I stumbled across this topic today and have read about it until I’m about cross eyed.

Most of the cases I read about were dealing with the V8s and one or two on the V6s. I also read where they were all affected during certain years and my 3.9 fell into the group. It’s my understanding from what I’ve read that there are 4 main symptoms. Ping or knock on acceleration, loss of power, can’t climb a hill, and excessive oil consumption. I don’t have the ping or knock, but I do have the other three. The oil consumption is not as bad as some I read about.

I’ve had this problem for a while and searched and tried everything I could think of and today was the first I’ve head about the plenum gasket. My truck’s get up and go has been gone for a while. Climbing hills is a problem and not long ago I was traveling at highway speed and the thing started acting like the fuel pump was going out (already experienced that) and then it straightened out. This happened several times in two or three weeks and hasn’t happened since. I’ve had times where it just almost wouldn’t go from a dead stop because it was spitting and sputtering. The lack of power and oil consumption has been going on the longest.

I read about looking down in the throttle body for oil. Some said it could be in the back, but I couldn’t pull off the dentist mirror trick. The only oil I saw looked like it was from the PVC valve.

I seem to have some of the symptoms, but no conclusive evidence. I was able to see the gasket right under the throttle body and it looked in tact.

What do you guys think?

 

Couldn't hurt to do the fix anyway. It is a known defect that should be fixed either way in my opinion. If the gasket isn't blown yet, it will blow soon.

 

x2 i had to to my plenum gasket last spring and it wasnt nearly as bad as i thought it would be. it me about three days to do it but i could only work on a little bit a time. bought a manifold gasket kit from rockauto.com for like $30 and it came with everything including a bypass hose, thermostat and all the bolts. i know the hughes plenum fix is better because it actually fixes the problem but im poor so...

 

Thanks for the input guys.

I would think the gasket is my problem. The gas mileage went and the power went and I noticed the oil consumption went up. I just finally figured age and miles and learned to live with it after trying several things.

From what I’ve seen in the pictures it’s not hard to figure the reason the gaskets blow out. Besides the difference in the metals and the thinness of the steel plate, the thing that sticks of to me is the number and spacing of the bolts. It looks to me like, if they had doubled the number and evenly spaced them things might have worked better. Then, I read where some say the bolts were too long and would bottom out. I’m not an engineer or rocket scientist, but the guy that designed this must have been on something.

I have a few of questions on the aftermath of this problem. When Dodge came out with the TSB was the replacement gasket change supposed to solve the problem? What was the difference in the original gaskets and the replacement gaskets? Could you guys see a difference in your replacement gaskets?

I stumbled across another site where one guy said he had changed a bunch and never changed the plate because the gasket was improved. Then yet another guy said he just changed the gasket and his engine had been 100K miles with no problems. I read where without the new improved plate the gasket was going to blow out a second time. Anybody out there have a second blowout after just a gasket change?

I guess what I’m asking is who came up with the plate change. I understand the theory. It just makes me wonder why these plates are only available from a couple of sources and there are major auto parts stores that could be selling replacement plates in kits from the major gasket makers as wide spread as the problem is. Just for example, Fel Pro has the gaskets and the manifold bolts, why not a replacement plate. I’m just curious.

I’m kind of straddling the fence here. Money is tight and I would like to try just the gasket change. I’m sure I could use the rest of the money on replacing the old brittle stuff I might break removing things.

I had one instance just this morning. I was looking around at what I would have to remove to get to the manifold. I reached in to unplug the PCV valve to check it and snap it broke. I pulled the hose off the intake to try and get the broken end out of the hose and snap again, the hose broke like it was glass. Needless to say, I’m kind of worried about all the unplugging and disconnecting I would have to do.

Maybe y’all can help get a better grip on this .

 

the difference between the original gasket and the new one is the original was paper gasket only. the new one is a steel gasket that has like an impregnated paper and rubber glued to it. as for the hoses and pvc breaking they are cheap and if they were that weak they needed to be replaced anyway. when i did mine (i have the 5.2 so it maybe a little different) i was able to leave the disributor, take the fuel rails off but left them connected to the main fuel line, take the throttle body off without disconecting any of the cables and then undo the accessory bracket and ac compressor(the compressor just swings out of the way so you dont have to worry about draining the system). the only thing on mine that gave me any trouble was the egr tube, the flare nut for it was rusted to the pipe and i had to unbot it from the exhaust manifold. its not a massive job and the parts are pretty cheap.

 

The first gen gasket was paper, the second gen gasket was stiffer with what looked like impregnated silicone. The last gasket offered is all steel. You have to ask for the superseded part, as most dealers try to get rid of the oldest stock first even if there is a better part available.

3.9's with miles will use oil from leaking valve stem seals. The telltale puff when you start it up and accelerate.

I would suggest replacing the timing chain and adding the tensioner. Your '94 will not have it. It helps tremendously with the fuel sync signal in the distributor. It's cheaper to buy as a Mopar Performance part.

You can pick up a little more oomph by switching controllers from a 3.9 Dodge B-van. This only works for SBEC controllers, which you have. No programming necessary. I used to do this for people a lot back in the day at the dealer. The B-van controller has a more aggressive timing curve and shift strategy for moving that pig heavy van with a V6. Makes the Dakota get up and go.

 

Thanks GeeWhiz.

Your description of the old and new gasket tells me a lot.

I've had most of the stuff off at one time or another. Just not all at once. I don't think it will be a big deal. Just getting in there and doing it I guess is my next step.

 

cjdautomotive

I did the timing chain and tensioner a couple of years back. It seemed to help a little.

Do you think I'd be spinning my wheels by changing plenum gasket?

Sounds like the controller is what I need.

I've been grasping at straws for some time now. If I ran across sombody in a Dakota with the 3.9 I'd quiz them about their truck to see what, if any, problems they had or were experiencing. To date nobody that I talked to has had my problems

Thanks for the info.

 

The plenum gasket becomes an issue if you are oil fouling plugs or can hear audible detonation. If neither of these is happening, I would agree you are not going to gain anything from changing the gasket. If you have significant carbon on the pistons from oil burning, you'll need to combustion clean it a few times before switching controllers. Spray it in a idle with the engine hot. Let it sit overnight and then fog out the neighbors. The timing curve is aggressive and will probably induce detonation if you don't.

And I have a '94 3.9 Dakota as a shop truck. So now you know someone with one...It's ugly, beat up, but has 300K on it and still does 18mpg. This is a 4wd ext cab. I built the trans at 77K and did the timing chain, tensioner, plenum gasket and WP at the same time. I think that was 2001 or so. Replaced valve stem seals at 180K. Never had to replace or fix anything else on it. It gets gas and oil changes. My wife lovingly refers to it as the "ghetto".

 

Thanks Graig,

I’ll just hold off. I just happened to pull the plugs the other day and they were clean. It’s just that all the reading I did on the subject it sounded like if I looked down the throttle body and the top of the pan wasn’t clean enough to eat off of you had a problem. I do see some gunk by where the PCV comes in and a light film on the opposite side, so I was just hoping that would help me.

I guess I’ll just have to hold off on the controller too. I’ve done a basic search and they are out of my range at the present time. I guess I’ll just keep on plugging along or should I say lugging along for now.

Thanks again.
Bryan