Rough Running Dually

[ryanmcb]

After 2 days, a broken exhaust bolt, and a few ruined spark plug wires...I got my gaskets replaced. The manifolds had no visible cracks but I did have a small gasket leak. It's nice to have it fixed but the truck is still back firing when cold.
I am going to re-check timing.
My nephew is a GM tech so I drove the truck in to his dealership. None of the techs could come up with an idea of what caused the backfire or the rough running.
Since my truck has thrown the EGR code, I have to believe it is related to the EGR system.
I appreciate all the help that I have received. I feel like I am out of parts that can be replaced with really no change in the trucks running condition.

Originally Posted by Chevy3+3

I hope my info will get you fixed up! I had the exact same problems with my 88' 454 TBI dually I recently purchased. It ran really rough on cold start ups when temps were 30-40 or below. It would stumble and pop and backfire through the exhaust pipes.

I followed everyones suggestions on here and and replaced the coolant temp sensor, tbi base gasket (which was leaking) and checked my EGR and still had the problem just as you are.

I noticed my passenger side exhaust manifold was cracked and I thought that was the problem for sure. So I installed a new passenger side manifold and also replaced both donut gaskets on each manifold-tailpipe connection. The next morning it was cold and it started backfiring again!!! I was so frustrated to say the least just as you are. I could still tell I had a little exhaust leak. It sounded like it was coming from the drivers side. So I unbolted the drivers side exhaust manifold to find the exhaust manifold gasket was shot. This was causing cold air to be drawn into the exhaust stream. It also throws off the O2 sensor reading.

After I replaced that gasket and all my exhaust leaks were fixed The problem no longer existed. The truck runs great now and starts great in cold weather as it should......Well as good as a freezing cold 454 wants to start, lol. She grunts and feel like the starter trying to turnover a chunk of lead, lol.

Anyway....my advice is inspect your exhasut system under the hood. I would almost bet money you have at least blown gasket or two or a cracked manifold. I would almost bet money its on the drivers side as well because I had a huge crack in my passenger side manifold and when I replaced it the problem was still present. The reason for that is because the O2 sensor is located on the drivers side tail pipe above the Y pipe connection.

Hope this helps.

[Chevy3+3]

Does it backfire only on a cold start up? Does it backfire after its warmed up?

[Chevy3+3]

Not doubting your abilities but after thinking about it make dang sure you have the firing order correct and your wires in the right location. Another thing to remember is to disconnect the computer wire on firewall going to distributer when checking your initial timing. If you check you timing or try to adjust distributed while running the computer will correct it and throw everything off.

When I bought my dually with 454 everyone said that the factory set 454 tbi at 0 degrees on the initial timing (with wire unplugged). Alot of people said that if I wanted it to rum better to advance my initial timing to 4-8 degrees it would wake it up some. I advanced to 5-6 degrees and made a noticeable difference in how she ran. Be careful not to go to far. Of you do it could cause pinging and your knock sensor will pick it up and retard the timing and reverse what you just did.

But double check your firing order and then double check your initial timing

[ryanmcb]

As far as I know, only when it is cold. I haven't towed with it in a while or taken any steep inclines but it never does it under normal driving conditions

Originally Posted by Chevy3+3

Does it backfire only on a cold start up? Does it backfire after its warmed up?

No sweat, thanks for the help. Firing order is good. I have double checked and all is well. I will re-check timing next thing and maybe try advancing just a hair. I'll make sure the wire on the firewall as well, I have made that mistake in the past. I'll give it a go and report back.

Any one else bumping up their timing a little?

Originally Posted by Chevy3+3

Not doubting your abilities but after thinking about it make dang sure you have the firing order correct and your wires in the right location. Another thing to remember is to disconnect the computer wire on firewall going to distributer when checking your initial timing. If you check you timing or try to adjust distributed while running the computer will correct it and throw everything off.

When I bought my dually with 454 everyone said that the factory set 454 tbi at 0 degrees on the initial timing (with wire unplugged). Alot of people said that if I wanted it to rum better to advance my initial timing to 4-8 degrees it would wake it up some. I advanced to 5-6 degrees and made a noticeable difference in how she ran. Be careful not to go to far. Of you do it could cause pinging and your knock sensor will pick it up and retard the timing and reverse what you just did.

But double check your firing order and then double check your initial timing