[NUTS FOR EL CAMINOS]

Greeting everybody. I had my ride out yesterday and my 427 began to backfire out of the right side bank. I pulled over and took a look under the hood, checked the spark plug wires and couldn't find any obvious problem. I started it back up and it ran fine for about fifteen minutes and again it began backfiring from the right side bank. Stop again, checked everything, started it back up and took it home without any more backfiring. Where would you suggest I start looking? Sticky valve, bad plug?
Thanks, Tom

 

[Dave427]

Try a set of plugs first. Was it backfiring at cruise or wide open?

Dave

 

[NUTS FOR EL CAMINOS]

Cruising - Thanks

 

[bobj_70]

Mine does when it's running out of gas. lol

Spark plugs, wires,etc. could be the problem

 

[69bu]

Might want to check the valve adjustment.

 

[NUTS FOR EL CAMINOS]

Well so far no luck. I've changed the plugs, changed one bad spark wire, pulled the R/S valve cover to look for broken springs or sticking exhaust valves, couldn't see anything wrong and it's still popping. I'm going to start running the motor and killing one R/S cylinder at a time by pulling the spark plug wire off. I figure this should tell me what cylinder is mis-firing. Any suggestions?

 

[BillyGman]

Are you sure that it was/is popping out of the exhaust, or could it be popping out of the carb? if it's the carb, then that can indicate a wiped out exhaust cam lobe. And that would be easy to diagnose. You just unhook the coil wire so the engine won't start, and with the valve covers off, have someone hold the key in the start position for 5 or 6 seconds at a time while you watch the rockerarms to see if any of them are staying still and not moving up and down like the rest of them are.

If you're sure the popping noise is coming out of the exhaust, and not out of the carb, then pulling the boots off of the plugs one at a time while the engine is running lie you said is a good idea. I'd also remove the distributor cap and take a good look at the contacts on the cap as well as on the rotor too. If atleast one of them looks completely fried, then it's time for a new cap and rotor. Take a good look inside and out for a crack in one of the towers on the cap too.

 

[NUTS FOR EL CAMINOS]

Well through a process of elimination I discovered that my distributor cap had failed. I replaced the cap and it's running great now. Looking at the distributor posts from inside the cap, it was very clear that two sets of posts were arcing across to each other. The center coil post was shot as well. I haven't been too impressed with MSD products that I've used over the past few years; distributors & Caps corroding, trouble with spark plug boots, etc. Oh well. Thanks for the help today. - Tom

 

[BillyGman]

I'm glad you got to the bottom of that, and that it was something easy and inexpensive. It sure is nice when things turn out like that. I'm not so sure that distributor caps from one manufacture can be, or are neccessarily any better or worse than caps from another. I could be wrong on that, but it would seem to me that a cap is a cap, especially when you're talking about the plastic cracking. As far as I know, it happens sometimes, and I've never really heard anyone explain WHY it happens. It's just something that DOES. Which is precisely why I had suggested that you check the cap in the first place if you were sure that the popping/backfiring was not coming out of the carb, but in fact out of the exhaust.

 

[CharlesKC]

Glad to hear it worked out. I had something similar happen a few years ago and it ended up being the cam going flat and back-firing out of the carb.

 

[BillyGman]

Glad to hear it worked out. I had something similar happen a few years ago and it ended up being the cam going flat and back-firing out of the carb.

Hmmmm....now where have I heard that^ before???