My 1986 F150 w/300 six backfires when I let off on the gas it's a real short POP! and at faster speeds it'll occasionally do a full blown BANG. I have replaced the manifold gasket, muffler, and tail pipe because they had leaks but it still does it. Need to fix it because it bloated my muffler. I don't want to do the same to the new one.

Could it be the cats? I have a book that says one cause of backfiring is improper valve timing. Has anyone had this problem?


I put a glass pack on it (Sounds Great, love goin through town an scarin people) but I don't want that embarassing backfire.


1986 F150 300 I-6 4 spd w/od 106,000 and still runnin strong

 

Check the heat riser valve, I think you will find that the bi-metalic spring is shot. I've seen the exact problem on my uncle's '86 F150.

On the plus side... Once you get the 'hang of it, you can do the "on-demand explosion" thing. REAL FUN sometimes!

 

i had to pull the belt off my air pump and that stopped all my back fire problems. But i still need to replace my muffler again it is ready to bust from backfireing.

 

When you let off the gas after "getting on it" you have a momentary rich fuel mixture passing through the exhaust. If you air injection is supposed to cutout to prevent extra oxygen from getting with the excess gas when it's somewhere hot like in your exhaust manifold or CAT. As posted above, if you remove the O2, you remove the likelihood of explosion. Look into why the air pump is not "dumping" when your getting on the gas. You may have a stuck bypass valve. Removing the air pump's belt would be a good place to start narrowing down the cause.

 

I had an 86 with the I-6 and it has this problem. Ended up the float in the carb had a hole in it, and was not floating. So it was running WAY rich, and the extra fuel was going off in the pipe. (thought it was gonna blow the muffler off a few times :-) )

 

I took the belt off to start and it is gone completely no matter how much gas I give it so that must be where the problem is tahnks for your advice.

 

NO PROBLEM. I left it unhooked with no problems.