P0306 on 1997 E320
 

Car bucking and nearly stalling at idle, driveable but underpowered. Scanner returns P0306 which I know is misfire on #6.

It is raining buckets here and I drove through a large puddle immediately before this happened. Other cars also pulled over after the puddle. But I have a hard time believing going through a puddle is somehow the cause for fouling cylinder #6 which is way back against the firewall. I would think MAF damage or cylinder #1 or #2 would be more likely.

In any event, I was able to nurse it home, so it's in the garage now. I'm gonna have to boot up my laptop and connect in to work before I get to it. I'll start by pulling and reseating the plug connector for #6.

QUESTION: If a coil failed, wouldn't it trip 2 cylinders? Also, isn't #6 under a coil connector? I know those frequently go bad. But these wires and connectors aren't very old, maybe 3 years old and 25K miles (I'd have to verify in my log).

Check the companion clyinder. coil packs control 2 clyinders. Since it happened when you went over a puddle you may have shorted out the coil or check the ground. If water got far enough it could have created short somewhere. Do you have belly pan installed?

The belly pan is still installed. I reset the codes and let the car dry out in my garage for a couple of hours, then tried it again. Same code - cylinder #6. I'm suspecting the coil resistor wire that sits under the coil, but I'm working from home and don't have the time to look at it right now. Does anyone know if a coil sits directly over #6?

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post #7

Can you get you hands on a oscilloscope? Would really help your diagnosis.

the mating clyinder for your engine is 1 the fartherest coil controls clyinders 1+6, the middle coil controls 3+4 and the first coil controls 2+5. A coil that failed wont necessary trip a code for the other clyinder.

also checking the DIS switching unit amd the ignition cables for frays, cracks etc

This why having a advanced scan tool is a necessary tool for working on the newer benz's

Dry things out.

Afterwards, the simple test is to swap coils with another hole.

If code doesnt move, check wires/grounds/etc.

If code moves to new cyl, the coil may be bad.

specs for coil:

Primary voltage with starter actuated:

pins 124+ 2 at N3/10=200-350Volts

resistance of coil: primary- pins 124+110(N3/10) with ignition off =.9-1.6ohms
secondary-pins 4a+4b=6-8.5kohms

ignition voltage: 8-20kilo volts with started actuated and kv sensor connector connected to each of the coil

another thing to keep in mind is fuel injectors that are leaking, not operating, have a bad spray pattern or that are not spraying at the same time. to do that remove the fuel distributor rail along with injectors as a complete assembly, place a cookie sheet underneath and turn ignition on but dont start. Make sure they spray, if they drip they are leaking

Friend,
we have found that moisture intruding into the engine compartment settles into #6 cylinder hole.
Don

Update. I was in Chicago for a long weekend, so the car had plenty of time to dry out. I'm back in Dallas today and started the car up when I got home. Same error code and running rough. I relocated the coil to position #2 and am getting P0302 now, so it *seems* that the problem followed the coil.

I'm inclined to order a coil, but am still a bit hesitant. Wouldn't a faulty coil throw a code for both cylinders 1 and 2?

I JUST remembered that when I moved the coil to cylinder #2, I did not swap out the spark plug connector attached to it. I just ran out and swapped the plug connector back to cylinder #6, but unfortunately after clearing the codes and getting a "check engine" light again, P0302 reappeared. I think that rules out the plug connector and points to a bad coil. I still can't figure out why I don't also get a P0301. Does that code maybe not exist for this car?

UPDATE: New coil solved the problem. Installed coil, cleared codes, and drove - nice and smooth again. So it seems that a bad coil can indeed trigger a fault code on just 1 cylinder, even though it fires for 2 cylinders. Thanks everyone.