Hello All, I hope you are all enjoying the Holiday Season. Even though under the weather and visiting relatives, I can't help but troll the forums for info!!

With regards to the Vacuum Delay Regulator that resides under the intake, should I should see zero vacuum to the line going to the vacuum advance on the distributor? I've read mixed information and my 86 Vanden Plas seems to have slight vacuum (enough to advance my timing about 4-6 degrees).

If it should be zero, does that point to failure of that valve?? If so, do you all tend to replace that valve or bypass it altogether?

Any insight would be greatly appreciated.

Thanks All!!!

 

As a followup,this is the language from an older Jag Lovers post about 4.2L tuneup that got me thinking about the removal of this delay valve:

"Under the manifold is a Dump Valve that is the source of a vacuum leak and we always get rid of it. There is one hose to it that goes to manifold vacuum and another that goes to ported vacuum. We take it out and connect the manifold vacuum directly to the supply for the ventilation system, removing the "T" in the line. We then connect the ported vacuum hose directly to the distributor vacuum advance module."

My initial question is, however, is should I have any vacuum at the line that supplies the vacuum advance of the distributor at idle?

 

It's been years since I gave that valve any thought but I'll do some mulling and remembering....

Here's some info that sounds correct.....but I can't 100% swear to it

Function of Vacuum Delay Valve

Cheers
DD

 

I did read that but didn't know when the "step" in vacuum should occur. Do you still use and maintain your delay valve or is it something you've bypassed??

Also, do you think additional advance above 17 degrees AT IDLE would improve idle quality, degrade it, or have no effect? Just looking for an educated guess!!

 

I've tried bypassing vs. keeping it in place and found no difference, at least not 'seat of the pants' difference, either way.

If the delay valve was flat-out inoperative, though, and allowed no advance at any time, ever....that would be a different story, I reckon !



In my experience it won't make any difference in idle quality, no. It costs nothing to do a little experimenting, though. You might have a different experience due to variables.

Cheers
DD

 

The emission theory would be my guess. Way back, weird ideas were promulgated as to vacuum advance. From blocking any advance at all to regulating it via temperature sensors. None made much sense to me.


I agree with Doug, bypass it and see how it does. any liklihood of a SMOG inspector noting it's absence is slight...


Max vacuum at idle translates to max advance at idle. Down on opening throttle and returning at cruise.


Put a variable strobe on your engine and watch the operation of the vacuum advance and the centrifugal. Using that and the tach, you can plot the advance curve. Road test and see how much initial gets the best "feel' sans ping. Just short of ping is an old "standard".



Carl

 

And still a perfectly good method IMHO, especially on older engines. Use the factory spec as a baseline and experiment a bit to find what's best for your car, the fuel you are using, your typical driving conditions, etc

Cheers
DD