M104, 95 E320 "Missing" or Rough running

[Jim Villers]

I am now at a dead end.

While driving to breakfast this morning, the engine began "missing"; running very rough. After getting home, I pulled the plugs with hope of identifying the problem cylinder. All six plugs looked the same. I checked the resistance on the plug wires and "plug stub" and they were 1.5 to 2K ohms (within spec).

I then checked the fuse on the over voltage protection relay and it was good.

I also checked for malfunction codes; pin #8 (HFM-SFI) responded with one blink (no malfunction). The check engine light is not lit.

The wiring harness has been replace on this car.

The only other clue is that the exhaust smells rich.

Could this be an over voltage protection relay?

Anyone have other tests or ideas?

[Arthur Dalton]

Hey Jim,

Long time since.

Pull the OVP and see if it is 000-540-52-45..
If it is , change it to the new part # 000-540-67-45

[Jim Villers]

Arthur .... Yes, it has been a while. With your 5K responses, I can see where you have spent your time after your 2K responses on the pagoda board. I am slow, I only have 3K with the 190SL Group.

Anyway, the OVP was also my guess as that would explain the lack of a malfunction code (still with the reader you send me in 2001). So I have a new 00 540 67 45 in my hand that I'll install tomorrow. If that dosen't work (or change anything) I am not sure where to look. I'll post the results tomorrow morning.

Thanks again, you always seem to be around when I need assistance.

[Arthur Dalton]

Originally Posted by Jim Villers

Arthur .... Yes, it has been a while. With your 5K responses, I can see where you have spent your time after your 2K responses on the pagoda board. I am slow, I only have 3K with the 190SL Group.

Anyway, the OVP was also my guess as that would explain the lack of a malfunction code (still with the reader you send me in 2001). So I have a new 00 540 67 45 in my hand that I'll install tomorrow. If that dosen't work (or change anything) I am not sure where to look. I'll post the results tomorrow morning.

Thanks again, you always seem to be around when I need assistance.

Very good..I think the OVP will do it..if not , we will go to the next step, but those HFM/SFI OVP set-ups are infamous and where we always start b/c that chassis is full Electronic and OVP is mandatory..if you pull it, the car will not run , whereas on the earlier models the car would still run b/c OVP was just on the control side. It is nice to see you have a single flash on pin 8..that is a real good sign on that chassis ..most have somethin in there..I think that new harness took care of that.
Have not been at Pagoda much..but I do go over once in a while to read some of those long -winded post...........and I mean Looooong..
Nice talkin' to you again.

[Jim Villers]

Arthur ..... I need "plan two". I installed the OVP this morning and it is still "missing" or running very rough.

You might want to visit the 190SL site and see my current "Barn Find" project project. It had last run in 1988.

My next thought would be in the fuel pressure area (probably not trip a malfunction code). Could it be the fuel pump or pressure regulator?

[Arthur Dalton]

< >>

I would check it... These HFM will fool you b/c if the HFM module sees an ignition misfire , it automatically cuts fuel to that cyl. injector for CAT protection, so an ignition failure on these seems like a fuel issue.
But fuel pressure is a next step.
On the top of the fuel rail, you will see a test port cap..That is where you can hook up a gauge. That fitting is the same as an R12 fitting, in case you do not have one.
So, first check is to start the engine and let it idle..now, pull the vac line at the regulator and see if any gas is shooting out that port on the reg. There should be none and if there is, the diaphragm is leaking and you need a new regulator. [ raw, unmetered gas getting sucked intio intake.]. Also check for any evidense of fuel in that vac line..again, you want none.
If all is well, then hook up gauge and do this simple 3 part test.
1-Engine @ idle, Vac line ON-- FP should be 3.2-3.6 Bar
2- " " , Vac line OFF-FP should jump to 3.7-4.2 Bar
3-Engine OFF , wait 30 min. -FP should maintain at least 2.5 Bar
*Bar = 14.5 PSI... [ you already know that, but this winds up in archieves]

See what's up w/FP...
..next suspect would be the 3 Resistor under the coils if we have a missing/misfire condition, or a vac leak could fit a Rough running condition.
If intermittant, that could be a sticking EGR [ common on 104] . I have a simple test for that after we see where you are w/FP.
You may aso want to try the DM led/sw [ the built-in one] while at idle in case there are any impending codes...
Are you using Bosch F8DC4 plugs?

[jcyuhn]

Now that the action seems to be over, may I toss in an aside? The waste spark system with the two plugs in series is quite common, in my experience. For many years I drove a Ford sedan equipped with a Yamaha built DOHC V6. It used three coils on six plugs, also setup in series. Interestingly, from the factory it was equipped with three each of two different part number platinum plugs. One part number had a platinum center electrode, the other a platinum side electrode. As you would guess, each circuit had one of each. I've also worked on a number of GM cars which used the same design.

- JimY

[ke6dcj]

great thread.

I'm thinking under GP, it's best to replace all coils and their "stubbies" at 150K miles, and keep the rest for spares . . .

:-) neil

[BMG]

Originally Posted by ke6dcj

great thread.

I'm thinking under GP, it's best to replace all coils and their "stubbies" at 150K miles, and keep the rest for spares . . .

:-) neil

I will second that.

After following this thread, I changed the connectors under the coils and my engine misbehavior disappeared! Now I actually notice the poor shocks in the front of the car and the non functional AC. Before I was too busy hiding behind the wheel trying to drive the backfiring beast back and forth to the airport each week.

Surprisingly, my car just hit 149,000 miles to boot. Perhaps the interval for the stubbies should be 125K.

Great Thread and thanks for the bump - I thought I lost this in the sea of posts. I now have bookmarked for further notes and evaluation.

[Texholdem]

Originally Posted by ke6dcj

great thread.

I'm thinking under GP, it's best to replace all coils and their "stubbies" at 150K miles, and keep the rest for spares . . .

:-) neil

Most interesting post! I just changed the coils of my 1996 E320 at 135K preventively. With "stubbies" do you mean the connectors, wires or plugs?

[Arthur Dalton]

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=2EI1B4MYE2EK12P51I&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1996&product=F1010-84561&application=000357357

Stubbies.

Altough I have never heard them referred to as such..

If you change them every few years , you might not need coils.
Most Techs change them with every plug change b/c they know what a problem they can be for misfires on a Waste Spark system.
Just the ones under the coils.

Most owners change the plugs and leave the old connectors on the coil , when in actuality, it is usually the connectors that are the problem and should always be considered the first suspect on 104 engines w/DIS ignition systems.

[amosfella]

I"m reviving an old thread by saying that I have a 95 S320V with the same problem. My first order of business was to check the spark plug gaps, and see how she runs tomorrow. If still missing, I'd probably do new plugs and wires.
Interesting thing is, that when I restarted the car (just shut off and restarted) it was almost gone......
I might start a new thread on this problem.....

[Dan]

I, too, found a bad coil pack on a '95 E320 with NO apparent codes with the homemade reader. Used the ignition timing light tip -- mine flashed on the good ones, did not on the bad -- to isolate the bad coil without swapping.

I know it's only OBDI, but it has defective ignition coil codes...hmm?