Zero compression 3 and 4 cylinder and engine knocking 61 tbird 390fe

[Ramos291]

15 yrs old rebuild 390fe engine that has been running mostly fine for 15 yrs. I pick car up after having some leaks fixed along with fluid change and brake work done recently. As I drove home it had a knock at driving speed. A few days later I drove car and the engine cut out twice for a few seconds each time. When I came to a stop the whole car was shaking like crazy. After checking carb adj. Timing distributor, plugs and wires and finally compression on each cylinder I found cylinder 3 and 4 to have none. Other cylinders were 130ish to 135ish. Old was full but I used a zink type oil this time. What are your thoughts?

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[inspector]

My guess is head gasket leaking between 3 & 4 cylendar

 

[DannyInNJ]

Yep, sounds like a head gasket. or a crack between 3 & 4. Were those 2 plugs clean & dry when you pulled them to test compression? They sell a cheap block tester on Amazon etc; uses test fluid that turns from blue to yellow if it detects exhaust gas in your coolant. Worth a try.

 

[mistfr]

Do a leak down test to find out where the pressure goes...

 

[Ramos291]

Yep, sounds like a head gasket. or a crack between 3 & 4. Were those 2 plugs clean & dry when you pulled them to test compression? They sell a cheap block tester on Amazon etc; uses test fluid that turns from blue to yellow if it detects exhaust gas in your coolant. Worth a try.

Yes plugs dry