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Discussion Starter #1
Since I seldom drive the truck, I don't get to be real familiar with it. It is my wife's. So this time when I drove it to find out what she was complaining about - bucking/missing under hard acceleration, I noticed that the oil pressure is high. It stays at 60 psi anytime the rpm is over 1000, and at idle it is 50.
I remember that it has usually been a little above 40 when driving, about 35 at idle.

She say's " I told you that it was high right after the last time you changed the oil, don't you listen"?

Ha, well nothing different was done on this oil change.

Does this thing have some kind of crank case vent that could clog and cause a high reading?
 

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Sounds like the OPS (Oil Pressure Switch) may be failing, I base this on your bucking/missing under load. The OPS supplies power to the fuel lift pump that resides on the driver's side frame rail. If the OPS fails, the pump won't be supplying fuel to the fuel injection pump. Fortunatly, the IP can pull fuel from the tank by itself to run, but not well. The OPS is also a combo unit, in that it is also your oil pressure sender unit.

Personally, the Oil pressure you're describing is what I PREFER on a 6.5 or 6.2.

But, sounds like you need to change the OPS, it's located on the rear of the engine on the driver's side, slightly behind the head. You'll need a OPS socket that's available at most auto parts stores (there is a generic one that fits many different models that works on ours).
 

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Discussion Starter #3
I changed the Ops last November for a similar problem, except the truck would die after the first start in the morning. I t has worked fine since then.

The Ops seems to be working now because the lift pump is getting power when the truck is running.
Anyway, I don't think the oil pressure gage gets it's signal from the same place as the Ops you are talking about does it?
 

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The Ops seems to be working now because the lift pump is getting power when the truck is running.
Anyway, I don't think the oil pressure gage gets it's signal from the same place as the Ops you are talking about does it?
Yes it does.
 

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Discussion Starter #5
Yes it does.
If that is the case, how would high oil pressure cause the lift pump not to run?
Also, in November, when I did have a faulty OPS, the indicated oil pressure was always normal.

I have never heard of anyone with a faulty OPS say they had low or no pressure indicated on the oil pressure gage in the cab, have you?
 

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Could it possibly be a faulty oil filter that is causing high pressure? Maybe since started at last oil change.
 

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If that is the case, how would high oil pressure cause the lift pump not to run?
Also, in November, when I did have a faulty OPS, the indicated oil pressure was always normal.

I have never heard of anyone with a faulty OPS say they had low or no pressure indicated on the oil pressure gage in the cab, have you?
I didn't say that. Your oil pressure reading, being high, has nothing to do with whether the ops is powering the lift pump or not.
 

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A plugged oil filter could result in higher readings on the oil gauge. This is because if the filter is plugged, the oil is forced through a more restrictive circuit through the bypass valve that is in the block (under the filter adapter on 4x4's).

The bucking problem needs more attention though...

Since the lift pump is working, thats a sign that the OPS is probably fine, but you could change it after doing other things.

To narrow out the filter possibility, you know what to do..

I'm still standing by my statement that 60psi oil pressure with engine load hot isn't a bad thing. The normal though (at least in my rigs) was ~35 at HOT idle and then immediatly shooting to 55-60 psi on acceleration. The 55-60 reading was consistant throughout driving down the highway.
 

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A plugged oil filter could result in higher readings on the oil gauge. This is because if the filter is plugged, the oil is forced through a more restrictive circuit through the bypass valve that is in the block (under the filter adapter on 4x4's).
Perhaps you can help me understand why this would be. Isn't the sensor downstream of the filter in the 6.5?
 

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Discussion Starter #10
I didn't say that. Your oil pressure reading, being high, has nothing to do with whether the ops is powering the lift pump or not.
Well then how does that work?
Are there two different sensors in that one OPS, one for the lift pump and one for the gage?
Cause when my OPS went out last year, and caused the lift pump to not run, it was still showing normal pressure on the gage.
 

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Cause when my OPS went out last year, and caused the lift pump to not run, it was still showing normal pressure on the gage.
I must not be saying it right. That's what I meant. Oil pressure gauge can be reading fine but you could still be getting an intermittent signal from the ops to the lift pump. Have you run a fuel pressure gauge while driving to see if it stays above zero? Just a thought.
 

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Discussion Starter #12
Changed the Filer

Changed the Oil and the filter today, and the oil pressure is back to normal.
NOthing in the filter to restrict flow but I looked and did not see the little relief button down in there I thought I had always seen before. Maybe I am imagining it but I thought there was a relief spring in the bottom.

I have always used AC DELCO filters. Need to get a new one and look down in there to see.

Now I wonder if this caused my OPS to fail prematurely.
Yes, I changed it today too and no more bucking jor missing under acceleration loads.
 

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Changed the Oil and the filter today, and the oil pressure is back to normal.
NOthing in the filter to restrict flow but I looked and did not see the little relief button down in there I thought I had always seen before. Maybe I am imagining it but I thought there was a relief spring in the bottom.

I have always used AC DELCO filters. Need to get a new one and look down in there to see.

Now I wonder if this caused my OPS to fail prematurely.
Yes, I changed it today too and no more bucking jor missing under acceleration loads.
Do a couple of searches on the site, the OPS cant handle the load of the Lift pump so it fails rather quickly, you can route the ops thru a relay so that the ops wont quit so quickly... I've seen here on the site how to
 

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Discussion Starter #14
Do a couple of searches on the site, the OPS cant handle the load of the Lift pump so it fails rather quickly, you can route the ops thru a relay so that the ops wont quit so quickly... I've seen here on the site how to
So why did the first one last 10 years?
 

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LUCKY I guess, I power my lift without the OPS carrying the load myself, many different ways to do that most can be found here by searching.
 

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So why did the first one last 10 years?
You could be lucky, ...
Is the lift pump 10yrs old too, I would imagine as the pump wears out the electrical load increases, thus shortening the life of the OPS
again just a guess..
 
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