i just swapped everything out of the old lt1 to the lt4 LB, and now it is only showing ~20psi oil pressure.... anyone know if there is something missing there that i didnt catch? trying to get all of the bugs worked out of the car. TIA

 

How old is the oil pressure sending unit? Actually, sometimes it doesn't even matter how old it is. I literally just changed mine out 4 minutes ago. I replaced it about 2500 miles before the motor went out, so i figured it would be fine.... sure enough, when we used a mechanical gauge in the port above the oil filter I was sitting about 60-70psi (which is far above the 15-17psi my gauge was displaying right after i got my motor in). Swapped it out and it reads fine now. If you got the lt4 block because the previous motor failed, it may be clogged with debris from when the motor let go.

 

i will check it out... when i primed the oil pump, all of the oil volume came out of the block right about where the cam is at... is it possible there is something missing in the block? i will get a mechanical gauge on there also.... thanks

 

sending unit

 

well pulled the valve covers and no oil is coming out through the pushrods... so what is there to check next??

 

20lbs should be plenty for idle. Are you saying you never get more than that?

 

If no oil is coming through the push rods... you have a BIG PROBLEM. How long did you run it for to see if there would be oil coming up to the top of the motor? You dont need to run it long, but you have to run it, it'll be pretty hard to do if you are just turnin the motor by hand. You can unscrew the sending unit and run the motor for a few seconds, oil will spray everywhere and make a mess, but at least you will know that you are getting oil to that point.

The weird thing is, you are getting at least 20psi at the sending unit, and if its not faulty there should be something coming out of the rockers since the unit is at the back of the intake manifold. You really only need approx. 6psi to safely run the motor (specified by GM). So the 20psi isn't the concerning factor (although it would be nice to have more). Are you sure you installed the oil pump drive gear/shaft correctly. If you did, the pressure should raise with rpm's increased.

The only other thing i can think of is that you have a blocked passage somewhere. Either that or all of your lifters failed... which is pretty unlikely.

 

If you pre-primed the motor with a drill motor attached to the oil pump drive shaft, you should be able to tell where the oil is going. I did one this morning and in only took about two minutes to have oil pumping out through all 16 pushrods. If the drill-motor tool that drives the oil pump doesn't have a collar that fits into the distributor boss (see Jeg's.com, part #809-12368084 for a picture) at the rear of the camshaft, oil can't reach the pushrods anyway. Based on your comment that "...all the oil volume came out of the block..." I would guess that you may not have had that tool.

Also, search old posts for information regarding the check-ball that swedges into the oil passage just above the rear main cap. It's been discussed on most message boards many times. It should be in place if you bought a replacement block but...?

Good luck,

 

^^ya i didnt have that tool... just an old distributor shaft on a drill. i will try and check for the check ball, but the motor is already in the car, so it will be a pain. other than checking for that, i am stumped

 

If the motor is installed in a 4th generation F-body, I doubt that you can see down the hole under the pressure sender. You can't get to the check ball without taking off the pan anyway. Try all other possible solutions before you pull the motor out. A missing check ball is a longshot answer especially if it's a factory crate motor. If it was built by someone else, there's a chance that the ball was left out. Hope you find a bad sender or some other logical explanation.

 

is there supposed to be something on the oil pump driveshaft that routes the oil from the back of the block, around the DS, and to the lifter galley? i dont think that the DS had anything on it that looks like the oil pump priming tool that summit has. i think that would be the problem. but i never looked into the original block to see if there was anything left in there

 

The oil pump stub drive that meshes with the camshaft gear takes care of that problem. It is designed to function like the lower part of a traditional distributor housing (not just the shaft inside the housing). Without that part, oil cannot find its way to the lifters. That would explain why no oil reached the pushrods.

Did you start the car and observe the 20# of oil pressure or did you measure that with a mechanical gauge while you were priming the system? When I'm priming the system with a mechanical gauge in place, I can get 40 to 50# of pressure just using a DeWalt battery powered drill.

When you start the car with everything in place, oil should be coming out the pushrods within a very short time. 20# of oil pressure while the car is idling isn't particularly a problem. Having enough pressure and volume higher on the RPM scale is essential, however.

If you're starting the car to measure pressure, pull the valve covers to make sure you have oil coming out of every pushrod. You may need to back off the rockers on some holes. I usually prime the system with the pushrods and rockers in place but before the final valve adjustment is made. That fills any of the lifters that might have bled down. After you pressurize the system, the final valve adjustment will be an easier process.

 

went to the car agian this morning... turned the motor over with ign and fuel off. first go around it had ~30-40 psi on stock gauges. let it set for a few min, then went and turned it over again and it only had ~20 psi. and i did that several times, then started it and ran for 30 sec, and still no oil is coming out of the pushrods...

and it seems like a couple of the lifters are collapsed. so im gonna get the intake off of it again and get the lifters out and soak them in oil for a few days. while im in there i will pull the oil pump DS and see if there is anything wrong and see if there is any fresh oil in the cam valley.

does anyone have a pic of the oil pump DS that i can use for comparison to see if the one i have is in one peice or if it is missing something. thanks

 

nevermind the pic... found some online...

 

dont worry I had something similar happen and it took several minutes of running before the oil came through the rockers prolly about 20 full minutes before it was a good amount on all of them, the first ones started within a min or two. Also remember that roller rockers don't flow as much oil as stamped.

 

You could just pull the valve covers off and poor oil all over the springs and rockers and just run it. keep the covers off and if the rockers start looking dry poor some more on there, keep doing this for about 5 minutes, and if you still have no oil.... well then you should start tearing stuff down.

But it shouldn't take anywhere near 20 minutes to get some oil to start flowing. I didnt even prime my oil pump on my rebuild and it took about 45 seconds before i was sitting right at 60psi.