2001ML55AMG

2001 ML55 105K miles.
I began noticing what sounded like a rod bearing going bad. Thanks to this wonderful forum I was able to confirm the left side catalytic converter had it's honeycomb guts bouncing around inside.
Made a cut about 3 inches back from rear O2 sensor and removed the header pipe and front cat. I dumped out honeycomb guts (used a piece of flat steel to break up it up what was left inside) also used a shop vac to try to retrieve the other pieces lodged in the rear cat.
Put everything back together and fired it up to check for exhaust leaks. Seem to run fine, but it was too late for a test drive.
The next morning when I started it it started and then stumbled and died. Restarted and this time it had a bad miss. After a few minutes it bagan to idle fine. During test drive it seemed ok if I ease into the throttle. Anything more than 1/4 throttle I could feel a stumble/missifre.
Scan for codes and came up with misfires on cylinders 5, 6, 7 8. Unforunatly I earased the codes assuming they would reappear. but they haven't.

For safe measure I replaced the front O2 sensor and disconnected the battery to clear memory, results were the same

Here is where I'm at. Cold start: stumbles and dies. Restart: idles rough, but does smooth out after a few minutes. Ok at part throttle if I ease into it, but stumbles fiercely at WOT. Currently not showing any codes.

Ran fine before cat clean out. Would a gutted cat cause this?

Any suggestions?

Rippin'AV

When I've gutted my primary cats on my S4 it didn't cause any issues with how it ran. The CEL would come on if you didn't code out the rear 02 sensors. Could be a coincidence that it started happening after you gutted the cat... Check plugs and gaps. Idle being rough sounds like it could be plugged or dirty injectors. If they look fine try a good shot of fuel system cleaner or run a cycle of seafoam. Carbon cleaning the engine could also help. GL

2001ML55AMG

Update: I wasn't sure how much of the front cat made it's way to the rear one so I installed the MagnaFlow cat setup on the drivers side. (ordered thru O'reilly) Nice piece. Only issue I had was the pipe connecting to the muffler was the same size as the muffler inlet. Had to use a tailpipe expander to open up muffler inlet.

The misfire and stumble during acceleration went away after a few trips around the block. It's running fine, but not great. Still feels like somethings wrong.
Codes:
P0170 - Fuel Trim Malfunction (Bank 1)
P0173 - Fuel Trim Malfunction (Bank 2)

I assume there must be an air leak in the intake somewhere after the MAS. But everything seems tight. I did remove the intake silencer/baffle and sealed the opening in the intake plenum (years of intense underhood heat caused the rubber connector to be hard and britle and possibly allow an air leak)

Still getting these codes and engine is still not performing.

betrezra

I would try another mass air meter if you have one handy.

Do you have acces to das star? Perhaps you can see what fuel trims are doing? Ltft and stft.
Also check o2 sensor voltage tracking.

Star should help narrow it down.

Ideas:
Mas
Plugged fuel filter
Weak fuel pump
Vac leak
Dirty fuel inj
O2 sensor or wiring issue
Massive exhaust leak before or around 02 sensors?
Ex manifold gasket leaks?

Gl

Rippin'AV

that has to be related to O2 sensors and fuel trim due to the readings. if you gutted the cats then the O2's will be all confused. you need a tune that can compensate for that and code out the rear O2 sensors or it wont run right.

PTE

Did I read this right> You only gutted the cat on the 5,6,7,8 side and left the side with 1,2,3,4 intact, as a full working cat! ON Boy!!
Cheers _PTEngineering

betrezra

Good catch p.
Prob need a matched set of cats l and r.

2001ML55AMG

Currently the left side cats are the new ones from MagnaFlow and the right side is the stock cats. I assume there is a marginal difference in flow.

Fuel filter is next on the list. I know its been at leat 60k miles since it's been changed.

I can't help but wonderig if my fuel trim issue caused the left cat to go bad.

betrezra

I would put new same type cats on both sides.

Check lt fuel trims and st fuel trims with star.

Gl

Rogair

Did you figure it out? I am looking at replacing cats on my 2001 ML55? Which magnaflows did you use? high flows? With the running issues you prolly don't have an idea on performance with the magnaflows...?

2001ML55AMG

Update: ML55 still giving P0170 & P0173 codes. However, wife has been able to drive it about 9k miles. Runs fines for her driving habits, but I've noticed it still runs horrible at WOT. 😜
About once every 2 weeks it will act up: horrible idle on start up and stumbles on anything above 1/4 throttle. Last time it happened, couldn't get up to 45mph. Pulling over, turning engine off and restart seems to clear this up.
Haven't had time to investigate. Still thinking fuel filter.

MercedesDad

After reading this thread...are you still running with half stock and half magnaflow in the cats department? If not, how long did you do that for?

2001ML55AMG

Yes. Still running magma flow cats on driver side and stock cats on Passenger side. Oriley says they can not get the passenger side.

ChrisMclass

Not to sound like a broken record but you gotta change both cats to the same thing at the same time. Do that then clear your codes and see if they return and how it runs. Clogged cats can cause a myriad of problems for you, and right now with one free flowing cat and one factory cat your going to get bad 02 readings, ecu thinks one is clogged.

MercedesDad

On point.

It sounds like self inflicted damage.

In any case, no way to expect an accurate assessment of what is going on with a broken exhaust/cat system.

Worse part is the car continues to be driven like that. God knows what other problems the car continues to develop by this.

2001ML55AMG

The ML55 is running great, now.

I'm confident that the Cat failure was the result of a bad MAF and not the cause of the drivability issues. Unfortunately, allowing the symptoms to continue for about 9500 miles must have killed the secondary/rear cat on the driver’s side again (yes, this was the new MagnaFlow system that I installed after the same cat failed on the factory original setup) Rattle rattle rattle.

Installed new Bosch MAF sensor and it resolved all the drivability symptoms. (Bosch unit from AutoZone $225.99)
My conclusion: bad MAF kill cats.

I ordered and installed another MagnaFlow cat system for the driver's side (PN# 24570). I also installed the MagnaFlow cat system for the passenger side (PN# 24571) while I under there. (Just in case the bad MAF had started to do damage to the other cats.)
**NOTE: MagnaFlow has the pipe dimensions reversed as they connect to the resonator. Rather than hobbling together connections, I opted to have my local muffler shop install a Y pipe in place of the resonator ($160, probably could have done it myself for about $35 if had time to wait for parts) ---No drone at any speed, just a little more exhaust tone.

Thanks for all the input and feedback. I hope someone finds this info useful.

rennwerkes

If you don't mind me asking, how was the fit of the Magnaflow?
Also, does it include both primary and secondary cats?
Thanks

vvrjrlaw

I recently suffered the dreaded death rattle from the front left cat on my 02 ml55. I changed out both left and right primary cats with Magnaflow hp cats part no. 54856. Truck runs fine no issues.

2001ML55AMG

Great fit, with the exception of the sizes being reversed as they connect to the resonator.

As for install: pretty shraight forward. It was nessecary to remove the inner fender sheild/cover on both driver and passenger side to get access to the bolts that connect to the exhaust manifold. Also, need to drop/remove the crossmember that supports the transmission/transfer case.


Yes, the MagnaFlow cat systems that I bought were complete and include both Primary and Secondary cats.
Driver's side (PN# 24570).
Passenger side (PN# 24571)
Mandrel bends, great welds, stainless steel, exact fit.