freelance031 Posted May 27, 2006 Share Posted May 27, 2006 I HAVE A 1956 MACK B-85F FIRETRUCK THAT BACKFIRES BAD. IT LOOKS LIKE THE PREVIOUS OWNER BLEW THE MUFFLER APART. I HAVE HEARD SEVERAL SUGGESTIONS ON POSSIBLE CAUSES-ANY IDEAS?THANKS.. Quote Link to comment https://www.bigmacktrucks.com/topic/1142-b-85f-backfire/ Share on other sites More sharing options...
1948-LS Posted August 19, 2007 Share Posted August 19, 2007 I am having the same problem with my 1948 mack l-model with a enf707a gas engine.I'm working on it now. Have you come up with any ideas yet? If I find the problem with mine, I'lllet you know. I HAVE A 1956 MACK B-85F FIRETRUCK THAT BACKFIRES BAD. IT LOOKS LIKE THE PREVIOUS OWNER BLEW THE MUFFLER APART. I HAVE HEARD SEVERAL SUGGESTIONS ON POSSIBLE CAUSES-ANY IDEAS?THANKS.. Quote Link to comment https://www.bigmacktrucks.com/topic/1142-b-85f-backfire/#findComment-13458 Share on other sites More sharing options...
HK Trucking Posted August 19, 2007 Share Posted August 19, 2007 Check for a blown gasket where the exhaust pipe attaches to the manifold, or any other loose connections in the exhaust system upstream from the muffler.I remember a long time ago I had a Ford F 750 with a big gas engine in it, and it would backfire something awful on deceleration.Noticed that it had a broken stud where the crossover pipe connected to the left exhaust manifold, which allowed the pipe to come loose.Fixed the stud and got that pipe to manifold connection tightened back up, and the backfiring went away.I've heard others talk of this happening too, caused by a loose connection in the exhaust system.Evidently on deceleration, air is pulled into the exhaust system thru the loose connection, and mixes with unburned fuel in the exhaust system, and then is ignited by the heat in the muffler, then you get a big "bang". Quote "If You Can't Shift It Smoothly, You Shouldn't Be Driving It" Link to comment https://www.bigmacktrucks.com/topic/1142-b-85f-backfire/#findComment-13459 Share on other sites More sharing options...
B42Art Posted August 20, 2007 Share Posted August 20, 2007 A bad condenser will also make a gas engine backfire like mad. Give that a try, Art Quote Link to comment https://www.bigmacktrucks.com/topic/1142-b-85f-backfire/#findComment-13461 Share on other sites More sharing options...
1948-LS Posted August 20, 2007 Share Posted August 20, 2007 Thanks for the advice, but I think it may be more than that. Right now it dosen't run. It cranks great, but dosen't even try to start. After about 7-10 seconds of cranking, it explodes out the muffler. All of the ignition parts are new on both systems: plugs, cap, rotors, ext. Carb has been rebuit. Adjusted the valves. Even the timing "looks good". It also has good compression. I think I will try disconnecting the muffler. It may be clogged up from the last owner running the truck for miles with the choke on when the throttle got stuck. The only ignition parts not replaced are the coils. Will test them next.Also in need of a manual for the ENF707A if anyone haas one for sale.THANKS Quote Link to comment https://www.bigmacktrucks.com/topic/1142-b-85f-backfire/#findComment-13462 Share on other sites More sharing options...
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