Oldewoodupes

I have two ‘78’s one has this part bypassing the aux air valve in the cis system, the other doesn’t. Both cars have a/c. Just wondering what this part does? Also wondering if both should or shouldn’t have it. It’s part “D” in this pic. And it’s clipped to the strut bar in the photo. Thanks

Rob Edwards

Early '78s don't have it, late(r) '78s do. Not sure when the changeover was. It provides a bit of extra air bypassing the throttle plate at idle, so the engine gets a little more air to compensate for the increased load of the AC compressor.

Oldewoodupes

That makes sense, thanks Rob

Petza914

Oldewoodupes, could you email me the photo diagram you posted to petza914@gmail.com I'd like to check my distributor advance and retard vacuum line connections and this looks to be the best diagram I've seen. Thanks a lot.

Rob Edwards

Here's the diagram, full size:

islaTurbine

My '78 is VIN #0338 and she doesn't have the valve....

Rob Edwards

Based on pics from BAT auctions, the change is somewhere between #585 and #917. Will poke around to narrow that down.

Hey_Allen

Does anyone know if this diagram is accurate for an early '78, other than the AC idle solenoid?
This is the best vacuum diagram for an early car that I've seen, but I'm still chasing ghosts in the vacuum plumbing, and finding bolts in hoses...

Hey_Allen

My car is #706 and doesn't have the AC idle solenoid, and while it might have "fallen off" somewhere along the line, I don't see anything obvious in the Idle Air path that looks like it is missing.

linderpat

Mine (#834, US spec) does not have it either.

Rob Edwards

Cool, so between 834 and 917, US market.

Here's a list of vacuum hose origins on the throttle body, as you look down on it from the front of the engine:


passenger rear 10:30 oclock: red to center of 30oC temp switch

passenger rear 11 oclock: blue to 12 oclock on EGR amp

center rear 12 o;clock: cloth to diverter valve

center rear 12:30 oclock - cloth to edge of barometric control unit

driver rear 1 o'clock: rubber to WUR on left rear side

passenger side 9 o'clock: rubber to WUR on top- vacuum at idle, fuel enrichment off idle

passenger side 9 oclock: white to 9 oclock on EGR amp

front 6 oclock: cloth (?) to distributor vacuum advance


From vacuum amplifier:

brown out of EGR valve to 3 oclock on EGR amp

orange out of 6 oclock on EGR amp to base of EGR valve

Hey_Allen

What year is that from?
I've been amazed at just how much variation there is between years, even in vacuum and wiring.
(the '78-'79 wiring differences drove me up the wall until I recognized that they were there...)

Rob Edwards

That's from 1978 #107, so it's early '78. The connections on the throttle body should be the same throughout '78, though the addition of the AC solenoid valve obviously changes some of the routing away from the throttle body. Here are two shots from #1117, showing the vacuum amplifier and the AC solenoid valve routing.

Hey_Allen

Thank you for those pics, I'm going to have to take another look at the plumbing on my engine now.
I think that the remaining bolt plugged line is one of the WUR lines, likely the one called 9-o'clock in that picture.
They all need new hoses though, as there is plenty of cracking on the ends, and likely in the middles also.

Rob Edwards

Those WUR hoses are f'ing expensive for what they are ($60ish, you need two) , I guess it's the 90 degree bend in the end.