Do I have oil pressure?

[DannyBtruckn]

Hi I have a 2005 M1087ai with the C7 Acert engine. My low oil pressure light is on and the gauge reads zero. Oil level on the long dipstick is reading nominal. Truck only has 800 miles on it so I’m betting it’s still got the original oil and filters from the factory.

I need to move the truck asap and am wondering if I have oil pressure. I only need to run it for 20 minutes or so to move it.

I have what seems like a small oil and tran fluid test port by remote switches for battery and ignition located behind the passenger tire. When I press the spring loaded port valve, while engine is running, I get a nice stream of oil out of it. My question is, is this oil pressure getting to the whole engine or will I damage the engine if I run it.

Thanks.


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[williamh]

You’re going to need to install a mechanical oil pressure gauge. No other way to tell. The sensors for the gauge could just be bad causing the low pressure issue. Normally if there’s no pressure , lots of noise from the top end than a thrown rod/ seized turbo

 

[DannyBtruckn]

Thanks. Follow up to this, is this the oil pressure sending unit? Located on driver side.



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[hike]

That looks right.

Here is a link to the Technical Manual (TM) here (which is actually for the AO) on the site for trouble shooting the oil pressure gauge https://www.steelsoldiers.com/upload/M1078/m1078_TM 9-2320-365-20-1.pdf Page 482 is where it starts for the gauge

 

[DannyBtruckn]

Thanks for sharing the manual, however it seems to be only for 2.5ton trucks. My sending unit is the three wire variety.

That was indeed the oil pressure sending unit. I’m going to go get the manual oil pressure gauge kit from harbor freight with all the different sizes.







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[hike]

Thanks for sharing the manual, however it seems to be only for 2.5ton trucks. My sending unit is the three wire variety.

That was indeed the oil pressure sending unit. I’m going to go get the manual oil pressure gauge kit from harbor freight with all the different sizes.


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My dyslexia, I read M1078. Using the TM tab above, then Present Conflict Vehicles leads you to pages for your M1087. Glad you found a solution past my misdirection—

 

[GeneralDisorder]

That's the correct sending unit. It's typically just the connector has a poor connection these use a Deutsch DT 3-pin connector and pins. You will find that both the oil pressure and the boost pressure sensor use the same connector and both are problematic - you don't want to plumb up some harbor freight garbage to your truck - fix it the right way with a new wiring harness connector. Otherwise you're going to get a code for the boost pressure sensor and go into limp mode - also that low oil pressure light isn't going to go away and it's setting a code on the ECM that's causing a check engine light and a flashing stop engine warning..... none of that is going to be fixed by chinese crap and you might introduce a nasty leak when the nylon tubing fails and sprays oil all over. Please don't do something hopelessly stupid like that.

 

[Ronmar]

Yea it would have destroyed itself with any running with no oil pressure. You can connect a mechanical gauge to the output port on that oil sample valve to confirm that you have decent oil pressure when you open the valve. If thats OK, move it as needed, then fix it with the correct sensor as General suggests…

 

[DannyBtruckn]

I’m just trying to verify pressure with a mechanical guage for now. Problem is I can’t find the correct fitting from the kit at harbor freight or at Lowe’s. The sending unit does thread nicely onto a 1/4 female flare gas fitting but all my local Lowe’s had was a cap and I’m sure it’s not going to seat correctly. I was just hoping I could use Teflon tape long enough to get a mechanical reading. Anyone know what thread this is?

But back to my original question, I think I may just drive the truck if I get a strong spray of oil out of where the sending unit mounts. I did get a stream of what seems like 50 psi out of the test port behind the passenger wheel.

I had this truck stored at a mechanic shop for a year and he said he started it for 15 minutes every few weeks. Turbo would be destroyed if it had zero oil pressure, right?




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[GeneralDisorder]

It's an O-Ring Boss port. -6 or -8 ORB would be my guess. They use straight threads and the o-ring does the sealing. Plug it back in with some WD-40 or Deoxit and wiggle the connection while the truck is running - it will probably show up on the gauge at least momentarily. If it doesn't - swap the sensor with the Boost pressure sensor (they are the same) and see if that gives you a reading.

 

[Ronmar]

Thats why it is probably easier to test pressure at the oil sample valve. It has a small AN/JIC fitting, but you could just slip a hose over it and clamp it in place with a hose clamp to get a pressure sample… it is also far easier to access than the oil pressure sensor…

with no/low oil pressure the turbo would be the last thing to fail as it is not really working untill you put it under load. All the bearings would be wiped, and it may not even run right, or at all, without system feed pressure to the HEUI pump…

 

[GeneralDisorder]

Thats why it is probably easier to test pressure at the oil sample valve. It has a small AN/JIC fitting, but you could just slip a hose over it and clamp it in place with a hose clamp to get a pressure sample… it is also far easier to access than the oil pressure sensor…

with no/low oil pressure the turbo would be the last thing to fail as it is not really working untill you put it under load. All the bearings would be wiped, and it may not even run right, or at all, without system feed pressure to the HEUI pump…

Yeah - a C7 engine wouldn't run without oil pressure. The HEUI injection wouldn't function.