1995 e320 w/ cyl 5 misfire
 

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?

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."

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.

Still not sure what this 'coil connector' is. I've only got one cylinder misfiring, cylinder #5, and it isn't getting spark. No spark. And again, no spark. So while there may very well be a fuel problem, not sure how that applies to *no spark*. ;)

If you are talking about the 'posts' that the coil sits on which connect to the spark plug under the coil, the new coil came with a boot. Still, I have some spares I ordered just in case so I'll try swapping them too.

The only item left that isn't new is the wires that supply energy to the coils.

If this was an older chevy engine I'd swear it was a cracked distributor cap. But that doesn't seem to apply to this car.

Thanks.

Coil wire boots that you are referring to are just a wire plug with a protective boot over the terminal. There are no resistor / supressors in this boot / plug.

The resistor connectors for these 3 ignition wires are at the other end of this ignition wire.

The parts you do want are the three (3) coil to plug connectors. No wires , no ends ..just a direct connector/resistor. PLUG to COIL. Nothing else.

All three coil-to-spark-plugs wires have been replaced. :thumbsup:

The confusion is the use of the word "WIRE"


The part that you want to check on is the Plug Connector/Resistor UNDER each coil..it has NO WIRES..it is a simple resistor encased connector between the coil and the plug under each coil. It requires NO wiring b/c it is Direct connector from the coil to the plug.

When one states coil to spark plug WIRE, that would refer to the plug wire that is between the plug and the coil on the other 3 plugs that are NOT under each coil. It is the connecting Ignition High Tension WIRE. Those 3 plugs require a WIRE to go from the coil to the plug.

This is a Plug/Resistor connector [ no WIRE]:

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1995@@1995&makeid=63@@MERCEDES%2DBENZ@@63&modelid=6392%3ABT%7C5%3AMBC%7C 1508%3AED%7C10000022@@E320+Sedan&catid=240798@@Engine+Electrical&subcatid=240801@@Spark+Plug+Connect or&applicationid=W0133-1634343&mode=PA

I think I said that earlier:

If you are talking about the 'posts' that the coil sits on which connect to the spark plug under the coil, the new coil came with a boot. Still, I have some spares I ordered just in case so I'll try swapping them too.

So from the coil for cylinder #5 to the spark plug under it is all new, ordered from ******** AZ.

Call it what you may, there are no wires under the coils and the boots are the connectors cover at the wires into the coil , not out.

Your post states that you verified no spark at 5..how did you verify that condition?

I understand what you are saying; I researched the 'cylinder 5 misfire' issue at mbworld.org and benzworld.org before I ordered all the replacement parts that would be suspect for the condition. The failures seem to follow the pattern: 1. plugs, 2. plug 'wires' (the 3 wires and the 3 posts/boots under the coil) and 3. the coil itself. I only replaced the coil and post/boot related to cylinder 5.

As far as testing for spark, unplugged spark plug wire from cylinder #5's new spark plug, leaving that spark plug in place, and using old spark plug in wire with base grounded. No spark appeared. Reattached to new spark plug in cylinder #5 and then repeated the same test with cylinder 1 spark plug wire and got a spark.

Greatly appreciate the help.

Bill

< I only replaced the coil and post/boot related to cylinder 5.

>

Ok

Let me ask this, as i do not know what a" post boot" is.
Did you replace the plug connector under the coil that operates cyl 5 ?
Did you replace the plug wire going to #5 from the same coil?
Did you have the plug connector under the coil hooked uo when you tested for spark at 5 ?
You are aware that this is a series circuit that fires two plugs , in series?

The post/boot is all I could think to call it because it looks like a 'post' and a spark plug boot combined. More basic: Rubberized sleeve with connectors on each end - one end connects to bottom of coil and the other the top of a spark plug.

To answer your questions:

Did you replace the plug connector under the coil that operates cyl 5 ?
B> Yes and the coil as well
Did you replace the plug wire going to #5 from the same coil?
B> Yes
Did you have the plug connector under the coil hooked uo when you tested for spark at 5 ?
B> Yes
You are aware that this is a series circuit that fires two plugs , in series?
B> Knew the 3 coils was different from what I'm accustomed to. So you are saying cylinder 2 and 5 fire simultaneously?