Ok I have a 99 ram 1500 with the 5.9 I have the sct tune from hemi fever I was running it and it was great. I recently turned it down to the 87 tune so I could run regular gas and about a mile down the road the truck starts to cough and sputter and have blowback through the air filter and had no power at all. but it shortly went away. now on my way back from camping today it did it again and for longer and it feels under powered.
Now I did look in the air intake and there is some pooling of oil in it on the drivers side, opposite the pvc so its not that. now would a blown plenum cause my problems? Oh and I was about to do a complete tune up on it.

 

when you mention blowback or backfire through the air filter, my first thought is either a bad intake valve or spring that is not closing, or a serious out of time condition, or a cross up plug wire or some other malfunction that's pushing compression, and maybe spark and fire, out the intake.

but - usually when something like this happens, it does it consistently. it doesn't come and go like you are describing.

for something that comes and goes, i'd think about a clogged cat, or bad cam position sensor. i'm not sure if i can connect the crank position sensor to this problem or not. i'll ask for help on that as i usually mess that up and hey-you has to correct me.

with nothing else to go on - and if this started when you changed the SCT tune, i'd put it back to the old tune and see if it fixes it...

leaking plenum is just a vac leak that burns oil and clogs the cat and runs lean. it doesn't really directly cause what you described.

 

ok I have been running ste sct tune for over 2 months now and nothing until this weekend. there are no codes or anything and it is not consistant at all

 

ok I have checked the plugs and they look pretty white. would the plenum leak cause me to run rich witch might cause the rough running? oh and when it was running rough and coughing and stuff the truck was already moving it is not agt idle it is at about 50km/h accelerating.?

 

Plenum would cause you to run lean. Which CAN lead to some of the symptoms you are describing, but, I don't think that is the only thing going on. Clogging cat can do funny things as well......

First thing I think I would try is rerouting plug wires per the tech service bulletin. (it's in the faq section.)

Next, I would run a can of seafoam thru the intake. See what that does......

How many miles on the truck?

White plugs indicate it is running hot... maybe a step cooler plugs? When was the last time any of the ignition stuff was changed?

If none of that helps, I would also lean toward bad valve seats, broken springs, or the others that dhvaughan suggested.

 

I looked through the cat it looks clean I ordered a plenum kit from hughes yesterday and when that is in I will change all of the ignition components. oh and it has 200000km on it

 

Sea Foam... just sayin

 

ya I have a can I will replace plenum and do a full tune up and sea foam it

 

while you have the intake off, replace dist cap, rotor, maybe cam position sensor, check plug wires (replace if old). its easy with intake off, very difficult with intake on.

 

If you have an extra $100 or so put in new lifters as well when the intake is off, better now than later. Also do a compression test before any of this work is done and parts bought, might as well see what you have for compression now.