HELP - Backfire/Popping thru Exhaust !!!!!

[6600DURAMAX]

Finally got the 454 off the test stand and dropped in the 72, and now the problems start. When the motor was on the test stand (about a month ago) everything seemed to run fine (ran it for about 1/2 hour or so). After I dropped it in and got everything hooked up the motor fired right up and sounded fine, ideled good, great throttle response and so on but.........once I take the motor to about 2500 rpm it begins to backfire/pop thru the exhaust.

Thought it was timing - re-dropped distributor in twice, adjusted the timing everywhere on the scale

Thought it was tight valves - readjusted all the vavles

NOTHING HELPED... do not know where to go from here.......

The only thing different from when the motor was on the test stand is the MSD Box (6AL)??? Could that be bad it is only 6 months old and ran fine when I pulled it off the sbc.

The motor is a used motor that I bought a while ago that is why we put it on the stand and fired it so we wouldn't have these issues

Any suggestion are greatly appriciated

thanks guys

[jhow66]

Run it without the box and see.

[Perchjerker]

It does sound like timing. I would check to see if the timing chain is loose. But only after you have exhausted everything else first.

[6600DURAMAX]

jhow - Hopefully tonight I can take the box off and see

Perchjerker - Timing was also my first guess, maybe the box off will help, maybe bad box ???

No one else can come up with something

thanks guys

[ddsmith]

It sounds like a timing issue to me also. Do you have a dial back timing light to check what timing you have at that RPM or a degreed balancer/damper? Timing is usually all in for mechanical and maybe your total timing is to much. Don't know what the distributor setup is. I would also take the box out of the equation and see what the results are. Electronics are great when they work and a big headache when you have problems. Also check 5 and 7 plug wires carefully. They are right next to each other in location and firing order. You might be getting a little cross fire going on.

[COBALT]

Sounds like your timing is too advanced. A motor will idle just fine with the timing too advanced sometimes. WOT will bring the engine to it's knees. Not enough fuel/air charge in the combustion chamber at the right time. The motor is already throwing it out the exhaust stroke.

[dubie]

also check your plug wires just to make sure they are all going to the proper plug. I thought I had mine on right and it would idle perfect but once it got to about 2400 rpm she would start chuggin and backfiring. I went by my Haynes manual for the plug wires and then looked at my intake and they were different. SO I lined em up as it said to on the intake and problem solved. Check the little things first bud and let us know what turns up

[wannabeburbowner]

What type of distributor are you running?? If it's an HEI maybe it is the ignition module. I have never had this problem, but I know when they test them they test low and high rpm not sure where the line is between low and high rpm though. Just an idea and it is free to get them tested at your closest Advance auto parts or whatever.

[6600DURAMAX]

Do not have a dial back timing light just the old school one - although that might be a good investment and no degreed balancer just stock with the TDC mark

It is a 50,000 volt HEI

Thanks guys, I am trying to leave work here in the next couple minutes and head that way. I will go over her one more time tonight with the following:

1.Check plug wires - both on the cap and at the cylinders
2. Make sure wires aren't crossfiring
3. take MSD off
4. Check module tomorrow at parts store if still not right

AGHAHAHG the good ole days

Thanks guys

[Alexis]

Check your spark plugs.............i had one plug loose and the whole time I thought it was a timing issue...............

[RabidScott]

I had a bent valve in a motor once and it did the exact same thing....

[6600DURAMAX]

Big Block update - Well last night went thru everthing we could think of

New cap and wire
Valves so loose they all rattled
Spark plugs
Timing advanced, retarted then advanced

Nothing helped, it was still popping and backfiring

soooooo....as of now she sits stripped down to the short block.
Heads on the floor going in for valve job, 292 cam off the shelf to slap in, then MAYBE when we get it back together the pop will be gone. WE HOPE????