gothamgoon

I just bought a 99 ML430 that I knew had some issues, I figured for $600 it was worth the risk, it wont go past 30mph, random misfire codes on cylinders 5,6,7,8. Any ideas?
After doing some research I am leaning towards one or more cats blocked, then thinking next would be changing the wires and plugs then ignition coils. I've done the pricing on all of these parts and found pretty decent prices but I would rather not go through a ton of money eliminating this or that. Any help from anyone is greatly appreciated.

art_arev

Check the CATS on bank 2. It cant be the wires & plugs. I am not saying don't change them. What I am saying is your bank 2 has a common problem. If the CATS on bank 2 are clogged, then your car is "chocking".......& you will have misfires on any or all of bank 2 cylinders.

DrX

I would say not to change the wires, plugs and coils. It's most likely to be the cats, and if you want to prove it, get an exhaust pressure gauge and attach it where the upstream O2 sensor goes. You'll have your answer. Cats are expensive but please don't compare them to the price you paid for the whole ML.

Change the plugs when they're due.

gothamgoon

thank you guys, after staying up all night thinking about this and with the information I learned on this forum I started leaning towards the cats. the previous owner said she had the plugs changed not too long ago and the wires so I was either going with the cats or the coils but the cats do make more sense when you sit down and think about what is going on.
I found magnaflow cats at Autozone/oreilly for $100 and $122, it crazy because magnaflows website tells me there are 2 diff cats for the ML430 but they say that they can be for left side or right side and autozone/oreilly say one is for the right and one is for the left and when I look up the cats on ebay by part number they say both not compatible with ML430. (part #'s 99204HM & 51204)
Thanks again guys, will let you know how it goes
P.S.
the previous owner spent about $3K-4K in the last year or 2taking the vehicle to some mechanic, she said he didn't know what was wrong, couldn't figure it out. she gave me all the records of what the mechanic has done so far, both rear whee bearings replaced,etc.
I'm starting to think this mechanic was taking advantage of this woman. She told me she just cant keep going with it she put it for sale

gothamgoon

I will do a proper tune up, plugs, wires, coils, etc and fix leaking power steering res/pump after I get r running right again

art_arev

You have 4 CAT's in total 2 upstream (left & right) & 2 downstream(left & right).