hey guys ive got a 400 motor atm that ive been trying to fix over the past month or so. some things ive done lately are i had headers edelbrock intake and carb put on new plugs and new cables it drove to arkansas from california fine but once i got here after a month or so it started acting up the oil pressure has always been a little on the low side not really low but slightly past the needle on the gauge it runs pretty cool atm i had to buy a higher temp thermostat to keep it in normal operating temp got a vacuum gauge and it read about 18 psi and did a compression check and was average 140 PSI on all cyllinders ive been told several times it sounds like a vacuum leak but ive sprayed starter fluid all around the manifold and carb and couldnt find any kind of leak when i was checking plugs i did find oil on the left 2 rear plugs as ur facing the motor not heavy oil but a light coat was on them was askin my dad what kind of oil i should use being out in arkansas from california and he said 20w-50 it had 10w-40 before after i changed the oil it ran with high oil pressure for about a week and it popped or somethin one day and it seems like the oil pressure is even lower than it was when i had 10w-40 the main problem is it isnt real responsive just kinda sluggish like i have to touble tap the gas or accelerate real slow to make sure the engine doesnt jolt i checked the electric choke and it works fine but it doesnt hold an idle well in the mornings until i actually drive it when i was putting oil in it the other day i noticed a snot like color substance in the oil so my guess is it might be a plug that went out and now fuel is getting in the oil on that cyllinder but i dont know for sure so i wanted to hear your guy's input im at sea level atm and the lowest temperature it gets here is around 10 degrees in the winter so any recommendations or anything would be a help also another thing that i dont know if this effects this problem but my heater sometimes when its on it makes sounds like a spring is jumpin off or somethin and it seems to do it more whenever i hit the brakes

 

forgot to mention that also at higher rpm's or in the mornings you can hear a light knocking coming from the motor as well

 

The acceleration hesitation is typical as well as the low oil pressure. Both mine and my cousins 351m have the same problem. What this all likely means is the engine should be rebuilt. These problems are common with high milage 351ms. It apparently has something to do with the bearings. The knock you here is a give away to what is wrong, my engine does't knock...yet! I assume the knock will only get worse.

 

Check all vacuum lines.
Heater controls and brakes use vacuum.