Missing vacuum advance hose

[mperickson]

New (to me) 1994 Disco. The vacuum advance hose comes out of the plenum but is just cut off. I bought new hose tonight to put on tomorrow. The port (on the distributor) where I'm supposed put the hose actually has cap on it.... My guess is that the distributor was replaced at some point and the hose was never installed. The truck doesn't idle right when its warm. Likes to surge then drop to the point where it stalls. Would this unattached hose cause this? (vacuum leak, vacuum advance, etc.) Any thoughts would be helpful. Thanks in advance.

 

[joey]

Yes a vacuum leak will cause your issue. If the Distributor has been changed, try putting a cap on the plenum side.

 

[mperickson]

So don't put the hose on at all?

 

[joey]

If it doesn't have a vacuum going to the distributor I would cap it (they sell vacuum caps at any autoparts store, then see if that helps. For $5 you will know real fast.

 

[mperickson]

I already replaced the hose. Seemed to help with idling. There is a hesitation when you first hit the throttle though. Engine runs fine when running casually. It dies if you give it hell and then let off throttle. Pulling my hair out.

 

[joey]

Sounds almost like a fuel issue. Have you checked the fuel filter? How much fuel pressure are you getting? Has the fuel pump ever been replaced?

 

[mperickson]

New fuel/air filters will be here tomorrow or Thursday. We will see if it helps.

 

[joey]

Remember the fuel pump has a screen on it in the fuel tank. It may very well be nasty dirty after all these year as well. If over 100k miles you may need to look into replacing the pump. After you change the fuel filter, check the fuel pressure to see how the pump is doing.

 

[BeemerNut]

I'd bet 75% plus all 3.9's with a distributor the vacuum advance unit diaphragm has failed not alone the mechanical advance unit not been cleaned, lubed and properly maintained.
The plenum top ****** for vacuum advance signal only has app 0.011" drilled diameter passage hence a slow and sluggish timing vacuum advance signal to vacuum unit.
Any vacuum advance unit diaphragm leakage or failure no matter how small of leak will absorb this very small and restrictive signal.
OEM units do not last very long (cheap crap material) as well are expensive for what they are.
Properly maintained distributor with full vacuum and mechanical advance will wake up these weak 3.9 engines.