The vents turning to defrost on hills indicates the AC controls are losing vacuum when the engine is under load. That could be a check valve problem, or your vacuum reservoir is leaking.

 

Was a bad check I hope...gonna try carb cleaner soon.

 

Sounds like the booster. The booster is a dual diaphram and mine started the same thing. It got so bad (me lazy) i could get the engine to stumble and die almost by moving my foot slightly on the pedal. It goes bad long before you hear the hiss. Might as well do master cyl as your at it. I had the same lean code/ registers going to defrostvetc.

 

Blocked the booster hose didn't cure anything...

 

So its the air tube from the egr valve. The seal at the plastic intake....Any ideas?
Would a fel pro 71202 work?

Dick

 

Looking at the catalog, it would take a Fel Pro 72266.

 

Thanks much. I couldn't find that....

 

Gonna get one of each and see what seems better.. Or maybe use both.

 

Wahhlaa Fixed...just when you thought the old 96 couldn't run any better....Runs like new. I used both the oring and the oem gasket. felpro 71202 and felpro 72266.
It aint gonna leak and i'll bet my green 96 could use them. Its not real hard getting at that seal you just have to be able to get the bolts out....The ac comp has to come out and be laid it aside. dipstick nut and pull stick just nuff to go over stud don't yank out of block.
Now the stud has to come out where the dip stick was fastened. Good luck. mine was ok because I did an intake gasket a few years ago. From the wheel well I removed the two egr bolts. Next I grabbed the egr and flexed it out of the way to get the pipe out.

The seal didn't look too good...I put the new oem on then the green oring and put everything back together.
I'll bet many 4.0L have this problem.. A little carb cleaner will tell or heat to defrost up a hill.

Thanks Guy's

Dick

 

Now that the engine runs good and I have the major vacuum leak fixed I did notice going up a hill the heat diverted to defrost....Tank and check valve check ok. Don't know what to look for or how to check the two lines that go into the dash area from outside in the engine compartment. Checking these with a vacuum pump depends on where the switches are turned..I do have my green van to compare to..but.

All three of my vans go to def when on a hill. The green mint one not all the time. grrrr. Vac tank is pretty small.

 

sounds like a cracked vacuum tube going to the RECIRCULATE valve/actuator, near where that check valve is also connected to the vacuum tubes.

 

Started the van the other day for the late 300 mile trip home . Engine stalling at idle wouldnt idle. Any way had to power brake in traffic until I hit 95 ok at speed but at1k rpm would miss and stumble. Long story short it had popped the vac hose from the intake next to pcv hose. Rubber nipple lost its tension. I had read your reply some days earlier. Thought it was plugs wiring.

 

I did a vac check of all the hoses they seem to be fine. Van doesn't have enough miles to have the lines go bad yet it seems.

Dick