M104 / E 320 Engine Frustration
 

The symptoms:
Car misses, sometimes idles smoothly, sometimes misses (seems like 1cyl only). Give it gas, it drops one cylinder. Idles a bit lean when cold (hunts at idle).

I replaced the plugs, #2 was wet, all had a bit of carbon on them.

No check engine light. Looks like (from the manual) I have the California OBD, pins 3 and 4 are a momentary button and an LED. Pushing the button per an earlier post gives no blinking / codes.

The nearest dealer is an hour away, and I'd like to fix it myself if possible. Bought it for my daughter, she wants it on the road soon (big surprise).

Wouldn't the coil pack affect both 1 and 2 if it were bad? Or, is this a common failure mode for the coil pack?

If an injector problem, would it idle on all six? Seems that an injector that injects at idle would also inject for a longer duration for higher outputs.

Any help appreciated. I'm kind of a dieselhead here, swore off gas Mercedes in '96 out of frustration because the dealer couldn't fix a similar problem on my '91 (which happened while it was in for fluids service) but would like to have my daughter in a gasser 124.

Go get the codes from the Ignition Module.

http://www.peachparts.com/shopforum/tech-help/107630-e320-16-pin-dtc-charts-inc-pin-8-pin-14-a.html

Thank you Arthur.

Pardon my confusion, I guess the built-in one doesn't cover all faults.

Wouldn't I have a CEL if there were a fault stored?

Back in an hour, after hitting the local Radio Shack.

BI/LED only notifies you that you have Emmissions code faults and it controls the CE lamp.

Thanks to the referenced thread and Arthur's diagnostic box, I have read the codes, several of them. The CEL has now illuminate also, and gives me a 21 code.

I am not able to clear the codes however, I hold the button down for 8seconds after reading the codes, and they're all still there. Any ideas?

You have to hold for 6-8 secs after each code is retrieved ..then you have to turn key off for 10s, on for 10 s and then start the car.

Clean out your purge valve with WD40
Archieves has all that info in triplicate

Has the engine wiring harness been replaced??

Wiring harness looks/feels good, so either it was replaced, or at 117,000 northern-climate miles it hasn't yet gotten brittle.

I tried the 6-8second thing, but not the key thing. Thanks.

Okay, on pin 8 I get a 47. Reset, and all is well, drive the car and it has a 47 again. The chart doesn't show a 47, any ideas?

Still runs on 5cylinders.

Test coils primary windings for resistance spec.
You are looking for .9 to 1.5 ohm.
Suspect willl be the one that had the wet plug.
I assume you are not using plats.

Try it again, there is a 46 and 48 - it's got to be tough to count that many flashes.

47 is HHT Benz code 107 ...Coil Primary ramp for HFM Module.
That is why I mention ohms test of primary.

I've spent much of my evening with the archives, your name comes up occasionally (!!!) Arthur. I bow to your knowledge and willingness to share it.

Anyway, I couldn't find Bosch copper, and used NGK copper instead to try and get it running correctly. No change. I'll order the proper Bosch plugs, going to put together a mammoth order for my upcoming "Mercedes appreciation weekend".

The coil and "stubby" or spark plug connector will be my next victims, I'll look them over well and measure resistance. Looking at the price, it looks like ordering a set if one is suspect is a good direction. The purge valve, EGR, and fuel pressure regulator are also on the list of checks.

If the FPR was leaking, would the fuel go directly to the #2 intake area? Could explain the wet plug too.

Thanks again, I feel like I'm at least starting to chip away at it.

Leave the NGK coppers ...they are better than the Bosch.

The FP regulator can be checked by simply pulling off the vac hose while the car is running,...look for any fuel coming out the vac port.

The purge is most likely just gummed up..try cleaning it ..a trick is to squirt WD into the vac hose upstream and let the engine suck it thru the valve. You can tell if it is working by feeling it for a heatbeat pulse . [ approx 5 hertz]

The wet plug indicates misfire, not FP reg....test coils and if the coils are Blue labelled , those were troublesome right from the start.
Most 104 Waste Spark misfires are plug connectors under each coil...most Techs just change them when doing plugs b/c they are aware of their high fail rate from heat deterioration.
A DIYer trick is a suspect coil can be moved to see if the misfire condition follows the coil

jeff just did one of these last week,same symptoms,found 3 & 4 not hitting,changed the coils and the miss moved,replaced coil and fixed it.