Plenum repairs

Silver Tex said:

Hello,
I'm going to repair the plenum on my son's (new to us) 99 5.9L Magnum - 158K on the clock. The site has provided great information and insight. I appreciate that.

Welcome, thats what were here for!

I thought while we were in there and at the suggestion of the plenum sticky, we'd swap the water pump and timing chain.

Good choice both are known to go in these trucks.

Question 1: The timing cover has 2 bolts that interface with the oil pan. What is the chance I have to pull the oil pan to complete this work. I'm thinking I can loosen the bolts and lower the pan sufficiently to remove/replace the timing cover. If I end up having to pull the pan, the manual states the motor mounts have to be unbolted and the engine lifted...yuck!

I do believe you can undo the front pan bolts to drop its enough to get the timing cover off. I'm not 100% sure of this so Ill let someone else confirm that. Probably will have to end up dropping the whole pan to replace the gasket. Should have enough room to raise the front end up enough to drop it.


Question 2: I have a cam shaft position sensor, but it was such a chore just to change out cap/rotor, I'm thinking I'll put it in while the manifold is out if for no other reason than I have good access to it.

Be your best plan while the manifolds off. If the sensors working fine I wouldnt change it though...

Question 3: What are the thoughts about mod's to the stock manifold, runners and injector ports? Have been doing some reading about it.

You can cut the runners back and move the power band up but you will lose bottom end power. Myself I'd just leave it the way it is.

Generally we are looking to achieve a sound running truck that gets the best mileage we can squeak out it.

Dont expect more then 13-14 mpg out of it if its 4x4. Quad cab even worse. These trucks were not built with mileage in mind LOL.

Went with recommendations in the stick - Hughes aluminum plate kit; 180 degree SS t-stat; gates water pump; cloyes double roller timing set (gaskets, crank seal included); Fel Pro gasket sets. Already did the wires, rotor, cap - all the hard way. Will change out the oil sending unit while the manifold is off.

Are you planning on running a hemifever tune? If not no need for a 180* run a 195* stat. In winter you will want a 195* stat. I use stant stats theyre a good quality. Wouldnt bother changing the oil sending unit if its working youd be better off installing a mechanical gauge instead. Otherwise list looks solid. Dont forget a new cat and o2 sensors as well. Cat will become clogged from the burning oil due to a leaky plenum and o2 sensors should be changed out as well.

Any thoughts would be appreciated.
Thank you,
Scott.

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Silver Tex said:

Thanks you guys.

I should have been more clear on the oil sending unit. It doesn't work. At idle shows 40 or so, then pegs. Maybe I can put a threaded tee in and run both. I do like the mechanical gauge and this would be a perfect time to do it.

Ahh fair enough definitely replace in that case. Yes you can use a tee to run both, many do that!

Cat/O2 sensors - I read somewhere not to worry about the backside sensor. Thoughts? No CEL, passed Colorado emissions. Is this any indication of cat status? How reliable is the pressure test for the cat - something like 1/4" in front of cat and measure pressure? If over some value, cat is plugged. I can't remember exactly what I read.

They can cause CEL's but the front is more worth replacing then the rear. Is your plenum blown? If it is leaking yes replace your cat, it will be ruined from the burning oil. An e-test may not pick that up, im not to sure on that. But if it IS leaking its in your best interest to replace.

Thoughts on cat and sensor manufacturers?

Some trucks prefer NTK sensors while others prefer Bosch. NTK is OEM. Cat go with magnaflow.

Last mileage check 9.75. 13 - 14 would be almost a 50% improvement.

What size tires? Quad cab or reg cab? 4x4 or 4x2? Bigger tires on a quad cab 4x4 would put you about there. Leaky plenums often lead to wors then normal fuel mileage.

Thanks again,
Scott.

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Silver Tex said:

Truck is
Quad Cab, 4 speed auto
265/17R-16 tires

Good size on the tires, I think a 265/75/16 is what ya meant though. Good size, you will get optimal mileage out of them. You will get a little worse then other rams being the quad cab though. They are heavier. Is it 4 wheel drive? That will make a difference as well.

I ordered a new front side O2 sensor. Had a little bit of a challenge confirming the correct side part number. RockAuto had L/R pre-cat shown (heavy duty motor). NTK - got it figured out and documented now.

Yeah I had the same headache trying to figure out which part number was the right one. Think I went to canadian tire twice to return different sensors lol. NTK should work good.

Cat - no new cat ordered yet. Considering 2 options - both MagnaFlow.
With or without added piping. Any comments? I'd like to go with the "without piping" and would take any thoughts on change out. About a $65 cost difference and ease of installation will weigh into to which one way I go based on any feedback received.

When I got mine, it was a direct fit. Two 2 1/4" inlets, One 2 1/2" outlet. Just need couplers and clamps , no clamps if you're gonna weld. I wouldn't bother buying one with piping. A direct fit will fit in the same spot as factory. Just beware you may need to lengthen the wires on the front o2 sensor, I know I had to. You can buy a wire extension, or just solder extensions in. No butt connectors or electrical tape tied connections!!

Hughes kit comes with new manifold bolts. Have both in/ft pound torque's and have made note of the sequence and which wrench to use.

Hughes kit is a good kit, I used it as well way worth the extra few bucks! Just watch out for broken bolts when you're removing the manifold.

I did order a new oil pan gasket in case. I appreciate the idea of lifting the body and letting the suspension hang in an effort to gain the necessary clearance if it needs to be changed. It doesn't leak now and I don't want it to leak after.

Good idea, much better to be safe then sorry!

I have a pretty high level of confidence the plenum has failed. Checked it through the TB - quite a bit of oil. Also confirmed steel plate with magnet.

Sounds like it, def will be a good fix. You will notice a difference after! You might consider replacing your distributor cab and rotor and spark plugs and wires while your in there. Definitely a good idea.

Truck doesn't use oil beyond what I would anticipate with this mileage. It came with pretty good maintenance records. This tank of fuel is showing better mileage - indications suggest double digits without the use of a decimal point .

Fuel rail line disconnect tool: I read somewhere size E - sound correct?

I have no idea, I pulled the rails and injectors to replace injector seals. FSM will tell you.

You guys have all offered good stuff! I may write a follow up after we are done. At a minimum there should be some entertaining anecdotes.

Love to see it if ya do! Just remember we need pics!

One other question. Do any of you have issues with log on when using MS Explorer? I switched to Firefox and it seems to work better. I have written this post 3 times now and I kept getting booted when trying to preview. Going without preview this time.

I have always used google chrome and the only issue I ever get with the site is im not logged in when the page first opens but it logs me in when I click a link on the home page. No issues otherwise.

Thanks again all! Any other thoughts or suggestions will be greatly appreciated.
Scott.

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Merc225hp said:

If you are going to drop the oil pan I would be installing a new HV oil pump and pick up tube. An HV pump will not suck all the oil out of the pan at anytime, unlike what you might hear.

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Merc225hp said:

This might hold true for diff motor makers, but not ours. My motor is built to go well past the stock redline and I have had it over that many a time wheeling in the snow, stock oil pan is under it, it has never once lost oil psi at 6000+rpm. If this was a problem we would have read about it many a time on the forums and lot's are using the HV oil pump in there trucks.

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