So I have started trying to take care of some nagging issues and I figured I would give chatgpt a shot. First off, it is dumb AF. Even if you tell it to not make stuff up and to give detailed and high confidence answers it will still happily tell you something wrong (the horn is located behind the grill on the passenger side, except that it is actually on the driver's side under the headlight assembly).

Anyway, the next two issues are likely vacuum or check valve related. HVAC goes into defrost under load and cruise control only works intermittently and cuts out under engine load. So I ask AI about diagnosing it with a smoke machine. It tells me to disconnect the vacuum line from the intake manifold by accessing it from the front of the van. From what I can tell, assuming I'm looking at the right tube, that is almost impossible without removing the doghouse. Is AI full of it?

Next, my sliding cargo door tends to not latch at the rear on close. I have to push it inwards to get it to latch as I slide it closed. AI is telling me that is because #17 at https://www.moparpartsgiant.com/part...55347146.html? is bad.

I have some doubts about that. It seems to roll just fine. It's just that the (spring loaded?) swing arm seems to resist the rear of the door going inwards. Hopefully that makes sense. First AI tried to tell me that the door is sagging so the latch is matching up. No, it is aligned just fine, it just doesn't like to latch without being pushed on.

 

For the cruise and HVAC, that is a lack of vacuum. Could be a leak, could be a blown plenum, could be bad check valves, or a combination of those.

For the door, I would start by lubing the crap out of EVERYTHING. Exercise the door a bit, to get it distributed, and see if that doesn't solve it. Some of them, gotta give it a pretty good shove to get it to latch properly.

 

vacuum for accessories i believe comes off the drive side of the intake manifold, there's a big hose for the brake booster and a smaller one for accessories. I wouldn't expect dog house removal to be necessary, but it could be a reach from the front side

 

I think pulling the doghouse, while a bit of an exercise, would make the operation a LOT easier......

 

Keep in mind, drivers side refers to left hand drive vehicles. If it was sold new in some place like South Africa, England, Japan or other places where they drive on the left side of the road, it will mean right hand drive referring to driver position. The cruise and HVAC shifting sounds like what I had with my 1996 Ram with the 5.9. There are two one way vacuum valves. One on the right hand side of the engine as you sit in the vehicle. Another one higher up in the vacuum lines. Removing the engine cover (dog house) will make working on the engine mounted valve MUCH easier. I have no idea where it would be on a van. I attended a seminar at the U of Y and found this.


Away from the body, your van is similar to the pickups. In some ways, working on the engine in a van is actually easier as the rear of the engine is right THERE. When I did a major tune up on my pickup a few years back, I had to climb inside to access the rear of the engine.

 

Got in there and the check valve immediately off of the intake manifold is bad. Not sure if there are any others, but this seems like a pretty likely culprit. Of course, no auto parts store anywhere has a replacement.

I've lubed the door a lot previously. It definitely rolls smoother than it used to but it still needs to be slid just right to latch without pushing it inward.

It seems to be off the passenger's side of the intake manifold. It goes rubber elbow to check valve to rubber elbow to Y fitting. Disconnected that and after a couple minutes the hvac went into defrost. The check valve is bad so that seems like the most likely culprit. We'll find out tomorrow when my Amazon order gets here.

Yeah, I pulled the doghouse. Hardest part was pulling the carpet back enough to get to the bolts. Maybe now that I know exactly what I'm looking for I could get there from the front but definitely a hell of a lot easier from the passenger side inside the van.

 

The check valve has a Dorman number. I think I had an extra for use as needed but it's probably somewhere in the truck under the chains, tie down straps, pry bars, work jackets, safety equipment and other things that build up in a working truck over time.

 

Quick update just to provide some closure. Ended up with an AC delco check valve as the dorman option was going to take longer to arrive. It definitely helped. I still lost vents on one long steep hill nearby but otherwise they stayed in the right position for the entirety of a 20 minute test drive. Not sure if I have another leak somewhere or if the hill was just so long that I ran out of vacuum (you only build vacuum at idle?). Could I just throw a generic reservoir in there?

 

Do you know if the (defective on seemingly every magnum engine) plenum gasket has been addressed? If not, you could be losing vacuum through there.

 

It probably hasn't. Previous owner's records don't mention it. It was a fleet van before that so who knows. I haven't had any of the usual symptoms though. It idles fine, no power loss, so air sucking sound.