Plenum gasket--maybe?

DodgeDrew71 · Oct 28, 2016

So the 3.9 in the '01 isn't burning crazy amount of oil like I've read some people have dealt with.

I have a P0420 code for the Cat efficiency below threshold. Just picked up pre & post O2 sensors, but if there is oil from the plenum then, they will just eventually go bad. Also going to call around and get the cat replaced--maybe new muffler while at it.

Should I be considering a Plenum replacement? Again, she isn't burning the oil like others have dealt with. I almost want to just do it (preventive maintenance) and replace lifters at same time. (Last year I took care of cap, rotor, wires, coil and plugs.)

Truck has just shy of 115k.

Gotta just love this forum and the wonderful info from folks!
-Drew

dudeman2009 · Oct 28, 2016

Go ahead, if you want to replace the lifters you will have to remove the intake anyway. I'd check with either a borescope or magnet to see if your plenum pan has been replaced with an aluminum one. If it has, don't worry, it's already been done. Otherwise Hughes Engines makes a good kit that includes all the gaskets you need. It also ships with all new bolts.

You won't ever truly know if your pan gasket is bad until you inspect it with your own eyes.

IMO, if you're replacing the lifters, might as well replace the push rods and rockers as well. I think there are roller rockers for these engines. That is, if you might ever plan on beefing it up for more power. Otherwise, just keep it stock.

Also, Just because i've seen plenty of people make this mistake, don't mix your rockers and pushrods around with each other, they are matched sets, and are also matched to the valve. A tip I learned awhile back, get a piece of cardboard or two, stick the pushrods into the corrugation in the center and label them with sharpie. They will not get accidentally confused that way. Then just wrap some numbered masking tape around the rockers or throw them in individual labeled ziplock bags. Since you are replacing the lifters, it really doesn't matter what you do with the old ones.

Just an FYI, take a video or something of the oil coming up from the pushrods so you have a baseline when re-installing. That way if you have a question about how much oil should be coming out, you have video.

Lastly, READ your torque specs.

Good luck

dapepper9 · Oct 28, 2016

I honestly wouldn't bother doing lifters and pushrods. With only 115k on these fairly bulletproof engines, mostly just a waste of time and money. If you're getting some clattering, yeah might be a good idea.

DodgeDrew71 · Oct 28, 2016

dudeman2009 said:
Go ahead, if you want to replace the lifters you will have to remove the intake anyway. I'd check with either a borescope or magnet to see if your plenum pan has been replaced with an aluminum one. If it has, don't worry, it's already been done. Otherwise Hughes Engines makes a good kit that includes all the gaskets you need. It also ships with all new bolts.

You won't ever truly know if your pan gasket is bad until you inspect it with your own eyes.

IMO, if you're replacing the lifters, might as well replace the push rods and rockers as well. I think there are roller rockers for these engines. That is, if you might ever plan on beefing it up for more power. Otherwise, just keep it stock.

Also, Just because i've seen plenty of people make this mistake, don't mix your rockers and pushrods around with each other, they are matched sets, and are also matched to the valve. A tip I learned awhile back, get a piece of cardboard or two, stick the pushrods into the corrugation in the center and label them with sharpie. They will not get accidentally confused that way. Then just wrap some numbered masking tape around the rockers or throw them in individual labeled ziplock bags. Since you are replacing the lifters, it really doesn't matter what you do with the old ones.

Just an FYI, take a video or something of the oil coming up from the pushrods so you have a baseline when re-installing. That way if you have a question about how much oil should be coming out, you have video.

Lastly, READ your torque specs.

Good luck

Yeah after some more reading and chatting with the old man we both decided to just take care of the Plenum. Going to take the TB off to give it a good cleaning and will see what I see and then go from there on ordering it from Hughes.
And oh yes, all over the torques specs, I have my inch lb wrench all set.

dodge dude94 · Oct 28, 2016

Do the plenum. Don't worry about lifters. Do the kegger mod, I'd be interested to see what it behaves like on a 3.9

Jimmy68 · Oct 29, 2016

A 3.9L in a fullsize? Dodge did that?

dodge dude94 · Oct 29, 2016

Uh....yeah. For a long time.

DodgeDrew71 · Oct 31, 2016

dodge dude94 said:
Do the plenum. Don't worry about lifters. Do the kegger mod, I'd be interested to see what it behaves like on a 3.9

Dude,
I did some research on the Kregger mod and a couple other things.
Guess what I want to know is what does the kregger mod accomplish?
Does removing that material help low end or top end--what's the performance benefit?
I'm definitely considering it.

Also thinking about port matching the intake to the gaskets, however I'm wondering if much benefit since the heads will not be port matched. Do the heads have a larger openings already compare to the intake?

Anyways, some great videos out there on the Plenum gasket replacement and other things for our trucks. I seem to keep adding things to my list to do. LOL :naughty:

dodge dude94 · Oct 31, 2016

DodgeDrew71 said:
Dude,
I did some research on the Kregger mod and a couple other things.
Guess what I want to know is what does the kregger mod accomplish?
Does removing that material help low end or top end--what's the performance benefit?
I'm definitely considering it.

Also thinking about port matching the intake to the gaskets, however I'm wondering if much benefit since the heads will not be port matched. Do the heads have a larger openings already compare to the intake?

Anyways, some great videos out there on the Plenum gasket replacement and other things for our trucks. I seem to keep adding things to my list to do. LOL

It opens up the runners to more air for more power in the mid and upper range of the power band. Basically moves peak power up a couple hundred RPM and in most cases gives you a more usable powerband as these trucks run out of air QUICK at 3500rpm.
Couple that with a 50-52mm throttle body and it'll definitely breathe better.

DodgeDrew71 · Nov 1, 2016

dodge dude94 said:
It opens up the runners to more air for more power in the mid and upper range of the power band. Basically moves peak power up a couple hundred RPM and in most cases gives you a more usable powerband as these trucks run out of air QUICK at 3500rpm.
Couple that with a 50-52mm throttle body and it'll definitely breathe better.

Thank you.
I'm sure since I have just the 3.9L there are some limitations on just how much air it can flow. I am curious and willing to do the Kregger as well as removing the air horn material on the top part of the TB. (picked up the cutting, grinding and polishing pieces for the dremel last night.)

Would like to get more low/mid power from the motor, but that is asking a lot from a 6 cyl. LOL Oh well I got a great deal on the truck and wanted a truck not a power monster. Guess all this fun is telling next time get a V8. :roflsquared:

Going to start this venture Wednesday night. Will document some of it and once I have it back on the road will create a thread on how it went and what I've noticed.

Thanks for the info!

dodge dude94 · Nov 1, 2016

Well....what are you gonna do with it? If it's not hauling anything I would say open that keg all the way up and bore the TB as big as you can on stock plates. Stock V6 tbs are somewhere around 48mm bore at the opening, so you should be able to open it to a 50 and it should be around 50 all the way through if I remember the V6 tb right.

Yeret · Nov 4, 2016

Jimmy68 said:
A 3.9L in a fullsize? Dodge did that?

My former mechanic had a Dakota with the 3.9. He used to do some crazy stuff to it. Hauled loads so heavy that the ass rode on the bump stops, towed my sister's Expedition some 40 miles. Never missed a beat though and was still going when his ex told him to **** off and took it.

Plenum gasket--maybe?

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