Howdy!

I've hit a brick wall on diagnosing my kids 1995 e320.

1. Ind. mechanic got code for cyl 5 misfire
2. he checked compression and it was fine
3. I replaced all spark plugs, wires, as well as the coil for cylinder 5 and 2
4. Verified there is *no* spark at plug for cyl # 5

The car has the normal sputter after startup and the faster it goes the less annoying it is, though it is still noticeable.

Any ideas on what to check next?

Did you change the three coil wire connectors?

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

This is the smaller wires? No; but was going to look at that next to see if the caps needed cleaning.

The three coil wire connectors are usually what cause a misfire. It is almost never the coil wires or the three high tension leads that piggy back to the next cylinder.

Search for posts by Arthur Dalton. He has posted frequently on misfire issues for your engine.

Here is one post:

"The wires can cause your problem, but they are the last place to look.
The problems with mis-fire on 104 Waste Spark ignitions is the connector/resistor UNDER the coil...that is just the way it is b/c they have an inferior connecting system and are heat trapped.
Any Tech will tell you to change them at a plug change b/c of their frequency of misfires.

So, that is the FIRST recommend , but not a diagnosis..it is a 'Change them regardless " recommendation b/c of their know failure rate.

And don't make the all too common mistake of moving the coils and watching the codes to move with the coil WITHOUT pulling the connector off the suspect coil..I see guys swap coils for that valid diagnostic trick , but they leave the connector on the coil they are swapping, not realiziing that it is the connector that is following the code . not the coil..
So , they buy a coil when all they needed in the first place was the connector under the offending coil."

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Since the car is at 197,000 miles I had no qualms about purchasing new spark plugs, the 3 'coil-to-spark plug' wires, and one new coil which came with the boot. Cylinder #5 is misfiring and it is not under the coil; it is connected via a spark plug wire, which is now new. So this connector 'under' the offending coil seems to have no bearing on my problem. However, if the wire lead connector on the opposite end from the spark plug wire connector on the new coil is bad, that could allow spark on the #2 cylinder but not allow it through to the #5 cylinder?

I have done tons of searches so far and not found one that seemed to apply directly to my situation. Usually see search results for no spark on any cylinder or replacing the coil fixes it, but neither apply here.

The high voltage path runs from one plug, through the coil connector, through the coil, through the wire, and to the other spark plug. So a bad plug connector can indeed affect spark quality on both plugs. The coil connectors only last so long. Folks who have been hanging around here long enough have learned to replace them every other set of plugs. Suggest you give it a shot. Shoot, they're not much more than 10 bucks each and only require 10 minutes to install.

If that doesn't fix it, then you've likely got a fuel problem on #5.

In support of what Arthur is saying, I have had a similar experience.

A single-plug misfire, replaced plugs, no change. Ordered new wire set and 1 new coil, didn't need the coil, it was one of the wires.

Seems odd that a bad wire (or one bad plug connector) would affect only one plug when there are two in series, but it is exactly how it worked for me. It ran as yours does: idled on 5cylinders, but easily made highway speed on 5, just a vibration at lower RPM, but never seemed to fire on all 6 (the engine management will cut injection to the misfiring cylinder so it doesn't get a second chance anyway, ... does save the CATs from damage though).

__________________

Gone to the dark side

- Jeff

I wasn't disagreeing with Arthur, primary problem was terminology. Second problem was me not believing I could have received defective parts. But as you can see in my response to Arthur's last posting, moving the coil to a different cylinder pair did result in a 'no spark' on the other cylinder. So the problem moved with the coil, indicating that one of the new parts is broken, and I'm leaning toward the coil being damaged since boot has been replaced multiple times.

I work in technology so I completely understand broken new parts and confusing terminology. Hopefully it can still benefit someone else to know that just because the part is new doesn't mean it is going to work.

I didn't take it that way, just offering my experience with this counter-intuitive symptom where a connector in a series system could affect one of the two series plugs, ... still don't get it but I do keep a spare coil, wire set (6pcs), and OVP around for the 104s.

Didn't make sense to me but it worked. Not the first time.

Happy it's running smooth now.

__________________

Gone to the dark side

- Jeff

Ouch. Glad all are okay.

__________________

Gone to the dark side

- Jeff