'95 E320 wagon misfire
 

Hey tech gurus!
So after 15 years of Volvos (my last 940 Turbo wagon was totalled last month), I recently bought a pristine E320 wagon with 63k miles on it, and 90% of the time the engine is like butter (3.2 liter in-line 6). The problem is, I have an intermittent misfire and really don't know where to start looking. A couple things I've noticed, which may or may not be connected...
1) It doesn't seem to happen when the car is cold.
2) There is definite interference with the AM radio signal. (i.e. when I hit the gas, the static noise gets louder and speeds up in relation to the rpms the engine is pulling.)
I took it to the dealer I bought it from and they thought it was related to an oil-flooded spark-plug socket (where the lead goes in, not in the cylinder), so they replaced the valve cover gaskets. It seemed to help for a day or so, but that's probably my imagination. I'm relatively certain that it's an ignition problem.
My thought is that I possibly have bad spark plug leads (does this mean I need to change out the coil packs?) I'm going to put some injector cleaner and dry gas in it today, on the off chance that it's just water in the gas.
For what it's worth the engine wiring harness was replaced in the last year or so, according to the paperwork that came with the car.
I'm a fairly adept mechanic, having restored a '64 Volvo, and maintained my own 240s and 940 for years and can do the actual work, but as far as diagnosing problems, some of this Mercedes stuff is still a little over my head. (I did buy the Bentley E320 owner's guide, and am working my way through it.) Thanks in advance for your help!
-Ethan H.

Oh, I should also mention that it cruises along just fine on the freeway (sometimes stumbles on hard acceleration, but not every time), idles beautifully (usually the stumble kicks in around 2000rpm), generally accelerates up to 2000 rpm very smoothly, and hot and cold starts are both fine. Any ideas?
--Ethan H.

Oh, and the check engine light isn't on. Right, I think that covers it....
-_Ethan

99% of misfires on M104 engines are due to bad coil wire supressor boots.

Change all three of them. They are cheap.

Also, it is critical that you are running original Bosch or Beru copper core non-resistor plugs.

The plugs must be the non-resistor type.

Not sure what the change interval is on the rotor and cap for the ignition, but this would explain the hot-only problem and AM interference.

Probably due for a change anyway at 60k.

Good luck,
Troy
1995 E420 107k

Unlike your E420, that chassis has DIS ignition.....

Okay, so I changed the coil wire suppressor boots out and installed new spark plugs, and it seems to have done the trick. The old plugs were definitely shot (gaps were around 1.10 mm), and the boots looked like they were probably the originals. Thanks for the help!
-Ethan

What did you use for plugs??

Copper core Bosch non-resistor type. I'm not sure what the designation was off-hand, but they were the ones that the dealer recommended and were the same as the old ones (which I suspect were the originals from the factory.) The car only has 63k on it....
--Ethan

Very Good

The # Is F8DC4, for future reference.

I only ask b/c some auto parts houses are known for giving out R plugs or Plats for this car, and the 104 just does't like them. [ Waste spark system]

Many of the discount parts counter guys came from "want Fries with that ? "...if you know what I mean...

That was the one.


--Ethan

sorry but what exactly is a "coil wire suppressor boot"

I dont see anything with that name on fastlane. I'm assuming is not the same as an "ignition coil"


my 95 e320 wagon (118k) suddenly has a horribly rough idle and loss of power under light acceleration. hasn't stalled and isn't throwing codes. I'm also looking into the O2 sensor, and various vac connections (but all look okay). any other ideas?

Referred to as Spark Plug Connector

Steve

Plug connectors are a supressor resistor ..there are 3 are under the coils.
[ one each]
Plug wire boots are at the end of the ignition wires at the coil end of the wire and are just a wire terminal/plug with a protective boot over the terminal ..there are NO resistor/Supressors in this boot/plug.. The resistor connectors for those 3 ignition wires is at the other end of this ignition wire
[ plug end]
The 3 connectors under the coils have NO Ignition wires ..only a resistor /connector.
.. ..so, there are only 3 Ignition Wires on a 104 waste spark ignition system, but all plugs get the resistor/suppressor...either in the connector under the coil or at the plug end of an ignition wire.

So, why do we always recommend changing the connectors under the coils.??? B/C they have a high fail rate due to 2 factors ..one is the are trapped in engine and coil heat and the other is they have a friction type commpression spring connection to the plug by design. Two things resistors do not like are heat and poor connections.
The resistors on the other plugs do not have these condition b/c they are not heat trapped and they have positive snap design connector..so, very seldom will one see a failure on them, but you frequently see failure on the ones under the coils..so much so that any tech familiar with these will just change them automatically when doing a plug change...
... the high percentage of 104 misfires are caused by these coil over plug connectors, along with incorrect plugs installed , specially Plats... these engine like the large electrode of the copper core standard plug b/c they are a series circuit of two plugs fired with one coil...meaning the first plug fires from the electrode to ground , but the second plug, being a series circuit, fires from ground to the electode and then back to the coil..completeing the series circuit. Plat have a tiny electrode and that may contribute to their mis-fire rate in waste spark systems like the 104 has.