Blocked Cat convertor?

unclejake, Nov 4, 6:25am
1996 E320 Mercedes. Japanese import. We got it at 145kms. It now has 225kms. The AMF was replaced around 10,000kms ago. No cat warning light is showing on the dash, even prior to starting the engine.

It has had a 'miss' under full throttle for several months. The miss is accompanied by a muted, yet irregular pop from the exhaust. At light throttle settings it drives fine.

The vehicle has suddenly (today) started surging and missing and is barely drivable. The exhaust stinks of sulphur, and a look under the vehicle suggests a catalytic convertor is present.

The two spark plugs I removed look dry but ancient.

Blocked cat, or something else!

johnf_456, Nov 4, 6:40am
Any fault codes!

mugenb20b, Nov 4, 6:47am
Fuel filter maybe! If the exhaust gas smells like sulfur then the catalytic converter is doing its job.

unclejake, Nov 4, 6:48am
I hadn't thought of the fuel filter. The exhaust didn't smell like this on Monday. The stench is amazing.

No faults showing on the dash, but I haven't got a diagnostic interface

saxman99, Nov 4, 8:17am
Faulty coil pack!

m16d, Nov 4, 8:29am
Change ya air filter.

unclejake, Nov 4, 8:31am
The air filter is fine. I checked it tonight.

I guess a coil pack would explain the rough running, but would it explain the new sulphur stench!

Others have suggested the Mass Air Flow sensor. We had a new Air Flow Meter fitted in the last year and a half

unclejake, Nov 4, 11:42am
Cool. Thanks guys. I will let you know what I find on Friday evening

andrewph, Nov 4, 6:23pm
Most likely plugs or coils. also check the condition of the wiring as some merc wiring in the engine bay has problems with the insulation breaking up. Engine looms are expensive.

intrade, Nov 4, 9:22pm
dont forget to check your wiring loom 96 is still biodegrading. could be degraded and there is one otherfault somone posted about mercs that it could be.

sr2, Nov 5, 2:29am
Repairing the ???biodegradable??? Engine loom is not a nightmare if you're handy with a soldering iron and heat shrink, I??

unclejake, Nov 5, 6:00am
Thanks SR2. Our loom is still OK (fortunately).

I am off to the shed now. I suspect a coil has died as I have been driving the car today and it is probably running on four cylinders. The exhaust temp warning came on when I was heading up a hill after work. I imagine it is un-burnt fuel in the exhaust.

I have a set of plugs for it, but if a coil is stuffed it is going to stay that way for the weekend.

neville48, Nov 5, 6:51am
Cut the converter out and throw it away anyway, they are a waste of time for us non-greenies.

dave653, Nov 5, 8:43am
If you can unbolt the cat you can have a look through it to see if it's blocked or not. Have you considered the oxygen sensor. if fitted! Coil packs usually pack up at revs, leads and plugs under power. Our Vn had similar problems a while ago, turned out it was the CAS, but I have removed the cat, replaced leads and plugs, tried a new coil pack (it's still in it's box in the shed) the O2 sensor has been replaced twice in 6 years!
I hate modern cars!

unclejake, Nov 5, 8:52am
Thanks team. I am just home from the shed.

A new set of spark-plugs seems to have fixed the problem. The old ones were very worn and the gaps had grown to a huge size. The car is running on six cylinders again. It isn't quite a crisp under load as it should be, but it is very, very drivable and a million times better than it was this afternoon. It may re-learn and get even better, but the leads might also be dodgy.

Spark-plugs were the culprit.

My thanks to you all again.

sr2, Nov 7, 8:44am
Glad to hear you??

franc123, Nov 7, 8:59am
Just a reminder to you all that spark plugs are a SERVICE item, they shouldn't be left to wear until the point that running problems occur!Periodic replacement is necessary.The manufacturers and distributors of coils, leads and ignition modules do a great trade out of selling parts that need replacing as a direct result of electrical stress caused by plugs that should have been replaced long ago!

johnf_456, Nov 7, 6:12pm
Good to hear and second the above comment

unclejake, Nov 7, 9:53pm
I can't disagree, but in my defence I don't usually do the work on this car. It goes to a proper mechanic for most things.

Anyway: I sold the Merc yesterday. Gone. She now has an Audi A6 to ruin

johnf_456, Feb 10, 7:05am
Indeed put it in the ground