Deceleration Valve Options

[Ian Stott]

This is a very difficult to get item to get! Many have said soaking the existing one in kerosene for a few days will do the trick, have not done that yet as I am still trying to track down a new one. Wondering what the success rate has been with soaking it in kerosene, also wondering would WD 40 do the same thing. Would hate to ruin the one I have, which is original to the car!

Ian Stott
Moncton
Canada

[GregAmy]

It doesn't "control the vacuum" (if I understand you correctly); it uses manifold vacuum to open itself, to add un-throttled air to the intake to lean it the mixture on decel to reduce backfire (and excessive emissions) due to a rich mixture.

Modern EFI simply backs off the injector pulse (or shuts off the injectors entirely) when the throttle is closed (as indicated by the TPS) and on engine over-run to lean out the mixture. For whatever reason, D-Jet was not able to do that back then (or maybe they didn't think of it?)

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?

[Ian Stott]

It doesn't "control the vacuum" (if I understand you correctly); it uses manifold vacuum to open itself, to add un-throttled air to the intake to lean it the mixture on decel to reduce backfire (and excessive emissions) due to a rich mixture.

Modern EFI simply backs off the injector pulse (or shuts off the injectors entirely) when the throttle is closed (as indicated by the TPS) and on engine over-run to lean out the mixture. For whatever reason, D-Jet was not able to do that back then (or maybe they didn't think of it?)

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?

Will talk to the mechanic about what you have posted, thanks so much for the info, will keep you posted!

Ian Stott