How to get to/replace oil pressure switch on 6.5 TD?

[Ms54Coupe]

Hello guys, I have been reading and reading and reading on the possible reasons for my diesel no start issue. I am wondering who has replaced their oil pressure switch and how they did it. Forgive me if there is a write up on this already, I did a quick search but did not see one.

Thanks,

Nate

[Robyn]

Normally the Oil Pressure Switch will not cause a NO start, BUUUUUUUUUUT its possible.

The oil pressure switch is located in the rear of the engine bay, on top of the engine to the drivers side (US RIGS) of center of the block.

The switch is mounted on a little brass fitting and sticks up on an angle from slightly behind the LH head.

To get to it, remove the plastic "TURBO POWER" cover if its still on the engine. Unhook the battery grounds.

Now you can unbolt and remove the glow plug controller to gain some room back there. (mounts to LH upper rear of the LH head.

The switch is about 2-1/2 inches long and about 1 inch in diameter with a weather pack connector on the end.

You should use the special socket to do the R&R so you dont damage the new one.

Now, lets make sure that your filter is in good order and the lift pump is working.

The 94 has the lift pump relay and fuse over in the junction box (Plastic cover right above the AC on the wirewall, right near the large silver accumulator)

Remove the little cover and in there you will find a small plastic fuse holder with two wires leading to it. The fuse is inside, release the clip and slide the fuse assembly out.

Now you can touch the little bare area of the fuses face to the 12V stud in the junction block, this should activate the lift pump.

Try this, if the pump comes to life and WHIIIIIIIIIIIIIIIRS your set.

Make sure the lift pump is actually doing something too.

Open the fuel filter drain valve at the front top of the engine and with the drain hose in a suitable container, run the lift pump.

You should get a nice stream of fuel from the hose, if not, the lift pump is bad.

If that fuse is blown, either the pump is bad or there are other issues in the wiring.

When changine the filter, once the filter is replaced, open the bleed screw at the top of the filter and run the lift pump to purge the air from the filter.

You dont need to open the valve very far. With a hose on the bleeder you can "USUALLY" get most of the fuel/air into a can and save the mess.

A rag stuffed in and around the filter is a good idea too as these normally do make a mess during the filter change.

The Oil pressure switch sends power to the lift pump once the engine starts and has oil pressure. During cranking the lift pump should get power from the cranking circuit.


Once this stuff is attended to, then you can better judge whats going on.

If you still do not get a start, try loosening the front LH side injector line and crank the engine. You should get fuel from the line as the engine is cranked.

If no fuel then the issue can be either the PMD has failed or possibly the fuel shutoff solenoid (top of IP with wires on it, little round device)

If there is fuel and no start then the issue is likely a glow plug problem or there is not any power to the plugs.


If its a glow plug issue, after a bit of cranking, you should smell diesel fuel at the tail pipe.


Let us know how it goes.


Missy

[Ms54Coupe]

Wow awesome thanks!!!! I did not realize that glow plugs could cause a no start if the engine was getting fuel...I figured they just assisted during colder weather...I am just starting with diesel after a lifetime of gas so far...lot to learn

Thanks so much to everyone and hopefully I'll have good news to report soon.

Nate

[JohnC]

Some engines will start without glow plugs, but a cold 6.5 isn't one of them. Even in warm weather you need them.

At some point the location of the oil pressure switch was moved to the intake valley. Not sure exactly when and I've never worked on one....

[6.5 Detroit Diesel]

Wow awesome thanks!!!! I did not realize that glow plugs could cause a no start if the engine was getting fuel...I figured they just assisted during colder weather...I am just starting with diesel after a lifetime of gas so far...lot to learn

Thanks so much to everyone and hopefully I'll have good news to report soon.

Nate

yea, maybe give the glowplugs a check. check that they are getting power, or that they are even getting hot.

drivers side is pretty easy to get out.