Is there even a check valve in there? It looks like the hose is just jammed in there, that'll do it.

98 does have a nice clean engine bay.

 

Ok got bored and self ingenuity came to mind, took a regular hose and put it in place of the one way valve, I can now feel the AC fade away more then a slight fade and total drop off suddenly, soo I think the valve has failed partly, as of now the ac works better with the new strait tube plugged in, the ac falls out at around 2000 now soo im good for freeway crusing hopefully.

I wonder if I can find a 1 way valve to put in the middle of this hose and see if that one works, I love having a garage with so much miscelaneous stuff i can test and fix so much.

 

One thing I see in your pic is the small section of hose on the bottom of the check valve has been replace with some ribbed hose it looks way thinner I have used this hose before and its very soft and thin walled I don’t think its designed as a vacuum hose.

The hose may be partly collapsing in and pinching down the vacuum coming through it if you look at my vacuum hose it’s very thick and strong.

So get a new check valve and some good strong vacuum hose at the same time. Any auto store may have this check valve ask they may have it or a replacement that could work as long as the hose barb works with the hose size.

 

Replaced the check valve, noticeably better then before but still kind of iffy in the cruising range, better then my tube tho that i just put there. There was a check valve covered in weather stripping.

I think I might have a small leak somewhere still, butt at least im making progress.

 

You might have a slight leak. With the engine off you should be able to move the controls and hear the doors move, maybe once or twice, depending on how tight the system is.

The valve cover gaskets probably need to be replaced. After a while they set and as things expand and contract loosen up. The PCV system helps reduce the amount of vapors in there but remember, there is a lot of oil up there too, to lubricate the valve train.

New valve cover gaskets are cheap, yes a bit of pain to do. I prefer Fel-Pro, even if they are a few dollars more, they're better quality than the "generic" ones.

Check your PCV valve while you're in there too.

 

I noticed something?

Looking at your pic’s something looked wrong to me what I see is the brake booster is an odd size different than stock and I see a Bosch sticker on it. Question are your brakes ok acting kind of strange you see I’m wondering if maybe this is part of the problem someone installed the wrong brake booster in your Dakota maybe it takes more vacuum for it to work robbing vacuum from the system or I’m thinking the hole that the vacuum line plugs into is a tad larger than it should be so some vacuum is being lost that way is that connection very loose or is it snug? now I’m just guessing on this but it does look off to me.

Is it hard braking or I should say do you need to put a lot force on the pedal to stop? Does you brake pedal feel kind of low or hit the floor when you use the brake?

Now if your valve covers are very loose that could be robbing vacuum power also from the HVAC system how is your oil cap is it loose also?

 

I may be wrong on the booster I just looked on rockauto and it looks like they changed it somewhat your year to a not so wide one so its squatty compared to my booster. Just another odd change Dodge made I guess.

 

I know my booster is bigger then the 2.5 and the 3.9, but its the same size as my friends 5.2 ram soo I think its just bigger because of the engine, and i think its fine cuz it holds vacuum well.

I have noticed my brake pedal is squishier then most dakotas but also i stop a good 20 feet shorter then others. I love that my town has like 20 dakotas here. Good for comparison of stuff.

 

Yea I looked on rockauto and the 5.2 had a squatty booster on it compared to the 2.5. I wonder why the booster was changed out on yours anyway it’s just normal I guess seeing the Bosch sticker on it got my attention.

Get that thing down to a cleaning booth and get it cleaned up. I keep my engines clean as can be I use a spray booth two times a year with some engine foam I think I picked that up from my Dad he kept his engines clean also he used to be an auto mec for a few years and did all his own repair work so I learned watching him.

In all the 35 years of spraying my engine I had only one time she would not start for me and I had to pop off the cap and dry it out before it would start again so to me it’s totally safe to clean them two times a year and the one time that happened it was because the sparkplug wires had gone bad not because of the cleaning. Just be careful not to spray wires too much and stay away from the distributor and throttle body I suggest not spraying the power steering pump and your starter.

 

Cleaning booth? Can I just use my pressure washer at home or the hose? Im kinda cheap like that, and is it better to clean a hot engine or a cold one? I know big diesels clean them hot to steam clean almost. Also Ill avoid the coil but wires wont bother me I think, i can just leave it in the driveway for a while till it starts like normal