'99 E320 V6 power loss
 

Car has 180k+ mi.

Can anyone point me in the right direction?
Car suddenly lost power (lots of power) earlier this week but after it sat for an hour it started right up and drove home fine.
Codes were thrown & I had Autozone read them.
Cylinder misfires and PO400 (EGR Flow).
I figured I would look into it this weekend but the car suddenly died again and would not move over 10MPH.
Check Engine light was flashing.
I got it towed home.
No code reader here so I don't have latest codes if any.

I inspected it this AM and there was a buildup of oily crud around the coils.
Thought this might be the cause of the misfires.
I cleaned them & the HT leads (removed & doused with WD-40), changed the plugs (they were due, nothing tell-tale there though), and cleaned out the EGR tube (It was about 95% plugged, EGR valve is new Pierburg this past winter).

I restarted it and it is still exhibiting poor idle/loss of power on acceleration.

Just for giggles, I cracked the air filter box and the engine started idling better but then went back to where it was earlier, a loping miss/catch.
If the throttle is pressed hard, it will stall, pressed slowly it will accelerate fitfully to a point beyond which it craps out.

I checked fuel pressure and it fluctuates rapidly between 52 & 64 PSI at idle, stays at 50 PSI with engine off. Flow seems OK at idle.

Any thoughts? Yeah, I know, a code reader is in my immediate future.

Is it possible there is a memory that I need to erase? Disconnect the battery to purge it like I can do to my old Volvo, will that work?

Classic symptoms of blocked catalytic convertor. Your car has (4) convertors total, two on each bank. Get under your car with a rubber hammer, hit on your convertors (especially the front ones) and see if you hear a rattling. These typically go out anywhere from 110K on.

more info
 

Blocked CAT sounds plausible, never thought of it as my Volvo has its original at almost 300K mi. The MBs crap out, disintegrate & block things up?
If that is indeed the case, can I dredge out the cat and run it empty 'til I scrounge up a replacement?

This last bit of info probably supports the CAT theory. 1500 rpm is the limit at which rpms drop and it stalls out.

HOT DAMN! Thank you Arkie! Right side cats (both) rattle. I assume this means the forward cat disintegrated & the detritus is blocking the rear one?
How long a job am I looking at?
Should the couplings come apart easily enough?
I'll hit them w/some PB Blaster tonight. Damn I wish my lift was working.

Sometimes MB actually has the cheapest deal on cats, shop them around - there should be someone cheap in the Atlanta area. They are sold as two cats on a single pipe, you order right side and/or left side as needed. They are typically about $800 a side. By the book, you replace both sides, the O2 sensors, and the air mass meter but you would be well into the $2k territory. I would probably just replace the right side (they are not too bad to replace, be sure to break the bolts loose while the exhaust is hot if you can, use the PB blaster) - shouldn't take more than a couple hours to do. Clear the codes when done, and be suspicious of any rough running afterwards. If you have an air mass causing the mixture to be too rich your new cats won't last long.

Got the cats/pipe out and there is no doubt. Most of the cat is dust with a few larger pieces, nothing bigger than about 3 sq. in in volume.
It was the forward cat that died, the puff of smoke was probably all those particles that fit through the honeycomb with the larger ones clogging the rear cat.
I dumped out the detritus and tapped the pipe to, hopefully, loosen any of the clogs. I'll reinstall it until the replacement pipe gets here.
I found a A&B direct fit pipe for $388, a Davico for $360 & a DEC here @ peachparts for $430, compared to the $800-900 I see quoted for a MB pipe (Bosal?), it seems like a no-brainer.
Any reason I should stay away from the off-brands?
How likely is it that I will be able to clear enough of the clog to run for a week or so while I wait for a paycheck?

Do the direct fit ones have two cats on a single pipe?

The Davico does, not sure of the others, no pics.
I would check before I ordered.

If the spark plug wires have never been replaced, I would do that before replacing the cats.

Spark plug wires can be tested. There is a resistance value to measure with a DMM. Sorry I'm not sure of correct value.

I don't think a test is valid.
A plugged cat will degrade engine performance but will likely not cause misfires. Bad plug wires will cause misfires and are a known source of such.
I replaced a set recently on 2000 E320 and the wires tested good. I replaced them on the advice of a friend who is the parts manager at the local dealership- I did not buy the wires from Benz and he knew I wasn't going to.

Yes it will cause misfires. I have one in the shop right now that has the exact symptoms as the OP, it would barely pull into the shop with the accelerator all the way to the floor. Left side cat was stopped up, and it had P0300, P0304, P0305, and P0306 (misfires cylinders 4, 5, and 6).

Did you change the plug wires?

I'm sorry but yes they can be tested. The nominal value is 2000 ohms. It's not a simple conductivity check. Zero ohms indicates a bad wire.

BTW, the odds of all 12 coil wires failing at once is higher than the winning lottery ticket. Mostly they last the life of the car although one or two may be damaged by someone trying to change the plugs with the wrong tools. In the good ole days, the carbon core plug wires were changed as a set since vibration was the culprit.

But the OP has solved his problem which is plugged cats. And they can cause misfires and/or other engine symptoms like stalling, etc.

Well I should have played the lottery the day I changed the wires that tested good but caused the car to run quite poorly and set a bunch of misfire codes.
I don't know if all 12 wires were bad. I don't see the sense in replacing a few of them just to have the car back next week with a few more bad plug wires.
I'm just offering advice to the OP. You fix your cars your way, I'll fix mine my way.