Can anyone tell me if the de-cell valve hurts fuel milage?
From Pintony
Hi Pintony hows weather over there? the valve will have no afect on fuel milage. If it's bad or out of ajustment could give you hi idle speed. But personaly things like that on my auto's end up in trash. :accident: hate that when that hapens. The aircraft guy.
Hey Fred,
Thank you for your answer to my question.
As I am keeping my Green Pinto factory correct I can just block if it were going to help with the MPG but if it doesn't matter then I will just leave it.
Still would like any opinions from other members.
From Pintony
IIRC: The decel valve cuts the fuel flow; would that not help fuel economy?
Bill
Pintony,
My "vintage " 1971-72 Chilton Pinto manual say's the purpose of the Decel valve is for emissions during sudden closing of the throttle. It slows down the rate at which the RPM can drop when the throttle is released. If defective, or severely out of adjustment, it can cause fuel economy to suffer during deceleration. I always took mine off to improve throttle response while racing. Later I went to BIG 38 DGAS Weber, no place to hook it up , and removed it.
Hope that helps,
Pintosopher
I'm not familiar with the Pinto de-cell valve, but Datsun used similar devices back in the early 70's.. The stated purpose was to prevent a lean condition that strange as it sound increased hydrocarbons. Apparently when a condition gets too lean the sustained burning in the cylinder is incomplete and the HC goes higher.
At least in the Datsun case there was an enrichment at the carburetor (their system was intigrated into the carb.). It also seems possible that just decreasing the rate of the throttle closure would be effective. However, a simple dashpot (a sort of shock absorber for the throttle) would seemingly do the same. So much of the early smog stuff was to "design around" the problem.
Tom
Quote from: pintosopher on March 30, 2008, 07:55:20 PM
Pintony,
My "vintage " 1971-72 Chilton Pinto manual say's the purpose of the Decel valve is for emissions during sudden closing of the throttle. It slows down the rate at which the RPM can drop when the throttle is released. If defective, or severely out of adjustment, it can cause fuel economy to suffer during deceleration. I always took mine off to improve throttle response while racing. Later I went to BIG 38 DGAS Weber, no place to hook it up , and removed it.
Hope that helps,
Pintosopher
Hey Pintosopher,
Is your Chiltions the Orange and Purple one??
Mine says lets a metered amount of a/f into the combustion during sudden close of the throttle plate.
That seems like it would be bad for MPG??/
From Pintony
The unofficial Ford line mechanic fix for the Decel valve problem was take it off place a penny in the cavity bolt it back on.
You'll never see that car again.
http://www.fordpinto.com/smf/index.php/topic,5249.msg32109.html#msg32109
i think they can hurt mileage IF they are not operating properly, ie: leaking excess air through a bad diaphragm. I'm with Map351 & Pintosopher though and some driveability issues are eliminated if the valve is blocked or removed
Pintony,
My Chiltons manual is the Orange one , 71-72 cars only.
Pintosopher
Back again,
Regarding drivability, if the intake vacuum is highest at Idle ,then bleeding in a specified amount of air into the intake beneath the carb butterflies would cause a leaning out of the mixture as the vacuum suddenly spikes when the butterflies close. This is good for emissions, bad for throttle response when you need the extra vacuum to help the fuel charge coming from the accelerator pump. Getting the most response and balancing the two parameters are near impossible without a sacrifice in one or the other.
Stone age Fuel mapping, I guess :read:
Pintosopher