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Only smokes when I hit the Brakes David 1-5-03  
I have a 1985 Ford 350 econoline 460? I think big block. It has 126 K - runs fine! But once the engine comes to temp or running for about a 1/2 hr - When I hit the brkes for a red light/stop sign - it lets out HUGE amounts of smoke from the tail pipe!! This only hpppens in deceleration!! Once stopped and engine rev'd a bit - it blows clean again! I there a Vacuum problem?
tia -- David
Re: Only smokes when I hit the Brakes Gary CC.NV. 1-5-03  
Carburetor or Fuel Injection? If Carburetor, sounds like the float level is to high, dumping over when you slow down. Float getting heavy, some fuel additives will do this, they penetrate the cork type floats and it makes them heavy. Needle and Seat could be worn out too, ever had the Carb. rebuilt with in in the last 50K miles? Does it do this too when making hard turns? another sign of Carb. problem. What color smoke, Black? If Black, Carburetor for sure. This type of Carb. problem is Nestorius for Ford's, "Design thing". The "rev'd" you talk about is called (Stumbling #2). Gas is dumping over,loading up,choking engine,gas burns out,engine catches it breath,leans out for a second, RPM comes up,and them settles back down to normal.
It won't do this when the engine is cold because of less engine heat, the gas does not burn as complete as it does with a hot engine, "not as noticeable".
Fuel Injection can do this too, a Diaphragm goes bad in the Throttle Body. Everyone knows Diaphragms are Vacuum Operated. Change in engine speed, change in vacuum.
Blue smoke, on deceleration= Valve Guides, but it usually doesn't affect the ideal, unless there Really Bad. So bad, the engine is almost to the point of no compression left. But you say it clears up,so I don't think so.
Check the Choke, maybe the Choke Butterfly is loose, linkage problem, or the Choke is just not opening all the way, burned out choke heater, or Hot Air Pipe pulled out, or broken=rusted out. Also check the Hot Air Tube, at mouth of air cleaner, "on the bottom side", might be off, the door inside on the front of air cleaner might not be opening, not giving the engine the air it needs to breath when its warmed up. Take the Vacuum Hose off to the Diaphragm operated door at the front of the air cleaner, plug the hose, this will keep this door open, than try it. Look inside (BE CAREFULL) to see if that door isn't stuck shut. With the hose hooked up, engine HOT, and running==(BE CAREFULL)look inside, door should be open, if not, it's stuck, or a Thermal Switch is not working right, and keeping this door Closed all the time. Or the Hot Air Tube is not hooked up, or leaking=big hole in it, or the shields are missing and not making enough hot exhaust manifold heat go up the hot air tube to make the door open.
I hope this helps.
Good Luck.
Happy New Year.
Re: Only smokes when I hit the Brakes Joe 1-6-03  
What color is the smoke? Is it blue or black? Blue is oil, and black is gasoline.
Re: Only smokes when I hit the Brakes Sam Watson 1-13-03  
Pull the large vacuum hose off of the brake booster and check for liquid (brake fluid) inside of it.
Re: Only smokes when I hit the Brakes Gary CC NV 1-13-03  
If the smoke smells "Sweet" it's trans. fluid. Usually when the Modulator goes bad, it will smoke like a train. Pull the vacuum hose off at the modulator, there will be a small amount of fluid dripping out of the modulator, and fluid in the hose.
Re: Only smokes when I hit the Brakes Sam Watson 1-13-03  
Pull the large vacuum hose off of the brake booster and check for liquid (brake fluid) inside of it.
Re: Only smokes when I hit the Brakes Sam Watson 1-13-03  
Pull thre large vacuum hose off of the brake booster and check for liquid (brake fluid) inside of it.
Re: Only smokes when I hit the Brakes Reinhardt 1-15-03  
That's funny that you say that about shifting because I have a 1982 school bus with a 454 and it smokes only when I hit the brakes and refuses to downshift correctly
Re: Only smokes when I hit the Brakes WAR EAGLE 1-15-03  
Re: Only smokes when I hit the Brakes Newbie 2-17-04  
Smoking engine only when decelerating in gasoline with automatic: Vacuum modulator valve in trans bad, sucks trans flu into intake. Smokes in a big, big way when high vacuum exists, mostly goes away when driving after a bit, depending on how big the hole in the modulator diaphram is.

Power brake unit: same as above, brake fluid leaks from hydraulic cylinder into vacuum booster, only those types where vac booster is directly bolted behind master (hydraulic) cylinder. Some say the vac booster should have to fill up with brake fluid before this happens, but perhaps when a few cupfuls have accumulated (symptom: power brakes dont work, not for long, burnt brake fluid smell.

Big block chevies: if the galley return holes are plugged (maybe only small blocks, but also generally true in any application) the valleys near the valves fill with oil, eventually when braking, oil rushes to front of valve-head-under valve cover-area. Indications are generally valve cover leak, but not always.

Understand, only general info here. Am attempting to solve exact same problem except with two (count em, two) matched ford F-700 inline 6 diesels. Both smoke unholy when decelerating. Both were driven very short, sporadic hops, both sitting and idling without a high idle.
Best wishes.

Dont forget to evaluate whether you only have a valve stem SEAL (cap) problem. sometimes the lubrication can crack the cap style permitting oil to permeate valve stem area.

All the above is meant to be filed under "if the rings and valve guides arent worn out"
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