Greetings. I'm new to the forum. I just got a 96 3.9 Dakota project. It runs but is missing a part on the back of the manifold on the passenger side. There's a threaded port below a rectangular plate that is wide open. Engine runs but noticed a definite air leak noise under certain loads, expected a vacuum leak but after a brief search, I found this port wide open. This truck sat for several years and was evidently cannibalized. I'm hoping to find maintenance manuals for it. Thanks for any help!!!

what goes here?

Passenger Side aft side of the manifold.

 

Ok my terminology might be off a little but with that plate being directly above it port. I'm thinking it is or was some sort of EGR or PCV type port thats either been "deleted" or maybe surplus parts being used up resulted in use of the intake on a vehicle that doesn't use it? I thought EGR was discontinued by 96, maybe its an older motor used in a newer truck. Sorry I'm not as familiar with the 3.9 but that's kinda what it looks like to me and there is just a missing plug causing a vacuum leak. Maybe this port was repurposed for something else. Hopefully someone else can chime in for you. At this point I'd say if you dont have an loose hoses hanging around back there I'd find a plug to fit the threads and plug it for now.

 

EGR Blockoff plate. EGR went away for 96, but, they still had some of the old manifolds layin' about, and wanted to use 'em up. My 96 full size with the 5.9 had the same thing. That is factory.

 

I see the plate, which I figured was EGR, but what about the hole below? Is the plug a pipe thread plug or sealed plug (O-ring/crush gasket)? I did just get access to a parts catalog, so hoping to cruise that tonight once I get access to my computer.

Thanks!

 

That would probably be national pipe threads. Second look maybe not. They look pretty fine they might be SAE threads.

 

Pipe thread. Yup. But, since the egr mounting spot is blocked, you don't need to do anything with it. Although, it IS a nice spot for hornets to build a nest. Don't ask how I know.......

 

I thought that was the cause of a vacuum leak I'm hearing. When under load (manual trans) there's a high-pitched wine like a vacuum leak but I've searched everywhere and can't locate it. I only hear the noise when over 2K RPM and under a load and I can't duplicate that in the driveway. I was hoping that open EGR port was the culprit. Are you sure it's blocked? I did rev the engine with my thumb over the port and didn't feel any suction, but wasn't sure when it might kick in. A 1/2" NPT plug is just barely too small. I'm going to look for a 5/8 tomorrow. The EGR tube I found online appears to have straight threads, but hard to tell for sure from the picture.

 

Yea, I checked when I had one off.... Block off plate does the job.

There are a lotta places that may whistle with high air demand. Is the gasket between the throttle body, and filter housing there? TB gasket itself is just thin paper.... (and are like two bucks at the parts store....)

 

I think I found the leak. I plugged the port to the evaporator emissions canister at the TB and the noise is gone. Can the Evap Emissions system be deleted or bypassed?

 

Not really a good idea. The PCM will whine about it. It's simple enough to repair though. Probably easier than bypassing it. Fuel tank needs to vent somewhere, you you don't wanna be smelling gas constantly.