I have a 1998 F-250 4.6. I've lost compression in 1,3,4,8 cylinders. The lifters have been replaced but it seems as though the valves are still not closing. Have there been any problems with the valve springs? I've talked to several mechanics and it seems as though nobody has seen this problem. I certainly hope one of you smart guys has had this problem and solved it.

Thanks.

 

I'm just taking a stab here, but if the timing chain broke, some of the valves will stay open. I'm assuming it doesn't run.

 

Joe :

Thanks for the response. This engine does run. Quite poorly but it does run. Everything in this motor has been checked (timing chain included) and seems to be in good shape. This problem is driving myself and a few good mechanics crazy. If you or anyone else reading this, can figure this one out, I would be elated!

 

Very odd since they are not all on the same head. I guess that the cam lobes checked ok? are all of the valves opening?

 

Here is where I am with this engine and why I think it's valve springs. I removed right side valve cover, turned cam till #1 cyl valves are closed. Filled cyl with air pressure, air leaking out intake. To check valve seat I removed rockers again, filled cyl with air. I am able to hold pressure, valves are seating. I changed lifters thinking the lifters are holding valves open. Ran engine to fill lifters, still no compression. The only thing on the other side of the rocker is that spring. If that is my problem how could all 4 cyls go bad at the same time? This means the valve spring overrides the hyd. lifter to close the valve. Could someone tell me how this system works?

 

i have seen 4.6l cars come in that will not start and sound like they have no compression, which turns out is true. now here is the kicker, let that car warm up in the shop (if it is during cooler weather) and it will start eventually. first thing u do is ck the oil service interval and make sure they are not running a heavier oil then what is recomended. now the what has happened, the oil is the wrong weight or has a ton of miles on it and is too thick, lifters pump up and can not bleed down, holding the valves open. change the oil and car is fixed, if this happened all at once and is effecting both sides my guess is this is what has happened. if this doesn't fix the problem and u can hold shop air with the rocker out then u may have warped intake valves and what happens here is that they have got hot enough that they actually fall into the head or stretch in effect.. have seen this happen on trucks and cars 5.4 and 4.6