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Discussion Starter · #1 ·
ok guys I'm new here and I am looking for some help about a few problems I am having. Here are the specs on my truck:

1999 Dodge Ram 1500 SLT 4x4 Quad Cab
5.9L V8 "Z" type
148K miles
3" skyjacker suspension lift
35x12.50 Mickey thompson Baja Claws
Super chips micro tuner, programmed for performance (running 93 Octane gas)

First off, I am getting a ton of antifreeze leaking on my passenger floorboard from under the dash... I think it possibly could be the heater core but am not certain..
Secondly, check engine light is on and superchip tuner is saying a misfire on 6&8, I had this problem before and changed the wires,plugs, dist. cap, rotor, and pcv valve and that did the trick yet it was about 1 year ago (about 30000 miles ago). I changed the plugs last week with autolite double platinum yet I still have 6 & 8 misfiring, it runs real rough especially in 4th gear crusing, the rpm's are jumping up and down and it can't hold 70 mph on flat ground. The motor has always burned oil since I bought it with 65k in 2003. I usually cant go 2k after an oil change without having to add 2 quarts cause it wont mark the stick. I am wondering if i need to change wires/plugs etc again and re route the wires according to info I found online so that they wont cross fire?
Also, the truck has never ran over 210 in temp, ever! and recently (about the time the AF started leaking) it will sometimes jump up to 260 then go back down, I have to keep adding coolant... I guess it could be due losing AF under the dash? but ti doesnt seem to be THAT much leaking.

If anyone can help me on these items I would greatly appreciate it!
 

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First, probably correct, it's common. You don't need to be losing much to develop a bubble in the cooling system, if it's not getting to pressure it'll not be purging the air out through the overflow, hence the overheating, the cooling system on these isn't particularly good at purging anyway.
Second, were the 6 and 8 plugs you took out fouled? All other symptoms classic signs of a failed plenum pan gasket, again common.
 

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Discussion Starter · #3 ·
When I took out the 6 & 8 plugs, they were both in pretty bad shape, in particular 8 was actually melted together on the bottom of the plug. Right after I changed the plugs, I cleared the DTC's and ran it for about 20 mins and about 10 miles down the road, the Ck engine light came back on with # 6 misfire code... I think I am getting cross-firing from 6 to 8.

What is the deal behind the plenum gasket? what is it and what does problems does it cause? also how to change it?
 

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I'd do everything above plus clean the throttle body, IAC, TPS, and MAP sensor, and check the O2 sensors. Don't forget the PCV valve.
 

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Here's the TSB for the plenum pan gasket, search on this board and there's plenty of information, but you're likely drawing oil in from the valley into the underside around the #7 plug corner, where the runners for the #6 and #8 cylinders open into the plenum, so those cylinders are drawing in an oil mist.
 

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Do the plenum gasket fix FIRST before you go and clean everything else up and redo all the plugs, wires, etc. As QCRam mentioned, there's a TON of info on here about it (search functions in the upper right hand corner). Hughes Engines makes a very popular kit, as do several others.

Heater core sounds shot. Mine just went too. I kinda enjoyed the anti-freeze smell at first.... but now its rediculous. And forget about turning on the A/C or defroster. You'll be scraping AF off the windshield for a week. It's going to cost me between $500 and $700 to get it fixed.

Good luck!
 

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Discussion Starter · #7 ·
I got my new plenum gasket today for a local parts store. Cna anyone tell me if there are any other gaskets, etc needed to perform this repair as per TSB 09-05-00 and also the importance of the combustion chamber conditioner? thanks
 

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If you didn't get the plenum gasket as part of the intake kit, you need the intake manifold to head gaskets, and also the rubber seals that run across the valley front and back. The throttle body gasket can usually be reused. I didn't do the cc clean afterwards, if it's running clean, a long journey will generally burn off the worst.
 

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you need a complete "upper gasket set" which includes the plenum gasket and intake manifold gaskets. i would recommend doing the cap/rotor, wires, thermostat, plugs, and the coolant hose on the thermostat housing while you have everything apart. you'll need the hose, thermostat, thermostat gasket, cap/rotor, wires, and plugs. you might also consider a water pump if you are still on the original. we're talking less than $300 in parts and a lot of saved headaches should one of these parts go. it's all easy and could be done in a day. the heater core, however, is a different beast.
 

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Discussion Starter · #10 ·
Thanks gentlemen
 
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