 

How much pressure should these trucks be running, if I get a mechanical gauge hooked up to check it out?

Edit: filters were changed 3000 miles ago, with about 3 fresh quarts added to make up for what was lost in the filter change. Oil is about double that, at 6000 miles, and due for a change. Just sent an analysis off to Blackstone to see how it looks. Could the oil be worn out enough to cause this?

 

oil is oil. as long as there is no air in it, it should build pressure and maintain pressure be it new or 6000 miles old. im thinking you have an electrical problem.

 

Didn't you have fresh oil put in when ya got the big oil installed? Well, maybe you log more miles than I do since I do have this company car and all.

I too am curious about the factory oil pressure. Certainly want to tap into it on the low pressure side of the HPOP, but what is it supposed to be?

Edit: I'm with Kris, but still want to know what the pressure # should be. We shouldn't have to wait too long. I believe many have a seperate oil gauge.

 

Tenn, I've been through two oil changes since Big Oil was installed. I put quite a few miles on the truck during the summer months.

Kris, I'm hoping it's electrical too. But, if it is, why is it directly related to how much throttle I give it? The amount of drop in the needle's gauge is affected by how far the pedal is pushed. If I'm just cruising at light throttle, it would not drop at all. A small amout of throttle to accelerate and the needle would only drop a little and then bounce around a bit. Heavy acceleration and the needle would drop hard. That's what makes me think it's the oil pump. But as stated, I thought the gauge on the dash was either all or nothing sort of affair.

 

JT I thought you had mechanical gauges installed? It could be a problem with your HPOP but to be really sure I'd put a gauge on it. I changed out my LPOP at the same time as my waterpump.(Kwik's advice there) I used a Milodon unit from ITP. 69 bucks. If you do have to change it out remember to also change the (I cant remember the proper name right now) the piece the seal rides on mounted on the vibration damper. I had to buy mine from IH. Now that my morning coffee has kicked in, with a LPOP problem ie low oil pressure, wouldnt the hpop be starving for oil and resulting in a crappy running engine? I'm just remembering back to Kennedyfords problems. Good luck

Duncan

 

i didnt see where you said that in the original post. yes, my educated guess would be the oil pump, or you have a leak somewhere internal from oil to oil passages, and as more engine RPM is fed to this leak spot, more pressure is squirted. what kind of oil presure regulator do these have? on the detroits at school, there is a valve with a spring on the pan rail that oil pressure compresses the spring and when it gets to a certain pressure it leaks off the excess oil pressure.

 

I remember reading that the hpop was last on the oil circuit-lpop. Do you think that your hpop set up has a problem?

 

JT with AE if you watch ICP pressure and IPR Duty Cycle and you see a drop in ICP and no change in IPR duty cycle it is an indication of low volume which could point you to a georotor problem on the LPOP

 

There's a port on the oil filter housing ( that you probably used for your bypass filter ) that I would use to check the oil pressure. I would also check the pressure at the HPOP housing as well.

 

oil pressure at 3300 rpm should be 40-70 psi. thats all mitchell on-demand tells me. i would guess that below 20 at idle you could have an issue. hopefully someone with a real gauge hooked up can tell us. if i get a chance i will hook a guage up to my truck at lunch and tell you what i got.