I totally rebuilt my 400 last year, it always had kind of a "skip" on the driver's side exhaust that kind of confused me, like i knew that shouldnt happen but it was hardly noticable so i said screw it. Now, it's kind of grown into a very loud "Pop" coming out the driver's side exhaust every two seconds or so, it gets worse as rpm goes up.
I figured maybe it was the cheap plugs i was using, i swapped them all out today and it's still doing it. any ideas what could cause it?
many things: a vacuum leak, valves not closing due to a broken spring or an excess in lifter preload, bad timming...
open the valve cover and cheak for a broken spring and due a compression test on the 4 cylinders....
just my opninion
__________________
"All right baby, see what I´ve got right here in my hands, I´ve got it right in my hands to score you baby, I think im gonna yank on a one town! Look Out!" Uncle Ted
I opened the cover, there werent any broken springs. I'm kind of doubting vacuum leak because i only have a brake booster and vacuum advance for the dist hooked up, everything else is plugged off.
Shouldn't it be 10-12 advanced BTDC? If every thing else is plugged off the stock distributer will put too much total advance into your timing because the motor used to have EGR which lets you run more advance so any stock timing spec is out the window. I had to unhook the vacume advance to get all the pinging out of mine but I never had any backfiring problems. I really don't think you have a timing problem since it sounds like you are only having trouble with drivers side cyls and mabey only one of them.
-Johnboy
__________________
-1979 F-250 4X4 400 4spd
-1989 Bronco 300six swapped in ZF 5spd
-1967 Mercury Comet Sports Coupe
Shouldn't it be 10-12 advanced BTDC? If every thing else is plugged off the stock distributer will put too much total advance into your timing because the motor used to have EGR which lets you run more advance so any stock timing spec is out the window. I had to unhook the vacume advance to get all the pinging out of mine but I never had any backfiring problems. I really don't think you have a timing problem since it sounds like you are only having trouble with drivers side cyls and mabey only one of them.
-Johnboy
You're right...I don't know where my head was at when I was typing this.
__________________
___'77 250 400 37 Boggers____'96 350 CC 460 35 SSR's_____'79 Bronco 351M 35 M/T's
Ben
A leaky exhaust valve. Do the compression test on those four cylinders. You should repeat several times on each cylinder, because the valve may seal sometimes. Look for one cylinder that's erratic.
__________________ JOIN THE DELAWARE CHAPTER,CLICK HERE
It doesnt do it on the passanger side, just the driver's. I dont have any egr or anything hooked up, it's all been removed. It is a stock distributor though.
I'm thinking maybe i put too much preload on one valve. I dont think i did but it seems like the only possibility. I did have trouble adjusting the valves, because i used that crane adjustable valvetrain conversion kit. Then i got these cheap ass locknuts with my rocker arms, they're all metal, and they stay on basically by just biting into the stud. I tried loosening one up once, and it just unscrewed the stud out of the head....so i had to make sure i got it right the first time when i adjusted them...maybe i spaced on one of them or something.
I guess i'm going to get some of those nuts with the allen nut in the head pretty soon, and just redo the whole valvetrain and re-adjust everything. Hopefully that'll fix it.
The 400m's known for valve problems. My 79 did the same thing, on the same side. If you can get a vacume gauge, hook it up to the hose coming from the intake manifold. If you have a bad valve that gauge is going to jump all over the place. Bob
__________________ 79 F150 4x4 01 F150 SprCab Short bed 4x2 08 Escape XLT 4x4
A leaky exhaust valve. Do the compression test on those four cylinders. You should repeat several times on each cylinder, because the valve may seal sometimes. Look for one cylinder that's erratic.
I agree with the bad exhaust valve. Check the compression on each of the four on that side. Put a little oil in a cyl at a time and recheck each immediatly after oiling. If the compression stays the same on one, you got a leaky valve (not seating or burnt seat).
Well the valves are all brand new, with new valve jobs in the head, so i highly doubt i'd have a burnt valve or seat already. The only possibility is one of them isnt seating....since none of the springs are broken i guess that means too much preload.
Too much preload will hold the valve open. Then hot exhaust gases can burn a valve in a New York second. If you listen to the exhaust on that side and it makes a spitting noise then that's probably your problem.
__________________
Bear Tracks
1977 F-100 Ranger XLT,400,C6,GV
Mod's Listed in Gallery
I would question the recent vlv job. 400's are known for their vlv problems, and if you don't get a super knowledgeable machinist to do the grounding correct...you will have a good running truck until you try to give a little gas and "pop-pop". This is the reason aftermarket heads are popular with the Ford modified motors. I get my heads back tomorrow and I'll be sure to thoughly inspect the seats...good luck.
Join Our Site - Its free, quick and easy!
Uncle Ted
