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the oil light comes on when engine is at idle, coupled with low oil pressure on the gauge. recently changed the oil and filter and crankcase is full enough. engine sounds fine.
could the oil pump be shot?
 

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Is it a faint flickering glow or a solid on condition? Check the idle speed of the truck I have seen trucks idling to slow have low Oil Pressure, Volts, Etc.
 

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it is not a constant condition. the light comes on briefly from time to time at low rpms and when the engine idles.

if it is just a result of low idle, could there be harm in letting it be? the engine never stalls.
 

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Check it with a manual gauge before you replace parts. There are allen head plugs on the side of the engine that are accessible.
 

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You mentioned that you had changed the oil, be sure that you used the correct oil and used a premium filter, not some cheap FoMoCo. If you are sure the oil is 15/40 and has no fuel in it, Buy a new filter, Fleetguard, Baldwin, Or AC Delco, punch a hole in the old one and drain it, cut the top of and inspect it for Bearing material, Brass, or iron with a magnet. do a drain plug swap to cheak it. With a manual gauge test your sensor, take of the valve cover and run it to be sure you are not sucking air, from a pick-up problem. If you have no fuel. no air, good filter and no contaminants in it then you can cheak internal pieces, regulator, oil cooler, or internal damage. Be sure you oil pan level is correct 15 quarts oil to full mark in oil pan 17 ish with filter after running. Play safe!
 

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Discussion Starter #6
yes, i changed the oil just previously to the light and the gauge acting up.
i used rotella 15w-40 oil and a K&N performance filter. is this a good filter?
check the drain plug for what? what am i looking for? there has been no irregular dripping of oil since i changed it, so it is sealed well.
what is a manual gauge? which sensor? where should i look for it? what does it do?
when i remove the valve cover, should it be pretty obvious, the sound it makes when it is sucking air?
how do i determine if there is fuel in the oil?
could this be part of the problem? when i put the clean oil in, i added a bottle of marvel mystery oil, one quart's worth, counting it against the total amount of oil added.
can you recommend a good service and repair manual for an amateur who wants to learn?
oil level is good.
everyone, thank you for your assistance thus far.
 

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the drain plug has a magnetic end, to show you if your oil has any metal filings indicating engine wear:peelout
 

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Check it with a manual gauge before you replace parts. There are allen head plugs on the side of the engine that are accessible.
Exactly, thats what I would do.
 

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Check it with a manual gauge before you replace parts. There are allen head plugs on the side of the engine that are accessible.
:agree2::agree2: never trust the guages, on my blazer the voltage gauge went to about 17 volts, i checked it and it was at 13.something at idle.
 
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Check it with a manual gauge before you replace parts. There are allen head plugs on the side of the engine that are accessible.

Yep Do that first. It could be a flakey sending unit.

What are we working on here anyway?
 

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Discussion Starter #11
thanks again yall. working on it.
i'm trying to find a manual pressure gauge at the local auto parts stores and on the internet and having difficulty. one auto parts store had nothing and another wanted to sell me a kit, though the guy on the phone wasn't sure what i was talking about, for $186.
can anyone recommend a specific manual pressure gauge tool for this engine that i could more easily find one?
 

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For that much I'd just buy a new sender. But here's what I'd do; Got to Burden Sales Surplus Center - Hydraulics, Engines, Electrical and More and order a 60 psi pressure gauge for 3.95. Get some adapters and a 1/4" hydraulic hose and viola! you have your own for about $30.

1/4" gauge (glycerine filled will bounce less) 60psi, 1/4" f to f adapter, 1/4" npt hose, 1/4" to 3/4" bushing. Probably more like $15.

I am assuming the plug is 3/4" npt, it sure looks like it. (npt is nominal, so it will look more like 1 1/8")
 

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diondega, It would be helpful to list what engine you have ? If you have an older 12V like me, then you don't have a problem as your idle is likely just under minimum and needs to be tweaked up. If you have a newer computer controlled CTD, then I can't help.
 

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i have a '93 D250, straight six cylinder cummins turbo. i hope you're right. as it would cost much less to fix. i'm still looking into acquiring or fabricating a manual pressure gauge to test with. looking for a local diesel mechanic in case the oil pump does appear to be failing. seems that the job is a little beyond what i can in the parking lot of my apartment complex. don't know.
can you easily describe how to adjust the idle?
 

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weird becuase mine is doing that too....except as soon as i get driving again its 40 pounds or more... mine is a 1998 12 valve with 125k on it
 

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Oh no! I hope that gauge works! I don't know what kind of threads the 12v has on the sensor!

Well as to the pressure, I would SERIOUSLY not worry about it. The way it works, is there is a gear pump that displaces the oil, and pushes it past a relief valve. At lower rpm, the volume obviously is less, and in this case not enough to build pressure. The oil still will be going where it needs to go, and leaking out past all the rod/main/cam journals. The pressure of the oil does NOT support the force of the operating parts. This is a very common misconception. It is the actual chemical properties of oil (surface tension) that support the load. As long as the clearances are OK, and there is oil in there, it will do it's thing. That's why some engines (granted cheesy or old) got by without an oil pump at all.

Oil pumps are not really a wear item. In normal service they last forever. What usually causes low oil pressure other than a low idle, is not a worn oil pump, but thrashed rod bearings. If that was going on, you would know it. I would also note that though it can play hell with your patience to get the oil pan off some of these rigs, you can platigauge and/or replace the rod bearings without pulling the engine. Just in case it ran without oil or something.

By the way, most mechanical diesels had a little tappet to adjust the idle right on the lever that the cable attaches to at the injection pump. Rotate it and it should be clear where the stop is. If you have a Haynes service manual there's a picture on 4b-33 in the 94 to 01 manual. Couldn't find it in the 74 to 93 manual.
 

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i have a '93 D250, straight six cylinder cummins turbo. i hope you're right. as it would cost much less to fix. i'm still looking into acquiring or fabricating a manual pressure gauge to test with. looking for a local diesel mechanic in case the oil pump does appear to be failing. seems that the job is a little beyond what i can in the parking lot of my apartment complex. don't know.
can you easily describe how to adjust the idle?
I used to stall in idle, heavy traffic, high heat. Our idle is a mechanical adjustment. Idle depends on tranny, engine hot, ac on. I think mine is 780 rpm in drive with brake applied, manual tranny was a bit more. When the oil light came on, I was thinking I was in big trouble, I bought a manual gauge and tied into the oil filter as there was an NPT fitting there, oil pressure was about 75 psi at idle on the aftermarket gauge, shoot well past 150 psi with some go pedal applied. The dash oil gauge is controlled by the computer, so think about it why would it hover aroud 40 psi and jump to 0 psi ? Just check your rpm, or turn the screw slightly, only at about 1/8 turn each time, it does not take much. I think you will be OK as I have never heard of the simple CTD oil pump going bad.
 
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