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Byekryam · 06-07-2024, 07:21 AM

Hi,

I know they don't make the deceleration valves for these anymore, but are there any NOS laying around? Or has anyone used another deceleration valve from another vehicle in it's place? Any insight would be appreciated.

Thanks,
Woody

Skip426 · 06-07-2024, 12:54 PM

Well even the mention of the " deceleration valve " brought back bad memories .

Can you post a picture of your set up , I don't know if the type that Chrysler tried is still available but there might be some around.

Used mostly as an emissions control device ; to change the type of exhaust gasses emitted on sudden throttle release , the engine should run without it ; or do you live in an area with emissions testing requirements?

Byekryam · 06-07-2024, 04:06 PM

I've been having problems with mine running correctly and I'm trying to step by step replace things to eliminate potential causes. I've done much of the other valves but this one I can't find. I know Pontiac also sells one for I think the 390 but I'm not sure if one for another make and size engine would work properly. I can't find a replacement anywhere new, NOS, or aftermarket. I'm not worried about the emissions aspect of it at all.

Byekryam · 06-07-2024, 04:09 PM

Here's some pics

EyezOpen · 06-09-2024, 04:21 PM

Now that's a first..De acceleration valve...that runs right up there with muffler bearings. I just had to do that, 80's emission strategy was mind numbing at times.

Don't forget to plug the access port that thing draws from.

Set your static timing to at least 8 degrees btdc that will pretty much end any backfire. Use some techron injector cleaner for a while and a combustion cleaner to decarbon your vintage engine.

yeloduster · 06-09-2024, 06:53 PM

There was a company that sold a "de-acceleration" valve. The company is now defunct. It was called Mountain Tamer then the sold to Decelomatic also defunct. The device blocked the exhaust coming out of the exhaust manifolds causing the engine to act as a brake.

It is out of business because an "exhaust brake" for a gasoline engine is a solution for a problem that doesn't exist. There were never enough customers to keep them in business. It may be possible to purchase a "Pac Brake" and find a way to install on a gasoline engine.

However, a gasoline engine does not need an exhaust brake. If the throttle is closed the engine works against a vacuum acting like a brake. I have drive a bunch of gasoline engine vehicles with heavy loads and found the engine itself to be a satisfactory brake. It may not be as 'good' a brake as the various engine brakes on diesel engines but it is good enough.

For instance, I live in Colorado I often descend down I70 into Denver. It is a LOOOONG down grade of 6-7%. I place my transmission in second gear and down the hill I go. The engine holds my speed to ≈45 MPH and engine speed at about 4000 RPM. That appears to be the speed most trucks and diesel RVs go down the hill as well. I seldom touch the brake except to slow for corners. I think that is good enough!

Byekryam · 06-10-2024, 06:09 AM

Eyezopen, can I eliminate that from the system? If so, does it work inline with anything else\in conjunction with anything else? Will the onboard computer be searching for it? For its input for everything to work efficiently? The lines going into it, do I just connect them together? Looks like two larger hoses and one smaller vacuum hose. Connect the two larger and plug the smaller?

Byekryam · 06-10-2024, 06:11 AM

Yeloduster, ask I asked of Eyezopen, can I eliminate that from the system? If so, does it work inline with anything else\in conjunction with anything else? Will the onboard computer be searching for it? For its input for everything to work efficiently? The lines going into it, do I just connect them together? Looks like two larger hoses and one smaller vacuum hose. Connect the two larger and plug the smaller?

yeloduster · 06-10-2024, 06:26 AM

I am mostly ignorant of your setup. However I do know that there is NO computer involved with your setup.

You 1986 454 is a carbureted engine. The various valves and gizmos are controlled with engine vacuum.

EyezOpen · 06-10-2024, 08:22 AM

Yes you can, it's design is to prevent backfiring on sudden deceleration. It does not effect emissions systems by any means.

To that point your emission systems are more than probably non functional. Turning your static timing up to 8/12 degrees btdc will rule out any possible backfiring.

As I suggested above use a cumbution chamber cleaner and techron gas for awhile.

Things to understand about our older engine's. The fuel they were designed to burn is no longer made, gasoline has been drastically reformulated. They can be retuned to run these new formulations however. They are just engine's that need a new diet made overly simple.