1986 280GE, 115k, head rebuilt at 90k. What would cause the Cat substrate to clog and then fail? Basicly I've had a plugged cat for sometime. Gee, now I know why the engine was losing power and trying to overheat. Trying to isolate the fault. My thoughts so far are rich running. SOurces: leaking cold start injector, idle set too rich, others...? What if the EGR valve has failed to the closed position? Would this lack of fresh air prevent a clean burn by the time the mix gets to the cat? What else? ------------------ S, J.R. Brown 1986 280GE LWB Anthracite 1980 450SEL Champange 1981 Volvo 240DL UPS Brown

It depends on how old the cat is...If it is the original one, It should have been replaced already anyway. I have replaced quite a few this year.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Burning a lot of oil will cause premature failure of the catalyst. Since you say that the head was redone at 90k, I'll bet you were burning oil..If the engine runs at all, even if it's running rich, you'd have to have gasoline pouring out the tailpipe to kill the cat. My bet is too much oil passed thru the cat bed...

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Jeff L
1987 300e
1989 300e
1987 BMW 325

Cats die because fuel control doesn't (control). Unburned hydrocarbons are the death to cats. This means all forms of incomplete combustion.

But, figuring that vehicle to be a converted car, I would highly suspect your feedback control. I would monitor its activity as the first choice even if it was a US model. Most of the Euro M110 engines had rather poorly constructed hang-on lambda control.

Without functioning lambda (closed-loop) control a three-way cat TWC will eat itself up rather quickly.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Thanks for the timely replys. In the vehicle's service record there were notes about using heavier weight oil up until the rebuilt the head. After that no mention. So I suspect the cat took the oil injestion and started its spiral towards death.

I won't ignore the possibility of it idling or running rich. As far as idle, there does not appear to be a lambda closed loop system. I am familiar with them as they exist in my 81 Volvo and 80 450. So I might have to make a trip to a mechanic and hookup an exhaust analyzer. As far as running rich, I'll check my plugs in a few thousand miles and see how they look.

Any other suggestions are welcome. Cheers.

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S, J.R. Brown
1986 280GE LWB Anthracite
1980 450SEL Champange
1981 Volvo 240DL UPS Brown