I have a 1996 Dodge B2500 with 5.9L V8. About 3 months ago, the AC would cut out when I would be accelerating up hills, usually steep hills or at high speeds. Cool air would come out of the defroster and floor vents when it happened. Happened a lot, but it would come right back when I eased up on gas pedal, so didn't worry too much. Then I noticed the heat do the same thing twice in the last week. It would cut out alltogether. On a long trip for Thanksgiving, about 5 hours into a drive, running flawlessley, heat working well, I was going up a mountian on the highway, and the van started shaking violently and loosing power, I let up off the gas and it came back, ran OK for a while, just couldn't accelerate too quickly. Within 15 minutes, I couldn't accelerate at all, had to get towed to town. When tow truck lifted back end, brake lights came on, and the van lost power brakes. Getting codes for misfire on cylinders 1,2 &3. Plugs, wires, cap & rotor look OK, as well as air filter. The van runs great and idles fine, after all of this, still no power brakes, and haven't been back on highway.

 

The issue with the heat/AC and the power brakes is likely due to a vacuum leak. The misfires could also be a result of a large vacuum leak, so a leak is what I'd be looking for first.

 

Check the Brake Booster, if you hear hissing sounds from under your feet or by the mastercylinder then the booster is probably it. These engines do not have a whole lot of vacuum systems on them. Another area I have heard of is the plenium, so if not the brake booster check the plenium carefully. And look over the vaccum lines, see any cracks then replace the line(s).

 

I checked over all vacuum lines over the weekend, all looked ok, except for 1 that was disconnected. Under the ac unit behind the passenger headlight, there was a black sphere with a small vacuum line attached to the top of it, that was disconnected, which I am thinking might have been the heat and ac problem. I am going to get a brake booster this week, the brake pedal is not returning up as far as it should, and there is a lot of corrosion on the outside of the booster, also, when you disconnect the booster vacuum line that goes to the plenum the engine revs up and when you reconnect it the engine dies, so I am thinking sonmething is clogged in there.
Thanks for the help.

 

The vacuum hose next to the sphere is for the heating system vent controls. The sphere is too. It's a vacuum reservoir and it's purpose is to keep the air blowing to the floor or wherever during times of low vacuum, such as, climbing a long hill.

The hose to the brake booster is not plugged. By disconnecting it, you created a large vacuum leak and them by reconnecting it you plugged the leak. The computer tried to compensate for the sudden change of vacuum but wasn't fast enough and the van stalled.

 

I replaced the brake booster, brakes work great now, and the van seems to idle better, I haven't had the chance to take it out on the highway to test it yet, going to do that tonight to see if the running problem is still there. Definitly fixed the heat/ac problem and the braking problem though. Does anyone out there think a bad brake booster would cause the vehicle to run poorly?
Also, I tried an OBD2 scanner on the van, it said waiting for vehicle to communicate for about 30min, then I gave up. The van is a 96, but a sticker says it was manufactured in 95, but it does have the correct 16 pin port under the dash, so I thought it should have worked. Anybody have experience with something like this?

 

Yes, a leaking brake booster will cause the engine to run poorly due to the vacuum loss.

It should only take a few seconds for the code reader to connect to the PCM. Either the scanner is not set correctly to your year and model, the cord is the wrong one, or there is a problem with the PCM itself.

 

I had one customer whom needed his brake booster replaced for it was hissing inside the vehicle. He complained the engine ran rough in drive and that the idle speed needed to be reduced for with the leak it was idling very high. I told him that I believed replacing the Booster would solve his problems, he was not convenced. But once the new booster was in the idling and running issues were solved.

 

The problem is back!!
I tohught I had fixed the problem by changing the brake booster. I have been driving this van for almost 2 months off and on since I have 2 vehicles and everything has been fine until today. I drove around for 2 hours looking for junkyards for the Coupling that connects the steering column to the gear box, didn't find it, but on the highway, going about 60 the van started loosing power again, and shaking like crazy. I couldn't go over 50mph, so I pulled off to the side and let traffic go by, once back on the road, I got to 55mph but it was shaking pretty bad, went about a mile to the first exit and then it was shaking just going 35. Yestrday I notices the heat switched from the forward vents to the floor when I was hitting the gas, which hasnt happened in a while, and was the first sign last time this problem happened. The brakes are still working, for now at least. This is really strange, I am going to check the very small vacuum line behind the headlight again, which I thought was the cause of the heat vent switching problem before, could that small line cause the whople vehicle to run poorly?
It kind of seems like the cat might be getting clogged, but it doesn't seem that hot, and why was the vehicle running well for 2 months?
Any help is appreciated.

 

I just realized that this problem occurrs when the vehicle gets around a quarter tank of gas. I am thinking that my fuel pump is on its way out. Van runs great as long as its above a quarter tank. It looks like at least a $400 part and I need a $250 steering intermediate shaft, so the costs are adding up, but at least I have found the problem.