I have a 6.6L 400 (remanufactured long block) with just around 2200 miles.

This morning while merging into traffic I noticed my oil pressure dropping when accelerating. It only dropped to about 1/3 normal and stayed there at highway speed (3300 4th @ about 65mph). As soon as I pulled up to a stop light I noticed it drop as usual but from the 1/3 to the 0 mark now.

I read through other threads and find that it could be the sending unit or the dash unit. To bypass that I bought a numbered mechanical oil PSI unit and installed it, from the pressure port to the new dash unit.

The pressure again reads 0 but only jumps up to about 15 PSI when revved up to around 3000 RPM. Before it used to sit at the high mark at high RPM's and drop to 1/3 at an idle.

There are no oil leaks, the lifters dont chatter at all even at idle with the pressure reading 0. There is no chatter during acceleration or engine braking.

The oil pump might be the old one but I cant remeber, does this seem like an oil pump issue or worse? I do have the off road oil pan from Miloden and bought the pick-up but cant remember if I bought the high flow oil pump but I am pretty sure I did. If this is the case...... worst case scenario??????????? Thanks for the help.

 

There is a plug in the block on the driver's side in the front. If you remove this plug and install an oil pressure gauge, you can determine if it is the pump/pickup not pumping oil or something internal causing a loss in pressure.

You should have good pressure at that point. If not it is a probably a pump/pickup problem.

 

I will try that danlee. I also checked my old order slips and the oil pump is an old one from a donor engine. a 6.6L 400 w/ 78,000 or so miles.

To also rule out I tried changing the oil filter in case anyone is going to try and suggest it. It bumped my PSI up to 18-20 when revved instead of 15 PSI.

If it comes down to it will it be easier to lift the motor & tranny or unbolt the motor and pull it for the oil pump change? I think it would be easier to just hoist the motor up and slip the pan off, unbolt the old pump, clean for install etc. If its easier the other way let me know.

 

You can change the pump without lifting the motor in your truck ( just changed the rear seal in mine). You may have to remove the front sway bar to get the pan all the way out, but you can change the pump by dropping the pan and rotating it to one side enough to get to the oil pump. Good luck!

 

Was reading this thread, mine is also not putting out oil pressure. If there is oil pressure at the port by the oil filter, where would be the likely culprit internally to cause full loss of oil pressure to the engine?

 

I think thats what hes saying that if its not good here its..........

 

If the oil pressure is good at the front of the motor and a lot less at the back, then it is probably in the main bearings where the pressure is being lost, although it could be lifters, but then you will have valve noise.

 

Just pulled the oil pan, and discovered a mangled push rod in it....arrgh.

 

mangled oil pump shaft, or push rod from the lifters?

 

Push rod from the lifters.

 

How in the world did a push rod get into the oil pan?

I'm confused...

 

I'm not sure either. 1/3 of it is broken off and twisted and pinched, the other 2/3rds is just bent. I'm hoping that it was left in there from it's overhaul, but once I get the pan back on, and the engine down, I'm gonna pull the tappet covers and see if any are missing.

 

ah, yes...the old "extra part" left in the bottom of the pan.

Man, I hope so.... Good luck.

 

you have probably lost a lifter also, all the oil pressure is leaking through the lifter pump up holes. MUCH better than bearings!

 

Pulled the lifter covers and intake, discovered six bent pushrods, and as many stuck lifters. Replaced entire set, and truck is running great now.