We're trying to figure out where to start to fix this. No clue, several mechanics and the dealer mechanics are finding nothing wrong, etc. All the dash lights are on, the catalytic converter sounds like it's popping popcorn, it's losing power and barely making it up hills, hesitates, spits, coughs, chokes, throws a heck of a fit. Some days it runs perfect and other days, just won't go. When started it's fine for a minute or so, then starts making the pinging, ratting noise and engine seems to hesitate (rpms go up and down, but not constantly). We've never changed the gas used, always the same for as long as we've had it, 87 octane. We hooked up the computer and it said catalyst malfunction, misfires on 2,4,7,8. We changed both oxygen sensors, gave it a complete tune up (plugs, wires, pvc valve), new coil, pressure tested the cylinders, pressure tested vacuum system, checked fuel pressure and replaced the speed sensor on the transmission. Everything is within specs of the manual, but the truck is still acting the same. Any idea of what could be wrong?

 

Sounds like you need a new catalytic converter.. lol

 

I would say you have a clogged catalytic converter.... Also, do a search for 'plenum' here, that's most likely what's causing your rattling and pinging. Very common issue with these motors, most of us here either have the pinging, or HAD it and fixed it correctly.... I've been driving mine like that for months now. I'd look into the cat a little more first....

Try temporarily pulling the PRE-cat O2 sensor and see if it runs any better. If it does, that's a good sign that the cat is plugged cause it will allow the trapped exhaust to get out of the system...


Oh and welcome to DF! Lots of good reliable guys (and girls) here to help ya out with any troubles

 

Thank You, that's what we thought. Any idea what could have led to the catalytic converter going bad? The "popcorn" noise just started recently, but the other problems have been there for a long time. We've been after this for over year.

 

Pull the clamp off and take a look in the cat. If you see debris or anything that looks amiss, i'd start there.

 

Cathy, get Bill to take a screwdriver or hammer, crawl under the passenger side & tap on the cat.
If he hears debris rattle inside then its shot.
Problem with letting it go this far is some debris could of made it back to the muff as well.
Replacing the cat may not completely get rid of the rattle sound if that has happened.

Dodge Ram V8 cats have been prone to blowing since day one.
If you drive them hard or do a lot of towing they go even faster.
Being a 99 if thats still an oem cat, than you have got more than your moneys worth out of it IMHO.

I wouldnt let the stealership replace your cat.
For what they will charge may as well get a Magnaflow replacement high flow cat from reputable muff shop.
That will give your 99 a better sound & gain a few hp above what it made before power started to drop off as the cat plugged.

Cats have been a real problem with V8 Rams.
Chrysler replaced them or reimbursed all owners that had to replace one back in 03.(paid for my 2nd h/f)
My 96 is winter stored & seldom seen rain, by 57k miles I was on my 3rd h/f cat.
Dragracing (cold engine) & high hp will kill a cat so fast I should of bought stock in Magnaflow

 

Bill took the exhaust off and found all kinds of cat goodies in there. He'll be replacing the cat and exhaust pipes this week. In the meantime, tires were rotated and brakes bled. And the truck is very, very loud, which Bill is kind of liking! Thanks for everyone's help, we really appreciate it!

 

Just remember, replacing the cat and the rest of the exhaust is not a permanent solution. The cat went bad because of the leaking plenum gasket, which F'd up the o2 in the process.

 

Zman, thank you, I'll make sure to tell him that. I have to say, you guys have been more help than any mechanic we've been to! I really appreciate the help. He loves his truck, it's the first really nice one he bought and I didn't want to see him have to replace it or not be able to enjoy it! Thanks again!

 

Bill talked to a mechanic this afternoon. He was telling Bill there is a part available that eliminates the plenum all together. The engine is a V8 Magnum and what he was told is the metals are different (aluminum and steel) and because of temperature change, that's what's doing the plenum in. Bill just wanted to check into it and see if any of you have heard of, know of or used this part and what you thought of it. Thanks so much!