454 with intermittant miss

[Cornfield creations]

We had the 454 in the 84 k-20 running good a couple weeks ago, but it seems that it has an intermittant miss on cylinder 8. It ran good and smooth for a long time but lately has slowly been getting worse and hasn't even left the shop yet. Has a brand new Accel distributor, good accel super coil, new accel wires, and ac delco plugs. We cleaned off the plug on cyl. 8 because it fouled out and seemed to run a little better. We checked the cap, no cracks and no apparent change between the terminals. We are stumped

So she is leaving the shop tomorrow to go to another shop where we are putting a bigger lift on. I figure that maybe getting driven and reemed on a bit will clean it out and maybe sure the problem (hopefully).

Has anyone else run into this problem before?

 

[gman454]

check the rocker arm bolts to tight or to loose can create problems also possable lifter issue if its not getting proper pressure. I had the same problem with Cylinder 8 and it was the rocker being to tight and the valve staying open
hope this helps!!!!!!

 

[Cornfield creations]

I'm sorry I didn't mention, the cylinder isn't firing. It sounds like a dead cylinder, so we took a timing light on each wire to see if it was firing, and it would fire on 8 every so often, not a steady fire.

 

[sweetk30]

the bbc eat cams more than sbc do. do a compression test.

 

[Fubeca]

I've had new wires be bad - have you tested the wire?

 

[Cornfield creations]

Yeah it was the kind you crimp the end on (cut to fit) so that's what I was thinking, so we grabbed a ac delco one off the pile of parts. Still did the same thing.

Would a worn cam cause the plug to not fire though?
It has a pretty new cam(rv cam supposedly, sounds a little rougher than an rv cam to me, just in there when it was bought)

We put the timing light on it to find out which cylinder it was, and at first it didn't fire at all. We cleaned the spark plug and went over everything and it at least tried firing but was intermittant, kind of like

... . . . . . ... .. .

Like it would fire and skip a couple of firings, it wasn't steady like

........................

If that makes any sense, thats the best way I could explain it on here.

 

[dyeager535]

Fix the firing issue first if you know that is a problem.

BBC's do eat cams, my dads rebuilt 454 ate a cam in a couple 1000 miles, and IIRC, it was #8 as well. Ran ok, steadily got worse though as the cam/lifter wore down.

 

[Inu-Hanyou1776]

I'm suspecting a slowly lunched cam too. Pull the cam and see what the #8 lobes look like compared to the others.

 

[hero]

Not that this helps much, but I've got a VERY simlar problem with my 454. It's on 8 that it keeps fouling a plug. I did a compression check and leakdown test, and everything was fine. I can only notice it at an idle, and it's intermitant. I've replace the plug and wire. Replacing the plug helped breifly, but the miss came back. I have no idea what it is, and at this point I'm just driving it until it gets worse so I can figure out what exactly it is that I need to fix. Anyway I will definatly post up if I find out what is causing it. Please keep us posted if you find anything.

 

[dyeager535]

Compression and leakdown won't indicate a "flat" cam or bad lifter, as the valve(s) just stay shut and build up pressure as if there was no problem.

 

[Boondocks]

I recently resolved a mis-fire issue on my GMPP HT-383. It turned out that with my new high-performance ignition and the close proximity of my plug boots to the header tubes, it would arc to the header tube even with new boots and heat socks.

I finally replaced the headers with a set that provided more space between the tubes and plug boots. Has run great ever since.

 

[Cornfield creations]

UPDATE


We took the truck out today to move it to the other shop, ran like crap half way there, but I told my buddy to reem on it and clean it out. He did. now it runs like a champ! The miss went away completely and runs great!