Topic: Early Pinto Decell-Valve ???

[Pintony]

Hello Group,
 In 1971 ford was under the gun for emission standards and the early Pinto had what was called a
 Deceleration Valve.
 This valve would open under high vacuum conditions and allow air to inter the intake system W/O going through the carb. I have been told by many since 1978 that this valve is totally unnecessary and eats fuel.
Actually I would think it would be the opposite that allowing extra air into the intake effectively causing a vacuum leak under deceleration would be a good thing for economy.
 I would like any info or opinions on this issue as a matter of general knowledge.
 NOW I will add that I am talking about a road-going Pinto. NOT Performance Pintos
 I would think that this valve was long gone with the advent of the smog pump???

Lets hear your comments on this issue.

 From Pintony

[Srt]

The decell valve was desined to operate under high vacuum (throttle closed) situations such as letting off the throttle between shifts or off the throttle when downshifting to a stop etc,; to allow fresh air into the intake in order to reduce the occurrence of unburned hydrocarbons in the exhaust gas stream

[High_Horse]

I understand the decel-valve to work as to not let the engine rpm decline as swiftly when the foot is off the pedal by allowing air into the intake. I do not understand it to be for emission purposes. I do not understand that automatics would be equipted with these valves.

                                                                                                      High_Horse
                                                                                                         #226
 
                                                                                                         

[UltimatePinto]

As I rummaged through my parts I found a two liter intake with said valve attached to it.
It's threaded right into the intake, right next to the PVC intake.
Now there is a rubber tube that runs down from the valve, (and I'll go out on a limb on this one), that I think was attached to the charcoal cannester that the vent from the gas tank was connected to.

Mind you that I haven't looked at any of my service manuals, just a guess on this one.

I can say from experience that they, (the decel valves), were the cause of one too many frayed nerve endings when the diaphragms in them let go. It created a monster vacuum leak that killed any normal engine operation, and was a very frustrating leak to find if one didn't know what they were looking for.

They show up on E-Bay from time to time although at this age, (from 71/72/73? to 2006),
I would question the shape of the diaphragm.

Al

[Starliner]

The large charcoal canister hose was attached to the air cleaner body on my 1600.  The decel valve hose went to the carb next to the fuel inlet.

Pintony is correct that the decel valve draws mostly air & not an fuel/air mixture.  As stated above the purpose is to get unburnt oxygen through the combustion chamber to finish the job of burning unburnt fuel in the exhaust system.  That is why I think the exhaust tone is different when the decel valve is in operation.     
 
The reason I think it effects gas mileage is two part.  One, drawing air from the upper portion of the carb during decel is going to effect the pressure and air flow in that region.  Fuel metering has got to be effected, at least momentarily during the changeover.   Especially if you are on & off the throttle.   Second, downstream of the carb will have a high content of oxygen versus fuel and that will effect the resumption of power.    If it is in decel mode and you get back on the throttle it again will have a transition period.    For steady cruising the mileage would be the same with or without a decel valve.     

For driveability I sure don't like the effect of a decel valve when backing of the throttle, especially on an automatic.   It's like having a sticking gas pedal.   

[Pintony]

That is the best answer so far!!
 Good job Starliner!!!

From Pintony